Fetal Circulation

Question 1

How is the primitive heart of the embryo formed? (4)

Answer 1

It begins as 2 oval clusters of mesoderm either side of embryo midline

Pericardic mesoderm migrates towards head and fuses in midline as 2 parallel cords of cells

These enlarge to develop internal canal (endocardial tubes)

Tubes fold over and fuse to create primitive cardiac tube

Question 2

When do primitive blood vessels start to form?

When does the primitive cardiac tube start to pulsate?

Answer 2

Week 3

Question 3

What 3 circulations become interconnected

Answer 3

Chorionic- umbilical veins
Vitelline- from yolksac
Cardinal- from various parts of the body

Question 4

Where does blood enter the fetal heart?

Answer 4

Via the sinus venosus

Question 5

4 layers of the endocardial tube

Answer 5

Endothelium
Myocardium
Cardiac jelly
Epicardium

Question 6

Oxygenated blood enters fetus via what

Answer 6

Umbilical vein

Question 7

As blood enters fetus via umbilical vein, half the blood goes where and the other half goes where?

Answer 7

50% enters hepatic circulation and later joins inferior vena cava via hepatic veins

50% goes directly to Inferior vena cava via ductus venosus

Question 8

What does fetal blood go via to reach the inferior vena cava?

Answer 8

Ductous venosus

Question 9

Ductus venosus

Answer 9

Vein that shunts blood from umbilical vein to inferior vena cava (allowing oxygenated blood to bypass the liver)

Question 10

What allows fetal blood to bypass the liver

Answer 10

Ductus venosus - Carey’s blood from umbilical vein to inferior vena cava

Question 11

When fetal blood enters heart from inferior vena cava it is directed where via what?

Answer 11

Directed into left atrium via foramen ovale

Question 12

Foramen ovale

Answer 12

Small hole in heart septum between the two atria

Question 13

Why does oxygenated fetal blood mix with deoxygenated blood?

Answer 13

Because of the foramen ovale

Question 14

Which chamber does blood from inferior vena cava and superior vena cava enter?

Answer 14

Right atrium

Question 15

Where does blood from pulmonary veins enter?

Answer 15

Left atrium

Question 16

Blood from right ventricle leaves via what?

Answer 16

Pulmonary artery to lungs

Question 17

Where does blood from the left ventricle leave via?

Answer 17

Aorta around the body

Question 18

Valve between left ventricle and aorta

Answer 18

Aortic valve

Question 19

Valve between right ventricle and pulmonary artery

Answer 19

Pulmonary valve

Question 20

Valve between left atrium and left ventricle

Answer 20

Mitral valve (bicuspid)

Question 21

Valve between right atrium and right ventricle

Answer 21

Tricuspid valve

Question 22

What divides the two atria, which has a foramen ovale in it?

Answer 22

Septum secundum

Question 23

Why does blood only go through the foramen ovale right to left flow?

Answer 23

It has a one way valve

Question 24

What type of arteries convey deoxygenated blood to the placenta?

Answer 24

Hypogastric arteries

Question 25

From the lungs where is blood shunted to the aorta?

Answer 25

Ductus arteriosus

Question 26

What happens to the foramen ovale after birth?

Answer 26

It closes

Question 27

What causes the foramen ovale to close?

Answer 27

Blood pressure becomes higher at birth due to increased blood flow. This causes pressure in left atrium to become higher then in right atrium which closes the hole

Question 28

At birth the right ventricle wall is thicker but this changes to the left ventricle wall when?

Answer 28

By the time the baby is 1 month old

Question 29

What helps to prevent blood loss at birth?

Answer 29

Hypogastric arteries constrict

Question 30

List the pathway of blood in fetal circulation starting from the umbilical vein

Answer 30

1) Oxygenated blood enters fetus via umbilical vein. Some of this goes to inferior vena cava via the ductus venosus.

The other half goes to the kidneys and then to the inferior vena cava via hepatic veins.

2) Blood in the inferior vena cava enters the right atrium
3) Most of this oxygenated blood in the right atrium moves into the left atrium due to the foramen ovale and mixes with the deoxygenated blood
4) blood in the left atrium is pushed into the left ventricle via the mitral valve
5) Blood in the left ventricle moves into the aorta via aortic valve
6) blood in the aorta is sent around the body and returns to the right atrium via the superior vena cava
7) most of this blood moves through the foramen ovale into the left atrium but the blood that doesn’t moves into the right ventricle via the tricuspid valve
8) the blood in the right ventricle will go towards the lungs via the pulmonary artery through the pulmonary valve
9) only a small amount of blood enters the lungs, the rest is shunted away from them via the ductus arteriosus to the aorta
10) deoxygenated blood from the aorta then enters the umbilical arteries and flows to placenta.
11) the rest of the blood returns to the heart via the superior vena cava