Fetal Circulation

Question 1

Primitive heart tube receives blood from what 3 venous sources?

Answer 1

1. Vitelline veins
   - umbilical vesicle/yolk sac to heart
2. Cardinal veins
   - body to heart
3. Umbilical veins
   - chorionic sac/placenta to heart

Question 2

During 4th week of development, where does oxygenated blood exit the heart?

Answer 2

via aortic sacs and the pharyngeal (aortic) arch arteries that supply the pharyngeal arches and flows to the dorsal aorta

Question 3

what does the dorsal aorta become?

Answer 3

-fuse caudally to become the common aorta which delivers blood to the rest of the body

Question 4

When do pharyngeal arch arteries develop?

Answer 4

4th week

Question 5

What do pharyngeal arch artery derivatives form?

Answer 5

form the fetal arterial system by 8th week

Question 6

How many pairs of pharyngeal arch arteries form?

Answer 6

• 6 pairs develop

- by the time the 6th pair forms, the first 2 have disappeared

Question 7

1st PAA derivative?

Answer 7

• mostly disappears

- contribution to Maxillary Artery

Question 8

2nd PAA derivative?

Answer 8

• disappears mostly

- contribution to Hyoid and Stapedial arteries

Question 9

3rd PAA?

Answer 9

• ventral part to Common Carotid

- dorsal part to Internal Carotid

Question 10

4th PAA?

Answer 10

• right side: proximal part of Subclavian artery

- left side: part of Aortic arch

Question 11

5th PAA?

Answer 11

rudimentary vessel

Question 12

6th PAA?

Answer 12

• right side: part of right pulmonary artery

- left side: part of left pulmonary artery and ductus arteriosus

Question 13

Change of course of Recurrent Laryngeal Nerve?

Answer 13

1. Asymmetric transformation of 6th PAA cause recurrent laryngeal to change
2. Right degenerates distally, moves to hook around proximal right Subclavian artery
3. Left hooks around ductus arteriosus which involutes to become ligamentum arteriosum after birth

Question 14

Coronary vessel formation?

Answer 14

1. Proepicardium provides cell precursors for coronary vessels
2. Proepicardial cells migrate out to form epicardium
3. Epicardium undergoes EMT to form vascular smooth muscle cells and endothelial cells of coronary vessels
4. Newly formed coronary arteries enter the Aorta

Question 15

Vitelline Veins development?

Answer 15

1. drain yolk sac and enter sinus venous
2. anastomose around duodenum to form portal vein
3. hepatic sinusoids incorporate into liver
4. Left vitelline regresses
5. Right vitelline form hepatic portal system (superior mesenteric) and part of IVC

Question 16

Umbilical veins development?

Answer 16

1. paired umbilical veins transport oxygenated blood from placenta to sinus venosus
2. right umbilical regresses
3. left umbilical forms shunt through liver to t he IVC, the ductus venosus

Question 17

Anterior Cardinal veins development?

Answer 17

1. Anastomosis between left and right allows shunting of blood
2. anastomotic shunt becomes left brachiocephalic vein upon losing connection with left common cardinal
3. right anterior cardinal becomes right brachiocephalic vein

Question 18

Posterior Cardinal veins development?

Answer 18

1. Subcardinals
   - anastomose between kidneys, forms IVC (renal), renal veins, and gonadal veins
2. Supracardinals
   - anastomose across midline
   - forms azygous and hemiazygous vein and superior intercostal veins
3. Sacrocardinals
   - anastomose between subcardinals and supracardinals
   - form IVC (lumbar) and common iliac veins

Question 19

Common cardinal veins development?

Answer 19

1. joins anterior and posterior cardinals
2. enters sinus venosus
3. left common cardinal forms oblique vein of left atrium
4. right common cardinal forms SVC

Question 20

How does oxygenated blood reach the fetus?

Answer 20

-form placenta to fetus via Umbilical Vein

Question 21

Ductus venosus?

Answer 21

-blood shunt that bypasses liver and enters IVC

Question 22

Foramen Ovale?

Answer 22

• blood shunt that bypasses the right ventricle
• goes straight from right to left atrium
• bypasses pulmonary circulation

Question 23

Ductus Arteriosus?

Answer 23

1. some blood passes through tricuspid valve into right ventricle
2. pumped through pulmonary artery
3. blood shunt that bypasses lungs, reaches descending Aorta

Question 24

How does deoxygenated blood return back to the mother?

Answer 24

-from fetus to placenta via Umbilical arteries

Question 25

What is the first thing that happens with the first breath?

Answer 25

Ductus venosus constricts into the ligamentum venosum

Question 26

What does the first aeration of the lungs cause?

Answer 26

- decreased pulmonary vascular resistance - increased pulmonary blood flow - thinning of pulmonary arterial walls - increased left atrial pressure to close the foramen ovale - increase pO2 through ductus arteriosus - increased Bradykinin secretion - decreased prostaglandin E2 and Prostacyclin I2 production - Ductus Arteriosus constricts into the ligamentum arteriosum - left ventricle hypertrophies

Question 27

Ventricular septal defect?

Answer 27

- most common type of congenital heart defect - membranous VSDs are the most common and result from failure of IV muscular and membranous ridges to align properly with bulbar ridges and AV cushions

Question 28

Atrial septal defects? 4 clinically significant?

Answer 28

- most common is patent foramen ovale - clinically insignificant unless accompanied by other defects - 4 types clinically significant ASDs: 1. ostium secundum 2. ostium primum with endocardial cushion defect 3. sinus venosus defect 4. common atrium

Question 29

Transposition great arteries?

Answer 29

- most common cause of cyanotic heart disease in newborns - Aorta lies anterior and to right of pulmonary trunk, arises from morphologic right ventricle - Pulmonary artery arises from morphologic left ventricle - associated with other anomalies (ASD, VSD) that permit shunt of blood between systemic and pulmonic circulations

Question 30

Chest xray of transposition of great arteries?

Answer 30

- egg on a string appearance with increased pulmonary vascularity - occurs more often in males

Question 31

Persistent truncus arteriosus?

Answer 31

- results from failed septation of truncus into an aortic and pulmonary trunk - single arterial trunk arises from heart to supply pulmonic, systemic and coronary circulation - cyanotic congenital defect that is always accompanied by VSD the allows for circulatory flow circuit completion