UNSW Embryology ANAT 3311 Notes Session 2 SYSTEMATIC EMBRYOLOGY					Embryology Home Page
	Lecture notes from the Anat 3311 1997 Science Embryology course compiled and written by Dr Mark Hill. Some notes derived from historic class notes.
			Human Homepage	Pig Homepage

COELOMIC CAVITY AND ITS DERIVATIVES

Reading Moore Ch9: p174-184 Larson Ch6: p111-125

Computer Activities

Embryo Images: Unit: Early Cell Populations & Establishment of Body Form, Body Cavities

UNSW Embryology:

Listed selected sections

Objectives

1. Describe the development of the intra- and extra-embryonic coeloms.

2. Describe the processes involved in the development of the three divisions of the

intra-embryonic coelom; pericardium, pleural cavities and peritoneum.

3. Describe the fate of the extra embryonic coelom.

4. Describe the development of the diaphragm.

Learning Activities

1. Review the development of the 3-layered embryo, with particular reference to the antero-posterior and lateral folding processes.

2. Examine the 6mm pig and 27mm human embryo microfiche cards identifying the main features of the developing coelom.

3. Identify the diaphragm in the 27mm human embryo and relate this to the development of the diaphragm.

4. Discuss the developmental anomalies associated with the formation of the diaphragm.

Self-Assessment Questions

1. What are the four main developmental components of the diaphragm.

2. What is the septum transversum

3. Describe the developmental observations associated with diaphragmatic hernia and its consequences on the individual with the malformation.

4. How does the innervation of the diaphragm develop.

Pig Embryo

G6-G7: The extent of the coelomic cavity is best seen on the sagittal sections of the pig embryo. G7: identify the pericardial cavity and its continuation posteriorly into the still small pleural cavity (pleuroperitoneal canals).The pleuroperitoneal (pericardio-peritoneal) canal.

G6: one of the lung buds is seen embedded in the dense tissue that is surrounded by the coelomic cavity.The abdominal (peritoneal) cavity is clearly continuous with the extra embryonic coelom and parts of the intestinal loop and accompanying mesentery are visible entering the umbilical region.

C5: The most cranial part of the coelom visible in cross sections is the pericardial cavity and from this level caudally it can be seen extending to the level of the liver, but anterior to it (D6). B7-C5: Posteriorly and cranially this cavity communicates with the primitive pleural cavity which are two canals connecting the pericardial and peritoneal cavities (C6-7, D1-6).

C5-7: These two channels are separated from the pericardium by a fold containing the common cardinal veins either side. (Pleuropericardial folds - see development of diaphragm).

D2-6: The peritoneal cavity is extensive; it consists of two, adjoining halves and a small cranial outpocketing next to the stomach, the lesser sac. Further caudally this cavity extends as far as the region of the urorectal septum E7 (tail). Much of the peritoneal cavity is occupied by the two parts of the mesonephros, which reduce most of the cavity to two crescent-shaped clefts.

Human Embryo

In the human embryo, the separation of the three cavities of coelom is complete.

D1-7&E1-4 : The pericardial cavity.

Dl-7, E1-7: The pleural cavity, almost the same frames, indicating the nearby equal extent of the two cavities at this stage, but also that eventually the pleural cavities will become much larger. E3-7: The diaphragm can be seen as a thin, distinct membrane around the liver. Two derivatives of the coelomic epithelium are to be observed here.

E6-7, F1-3: The adrenal glands. Notice the large fetal cortex, (most of the gland) and the narrow (more compact and darker staining) early permanent cortex encapsulating it.

F1-3: The spleen develops in the dorsal mesogastrium and appears as a dense body on it lateral to the left adrenal gland and kidney. Review in Endocrine Development.

F3-7, G1: The gonads are also in part derivatives of the coelomic epithelium but they will be discussed with the rest of the genital system.

G4-5: The caudal extent of the peritoneal cavity; this appears as the rectovesical pouch in the male or as the rectouterine pouch in the female.

Human Embryo (selected sections)

E6: The histological appearance of the fetal adrenal cortex is seen.

F3: Fetal and permanent adrenal cortex. The medulla of the adrenal gland is of neural crest origin and it is not yet encapsulated by the cortex.

DIAPHRAGMATIC HERNIA (POSTERO-LATERAL)