Embryology

Question 1

Which germ layer is the heart derived from?

Answer 1

(visceral) mesoderm

Question 2

Name the heart tube regions. What they give rise to?

Answer 2

truncus arteriosus ->aorta and pulmonary trunk
bulbus cordis -> trabeculated region of RV, outflow part of both ventricles
ventricle ->trabeculated part of LV
atrium -> trabeculated part of both atria
-sinus venosus -> smooth part of RA, coronary sinus

Question 3

key steps in septa formation

Answer 3

Atrial: septum primum and septum secundum form. These septa are incomplete - enclosing the foramen ovale. This closes at birth when the LA pressure rises.
Ventricular: muscular upgrowth from the floor of the ventricles plus a membrane component from the endocardial cushions - to form the interventricular septum.

Question 4

number the aortic arches and the major vessels they give rise to

Answer 4

The truncus arteriosus initially gives rise to 5/6 symmetrical pairs of aortic arches, which feed into the 2 dorsal aorta. Symmetry is lost as development progresses.
1 & 2: mostly obliterated (small part becomes maxillary artery)
3: common carotid arteries, external carotid, internal carotid
4: right side = proximal right subclavian artery. Left side = contributes part of the aortic arch
5: never makes any significant appearance
6: pulmonary arteries. Also, left = ductus arteriosus. Right = distal right subclavian arteries.

Question 5

how is division of the truncus arteriosus accomplished?

Answer 5

appearance of the spiral aortico-pulmonary septum - which separated the pulmonary trunk from the ascending aorta

Question 6

changes at birth?

Answer 6

• ductus arteriosum is made redundant when start breathing - it becomes the ligamentum arteriosum
• foramen ovale seals due to increased LA pressure
• ductus venosus (which short circuited the circulation of the liver) degenerates into the ligamentum venosum
• umbilical vein becomes the ligamentum teres

Question 7

Which area does the vitelline system drain in the embryo?

Answer 7

Yolk sac

Question 8

Which area does the umbilical system drain?

Answer 8

placenta

Question 9

What do the anterior an posterior cardinal veins (common cardinal vein) drain?

Answer 9

body

Question 10

What do the anterior an posterior cardinal veins (common cardinal vein) drain?

Answer 10

body

Question 11

during development, what happens to the initially symmetrical systems of veins which drain into the sinus venosus?

Answer 11

On the left:
-left vitelline and left umbilical disappear
-left cardinal remains (eventually becomes coronary sinus - which drains all the venous blood from the heart)
On the right:
-right umbilical loses its connection
-right vitelline, right anterior and right posterior cardinal veins remain - giving an enlarged venous horn
-Right sinus horn is now the main venous inflow into the heart
-right vitelline becomes the IVC
-right cardinal becomes the SVC
-much of the right sinus horn becomes part of the RA wall

Question 12

what are the adult functions of the 3 venous systems?

Answer 12

• vitelline (drains the yolk sac): portal venous system draining gut, hepatic sinusoids and veins, hepatic portion of IVC
• umbilical veins (oxygenated blood from placenta): right degenerates, left remains as definitive umbilical vein
• cardinal veins: give systemic venous system (anterior drain head and neck, posterior drain the body wall, gonadal and renal veins, iliac veins, IVC)