UNSW Embryology

DEVELOPMENT OF THE HEART AND CARDIOVASCULAR SYSTEM
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Introduction

The heart develops very early from cardiogenic mesoderm that originally lies above the cranial end of the developing neural tube. Enlargement of the cranial neural fold brings this region ventrally to its correct anatomical position. The original paired cardiac tubes fuse, with the "ventricular" primordia initially lying above the "atria". Growth of the cardiac tube flexes it into an "S-shape" tube, rotating the "ventricles" downward and pushing the "atria" upward. This is then followed by septation, a complex process which converts this simple tube into a four chambered heart. A key part of this process is the separation of cardiac outflow (truncus arteriosus) into a separate pulmonary and aortic arch outflow. During embryonic development there is extensive remodelling of the initially r/l symetrical cardiovascular system and a contribution from the neural crest to some vessels. Their are 3 aortic/venous circulatory systems: umbilical, embryonic and vitelline. The umbilical system is is lost at birth, the vitelline contributes to the portal system and the embryonic matures into the cardiovascular system.

At birth there is a complete change with activation of the pulmonary system (lungs) and eventual closure of the channel between r. and l. atria (foramen ovale).

The molecular mechanisms regulating cardiac development are still largely unknown. Development does appear to be an independent mechanism preceding both skeletal and smooth muscle development and using different regulatory mechanisms (not MyoD or myogenin).

Reading

  • Human Embryology (2nd ed.) Larson Ch7 p151-188 Heart, Ch8 p189-228 Vasculature
  • The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud Ch14: p304-349
  • Before we Are Born (5th ed.) Moore and Persaud Ch12; p241-254
  • Essentials of Human Embryology Larson Ch7 p97-122 Heart, Ch8 p123-146 Vasculature
  • Human Embryology Fitzgerald and Fitzgerald Ch13-17: p77-111
  • Additional References
  • Search PubMed- Medline

Computer Activities

UNSW Embryology:

Embryo Images Unit:

Early Cell Populations (cardiogenic section), Cardiovascular System Development

Objectives

  • Describe the main features of heart development to the four-chambered system.
  • Describe the development of the pericardium.
  • Describe the development of primary and secondary atrial septa and the ventricular septum.
  • Explain the changes occurring in the bulbis cordis and truncus arteriosus in its transformation from a single to a double tube.
  • Describe the development of the aortic arches on the right and left sides from the fetus to the adult.
  • Describe the development of arteries and veins.
  • Describe the developmental aberrations responsible for the following malformations: patent ductus arteriosus (P.D.A.); atrial septal defects (A.S.D.) and ventricular septal defects (V.S.D.); tetralogy of Fallot.

Learning activities

  • Review the developmental principles of the C.V.S.
  • Examine the models and diagrams of the developing heart and list the main stages in heart development.
  • Examine microfiche cards of the 6mm pig and 8 week human embryos identifying the main features of the C.V.S.
  • Relate developmental principles of the heart to the gross anatomy models.
  • Introductory session on the development of blood, blood vessels and lymphatics.
  • Discuss the selected malformations P.D.A., A.S.D. and V.S.D. and tetralogy of Fallot giving special reference to the developmental aberrations causing the malformations and the consequences of the malformations on the individuals.

Development of the Heart

  • Week 2 pair of thin-walled tubes
  • Week 3 tubes fused, truncus arteriosus outflow, heart contracting
  • Week 4 heart tube continues to elongate, curving to form S shape
  • Week 5 Septation starts, atrial and ventricular
  • Septation continues, atrial septa remains open, foramen ovale
  • Week 40 At birth pressure difference closes foramen ovale leaving a fossa ovalis

Blood flow through the Embryo

Maternal Blood | -> umbilical vein -> liver -> anastomosis -> sinus venosus -> atria ventricles-> truncus arteriosus -> aortic sac -> aortic arches-> dorsal aorta-> pair of umbilical arteries | Maternal Blood

This is shown on the stage 13/14 pig G6 section.

Image
Description

Transverse section

Heart is 2 tubes that fuse in the midline anterioe to pharynx.

The pericardial cavity can be imagined as the top of the "horseshoe" of the intraembryonic coelom. (where the arms become the pleural cavity and the ends fuse anteriorly to form a single peritoneal cavity).

This view shows the initial positioning of the ventricles above the atria. The ventricles are rotated into their correct anatomical position by the growth of the heart tube, bending into an "S" shape.

Initially...

Cardiac inflow- at the bottom (sinus venosus)

Cardiac outflow- at the top (truncus arteriosus)

References

About Notes

  • Lecture notes from the Anat 3311 1997 Science Embryology course compiled and written by Dr Mark Hill. Some notes derived from historic class notes.
  • Note Links to OMIM Entries are copies of originals for computers without internet access. Computers with internet access can directly access the database.

Links
Serial Sections Homepage
Human Homepage
Pig Homepage

m.hill@unsw.edu.au
Date Last Modified: 11/3/99
This site maintained by Dr M. Hill