Week 4: Cardiovascular development

Question 1

Describe early human circulation.

Answer 1

• heart forms via lateral folding, starts beating at day 21
• is in shape of linear tube, from cranial to caudal name: outflow-ventricle-atrial-inflow (sinus venous)
• inflow from embryo, yolk sac, placenta (via cardinal, vitelline, umbilical veins)
• outflow via aortic (pharyngeal) arch arteries

Question 2

What is looping in the dev. of the heart?

Answer 2

• converts linear heart tube to more similar to mature heart
• atrial chamber brought from caudal to a position dorsal and cranial to ventricle
• still single atrial and single ventricle chamber connected by AV canal (outflow connected to right ventricle which is a continuation of left ventricle)

Question 3

How do the AV valves develop?

Answer 3

• endocardial cushions form around AV canal by proliferation and migration of mesenchymal cells
• AV canal divided into left and right canals, become mitral and tricuspid valves

Question 4

Describe the maturation of the atria and development of venous inflow.

Answer 4

• SVC from right cardinal vein, IVC from right vitelline vein, coronary sinus a vestige of sinus venous
• sinus venosus, originally medial, moves to the right and is incorporated into primitive right atrium
• Sinus venarum: portion of sinus venosus which was incorporated into RA
• smooth part of RA: sinus venosus
• rough part of RA represents primitive RA
• auricle: most of primitive RA
• sulcus terminals (outer surface) and crista terminalis: jxn between sinus venous and primitive RA

Question 5

Describe atrial septation and the formation of foramen ovale.

Answer 5

1. septum primum (crescent shaped) forms on roof of atria and grows down
   - large opening appears in upper region
2. septum secundum forms from roof to the right of septum primum and grows down but doesn’t completely fuse with endocardial cushion
   - there’s a hole in both, offset from each other. Gap left is called foramen ovale
   - septum primum is basically a flap over the gap in septum secundum (1 way valve from RA to LA)

Question 6

Describe ventricular maturation and outflow tract septation.

Answer 6

• proliferation of ventricular cardiomyocytes–>thickening of chamber wall and formation of muscular portion of IVS
• Muscular portion fuses with endocardial cushion and tissue that grows down from outflow tract septum- (becomes membraneous portion)
• 2 opposing cushions form on inner surface of outflow tract, these grow towards each other and fuse to form septum that separates single outflow vessel into pulmonary and aorta

Question 7

What is the fate of the aortic arch arteries?

Answer 7

1 and 2nd form and regress once lower arteries form

• 3rd: common carotid arteries
• left 4th: arch of aorta
• rt 4th: brachiocephalic
• left 6th: left pulmonary artery and ductus arterioles
• rt 6th: forms right pulmonary artery, distal portion regresses

Question 8

Describe the three fetal shunts.

Answer 8

1. ductus venosus: carries oxygenated blood from umbilical vein (from placenta) through the liver to IVC to RA
2. foramen ovale: oxygen rich blood from IVC to RA shunted through FO to LA
   - minimal mixing of blood from SVC (deoxy) and IVC
3. ductus arteriosus: flow from RV to bypass lungs to distal part of aortic arch
   - This system allows more oxygenated blood to go to the head. Need to have blood in RV b/c needs to pump and grow muscle

Question 9

What changes occurs after birth?

Answer 9

• pre-natal: pressure in LA low vs. RA which shunts blood through FO to LA
• with birth, pulmonary resistance drops with expansion of lungs w/ inspiration. Increases blood flow to lungs, more return of blood to LA. Pressure changes where it is greater in LA than RA. Closes the septum primum flap against septum secundum.
• they eventually fuse. Fossa ovalis=thin septum primum
• ductus arteriosus closes by constriction–>ligamentum arteriosum
• ductus venous becomes redundant–>ligamentum venosum