Embryology and Foetal Development

Question 1

What germ layer is the heart derived from?

Answer 1

(Visceral) Mesoderm, cranial to the developing neural tube.

Mesoderm forms skeletal muscle, smooth muscle, the heart, blood vessels, blood cells, kidney, spleen, fat cells, the skeleton, most connective tissues and most of the urogenital system.

Question 2

The primary heart field will form

Answer 2

The left and right atria and the left ventricle.

Question 3

The secondary heart field will form

Answer 3

The right ventricle and the outflow tract.

Question 4

3 mechanisms which cause repositioning of the cardiogenic fields;

Answer 4

Lateral folding
Cranio-caudal folding
Differential growth of the embryo

Question 5

What role does Lateral Folding play in repositioning the cardiogenic fields?

Answer 5

brings the forming heart tubes to the midline to fuse into a single tube

Question 6

What role does Cranio-Caudal Folding play in repositioning the cardiogenic fields?

Answer 6

Swings the heart tube into a position just ventral to the foregut pocket in the neck of the embryo with the inflow oriented toward the tail of the embryo and outflow oriented toward the head- heart tube now suspended from body wall by connective tissue called dorsal mesocardium.

Question 7

What role does Differential Growth of the Embryo play in repositioning the cardiogenic fields?

Answer 7

Causes the heart to be displaced toward the tail of the embryo, such that the heart ends up in the chest.

Question 8

The five dilatations of the heart tube, and what adult structures they develop into.

Answer 8

Truncus Arteriosus - aorta, pulmonary trunk.
Bulbus Cordis - trabeculated part of the RV, outflow part of both ventricles.
Ventricle - trabeculated part of the left ventricle.
Atrium- trabeculated part of both atria.
Sinus Venosus (right and left horns) - smooth part of the RA and the coronary sinus.

Question 9

Direction of blood flow through the primitive heart

Answer 9

Caudal to cranial

Question 10

When does looping/folding begin and what are the first movements at this stage?

Answer 10

Around day 23 of development.
Atrium- dorsal and cranial.
Ventricle - displaced left.
Bulbus Cordis - inferiorly, ventrally to the right.

Question 11

Degeneration of the central portion of the dorsal mesocardium…

Answer 11

leaves the primitive heart attached at the outflow and inflow ends- formation of the transverse pericardial sinus.