UNSW Embryology

Anat 2007
Medicine 2 Class Notes

Textbooks

Anat 3311 Notes

The following text has been edited from the original Medicine II Embryology Handbook.

Notes are edited with permission of Dr B. Freeman, from his Course Manual for Human Embryology (1995). Other staff and former staff who had contributed to these notes prior to 1989 are Dr M.S.R. Smith, the late Prof. I. Tork, Em. Prof. H.ZawTun, Prof. C.R.R. Watson and Prof. R. Wheeler-Haines.

At present you can only view the text related to each Practical.

The material is for tutorial/revision purposes and cannot be reproduced electronically or in writing without permission.

WEEK 5: CRANIOFACIAL DEVELOPMENT AND PHARYNX

A. Recommended Preparation

W.J. Larsen, Chapt. 12, 309-340.

B. Objectives - students will be required to

1. List the main structures derived from the pharyngeal (branchial) arches, pouches and clefts.

2. Briefly summarise the development of the tongue.

3. Know the stages and structures involved in the development of the face.

4. Predict the results of abnormal development of the face and palate.

C. Learning Activities

1. Review the development of endodermal derivatives of the pharynx

2. Review the development of the face and palate

3. Discuss cleft lip and palate and Pierre Robin Syndrome giving special reference to the development aberrations causing the malformations and the consequences of the malformations to the individuals.

D. Microfiche Activities

Pig Embryo

A2,A3: Otocyst, otic capsule, rhombencephalon and rhombomeres.

A3,A4: Trigeminal ganglion, dorsal end of 1st pharyngeal arch, vestibulocochlear ganglion (rostral to otocyst), superior glossopharyngeal ganglion.

A4: Large head vein lateral to otocyst. Mesencephalon

A5: Trigeminal ganglion, facial ganglion, large head (superior (anterior) cardinal) vein lateral to inferior (cut) end of otocyst, mesencephalon (midbrain). 2nd pharyngeal arch. Vagus nerve in lateral wall of superior cardinal vein.

A6: Midbrain, floor of hindbrain with 4th ventricle, spinal cord, notochord. 1st, 2nd, 3rd pharyngeal arches with 1st and 2nd pharyngeal pouches, pharyngeal clefts. Trigeminal, facial, inferior glossopharyngeal ganglia, vagus nerve.

A7: 4th arch with inferior vagal ganglion. Arch arteries (cf. B 1, B2). Cut roof of pharyngeal cavity in midline and laterally.

B1: Division of 1st arch into mandibular and maxillary components on one side (undivided on other side due to alignment of embryo at sectioning). Dorsal portion of hypopharyngeal hypo-branchial) eminence. Prominent 3rd arch artery, dorsal aortae.

Rathke's pouch (derived from ectoderm anterior to the buccopharyngeal membrane). prosencephalon. Note thin pharyngeal pouch/groove membranes

B2: Rathke's pouch. Dorsal part of pharyngeal cavity. 3rd arch artery. 4th arch artery joining to dorsal aorta. 2nd and 3rd pouches with their corresponding grooves. Optic cup and lens placode. Thyroid rudiment (cords) near midline. Note that the opening to the pharynx is located between Bl and B2 - the site of the former buccopharyngeal membrane.

B3: Aortic sac with emerging 3rd arch artery. Thyroid cords.

Arches l-4. 4th arch arteries.

B4: Aortic sac with emerging 4th arch artery. Tangential section through optic stalk. Division of first arch into mandibular and maxillary processes. Pharynx. Note increasingly thick ectoderm of pharyngeal arches.

B5: Ventral ends of mandibular processes, maxillary process on one side and nasal placode on other side. Optic cup connected by optic stalk to wall of forebrain (continuous lumen). Note that pharynx has become compressed laterally (compare B4).

B6: Note the ventral compression of the pharynx into a plate and the dense mesenchyme laterally. Two atria and midline truncus arteriosus of heart. Thick nasal placode.

B7: Glottis coming off pharyngeal foregut. Nasal placode. Prosencephalon.

C1-C7: Beginning of trachea, oesophagus. Nasal placodes (nasal pit forming on one side). Forebrain. note proximity of nasal pit to prosencephalon (future site of olfactory nerve). In C2-C4, identify the medial and lateral nasal swellings.

G7: (Close to midline in head region). Forebrain, midbrain, hindbrain (with thin roof). Rathke's pouch. Floor of pharynx with foramen caecum (the tongue has not yet formed). Aortic sac. Cephalic flexure at side of midbrain between forebrain and hindbrain. Cervical flexure at junction of spinal cord and hindbrain.

G6: Mandibular process of 1st arch. Pharyngeal aspect of 1st, 2nd, 3rd arches. 3rd arch artery above truncus arteriosus. Pharynx leading into oesophagus. Ventral to oesophagus is the dense mesenchyme laterally compressing the pharynx. Notochord. Cephalic flexure and cervical flexure.

Human Embryo

In the human embryo microfiche H1 identify:

A5: Root of nose with interorbital ligament behind. Developing calvaria. Olfactory bulbs.

A6: Nose. Interorbital ligament. Nasal septum and nasal capsule. Eyes and eyelids. thalamus/hypothalamus. Part of circle of Willis.

A7: Eyes. Nasal septum. Middle conchae. Sphenoid cartilage.

B1: Optic nerve.

B2: Neurohyophysis and adenohypophysis. Remnant of Rathke's pouch (residual lumen) in adenohypophysis. Trigeminal ganglion. Internal carotid arteries. Vomeronasal organs, lateral to nasal septum. Nasal plug (transient). Nasal conchae.

B3: Trigeminal nerve and ganglion, with maxillary division emerging. Pterygopalatine ganglion. Nasalconchae. Adenohypophysis.

B4: Tongue. Otic capsule. Cochlea. Between B3 and B4, the junction of nasopharynx and oropharynx.

B5: Tongue with palatal process either side. Pharyngotympanic tubes (Eustachian tube - derived from pharyngeal pouch 1). External ear pinna.

B6: External auditory meatus (from pharyngeal groove 1). Meckel's cartilage with mandible ossifying lateral to it. Tongue with intrinsic muscles. palatal processes. Developing teeth.

B7: Pharynx (compressed dorsoventrally). Mylohyoid muscle and submandibular gland. Platysma muscle (R side). Junction of sigmoid sinus and internal jugular vein on one side. Vagal ganglia (medial). Vertebral arteries.

C1: Pharynx. Carotid neurovascular bundle with prominent ganglia.

C2: Pharynx. Carotid neurovascular bundle. Sternomastoid muscle.

C3: Glottic region with cricoid cartilage and descending process of thyroid cartilage laterally. Carotid neurovascular bundle.

C4: Section damaged, but shows thyroid gland lateral to trachea. Oesophagus.

C5: Thyroid gland. Trachea. Oesophagus. Recurrent laryngeal nerve. Common carotid arteries. Jugular veins. Vagus nerves.

C6,C7: Jugular veins. In C7 brachiocephalic vein.

Dl: Thymus gland.

Human Embryo (High power)

A7: Nasal septum. Vomeronasal organs. Hypophysis.

B1: Trigeminal ganglion and central root of trigeminal nerve.]

B2: Neurohypophysis (infundibular part with hypothalamic recess of 3rd ventricle). Residual lumen of Rathke's pouch. Anlage of pars intermedia Sphenoid cartilage.

C2,C3: Thyroid gland.

C5,C6: Thymus gland.

DEVELOPMENTAL ANOMALIES OF CRANIOFACIAL REGION

The malformations cleft lip and palate and Pierre Robin Syndrome will be discussed during the lecture and practical session.

Cleft lip and palate develop between the 4th and 8th week of gestation and is dominated by changes resulting in the formation of the nose. Palatal development occurs between the 7th and 12th week of gestation and is divided into the formation of the primary palate (prolabium), premaxilla and cartilaginous septum and formation of the secondary palate (hard and soft palate).

In the treatment and repair of cleft lip the following results are hopefully achieved:

(i) a symmetrical lip

(ii) a natural appearing philtral ridge and dimple

(iii) negligible scarring

(iv) a symmetrical nose and restoration of the nostril floor

The major objectives of the repair of the cleft palate includes construction of a competent, functioning and watertight valve at the junction of the soft palate and pharynx; repair is performed early enough to allow the child to begin speech with a functioning velopharyngeal valve. Presentation of normal hearing must also be maintained along with normal development and bone growth in the central facial region along with a functional and attractive dentition.

WEEK 6: DEVELOPMENT OF RESPIRATORY SYSTEM AND G.I.T. 1

A. Recommended Preparation

W J. Larsen Chapt. 6, 111-1 30.

B. Objectives - students will be required to:

1. Describe the development of the respiratory system from the endodermal and mesodermal components.

2. Describe the main steps in the development of the lungs.

3. Describe the development of the diaphragm and thoracic cavities.

4. List the respiratory changes before and after birth.

5. Describe the developmental aberrations responsible for the following malformations: tracheo-oesophageal fistula (T.O.F.); oesophageal atresia; diaphragmatic hernia; lobar emphysema

C. Learning Activities

1. Summarise the changes in the respiratory system and the C.V.S. at birth.

2. Discuss the main features of physiological maturation of the lung and the importance of this to fetal and newborn viability.

3. Examine the serial sections of human and pig with reference to the respiratory system.

4. Discuss the selected malformations; tracheo-oesophageal fistula (T.O.F.), diaphragmatic hernia and lobar emphysema giving special reference to the developmental aberrations causing the malformations to the individuals.

D. Self Assessment Questions (Respiratory System)

1. How is the trachea formed and what are the basic derivations of the lung?

2. How does the thoracic cavity develop?

3. What processes occur during the maturation of the lung in the fetus?

4. What is a tracheo-oesophageal fistula? How does this affect the amount of amniotic fluid present?

5. How is the larynx formed?

E. Microfiche Activities

Pig Embryo

B1,B2: Pharynx. Crest in ventral floor of pharynx formed by fusion of 3rd pharyngeal arches = hypopharyngeal eminence (precursor of root of tongue). Rathke's pouch = rudimentary adenohypophysis.

B3: Rudimentary thyroid ventral to aortic sac (also seen in B2, ventral to the hypopharyngeal eminence).

B4: Caudal pharynx compressed dorsoventrally.

B6: Further compression of ventral part of pharynx to form a fused epithelial lamina - the anlage of the vocal fold. Note surrounding dense mesenchyme. Nasal placode.

B7: Glottis drawn off from pharyngeal foregut. Nasal placodes. Pulmonary arteries.

C1,C2: Commencement of trachea and oesophagus with dense mesenchyme. R. nasal pit. Prosencephalon.

C3,C4: Common cardinal vein in the posterior wall of the intraembryonic coelom - the pleuropericardial folds which contribute later to the formation of the pleura and pericardium. L. nasal pit. In C4, junction of R common cardinal vein with dorsal wall of sinus venosus.

C5: Smaller oesophagus, expanding trachea. Note ventral anchoring of attachment site is at the most cranial extension of the septum transversum. Note also that this attachment now divides the intraembryonic coelom around the trachea into two canals, the L and R

pleuro (pericardio-peritoneal) canals. (Canals are lined by coelomic mesothelium and are continuous with whole I-E coelom - they will be referred to hereafter simply as coelomic canals). Note the pleuroperitoneal fold on the medial side of the R common cardinal vein - this fold will form part of the diaphragm.

C5,C6: Lateral extension of pulmonary mesenchyme is moulded to shape of coelomic canals. R common cardinal draining directly into sinus venosus; L common cardinal vein with prominent L pleuropericardial fold. Oesophagus lumen obliterated (common site of oesophageal atresia and/or tracheo-oesophageal fistula). Prominent R pleuroperitoneal

fold.

C7: Bifurcation of trachea into L, R lung buds. Junction of L common cardinal vein and L "horn" of sinus venosus. Note dorsal extent of coelomic canals. Oesophagus lumen reappears caudal to bifurcation. Distinct R (smaller on L) pleuroperitoneal fold below the common cardinal vein.

Dl: Oesophagus/stomach junction. R lung bud prominent. (L lung bud is more cranial, therefore R primary bronchus is more vertical than the left - cf. Gross Anatomy). note ventral anchoring of pulmonary mesenchyme to the septum transversum, in which is also embedded the sinus venous. Coelomic canals.

D2: Ovoid stomach with developing space of the lesser sac on R. Dorsal and ventral attachments of the mesenchyme are now known as dorsal and ventral mesogastria. Coelomic canals.

D3: Rotation of stomach (seen from above) to R side. Note change in outline of coelomic canals due to presence of liver. Lesser sac. Note thick mesothelium lining the coelom along Ledge of stomach, the primordium of the spleen and greater omentum along greater curvature. Liver embedded in septum transversum (ventral border of septum transversum contributes to diaphragm).

G7: Rathke's pouch. Floor of pharynx with foramen caecum (remains of thyroglossal duct), and caudally to it, the hypopharyngeal eminence. Aortic sac ventral to H-P eminence. Caudal pharynx (extending laterally, ventral to dorsal aorta - cf B4). L lung bud caudal to L atrium with attachment of pulmonary mesenchyme to septum transversum.

Stomach, mesentery.

G6: Fusion of mandibular arches, second and third arches. Hypopharyngeal eminence. Aortic sac. Truncus arteriosus. Pharynx, initially compressed dorsoventrally then more caudally, compressed mediolaterally in region of dense mass of mesenchyme (cf B6). Narrow oesophagus. Tracheal bifurcation dorsal to sinus venosus. Attachment of pulmonary mesenchyme to septum transversum.

Human embryo

A5: Bridge of nose. R and L olfactory bulbs from forebrain (cf. A4).

A6: Nose. Nasal septum. Nasal capsule. Olfactory epithelium lining roof of nasal cavity. Orbital part of the developing sphenoid bone (intramembranous ossification).

A7: Conchae. Nasal capsule and septum.

B1: Conchae. Optic nerve.

B2: Perpendicular plate of ethmoid cartilage. Adenohypophysis. Neurohypophysis. Ant. and post. walls of hypopophysial fossa. Lesser wings of sphenoid cartilage. Internal carotid arteries.

B4: Dorsum of tongue. Oropharynx communicating with naso-pharynx (cf. B3 - palatal processes not fused).

B5: Tongue with palatal processes at either side. Transverse (intrinsic) muscle of tongue. Pharyngotympanic tubes.

B6: Tongue with transverse muscle, genioglossus muscle (medial) and hyoglossus muscle (lateral). Meckel's cartilage. Palatal processes. Note teeth enamel organs (dark masses at sides of tongue attachment).

B7: Transverse caudal pharynx. epiglottis. Hyoid musculature. Pharyngeal constrictor muscle. Submandibular gland.

C1: Pharynx. Pharyngeal constrictor muscle. laryngeal caecum (ventral). Arytenoid swellings in contact. Thyroid cartilage laminae (anterolateral), with superior horns (posterolateral). Hyoid cartilage. Internal jugular veins.

C2: Pharynx. Thyroid cartilage. Smaller laryngeal caecum (cf.C1). Carotid neurovascular bundle.

C3: Pharynx with its inferior constrictor muscle. Glottis region.

C4: (Section damaged) Oesophagus with muscle layer and trachea with thyroid gland laterally. Common carotid arteries. Vagus nerve. Internal jugular veins.

C5: Oesophagus, smaller than in C4. Trachea. Thyroid gland (isthmus). Clavicle. Small dark masses near posterolateral borders of thyroid gland are the parathyroid glands from the caudal part of 3rd pharyngeal pouch.

C6: Clavicles. Dark connecting stalk between parathyroid gland and thymus (rostral end of 3rd pharyngeal pouch). Trachea. Common carotid artery.

C7: Sternum. Thymus gland. L brachiocephalic vein. Brachiocephalic trunk. Trachea. Oesphagus. Apex of R lung in pleural cavity.

Dl: Sternum. Thymus. Lungs. Visceral and parietal pleurae. Pleural cavities. Other contents of superior mediastinum.

D3: Tracheal bifurcation.

D4: R primary bronchus (torn) and R superior lobe bronchus. L primary bronchus. L, R pulmonary arteries. Ribs joining to sternum.

D5: R, L primary bronchi. R anterior and posterior segmental bronchi coming off R superior lobe bronchus. L, R pulmonary arteries. Hilar attachments of lungs to mediastinal tissues - note extent of R, L pleural cavities.

D6: R, L primary bronchi (note left still has not branched). R pulmonary artery.

D7: R, L primary bronchi: note distinct horizontal course of L, vertical course of R, L pulmonary veins (L empty). R pulmonary artery.

E1,E2: Pulmonary veins. Azygos, hemiazygos veins. Ribs. Intercostal muscles.

E3: R dome of diaphragm. Liver. R long middle and inferior lobes. L long superior and inferior lobes. Xiphoid process.

E4: Diaphragm (note costal attachment). R lung inferior lobe. Inferior vena cava, dorsal to diaphragm.

E5: Liver. Diaphragm with sternal attachments. Inferior vena cava, now ventral to diaphragm (vena caval foramen). Inferior lobes of lungs.

E6: Liver. Thoracic aorta. Large adrenal glands.

E7: Lumbar diaphragm. Thoracic aorta. Note ribs 11 and 12 on L and three layers of abdominal muscles extending ventrally.

Fl: Lumbar diaphragm. Thoracic aorta.

F2: Attachment of lumbar diaphragm near L 1 on R with psoas muscle dorsal to it. Note abdominal aorta giving rise to superior mesenteric artery.

Higher-power views

B7,C1: Laryngeal caecum. Arytenoid swellings. Thyroid cartilage. L,R laminae and superior processes. Hyoid cartilage with sternohyoid muscles.

C2,C3: Tracheal epithelium. Note in C2, ventral tracheal cartilage. In C3 note rounded cells of hyaline tracheal cartilage, starting to push apart in central midline zone but compressed together at lateral margins. Thyroid gland.

C4: Tracheal epithelium (vacuolated) and trachealis muscle. Note regional changes in cartilage as in C3 above. Oesophagus - epithelium (vacuolated), submucosa and muscularis externa with a few inner spiral and isolated, outer longitudinal muscle bundles.

C5,C6: Developing thymus.

Dl: Note bronchial epithelium (tall wedge-shaped cells) with subepithelial smooth muscle, surrounding loose connective tissue and visceral pleura.

RESPIRATORY SYSTEM DEVELOPMENTAL ANOMALIES

1. TRACHEO-OESOPHAGEAL FISTULA (OESOPHAGEAL ATRESIA)

History

1. Mother had polyhydramnios 40/52

2. The child (a boy) had cyanotic attacks in the first few hours or days after birth.

3. Mucous secretions built up in the mouth even tough they were frequently sucked out.

4. Any attempts at feeding produced choking attacks.

Examination

1. Mucous collection in the mouth.

2. The breath sounds are noisy.

3. An attempt to pass the catheter into the stomach is presented by an obstruction at the manubrio-sternal level.

4. A test of the oral mucous reveals that gastric acid is present.

Investigations

1. The chest X-ray with catheter in place shows a blind oesophagus at the manubrio-sternal level.

2. Gas is observed in the gut indicating communication between the distal oesophagus and bronchi.

Summary

This is oesophageal atresia as suggested by

(a) Polyhydramnios

(b) Reflex increase in salivation

(c) Holdup of the catheter confirmed by the X-ray appearance of the dilated blind proximal oesophagus. The fistula is confirmed by the presence of gas in the intestines.

Management

1. Operative closure of the trachea end of the fistula.

2. Restoration of the continuity of the oesophagus

N.B. This is a serious malformation with significant risk of mortality.

Associated Malformations

(a) Stratified squamous epithelium and columnar epithelia (mixture of tracheal and oesophageal epithelial) are found in the trachea and oesophagus.

(b) This often occurs as one of a complex of malformations in a child. The origin is in early embryogenesis and often associated with

(i) cloacal malformation

(ii) cardiac septal defects

(iii) renal malformations

Questions

(a) The failure of what embryological process might give rise to this malformation?

(b) Why is there almost invariable association of tracheo oesophageal fistula with polyhydramnios?

(d) How might the defect possible be corrected?

2. LOBAR EMPHYSEMA (Overinflated lung)

History

1. There was a normal pregnancy and birth 41/52

2. The child (boy) was well for fifteen days (this could be weeks) and then there is the development of progressive respiratory distress.

Examination

1. There is an overinflated chest on the left side.

2. There is diminished air entry into the left chest.

3. The left chest is hyper-resonant except for a dull left base.

4. The mediastinum is displaced to the right.

Investigations (for 1, 2, 3 see X-ray and diagram photographs)

1. There is an overinflated left upper lobe.

2. There is a collapsed lower lobe

3. The left lung is herniating across the mediastinum.

Description of lesion - there is congenital deficiency of cartilage in the left upper lobe bronchus. The anatomical nature of the lesion was demonstrated by autopsy specimens and usually reveals no abnormality other than cartilage deficiency throughout the lobe.

Summary

(a) Respiration is normal at first.

(b) Once distress occurs overinflation is rapidly progressive and may kill by asphyxia.

Management - The affected lobe must be resected.

Questions

1. How does broncho-malacia (soft bronchi) lead to overinflation of the affected lobe and collapse of the adjacent lobe?

2. What is the embryological process involved in cartilage development?

3. At what stage of embryogenesis would this malformation occur?

4. Why would it not become apparent until some time after birth?

3. RESPIRATORY DISTRESS SYNDROME IN THE NEWBORN (Hyaline Membrane Disease)

History and Examination

1. This was a caesarian delivery 36/52.

2. Respiratory distress syndrome (RDS) appears within 12 hours and increases with the following features:-

(i) Rapid respiration

(ii) Subcostal and supraclavicular indrawing with inspiration

(iii) Cyanosis with grunting respiration

(iv) Air entry uniformly diminished over the whole chest

Investigations

1. The chest X-ray displays a "ground glass" appearance over the lung field.

2. Arterial blood gases (Breathing 100% 02)

RDS Normal

P.02-5Omm Hg 100mm Hg

P.C02-45mm Hg 35 - 42mm Hg

pH 4.5 pH 7.2

Note that blood gases are indicative of hypoxia with a very large arterial-alveolar 02 tension

gradient and mild acidosis. Note that increased acidosis increases the possibility of cardiac

arrest.

Management

1. R.D.S. is normally treated conservatively with 02, intravenous bicarbonate and general supportive measures but the mortality rate is high in more premature infants. At autopsy the principle change to be seen is an eosinophilic hyaline membrane filling the alveoli.

2. If the child is treated with constant positive airway pressure this increases arterial 02 tension and help prevent the collapse of alveoli which deficient surfactant otherwise causes. This increases the functional residual capacity of the lungs. This support system is effective in the nearly mature infants but the more premature still have a high mortality rate.

Complications

(a) Interstitial pulmonary emphysema leading to pneumo- mediastinum and/or pneumothorax.

(b) Intracranial haemorrhage.

Questions

1. Why should severe acidosis occur?

2. If the R.D.S. is associated with a deficiency of surfactant in premature lungs, why does it become more severe in the first 12-24 hours?

3. How does alveolar rupture occur?

WEEK 7: DEVELOPMENT OF THE GUT

A. Recommended preparation

W.J. Larsen, Chapt. 9, 205-234.

Part1: Midgut and Hindgut

B. Objectives - Students will be required to:

1. Name the adult structures developed from the fore-, mid- and hind-gut and list the arterial supply to each.

2. Explain the elongation and rotation of the mid-gut and appreciate the consequences of malrotation.

3. Describe the development of the nerve supply of the gut.

4. Describe the development of the liver and pancreas and state the functions of these organs in the fetus, in particular the role of the liver in blood formation.

5. Summarise the formation of the adult mesenteries of the gut.

6. Describe the developmental aberrations responsible for the following selected congenital malformations; Meckels's diverticulum; intestinal malrotation (situs inversus); Hirschsprung's disease (aganglionic bowel).

C. Learning Activities

1. Review the development of endodermal derivatives of the embryo using photographs and diagrams, the serial sections of the human (8 week) embryo pig (l0 mm) embryo microfiche cards and review booklet.

2. Observe a demonstration of the elongation and rotation of the mid-gut loop and relate this to the final adult situation using gross anatomy prosected materials.

3. Summarise the development of the liver and pancreas and deduce the importance of these structures to the fetus.

4. Discuss the selected malformations below giving special reference to the developmental aberrations causing the malformations and the consequences of the malformations to the individuals.

(i) Intestinal malrotation and situs inversus.

(ii) Meckel's diverticulum

(iii) Hirschsprung's disease.

D. Self Assessment Questions (Gastro-intestinal system)

1. What is a pharyngeal arch and pouch? List the muscle, arch cartilage and nerves of each arch. List the derivatives of each pharyngeal pouch.

2. Describe the main steps in the development of the tongue.

3. How is the thyroid gland developed?

4. What are the derivatives of the fore-, mid- and hind-gut?

5. What is the buccopharyngeal membrane?

6. Describe the normal development of the face and palate. List the major malformations of this region and their possible causes.

7. How is the liver developed?

8. What are the main processes involved in the elongation and rotation of the stomach and intestinal region?

9. Describe the development of the pancreas.

10. How does the myenteric plexus develop?

11. List the basic principles in the development of the peritoneum.

Pig Embryo

Follow the main features of the gut from the stomach onwards

D5: Stomach, dorsal and ventral mesogastrium (gastrohepatic ligament). Greater and lesser curvature. Liver and liver trabeculae, sinusoids. Follow the outline of the septum transversum containing the liver. Note lesser sac and outline of intraembryonic coelom.

D6: Gall bladder. Junction of lesser sac with R coelomic canal.

D7,E1: Gall bladder, duodenum.

E2: Duodenum. Vitelline veins. Coelomic canals.

E3-E6: Small intestine. Loss of ventral attachment of mesentery to body wall as the two canals of I-E coelom open to the extra-embryonic coelom (chorionic sac). In E5 and E6, vitelline duct of yolk sac stalk is cut close to its attachment to the yolk sac in the embryo-embryonic coelom (yolk sac removed).

E7: Mesentery. Midgut. Junction of vitelline duct and midgut. Vitelline vessels. Note communication of coeloms and the separate amniotic cavity:

Fl: Mesentery with midgut loop sectioned in 2 places. Note body wall jelly extending towards sacral region on one side.

F2,F3: Mesentery. Returning limb of midgut loop.

F4: Attachment of mesentery to sacral part of dorsal abdominal wall. I-E coelom (now cut deep to its opening into the extraembryonic coelom). Hindgut. Sacral dorsal aortae.

F5,F6: Mesentery. Caudal loop of midgut/hindgut.

F7,G1: Mesentery

G2: Posterior wall of intraembryonic coelomic cavity near site of attachment of mesentery.

Now return to F6 and follow the caudal limb of the gut loop into the sacral region.

F6-Fl: Gut loop extending caudally "up" into sacral region, attached by a dorsal mesentery. Separation of dorsal aorta.

E7: Hindgut

E6-E4: Junction of hindgut and urogenital sinus (whole region called cloaca).

E4-E3: Urogenital sinus receiving two lateral ducts - the mesonephric ducts. Note fusion of urogenital sinus endoderm and ectoderm - the cloacal membrane. Rectum.

E2: Distal region of urogenital sinus and rectum, still receiving lateral mesonephric ducts. (The blind end of the sinus occurs between E2 and E1). Sacral neural tube. Somites and somitocoeles.

Now return slowly to E7 and note the gradual separation of the urogenital sinus from the rectum by the urorectal septum of mesenchyme. Then follow the more ventrally-located urogenital sinus from E7 to Fl, where the allantois is seen joining the sinus.

Fl: Junction of urogenital sinus and midline allantois. Note how this junction lies in the anterior body wall, now separated from the hindgut by the intraembryonic coelom. umbilical artery to one side (missing - damaged - on other side), and umbilical veins further to the side.

F2: L umbilical vein, both umbilical arteries. Allantois.

G7: Stomach and lesser sac in mesentery. Triangular flange of mesentery with triangular hole and intervitelline anastomosis. Hindgut (without lumen) seen at caudal end of mesentery.

G6: Liver. Gall bladder. Cranial limb of midgut loop in mesentery with intervitelline anastomoses. Caudal attachment of mesentery with hindgut inside. Communication of intra- and extra-embryonic coeloms.

Human Embryo

E6: Liver. Ductus venosus. Cardio-oesophageal junction (cf. E5). Inferior vena cava.

E7: Stomach body, with mucosa, submucosa and muscularis externa. Lesser sac. Lesser omentum. Pyloroduodenal junction. Folded duodenal mucosa. Inferior vena cava. Portal vein. Hepatic ducts. Gallbladder.

Fl: Stomach body. Spleen. Pyloric canal. Duodenum. Portal vein. Pancreas. Small intestine loop (jejunum) cut tangentially, ventral to liver.

F2,F3: Stomach, spleen. Superior mesenteric artery. Superior mesenteric vein crossing cranial to body of pancreas. Tail of pancreas. Duodenum. Small intestinal loop herniating from abdominal cavity into the coelom of the umbilical cord (remnant of extra-embryonic coelom).

F4: Greater curvature of stomach (tangential section). Lesser sac. Greater omentum. Duodenal/jejunal junction. Note colon (small lumen, darkly-staining wall) and its mesocolon. Note the sections of small and large intestine within the umbilical cord coelom and their mesenteries. Note the thickened jelly to one side of the umbilical cord, containing

umbilical vein and R umbilical artery.

F5: Lesser sac. Greater omentum. Duodenum. Jejunum (cut twice with mesentery in between). Colon and mesocolon.

F6: Both umbilical arteries now inside abdominal cavity with urachus between them. Greater omentum and lesser sac. Jejunum with mesentery. Colon with mesocolon. Three layers of abdominal muscles.

F7: Umbilical cord containing umbilical arteries and small dark allantois. Umbilical cord coelom containing mainly, small intestinal loops with their mesentery. In abdominal cavity: colon with mesocolon, jejunum. Greater omentum and lesser sac.

G1,G2: Umbilical cord and coelom containing small intestine loops. Knees. Bladder with umbilical arteries either side. Colon and mesocolon. Jejunum (G1 only).

G3: Bladder. Rectum. Umbilical arteries arising from common iliac arteries.

G4: Rectum.

G5: Recto-anal junction with rectovesical pouch of peritoneal cavity.

G6-G7: Anal canal with triangular lumen.

Higher Power (H2)

E3,E4: Central veins of liver. Radiating appearance of hepatic sinusoids.

E5: Central vein with endothelial lining, containing nucleated erythrocytes (haemopoietic role of fetal liver).

E6,E7: Pyloroduodenal junction. Note tall columnar entodermal cells, submucosa,

muscularis externa with inner spiral, outer longitudinal smooth muscle. Tunica serosa.

Fl,F2: Pancreas and pancreatic duct joining duodenum. Superior mesenteric vein crossing cranial to pancreas. Note folds of duodenal mucosa.

G5-G7: Rectocolic junction. Mesocolon. Note layers of wall.

GASTRO INTESTINAL SYSTEM DEVELOPMENTAL ANOMALIES

1. INTESTINAL MALROTATION

History:

1. A previously well infant presented on the 7th day after birth with intestinal obstruction and strangulation (usually associated with hypovolemic shock).

2. The plain X-ray (Diag. A) shows a partial obstruction of the duodenum. The combined barium meal plus enema (Diag. B) shows the descending and ascending colon on the left side of the abdomen.

3 . At operation, there was a mid-gut volvulus (the mid-gut and mesentery twisted upon itself) obstructing the passage of food out of the duodenum and constricting within the mesenteric vessels. There was also a primitive mesentery (see Diag. C).

(N.B. The ascending and descending mesocolon is normally absorbed by zygosis after rotation is complete. This means that the mesentery root is fixed along a diagonal line between the duodenum and the caecum rendering volvulus formation impossible).

Treatment

(a) Undo the volvulus

(b) Fix gut in the non-rotated position. i.e. Colon - left, Small bowel - right.

(c) Suture the mesentery to the posterior abdominal wall from duodenum in the upper right to caecum in the upper left. (If there is any attempt to replace the gut with normal relations then obstruction could be caused by twisting).

Question: What abnormal embryological processes could interfere with normal rotation and fixation of the gut?

2. SITUS INVERSUS VISCERA

Compare Diag. D (autopsy) with Diag. E2 and note the transposed positions of the heart, liver and spleen. Diag. F. shows how the normal pattern of obliteration of the left vitelline vein caused the right lobe of the liver to become the larger lobe thus drawing the ventral mesogastrium to the right (Diag. F2). The greater curve of the stomach and the dorsal mesogastrium including the spleen comes to lie on the left.

Disturbance of the lateralisation of the liver may produce transposition of some or all of the foregut and its derivatives.

1. Stomach

2. Pancreas

3. Duodenum - jejunum

4. Spleen

5. Bile

(Diag. G shows the development of the pancreas)

Also in situs inversus the anatomical relations of the duodenum, pancreas, bile ducts and portal veins may be reversed or disordered.

Question: What developmental anomalies of the pancreas could be associated with this condition?

3. MECKEL'S DIVERTICULUM

History

1. No maternal complications

2. A male child at five years of age presented with a sudden attack of peritonitis having been previously quite well.

Questions

1. What is the nature of this outpouching?

2. Why could the outpouching be prone to ulceration?

3. Not infrequently a band from the apex of Meckel's Diverticulum traverses the peritoneal cavity. Where would this terminate? Another rare variant of this malformation results in fecal discharge from the umbilicus.

4. How might this arise embryologically?

4. HIRSCHSPRUNG'S DISEASE (INTESTINAL AGANGLIONOSIS)

(cf. Urogenital System)

History:

1. Mother normal but there may be a family history of Hirschsprung's disease.

2. A male child presented at 3 days of age with

(a) Persistent vomiting

(b) Distended abdomen

Some meconium had been passed and there was infrequent flatus.

(In this disease constipation is common dating from birth).

Investigations:

1. The X-ray of the abdomen confirms a low intestinal obstruction (Diag. Al) and the barium enema shows a normal calibre rectum transition cone from a dilated proximal colon (A2). (Compare this with diagram B).

2. A rectal biopsy shows total absence of ganglion cells. Diag. C 1 is a histological preparation from an affected area of gut and it shows complete absence ganglia in the plexus.

Summary:

Diagnosis confirmed that the child had an intestinal obstruction due to aganglionosis of the rectum and lower sigmoid colon.

Management:

Temporary relief is obtained by making a colostomy proximal to the obstruction. The child will then thrive normally until fit for resection of the aganglionic segment, restoration of anal continuity and closure of the colostomy. (See Diag. D - The Duhamel Operation. This is a modified form of the resection operation. Retention of the anterior half of the rectum protects rectal sensations while overcoming the obstruction).

Associated Malformations

No associated malformations. (It is important to recognise that the aganglionic always extends to the ano-rectal junction; the proximal extent varies from patient to patient). See Diag. E. The Okamoto and Ueda demonstration.

Genetic History

There is a familial disposition which is greatest in the long segment examples.

Questions:

1. What elements of the G.I.T. are formed from the hind gut?

2. Why does the aganglionic bowel cause obstruction?

3 . Would anything other than motility 1:v h~ defective in the anglionic bowel

4. On what embryological basis could aganglionosis of variable lengths be explained?

WEEK 10: DEVELOPMENT OF THE MUSCULOSKELETAL SYSTEM

A. Recommended Preparation

W.J. Larsen, Chapt. 11, 281-308

B. Objectives - students will be required to:

1. Name the components of a somite and the adult derivatives of each component.

2. Give examples of sites of (a) endochondral and (b) intramembranous ossification and to compare these two processes (consult Histology Manual).

3. Enumerate the general times (a) of formation of primary and (b) of formation of secondary ossification cenhres, and (c) of fusion of such centres with each other. (Refer to Introductory Anatomy notes).

4. Briefly summarise the development of the limbs.

5. Describe the developmental aberrations responsible for the following malformations: selected growth plate disorders;congenital dislocation of the hip; scoliosis; arthrogryposis; and limb reduction deformities.

C. Learning Activities

1. Identify the component parts of a somite in a 6-7 mm pig embryo (from 6 mm pig microfiche).

2. List the derivatives of a thoracic somite.

3. Revision - types of ossification.

4. Review X-rays of the fetus and newborn.

5. List the stages of the two processes of ossification.

6. Discuss the development of vertebrae.

7. Discuss the development of joints.

8. Discuss the selected malformations below giving special reference to the developmental aberrations causing the malformations and the consequences of malformations to the individual: growth plate disorders; congenital dislocation of the hip; scoliosis; arthrogryosis; limb reduction deformities.

D. Self Assessment Questions

1. List the main steps in the development of a vertebra.

2. What is the cartilage model in bone growth?

3. Compare and contrast endochondral and intramembranous ossification.

4. Describe the main steps in the development of a long bone.

5. What are the derivatives of myotomes and dermatomes?

6. Describe the main events in the development of the limbs.

7. What is an epimere and a hypomere?

8. Describe the biochemical disorders associated with the major growth plate disorders?

9. What are the major causes and consequences of congenital dislocation of the hip and scoliosis?

E. Microfiche Activities

Pig Embryo

Somites

G5: Tangential section through the rump of the embryo (neural tube cut twice). Young somites containing somitocoeles and consisting of dark, lateral dermomyotomes and more diffuse, medial sclerotomes. Notochord. Amnion and amniotic cavity.

D1: Surface bulge of a somite, either side of neural tube. Somite components: dermatome, myotome, sclerotome. Notochord. Paired dorsal aortae, with inferior cardinal veins (lateral). Dorsal root ganglion. Spinal nerve passing between sclerotome and myotome.

Dl-D3: Dermatome, myotome, sclerotome. Dorsal root ganglia. Notochord. Note the dorsal segmental branches of the dorsal aortae and the inferior cardinal veins. In the walls of the neural tube, note the alar and basal laminae of cells, sulcus limitans.

Axial Skeleton - Vertebrae:

G7: Cervical region: dark masses of dorsal root ganglia. Lumbar region: dorsal aorta with its dorsal segmental arterial branches. Between each dorsal segmental artery is a darker-staining mass of mesenchyme (the dark part of a sclerotome) which is the anlage of the intervertebral disc. The dorsal segmenta lartery itself marks the location of the centre of the light-staining part of the sclerotome, which is the future vertebral body. The dark band dorsal to the sclerotomes is the basal lamina of the wall of the neural tube.

G6: Cervical region (neural tube cut very obliquely): note the wavy notochord and thin roof and floor plates. Thoracic region: alternating light and dark parts of the sclerotomes (vertebral bodies and I.V. Discs, respectively). Lumbar region: tiny, dorsal segmental branches of dorsal aorta Each little branch is aligned almost parallel to the cranial border

of the next caudal dorsal root ganglion (segmented dark masses). Sacral region: oblique section of neural tube, notochord.

Limbs

D3: Cranial edge of forelimb fold (future shoulder region). Note the superolateral extent of the coelomic serosa with respect to the limb fold.

D4,D5: Note axillary fossa appearing on each side and local thickening of the ectoderm in the region of the fossa. Note thinnest ectoderm stretched over heart and neural tube.

D6,D7: Limb folds and fossae. Greatest thickening of the ectoderm is at apex of the limb fold: the apical ectodermal ridge. The mesenchyme of the limb is densest under the ectoderm. Note the narrow distance between the ectoderm of the axillary fossa and the serosa of the body cavity. The limb fold has distinct flexor and extensor surfaces: the

flexor surface is narrower and has thicker ectoderm. Note blood vessels close to flexor surface

E1-E3: Note blood vessels in limb fold mesenchyme, and pale-staining nerves at root of limb (E1).

E4: Spinal nerves (part of future brachial plexus) directed towards the flexor side of the limb fold. Note also the section of the lumbosacral region with neural tube and hindlimb bulge.

E5-E7: Hindlimb fold. Forelimb fold

F1,F2: Caudal limit of forelimb. Broad extensor surface. Dense mesenchyme of hindlimb. Note lumbar somites, somitocoeles.

Human Embryo

Axial Skeleton

D1,D2: Vertebral body (centrum). Head of rib. Lamina of vertebral arch. Transverse processes. Vertebral canal. Spinal cord. Dura. Intervertebral foramen containing dorsal root ganglion (now in a ventral position!). Ribs. Sympathetic ganglia. Costovertebral and costotransverse joints. Note that laminae of the arches have not fused dorsally but are united by a connective tissue membrane (dorsal uniting membrane or ligament) which provides the guide-path for the growth and subsequent fusion of the laminae. The dura constitutes the ventral uniting membrane or ligament. Part of I.V. disc seen in D2.

D3: Ganglia in intervertebral foramina. Costovertebral joint.

D4: Pedicle of vertebral arch. The dark, fibrous tissue at the anterior margin of the vertebral column is the intervertebral disc (derived from dark part of sclerotome). Note ribs joining the sternum, intercostal muscles and erector spinae group of muscles.

E4: Vertebral body with I.V. disc ventrally. Notochord remnant at junction of body and I.V. disc.

E6: Next vertebral body (notochord incorporated into cartilage).

F1: Mostly I.V. disc with notochord remnant (cf. F2)

F2: Transverse abdominal muscle, internal and external oblique abdominal muscle, rectus abdominis muscles.

F7,G1: (Lumbar cross-section). Vertebral body and I.V. disc. Psoas major muscle. Erector spinae muscles. Note short laminae of the arches and wide dorsal uniting ligament.

Upper limb (Rows C-D)

C5,C6: Scapula. Spine of scapula. Humerus (head). Clavicles. Deltoid muscle. Trapezius muscle.

C7: Scapula spine. Deltoid muscle. Trapezius muscle

D1,D2: Flexor and extensor muscles of arm.

D3: Elbow mesenchyme (elbow flexed)

D5: Carpal and metacarpal cartilages. Phalanges. (Note flexed, pronated position of arms). Humerus. Radius.

Lower limb (Row G)

G1: Knee mesenchyme

G2: Patella. Femur. Flexor and extensor muscles.

G4: Knee joint. Tibia and femur. Hip bone: pubis, ischium, ilium, head of femur. Developing acetabulum. Adductor group of muscles.

G5: Hip joint. Acetabulum. Head and greater trochanter of femur. Sacro-iliac joint.

G6: Heel. Ischium. Sacro-iliac joint.

G7: Tarsal cartilages (note inverted position of feet). Heel. Phalangeal cartilages.

Higher power Human Embryo

D4,D6: Dura (ventral uniting ligament). Spinal ganglia. Intervertebral foramen. Ependyma of spinal canal. Ventral horn. Dorsal horn. Anterior spinal artery. Centrum of vertebra. Lamina of arch. Note that the dura invests the spinal ganglion and then dorsally fuses with the perichondrium of the neural arch before continuing to the opposite side as the dorsal uniting ligament (not seen in D6)

MUSCULO-SKELETAL SYSTEM DEVELOPMENTAL ANOMALIES

Clinical Introduction:

1. Normal growth and development of the limb requires (a) normal cell numbers; (b) normal locomotor elements, e.g. bone, joint, muscle; (c) normal blood and nerve supply.

2. Retardation of limb growth is produced by (a) deficient nerve supply; (b) impaired blood supply of (c) systemic abnormalities affecting the growth plate.

3. Increased limb growth is produced by some nerve malformations and by increased blood supply to the growth plate.

1. GROWTH PLATE DISORDERS

(a) Hurler's syndrome

(b) Morquios Syndrome

(d) Osteogenesis imperfecta (Fragilitas ossium) (Brittle Bone disease)

(e) Marfan's Syndrome

(a) Hurler's Syndrome: Photo GP1 ((a & b) Genetic Mucopolysaccharides)

A seemingly normal infant, in a matter of a few years, may be transformed into a mentally retarded, physically deformed, severely handicapped individual. No organ or tissue appears to be spared the inbuilt error of metabolism, which is the accumulation of mucopolysaccharides (chondroitin sulphate B and heparin sulphate). The form inherited as an autosomal recessive is most severe: the sex linked recessive form affects males only and is less severe. Death occurs in childhood or early adult life. The main histological features are the presence of inclusion bodies composed of mucopolysaccharides within cells of the growth plate, the C.N.S. and parenchymal and connective tissue cells.

(b) Morquios Syndrome: Photo GP2

In this disease keratosulphate accumulates in cartilage and cornea The patients excrete excessive keratosulphate in the urine - a diagnostic criterion). Severe stunting becomes apparent in the second and third year of life. The joints then become involved and osteoporosis becomes prominent. The cartilage has abnormal chemistry, and the problem is a systemic metabolic disorder.

This is a deficiency of endochondral ossification and all growth plates are affected - other forms of cartilage such as articular cartilage and hyaline cartilage are normal. These are the characteristic circus dwarfs, healthy, well muscled, short adults with limbs short relative to the trunk. A major problem in this disease is the failure of the germinal cells of the growth plate to proliferate. There are two possible mechanisms for this disease:-

1. An abnormality of vascular invasion of calcified cartilage leading to an accumulation of uncalcified cartilage.

2. An abnormality of cartilage which precludes calcification.

(d) Osteogenesis imperfecta - Fragilitas ossium. Brittle bone disease (autosomal dominant with variable expressivity). Photo GP4.

This is a generalised disorder of connective tissue which has a variable expression. In its most severe form there are brittle bones, lax joints and hypotonic (floppy) muscles.

The pathological change underlying this disorder is a failure of collagen production throughout the body. Normally collagen becomes a thicker and stronger fibre as it matures. In osteogenesis imperfecta collagen remains in the form of reticulin. In place of normal compact bone, a coarse fibrlllary type of immature bone is found without haversian

systems and with a very irregular distribution of abnormal collagen fibres in the bone. Photo GP5; GP6. Photo 5 shows a typical example of Osteogenesis Imperfecta with malformation due multiple fractures and Photo 6 the typical appearance of bone.

(e) Marfan's Syndrome: Photo 7 (autosomal dominant)

This is a generalised disorder of the connective tissue of the body with manifestations in the skeleton, eye and vascular system. The individuals are tall and thin and there is an overgrowth of endochondral ossification. There are also systemic and locomotor disabilities. Aortic incompetence often occurs. There is an abnormality of elastic fibres in

this disease but the connections between this and the malfunction of the growth plate is obscure.

2. CONGENITAL DISLOCATION OF THE HIP (C.D.H.)

Introduction; (Instabiliby: 1:60 at birth; 1.240 at 1 week: Dislocation untreated: 1:700).

(a) There is originally a congenital instability of the hip which later dislocates by muscle pulls or gravity if untreated.

(b) There is familial predisposition for this problem and female predominance.

(c) Growth of the femoral head, acetabulum and innominate bone are delayed until the femoral head fits firmly into the acetabulum.

Mechanisms of Production

(a) There is familial displasia of the hip

(b) There is a relationship between placental transmission of material joint softening hormones (e.g. Relaxin) which are inhibited by androgens in the male foetus. When a and b are present there is instability of the hip

(c) Dislocation is produced by the small head slipping out of the shallow acetabulum in the extended position of the hip and is inhibited by the abducted position of the hip.

Treatment

Treatment must be instituted early to avoid a growth deformity of the hip. To ensure there is no instability, infants are tested at birth for hip stability and unstable hip children are nursed in the Frog Position (abducted hip posture).

Photo CDH1 Pawich Brace

Photo CDH2 Frog Plaster

Delay in treatment leads to frank dislocation of the hip (the femoral head comes out of joint), and there is a shallow acetabulum and a small femoral head. See Photo CDH3. If this condition is allowed to occur an operation may be necessary to produce a more horizontal roof to the acetabulum and produce hip stability. See Photo CDH4.

Posterior dislocation of the hip produces flexion deformities of the hip with compensatory Lordosis - exaggerated lumbar curvature. See Photo CDH5 (both female).

Questions

1. In CDH5 the smaller child on the right shows Trendelenberg' s Sign - as she raises her right foot the right side of the pelvis lowers instead of raising. In the normal patient the hip rises when the ipsilateral foot is raised from the ground. What muscle is chiefly responsible for the normal tilting of the hip?

2. What conditions may give rise to Tredelenberg's Sign?

3. ARTEROGRYPOSIS (MULTIPLEX CONGENITA)

Rare with severe cases are characterised by multiple deformities at birth with gross stiffening of joints and hypotonia or wasting of muscles.

Photo AG1. Such a stiff fetus frequently sustains fractures before or during delivery. AG1 has had a fractured right humerus.

Photo AG2 shows deformities originally thought to be joints, then joints and muscles then finally innervation was also implicated.

Photo AG3 shows normal and abnormal muscles in close proximity. Variations in the degree of severity of joint deformity are expressions of varying degrees of muscular and neurological abnormality.

4. SYNDACTYLY

Fusion of fingers or toes. This may be single or multiple and may affect

(i) Skin only

(ii) Skin and soft tissues

(iii) Skin, soft tissues and bone

The condition is unimportant in toes but disabling in fingers and requires operative separation. This is frequently inherited as an autosomal dominant. Photo.

5. SCOLIOSIS

This is involved with assymetric growth impairment of the vertebral bodies. There is lateral deviation of the spin with a 3-fold deformity:

1. Lateral flexion

2. Forward flexion

3. Rotation of the vertebral column on the long axis

Photos:

Sco 1: Shows Scoliosis

Sco 2: Rotational deformity producing rib hump when the child bends

Sco 3: X-ray of spine

The deformity is compensated by movement of the vertebral column above and below the affected region producing a primary and two secondary curves. This deformity progresses rapidly in adolescence and becomes fixed once bone growth is complete.

Questions: Why does the deformity

progress rapidly in early adolescence?

6. CONGENITAL LIMB REDUCTION DEFECTS

Thalidomide was the most celebrated limb reducing insult in humans which produced other deformities as well. There was probably a primary neuronal deprivation. There are two elements in the production of limb reduction defects.

(a) Agents - Many substances have been found capable of producing limb reduction defects in experimental animals but few have been related to humans.

(b) Mechanisms - Limb reduction defects may be due to loss of blood supply to part of the limb or to defects in innervation at the spinal or cerebral level. Also there are a number of as yet undefined mechanisms involved.

Limb reduction defects may be apical (congenital amputation) or pre or post-axial (absence of radius and lateral digits; ulnar and medial digits).

Photo LRD l and 2 shows a limb reduction defect and the accompanying X-ray.

Questions:

What area is missing in the reduced limb?

What will be the relative growth rates of the right and left humeri in this child?

Other examples of limb reduction defects are shown by:-

Photos: LRD 3: A reduction defect, largely preaxial hemimelia

LRD 4: An apical defect

LRD 5: A severe apical defect, the lobster claw foot

Question: What problems would a patient with the lobster-claw foot defect encounter when walking?

WEEK 9: DEVELOPMENT OF THE NERVOUS SYSTEM

NERVOUS SYSTEM

Recommended reading

W.J. Larsen, Chapt. 13, 375-418

B. Objectives - Students will be required to:

1. Understand the formation of spinal cord; grey and white matter from the neural tube.

2. To know the main derivatives of the brain vesicles and their walls.

3. To know the derivatives of the neural crest.

4. Understand the developmental basis of certain congenital anomalies of the nervous system, including hydrocephalus, spina bifida, anencephaly and encephalocele.

C. Learning Activities

1. Review the formation of the neural tube and its subdivision into the primary and secondary cerebral vesicles and spinal cord: (see demonstration graphics)

2. Identify, in the 6-7mm pig embryo, the marginal and ventricular zone of the neural tube wall, and the developing spinal ganglia.

3. In the 8-week human identify the main derivatives of the fore-, mid- and hind-brain and list the adult derivatives of these areas. 4.Examine slides 56, 56A and 57 for neuroectodermal derivatives.

5. List the derivatives of neural crest tissue.

6. Discuss the underlying developmental processes in the following congenital anomalies:

(a) meningomyelocele (spina bifida)

(b) hydrocephalus

(d) encephalocele

7. View a graphic on development of the nervous system.

D. Self-Assessment Questions (Nervous System)

1. Describe the development of the neural tube. What structures develop from neurectoderm?

2. List the derivatives of neural crest tissue.

3. What are the developmental differences between the brain and spinal cord?

4. Describe the main features of ependymal development.

5. Describe the development of brain ventricles

6. How and where is the choroid plexus developed?

7. Describe the development of the cerebellum

8. Construct and label simple diagrams showing the early development of the CNS and define the following terms:

(a) neural plate

(b) neural groove

(d) neural crest

(e) neuropores

9. What elements of the CNS are peripheral nervous system are derived from the neural crest?

E. Microfiche Activities

1. In the pig embryo identify the cerebral vesicles and flexures; first study the sagittal section (P:G7). Identify the forebrain, midbrain and hindbrain. The roof of the hindbrain is thin (formed by a membrane only). Midbrain and hindbrain: P:Al-7 Forebrain: P:B1-7, C1-5. The isthmus can be observed on P:A3-4 as a constriction between the mid- and hind-brain. The hindbrain is already subdivided into two parts, the slim myelencephalon and the wider metencephalon. The boundary between these two parts is roughly at the level of the otic vesicles (P:A3-4). identify the optic cup and stalk, which are derived from the forebrain (P:B2-6). Caudally one can identify the spinal cord along the entire length of the embryo.

2. Study the histological appearance of the neural tube in the pig embryo. Identify the venricular and marginal zones. Also identify the sulcus limitans separating the alar and basal plates (P:C1 & Dl). Notice the position of the spinal ganglion (D.R.G.) ventrolateral to the spinal cord (P:D3).

3. In the human embryo identify the large telencephalic vesicles (HI:Al-4). The cavity in these (the lateral ventricles) communicate with the ventricle of the diencephalon (3rd ventricle) through the interventricular foramen (HI:A3). inside the lateral ventricle the choroid plexus is seen (HI:Al).

4. Distinguish the wall of the forebrain, best seen in HI:Al-2, H2:Al-2. In H2:A2 a high power picture of the wall is seen. Identify in this picture the ventricular zone, intermediate zone and cortical plate. Mitotic activity occurs in the ventricular zone to produce neuronal and glial cells which migrate through the intermediate zone to the cortical plate. The basal part of the telencephalon forms the basal ganglia (H1:A3-4), a solid mass. Posteromedially these basal ganglia are in contact with the diencephalon. The large masses in either side of the diencephalon form the thalami.

5. Identify the diencephalon (H1:Al-7, B1). In these levels the brain comes into section twice, because of the cephalic flexure, but in H1:A2-4 the two parts are connected. Ventral to the thalamus (H1:Al-5) one can identify the hypothalamus (Hl:A6-7, B1) and the original anterior end of the neural tube, the lamina terminalis (H1:A6). Notice the position of the optic nerves in relation to the hypothalamic part of the diencephalon (H1:B1). Further caudally the pituitary gland is seen, the neural part of which is a derivative of the diencephalon (H1:B2-3).

6. Identify the midbrain (mesencephalon) in H1:Al-7. Its dorsal part is the mesencephalic vesicle, a large, thin-walled structure (H1:A2-6) which overlaps the initial part of the metencephalon (H1:A6-7) (The ventral part of the mesencephalon is seen to be continuous with the diencephalon in H1:A3-4. The tectal recess, an extension of the roof the mesencephalic vesicle is seen in H1:A6.

7. The junction between the mesencephalon and metencephalon is called the isthmus (H1:A6). The main metencephalic derivatives are the pons and cerebellum. The ventricular lumen of the hind brain is the 4th ventricle (H1:A7, B1-7, C1-3). The roof of the metencephalic part of the 4th ventricle is formed by the developing cerebellum (H1:B2-3), beyond which the ventricle forms two large lateral recesses (H1:B2-3). In more caudal sections the roof of the ventricle is seen as a thin membrane only, bearing choroid plexus. In H1:B2-3 and H2:B1 observe the root of the trigeminal nerve and its ganglion.

8. The myelencephalic part of the hind brain will form the medulla oblongata, the embryonic appearance of which is hardly different from the fully developed structure. The vagus nerve and its ganglion are seen to leave the base of the brain in H1:B7, through the jugular foramen.

9. At all levels where the brain is present notice the meninges enveloping it and creating the large subarachnoid space which is filled with cerebrospinal fluid.

10. Study the histological appearance of the spinal cord. Note the alar and basal laminae, the dorsal root ganglia and the sympathetic trunk.

WEEK 10: DEVELOPMENT AND HISTOLOGY OF THE EYE

EMBRYOLOGY

Objective: To know the development of the eye and orbital adnexa

Pig Embryo

A7: Mesencephalon. Rostral extensions of superior cardinal vein

B1: Developing diencephalon. Rathke's pouch. Lens pit (derived from thickened ectoderm of lens or "optic" placode).

B2,B3: Optic cup with optic ventricle. Note unequal thickness of walls of optic cup (inner wall; sensory retina: outer wall; pigment epithelium). Lens pit (incorrectly labelled: "Optic placode"). Note position of eye with respect to maxillary arch. Hyaloid vessels near

ventral margin of optic cup.

B4: Junction of optic stalk to wall of prosencephalon (diencephalon). Note small branches of hyaloid blood vessels in region between lens pit and optic stalk.

B5: Continuity of optic ventricle and single forebrain ventricle via optic stalk. Note proximity of eye to nasal placode (R).

B6: Hyaloid vessels ventral to optic stalk. Optic mesenchyme (mesectoderm) arising directly from epithelium of dorsal surface of optic cup. Nasal placodes.

B7: Tangential section through optic cup, with surrounding optic mesenchyme. Nasal placode Interorbital ligament. Bridge of nose.

A6: Interorbitalligament. Nose. uppereyelids. Cornea. Anteriorchamber. Lens. Vitreous body. Sensory retina. optic ventricle (artefact). Pigment epithelium. Conjunctival sac. Anlage of lacrimal glands (near lateral fornix of conjunctival sac).

A7: Medial rectus m. Anlagen of nasolacrimal ducts. Upper eyelid (lateral). Lower eyelid (medial).

B1: Optic nerve. Note extensive temporal region of retina. Anlagen of nasolacrimal ducts.

B2: Medial and lateral rectus m. Pigment epithelium. Note relationship of eye to nasal capsule, sphenoid cartilage and trigeminal ganglion. Anlagen of nasolacrimal ducts (cut obliquely).

B3: On L, note course of maxillary division of trigeminal in relation to position of eye (superior to this level).

Higher Power Human Embryo

A3,A4: Optic ventricle (artefactually enlarged). Optic nerve. Sensory retina. Pigment epithelium. Choroid and sclera (not separable).

A5: Sensory retina with optic nerve fibre layer and young retinal ganglion cells. note radial orientation of deeper retinal cells. Pigment epithelium. Sclera plus choroid.

A6: Anterior corneal epithelium and posterior corneal endothelium. Corneal stroma. Angle of anterior chamber with developing trabecular meshwork. Anterior and posterior lens epithelium. Note change in height of lens cells at the equator of the lens. Double-layered epithelium of iris arising from rim of optic cup. Stroma of iris lies anteriorly across

lens. Kink in internal wall of optic cup indicates site where the ciliary body will form.

HISTOLOGY OF THE EYE AND ORBITAL ADNEXA

Objective: To know the microanatomy and histology of the eye and eyelid.

Examine the following slides for the features listed:

58: monkey eye (anterior segment): cornea; stratified squamous corneal epithelium with thick basement (Bowman's) membrane; substantia propria with keratocytes (cornealocytes); corneal endothelium with basement (Descemet's) membrane; iris; iridial stroma with iridial chromatophores (brown); sphincter pupillae smooth muscle with nearby

large pigmented clump cells (brown); pigmented iridial (bilaminar) epithelium; ciliary epithelium, (bilaminar, cuboidal, deep layer containing melanin), ciliary body (muscle); ora serrata; canal of Schlemm lined by endothelium near limbus; lens fibres (anucleate in centre of lens); lens capsule; simple cuboidal (anterior) lens epithelium; zonular ligaments; periphery of neural retina and cut sclera; bulbar conjunctiva arising from corneal epithelium. Anterior and posterior chambers. Angle of the anterior chamber with trabecular meshwork. Note that ciliary muscle attaches to sclera at the scleral spur, close to the angle of the anterior chamber.

59: monkey eye (posterior segment); note division into three main layers; the sclera, the uvea (choroid) and the retina. Layers of neural retina - nerve fibre layer, ganglion cell layer, inner plexiform layer, bipolar cell layer, outer plexiform layer, layer of photoreceptor nuclei; inner segments (red-staining) of photoreceptors, outer segments of photoreceptors 6cone outer segment is red-staining and rod outer segment is pale blue-staining); retinal (pigment) epithelium with melanin granules and distinct basement (Bruch's) membrane; retinal blood vessels; choriocapillaries; choroid with melanocytes and large blood vessels; sclera with fibroblasts. Ciliary body (muscle), ciliary (bilaminar) epithelium and ciliary folds ("processes"). Optic nerve with accompanying ciliary nerves and ciliary vessels (may not be present in all sections). Extraocular muscles. Bulbar conjunctiva.

56,56A: developing eye: eyelids; cornea; iris; lens with lens fibres (cells); developing retina Note blood vessels from hyaloid artery near inner surface of retina and on posterior surface of lens.

44: eyelid; palpebral conjunctiva with stratified cuboidal epithelium; skin surface; muscularis orbicularis oculi; eyelashes (cilia); muscle in vicinity of eyelashes (ciliary muscle of Riolan); tarasus (collagen plate); tarsal gland (Meibom - sebaceous); ciliary gland (Moll - apocrine); sebaceous glands (Zeis). Note lymphocyte infiltration of conjunctiva. Accessory lacrimal glands (serous) may be present under conjunctiva (Glands of Moll and Zeis may not be present in all slides).

Examine electron micrographs; identify photoreceptor outer segments.

WEEK 11: DEVELOPMENT AND HISTOLOGY OF THE EAR EMBRYOLOGY

Objective: To know the development of the inner, middle and external parts of the ear.

Pig Embryo

Al: Thin caudolateral walls of rhombencephalon.

A2: Otocyst (R). Apex of otocyst (anlage of L endolymphatic sac)

A3: Otocyst; surrounding mesenchyme = otic capsule. Note proximity of otocyst to wall of rhombencephalon. Superior glossopharyngealganglion. Vestibulo-cochlear-facial ganglion complex (R). Trigeminal ganglion.

A4: Indentation in rostral margin of otocyst = anlage of utriculosaccular canal. Note alignment of superior cardinal vein (LS) in relation to the nerve trunks (XS). Trigeminal ganglion. Dorsal end of 1st pharyngeal arch and groove. Note variation in height of cells of

L otocyst wall.

A5: Facial ganglion (R). "Floor" of L otocyst. Note on R, the former position of the otocyst in relation to the 2nd pharyngeal arch.

A6: 1st, 2nd arches, grooves and pouches on R. Inferior glossopharyngeal and facial ganglia on L.

A7,B1: 1st pharyngeal pouch opening into pharynx.

Human Embryo

B3: Rhombic lip (developing cerebellum). IVth ventricle. Trigeminal ganglion. Adenohypophysis. Sphenoid cartilage.

B4: Cochlear duct and temporal cartilage. Semicircular duct (ampulla on L). precartilage of auricle (pinna). malleus (medial, L). Incus

(lateral, L).

B5: Extemal auditory meatus. Auricle. Incus (dorsal). Malleus (ventral). Tubotympanic recess (auditory rube). Tensor tympani m. (L). Utricle. Semicircular ducts. Intemal auditory meatus (R), containing vestibular and spiral ganglia. Endolymphatic sac (L). Note proximity of sac to choroid plexus of 4th ventricle.

B6: External auditory meatus. Anlage of tympanic membrane (L). Manubrium of malleus (L). Basal turn of cochlea duct (L). Endolymphatic sac (R). Common crus (R). Junction of utricle and saccule (R). Meckel's cartilage. Stapes (R). Auditory tube.

Higher Power Human Embryo

B3,B5: Cochlear duct. Spiral ganglion. Tubotympanic recess (auditory tube). Internal carotid artery. Malleus and incus. Meckel's cartilage. Tensor tympani muscle. Crista ampullaris of a semicircular duct. Semicircular duct. Utricle with macula. Saccule (cut tangentially) adjacent to utricle. Otic capsule.

B6: Turns of cochlea duct. Note changes in height of the wedge-shaped epithelial cells at different sites in wall of cochlear duct; the region of tallest cells is the anlage of Corti's organ and the clear luminal cytoplasm is the anlage of the tectorial membrane; the thickening on the outer wall of the cochlear duct is the anlage of the stria vascularis; the thinnest part of the wall is the anlage of the vestibular membrane. Spiral ganglion in modiolus. Vestibular ganglion (collectively VIII cranial nerve ganglion - both parts composed of bipolar neurones). Saccule. Temporal cartilage. Internal auditory meatus.

HISTOLOGY OF THE EAR

Objective

To know the microanatomy of the ear and the histological features of the labyrinth and of the sensory organs of the vestibular and auditory systems.

Slide 57: Cochlea (guinea pig; perfusion fixation; resin embedded; H & phloxine). At low power identify: modiolus, spiral ganglion, cochlear nerve, bony spiral lamina, basilar membrane, spiral ligament, cochlear duct (scala media), vestibular (Reissner' s) membrane, scala tympani, scala vestibuli. At higher power, choose one of the basal turns of the

cochlea where the fixation is better and examine the wall of the cochlear duct. Identify: basilar membrane with cellular and amorphous components (auditory strings may be seen radiating into spiral ligament and at endosteum of the bony spiral lamina); organ of Corti

(possibly disrupted) with a triangular tunnel of Corti made of dark-staining pillar cells; one row of inner (inner = towards modiolus) hair cells and three rows of outer hair cells; pale "washed-out" supporting cells (phalangeal cells); tectorial membrane (shrunken) attached to

spiral limbus, which is a mound of tall columnar cells (interdental cells) on the bony spiral lamina; inner spiral sulcus (groove under tectorial membrane); vestibular membrane; stria vascularis with intraepithelial capillaries; spiral ligament attached to endosteum of outer wall of cochlear canal; bipolar neurones of spiral ganglion; neurokeratin of myelin sheaths of cochlear nerve; Haversian systems in temporal bone.

Slide 8: (Auricle) Helix; antihelix; triangular fossa; elastic cartilage; dermis; epidermis (thin skin); hair follicles; sebaceous & sweat glands; nerve fascicles; striated muscle fascicles (possibly oblique and transverse auricular mm). on the extemal (dorsal) side. In the human ear the ventral skin is bound directly to the perichondrium of the cartilage, particularly over the antihelix, whereas dorsally, the skin is often more mobile and contains fat deposits as part of a true hypodermis. Note elastic fibres in dermis.

The following features will be demonstrated over the CCTV system

1. Developing ear showing: otic capsule; early stage in development of organ of Corti; early development of scala vestibuli and scala tympani.

2. Vestibular apparatus (guinea pig); utricle or saccule; macula of utricle (or saccule); otoliths; ampulla and crista ampullaris of a semicircular duct; cupula (shrunken); semicircular duct; semicircular canal containing the duct and perilymphatic space with loose supporting tissue.

Also examine the electron micrographs of the cochlea and the organ of Corti, showing rows of hair cells and W-shaped and V-shaped arrangements of stereocilia (with different lengths) at tectorial surface of the hair cell (N.B. The tallest stereocilia are always on the

stria vascularis or outer side of the hair cell).

WEEKS 12 & 13: DEVELOPMENT OF THE URINARY AND GENITAL

SYSTEMS

URINARY SYSTEM

A. Recommended reading

W.J. Larsen, Chapt. 10, 235-280

B. Objectives - Students will be required to:-

1. Compare the development and functions of the pronephros, mesonephros and metanephros.

2. Summarise the development of the ureter and bladder.

3. Compare the development of the cloaca in the male and female

4. Describe the developmental aberrations responsible for the following congenital malformations: renal agenesis; polycystic kidney (adult and juvenile); horseshoe kidney; neurogenic bladder; urinary tract reflux, megaureter and ectopia vesicae.

C. Learning Activities

1. Revise the development of the pronephros, mesonephros and metanephros. The development of the meso- and metanephros should be related to the development of the gut, ureters and bladder, testis and ovary.

2. Discuss the part played by the allantois and urorectal septum in he development of the bladder and rectum.

3. Discuss the developmental causes of polycystic kidney (adult and juvenile types) horseshoe kidney, renal agenesis and ectopia vesicae.

D. Self Assessment Questions (Urinary system)

1. How does the allantois develop and what is its function in the fetus?

2. List the derivatives of the intermediate mesoderm.

3. How does the 'adult' kidney develop in the fetus?

4. What are the derivatives of the mesonephric tubules?

5. What are the derivatives of the mesonephric duct?

6. How does the bladder develop?

7. What is the cloacal membrane? What is the importance of the urorectal septum?

8. What are the main causes and consequences of a neurogenic bladder?

9. What developmental processes are essential to prevent renal agenesis?

10. What is essential in the development of the ureter and bladder to prevent reflux?

GENITAL SYSTEM

A. Recommended Reading

W.J.Larsen, Chapt. 10, 235-280

B. Objectives - Students will be required to:

1. Compare the main features in the development of the male and female reproductive systems.

2. Understand the developmental causes of certain abnormalities of the male and female reproductive systems.

3. Describe the developmental aberrations responsible for the following malformations: Turner's syndrome, Klinefelter's syndrome, adrenogential syndrome, Mullerian duct anomalies, selected cloacal anomalies, epispadias, hypospadias and maldescent of the testis (cryptorchism).

C. Learning Activities

1. Describe the development and normal descent of the testis, and the development of the male extemal genitalia, hypospadias and epispadias. Discuss the consequences of maldescent of the testis on the individual.

2. Discuss the development of the ovary, uterus, cervix and vagina and the development of the female extemal genitalia.

3. Discuss the developmental causes of Mullerian duct anomalies and cloacal anomalies, adrenogenital syndrome, Turner's syndrome and Klinefelter's syndrome.

D. Questions

1. Describe the development of the testis and ovaries.

2. What are the main features of testis development in the late fetus and early childhood?

3. Compare and contrast the development of extemal genitalia of the male and female.

4. What are the consequences of incomplete masculinisation?

5. How is the urethra developed in the male and female?

6. Describe the main steps in uterine and vaginal development.

7. Describe the main factors controlling the development of the male reproductive system.

8. What is the cause and the consequences of Turner's and Klinefelter's syndrome?

9. List the main events necessary for the possible production of adrenogenital syndrome.

E. Microfiche Activities on Urinary and Genital Systems

Urinary System

Pig Embryo

G6,G7: Cranial and caudal extent of mesonephros (the mesonephros is never so well-developed in equivalent human embryos). Youngest mesonephric tubules at caudal end. Mesonephric duct in G7.

D6: Mesonephric tubule at medial wall of inferior cardinal vein. Broad urogenital ridge. Paired dorsal aortae.

D7-E1: Glomeruli. In E1, note form of urogenital (UG) ridge and urogenital "mesentery". In the UG ridge, identify the subcardinal vein and the mesonephric (Wolffian) duct. Dorsal aortae fuse.

E4: Afferent glomerular arteriole from dorsal aorta. In UG ridge, note medial location of glomeruli and lateral location of convoluted tubules and mesonephric duct.

E5-F4: Note further lateral displacement of mesonephric duct in UG ridge. Note medial thickening of coelomic epithelium of the UG ridge (gonad precursor - prominent in F2).

F7: Afferent arteriole. Mesonephric duct.

G1-G4: Lumbar region of mesonephros. Mesonephric ducts. Dorsal aorta.

Intraembryonic coelom. In G3, note many tubules are cut in LS.

G5-G4: Section passes dorsally to the mesonephros. Return to G4 and then follow the caudal route of the mesonephric duct into the sacral region.

G3-Fl: Sacral mesonephric ducts, located laterally in the UG ridge. Mesonephric structures smaller in more caudal regions. Division of dorsal aorta. In Fl, note rectum, urogenital sinus, allantois and intra-embryonic coelom.

E7: Most caudal extent of mesonephros, with mesonephric ducts (lateral). Rectum and urogenital sinus with urorectal septum in between. Umbilical artery (L side). note shape of Intraembryonic coelom on L. Site of caudal attachment of connecting stalk to body wall.

E6: Lateral branch of dorsal aorta forming common iliac artery. Umbilical artery. Smaller I-E coelom. Lower limb bud (damaged on R side). Junction of rectum and urogenital sinus. Urorectal septum continues laterally as two crests. Detached connecting stalk.

E5: Near caudal limit of I-E coleom. Umbilical artery sweeps lateral to the coelom, which in turn, lies lateral to the mesonephric duct.

E4: Mesonephric duct. Dark mass of mesenchyme (medial) is the metanephrogenic cap = precursor of the definitive kidney. Note lateral extensions of urogenital sinus - the terminal mesonephric ducts. The two crests between the rectum and each mesonephric duct are still the lateral extensions of the urorectal septum.

E3,E2: Mesonephric ducts joining to urogenital sinus. Urorectal septum.

Metanephrogenic caps. Cloacal membrane.

Human embryo

E6: R,L adrenal glands under diaphragm.

E7: Large adrenal glands. Inferior vena cava. Thoracic aorta.

Fl: Adrenal glands. R. Kidney. Autonomic ganglia (partly the adrenal medulla precursors).

F2: Kidneys (note retroperitoneal location). Cortex. Medulla. L. Adrenal gland. Superior mesenteric artery. Inferior vena cava.

F3: R testis (note its location relative to the R adrenal). L adrenal. R renal hilus. large channels are branches of ureteric tree.

F4: R kidney and R ureter. Inferior vena cava. L. kidney, L renal hilus and L ureter. R testis with R mesonephric duct (precursor of vas deferens). L testis. Umbilical arteries passing into umbilical cord allantois between them.

F5,F6: Kidneys. Ureters. Note umbilical arteries and allantois. Also note how R testis and mesonephric structures are attached to parietal peritoneum by a mesogonad.

F7: In F7, note "inebriated Puffin" (dorsal to R testis and liver) with the distinct lumen of the mesonephric duct (eye), almost solid column of paramesonephric cells (beak) and remnants of mesonephric tubules (body). "mesogonad". Ureters. Bladder with submucosa and detrusor muscle. Umbilical arteries. Division of aorta.

G1: Ureters, Bladder. Umbilical arteries. Testis with remains of mesonephros (dorsal), mesonephric duct and paramesonephric cells. Sigmoid colon and mesocolon.

G2: Ureters being displaced ventrally, crossing common iliac arteries. Sigmoid colon. Bladder. Mesonephric ducts (lateral) and paramesonephric ducts (smaller, medial) located dorsal to bladder.

G3: Ureters (cut twice): descending dorsal to bladder and ascending ventrally to enter the bladder at trigone, through the submucosa). Fusion of paramesonephric ducts. Paired mesonephric ducts. Umbilical arteries looping off common iliac arteries. Pubic symphysis. Colon.

G4: Most caudal part of loop of ureters. Urethra emerging from bladder. Mesonephric ducts. Rectocolic junction.

G5: Urethra (in region of future prostate gland - note crescentic shape). Rectum. Rectovesical pouch. Between G4 and G5, each mesonephric duct (vas deferens) has joined the prostatic urethra (caudal to the ureters), thereby increasing the caliber of the latter.

G6,G7: Penile urethra, emerging inferiorly to the glans penis. Scrotal swellings (appear before testis descends).

Higher Power (H2)

F4,F5: Kidneys. Ureters. In F5, note the great volume of renal interstitium and the younger nephrons at the periphery of the kidney and the older nephrons closer to the hilus. Renal capsule, corpuscle, tubules. Note dilated extensions of the ureteric tree - the collecting tubule system, derived from the ureteric bud. The strands across the lumen of the large, calyx-like structure are degenerating partitions - i.e. sites of corrosion fields. Similarly, the junction of the collecting tubule and nephron tubule at top-right of screen is site of a corrosion field. Note comma-like shapes of young nephrons.

F6: Renal corpuscles with glomeruli inside Bowman's space. Narrow renal tubules and collecting ducts. Interstitium. Proximal and distal tubules defined by cell height. Macula densa region developing at the most central glomerulus.

G1: Aorta. Inferior vena cava. Ureters with spiral smooth muscle developing in an extensive dilation field (cf. thick muscularis of adult ureter).

G2: Mesonephros with tubules and remnants of glomeruli. Mesonephric duct. paramesonephric duct.

G3: Testis. Degenerating mesonephric glomeruli and tubules (precursors of outflow ducts of testis).

G6,G7: Bladder with ureters entering laterally (ureters also descending retroperitoneally beside rectum). Fusion of paramesonephric ducts in midline, with mesonephric ducts laterally.

Genital System Embryo

Pig Embryo

E1-F4: Urogenital (UG) ridge with broad attachment to dorsal abdominal wall. Medial thickening of coelomic epithelium of UG ridge is site of gonad development (prominent in F2). Mesonephric duct.

F4-G4: Follow the caudal course of the mesonephric ducts.

G2-F2: Follow further the caudal course of the mesonephric ducts up into the sacral region of the embryo. In F2 note colon and mesocolon attaching to dorsal body wall; also allantois, umbilical artery, umbilical vein. (Limb etc. missing on one side - artefact).

F1: Umbilical vessels. Allantois joining to urogenital sinus. Mesonephric ducts. note coelom joining of ventral and dorsal body walls with rectum in between, and urogenital sinus in ventral body wall. Urorectal (UR) septum in tissue between hindgut and UG sinus. Site of attachment of umbilical cord (connecting stalk component) to the ventral body wall. Note shape of coelom.

E6: Junction of hindgut and UG sinus. UR septum continues laterally and caudally ("upwards") as two crests or flanges. Small coelom. Umbilical artery near junction to iliac artery, aorta. Mesonephric duct.

E5: Umbilical artery arcs to side of the coelom. Mesonephric duct. E4: Increase in caliber of mesonephric duct at site where ureteric bud arises. Definitive kidney anlage to medial side. Lateral extensions of UF sinus.

E3-E2: Mesonephric ducts joining UG sinus. Hindgut. Cloacal membrane.

Human Embryo (male)

F3: R testis with thick tunica albuginea (pale) and thin urogenital mesentery. Note spleen on L.

F4: Testes. Narrow urogenital mesentery. Remains of mesonephric tubules near hilus (future efferent ductules at mediastinum testis).

F5: Broader urogenital mesentery on R (still narrow on L).

F6: On R: Remnants of mesonephric tubules (anlagen of ductuli efferentes). Mesonephric duct (anlage of vas deferens). Laterally, the paramesonephric duct (anlage of appendix testis). Note abdominal location of testes in relation to adjacent structures.

F7: Inebriated Puffin on R, with developing efferent ductules, mesonephric duct and medially, the paramesonephric duct (appearing solid). Note how the paramesonephric duct crossed the mesonephric duct ventromedially. Urogenital mesentery - note how testis is attached to the developing efferent ductules by a separate narrow flange,the mesorchium.

G1: On R: Lateral mesonephric duct and medial paramesonephric groove. (Changing from a tube to a groove). On L: testis (lower than on R), mesonephric tubules, mesonephric duct (lateral), paramesonephric duct (ventromedial - appearing solid).Bladder. Umbilical arteries. Sigmoid colon and mesocolon.

G1-G2: Transition from abdominal cavity to superior pelvis. In G2, note iliac crest, femoral nerve, psoas major muscle, internal iliac vein and artery. Medial convergence of paramesonephric cords and more laterally-located mesonephric ducts, ventral to the colon and dorsal to the bladder. Note position of ureters. N.B. Testis lies above this level which is close to the plane of the future inguinal canal.

G3-G4: Transition from superior (major) pelvis to inferior (minor) pelvis. Rectovesical pouch. Note wide expanse of loose tissue ventral to the pubic symphysis: site of testicular descent.

G3: Fusion of paramesonephric cords in midline. Mesonephric ducts. Cranial border of trigone of bladder. Pubic symphysis.

G4: Bladder (trigone region). Ureters. Mesonephric ducts. Caudal extension of peritoneal cavity (rectovesical pouch). Rectum.

G5: Minor pelvis. Obturator foramen. Ischium. Head of femur. Acetabulum. Ganglion cells of pelvis plexus. Obturator externus muscle. Urogenital sinus (the caudal enlargement is due to junction of mesonephric ducts).

G6: Level of pelvic floor. Pelvic plexus. Recto-anal junction. Ischium. obturator internus muscle. Greater sciatic notch. Alar of sacrum. Sacro-iliac joint.

External genitalia (male)

E3,E4: Xiphoid processes of sternum (cranial attachment of ventromedial ligament).

E6,E7: Rectus abdominis muscles.

G4: Median swelling is dorsum of glans penis. Two lateral interfemoral (scrotal) thickenings of the ectoderm covering condensations of the split ends of the ventromedial ligament.

G5: Lateral interfemoral folds (scrotal swellings - attachment points of VML). Medial interfemoral folds (merging distally). Note the corpora cavernosa, each arising from a crus attached to the corresponding descending pubic ramus, and the midline, cranially-projecting bulb of the corpus spongiosum penis. Urethra (pelvic) with crest in posterior wall (anlage of prostatic colliculus).

G6: Scrotal swellings. Fusion of medial interfemoral folds. Urethral plate and urogenital sinus or groove (future penile urethra surrounded by an anlage of corpus spongiosum).

G7: Urethra opening ventrally. Genital tubercle (anlage of glans penis).

Higher Power human H2

F7,G2: Paramesonephric duct (regressing in male). Mesonephric duct. Mesonephric tubules. Mesorchium. Urogenital mesentery.

G3: Testis with radiating cell sheets becoming cords (defines the gonad as the testis). Mesonephric tubules (ductuli efferentes). Mesonephric glomeruli. Mesonephric duct and, more laterally the thickened coelomic epithelium of the paramesonephric groove. Narrow mesorchium and pale external layer of tunica albuginea. Definitive kidney.

G4: Cell plates of testis (becoming cords) containing the germ cells. interstitial cells. large cells with dark nuclei and distinct halo of unstained cytoplasm are the germ cells (spermatogonia).

G5-G7: Fusion of paramesonephric ducts (forming prostatis utriculus in male; uterus and part of vagina in female). Mesonephric ducts. Ureters. Bladder. Umbilical arteries.

DIAGRAMS

Please consult diagrams in the folders Systematic Embryology and identify the following features:-

Fig. G-1. Future pelvic floor region of a .3 mm long embryo, and a 25 mm long embryo. Note small extension of body cavity into pelvis.

1 Left mesonephric duct. Between 2 and 3, urorectal septum. 2 Hindgut. 3 Allantois. Between 3 and 4, the epithelial wall of the bladder merges continuously with that of the allantois. 4 Cloacal membrane. 5 Terminal hindgut ("post--anal" gut). 6 Neural tube. Mesonephric duct near 7 will be drawn into wall of bladder. 8 Region of metanephric cap. 9 Ureteric bud. 10 Fold-like mesonephros projecting into peritoneal cavity.

11 Symphysis pubis. 12 Urethral p[late (aligned sagittally). 13 Ureter. 14 Left mesonephric duct. 15 Fused paramesonephric ducts. 16 Urorectal septum (projecting more distally as the lower region of the trunk "unrolls").

Fig. G-2. Uterus, vagina and vulva in ca 70 mm, 131 mm and 162 mm long fetuses. All at the same magnification ca. 5.5x. 1 Rectum.

2 Peritoneum. 3 uterine lumen. 4 Region of uterine cervix anlage.

5 Vaginal lumen. 6 Urethral lumen. 7 Labium minus (lateral boundary of the urogenital sinus formed by the medial interfemoral fold). Note: As the minor pelvis widens dorsoventrally and elongates, the vagina also elongates and a lumen forms in a suction field. During this time, the uterus remains small in relation to the vagina.

Fig. G-3. Excretory apparatus and gonads of a 27.2 mm long human embryo. Hindgut. 2 Gonad (indifferent). 3 Mesonephros.

4 Paramesonephric duct (uterine tube in female).

Fig. G-4. Pelvic organs of a ca. 100 mm long female fetus. 1 Rectum (cross-section). 2 Ovary. 3 Uterine tube. 4 (above) Uterus forming at junction of uterine tubes.

Fig. G-5. Commencement of descent of the testis in a 55 mm long fetus. Superior pelvis is partially opened. Testis coarsely cross-hatched; epididymis and vas deferens shown in black. 1 Entrance to inferior (minor) pelvis.

Fig. G-6. Pelvis organs of a ca. 115 mm long male fetus. 1 Colon. 2 Entrance into the inguinal canal (internal inguinal ring) with testis, epididymis and vas deferens adjacent. 3 Umbilical cord.

Fig. G-7. Descended testis in a 240mm long fetus. 1 Entrance to inferior (minor) pelvis (cf Fig. 3). 2 Vas Deferens. 3 Glans penis.

Fig. G-8. Fetus 40 mm, 3rd month (ventral view) 5 Xiphoid process. 6 Ventromedial ligament.

Fig. G-9. Fetus 30mm long. 5 Medial interfemoral fold. 6 Lateral interfemoral fold. 8 Genital tubercle. 9 Anus. 10 Tuberculum coccygis.

Fig. G-10. External genital apparatus. Above: female fetus 49 mm and female newborn. Below: male fetus 45 mm and male new-born. 1 Genital tubercle. 2 Medial interfemoral fold 3 Lateral interfemoral fold. 4 Anus. 5 Clitoris. 6 External urethral opening and labium minus. 7 Hymen and labium minus. 8 Anus. 9 Medial interfemoral fold with glans

penis above it. 10 External opening of wide, male urogenital sinus (closed distally as the urethral plate). 11 Lateral interfemoral fold (anlage of scrotum). 12 Scrotum and raphe.

Fig. G-11. Descent of testis. Human fetuses 15, 21, 24 and 31 cm crown-rump length. All drawn at same magnification, approximately natural size. The pubic symphysis is shaded, as well as the vertebral bodies. The 15 and 21 cm diagrams are based on sagittal sections. The 24 cm diagram is based on a sagittal dissection with the shaft of the penis removed. The 31 cm diagram is based on a sagittal dissection and shows corpus cavernosum and corpus spongiosum. Note: The most ventral segment of the pararectal band, between the testis and the scrotal fold (lateral interfemoral fold) is called the gubernaculum testis. The whole band is involved in descent of the testis as the pelvis

enlarges and rotates.

Urogenital System Developmental Anomalies

Preamble: Note that upper G.I.T. obstruction is associated with

POLYHYDRAMNIOS whereas failure of renal micturition is associated with OLIGOHYDRAMNIOS with consequent firm uterine moulding on the fetus, leading to facial, locomotor and palatal deformities.

1. RENAL AGENESIS

(a) In the complete form the child is not viable and the child dies within a few days of birth.

(b) Features associated with this anomaly are:-

(i) Oligohydramnios

(ii) Amnion nodosum (small warty amnion with accretions of squamous cells on the inner wall). This is tangible evidence for oligohydramnios.

(iii) Facial deformities: This results from uterine moulding around the head.

(Figure 1). The ears are low slung and simple, the mandible is small, the nose flattened and the eyes exhibit Pre-epicanthic folds (Figure 2). This is a horseshoe shaped flap of skin from the upper lid to the cheek in front of the epicanthus. (Downs syndrome has an epicanthic fold).

Note that the genesis is occasionally incomplete allowing survival (e.g.) Figure 2. Causal factors are largely unknown although there is some familial predisposition.

2. POLYCYSTIC KIDNEYS

This is a diffuse cystic malformation of both kidneys with cystic malformations of the liver

and lung etc. often being associated. There is often familial disposition with this malformation. There are TWO types.

(i) Infantile (inconsistent with prolonged survival)

(ii) Adult (less severe and allows survival)

Figure 3 is an example of the Infantile Polycystic Kidney. Figure 4 is an excretory pyelogram (IVP) of the infantile type. Injected dye instead of being cleared from the kidney in about 30 min. stays almost indefinitely.

e. g. Figure 4 Pyelogram after 48 hr.

Figure 5 Pylegram after 72 hr.

Figure 6 is a normal IVP of a newborn and this shows most of the dye in the bladder 15 min. after injection. The adult type of polycystic kidneys is shown by Figure 7 and in this type there is No more functional kidney tissue developed, and a small number of cysts which become larger distorting the renal pelvis like a "Dragon's Claw".

3. MULTICYSTIC KIDNEY

(i) This is non familial and is produced by atresia of a ureter

(ii) It is always unilateral

(iii) There is no functional kidney tissue present in the kidney

(iv) The kidney is replaced by a multiocular cyst.

See Figure 8.

4. URINARY TRACT OUTFLOW OBSTRUCTION

1. (E.G.) Urethral valves (Figure 9) - This figure is a micturating urethrogram and shows a valve obstruction (arrow) with dilatation of the urethra between the valve and the bladder. This type of pre-natal obstruction produces gross hydronephrosis and hydroureter before birth. Figure 10 shows gross dilatation of the pelves and ureters. There is extensive destruction of renal tissue.

2. Congenital Hydronephrosis is usually due to partial obstruction at the pelvi-ureteric junction (Figure 11). The pelvis is shown to be grossly dilated and there is extensive renal damage before birth.

*This may be familial, may be lateral and is most commonly an intrinsic defect in the wall of the ureter (structural or functional). The less severe cases may be salvaged by reconstruction of the pelvi-ureteric junction.

5. PRUNE BELLY SYNDROME (Triad Syndrome)

The Triad is

(i) Agenesis of abdominal wall muscles

(ii) Bladder outflow obstruction

(iii) Bilateral undescended testes

* The causes of this malformation are little known, but maternal therapy with Oestrogens in the first trimester has been implicated frequently.

Question: Does oestrogen possibly inhibit the development of the male bladder outflow and genital system?

In some cases there are vestiges of muscle in the abdominal wall and it is not known whether this represents

(a) destruction of muscle, or

(b) failure of development of muscle

Figures 12 and 13 show a typical prune belly. Survival of the prune belly child depends on the number of functioning remaining nephrons at birth and the operability of the obstruction.

6. HORSESHOE KIDNEY

In the horseshoe kidney there is fusion of the lower poles of the kidney. During migration from the sacral region the two metanephric blastemas can come into contact as shown in Figure 14 mainly at the lower pole. The ureters pass in front of the zone of fusion of the kidneys. The kidneys and ureters usually function adequately but there is an increased incidence of upper urinary tract obstruction or infection.

Questions:

How does the kidney develop normally?

At what level is the adult kidney found?

What arterial changes take place during kidney development?

Why does dye remain in the kidney in the IVP of an infantile polycystic kidney?

How do children with non-functioning kidneys survive to birth?

7. EXSTROPHY OF THE BLADDER

Figure 15 shows the malformation at birth. The umbilical cord is clamped above the bladder. The short epispadiac penis below the bladder and the deficiency of midline connective tissue derivatives between the body stalk and urethra is obvious.

The following features are obvious in Figs. 15,16, 17. (i) Diastis of pubic bones (ii) Separation of recti abdominis associated with the body wall defect (iii) the interior of the bladder is exposed on the abdominal wall.

Possible causes of the anomaly

(a) The following steps occur in the normal development of the cloacal region -

(i) 3rd week - development of cloacal membrane

(ii) 4th week - tail has elongated and the cloacal membrane is just caudal to the body stalk. Cloacal membrane now forms ventral wall of urinogenital sinus.

(iii) Mesoderm from the body wall of the cloacal membrane migrates toward the midline and by the 5th week this mesoderm unites cranial to the cloacal membrane to form the genital tubercle.

(iv) The mesodermal component of the infraumbilical portion of the ventral body wall converges toward the midline of the embryo increasing the distance between the umbilicus and the cloacal membrane.

(b) In the case of exstrophy it is suggested that the mesodermal components that form the genital tubercle arise lateral instead of cranial to where the urorectal septum fuses with the cloacal membrane. When the genital tubercle is in the abnormal position it may help to rupture the ventral mesoderm especially if ectoderm and endoderm remain in contact. The rupture of the infraumbilical region of the body wall produces diastisis of the pubic symphysis, flared ilia and posterolaterally rotated hip sockets.

In bladder exstrophy the ureters open into the base of the bladder. Also the anterior portion of the bladder and dorsal portion of the urethra are missing. The urethral floor runs along the dorsum of the epispadiac penis. The penis has corpora cavernosa but lacks a corpus spongiosum.

Figure 16 shows the bilateral inguinal herniae and externally rotated thighs which result from the failure of the pubic bones to meet at the symphysis.

Figure 17: Pubic bones open - pre-operative

Pubic bones closed - post-operative

Figure 18 - Epispadias diagrams. If epispadias is complete the sphincter is incomplete producing incontinence.

Management of Bladder Exstrophy

The deformity is non-familial, of no known cause and is obvious at birth. This malformation produced incontinence. The surgical reconstruction is complex and requires simultaneous repair of the bony pelvis and covering of the bladder and bladder neck. The epispadiac urethra is reconstructed later. (Ref. Snell, Clinical Embryology, P. 215, fig. 15-16)

Question: What problems confront the child with bladder exstrophy?