Thorax 7: Foetal Circulation

Question 1

How does blood circulate through the foetal heart?

Answer 1

enters the Right atrium, bypasses pulmonary circulation and enters the left atrium, enters the left ventricle, goes up into the aorta to the systemic circulation

Question 2

What is the function of the placenta?

Answer 2

Nutrients and metabolites diffuse across the placental barrier from mother to foetus and vice versa

Question 3

Describe the composition of placenta

Answer 3

formed of foetal tissue which thins as pregnancy progresses

Question 4

Explain the structure of the placenta

Answer 4

• membrane between 2 circulations= foetal and maternal
• endothelium of foetal capillaries is covered by syncitiotrophoblast presenting a huge surface area of microvilli
• maternal capillaries break down and maternal blood bathes foetal microvilli directly

Question 5

How is oxygenated blood transported from the placenta to the foetus?

Answer 5

1 Umbilical vein

Question 6

what vessels carry deoxygenated blood from the foetus? how many are there?

Answer 6

2 umbilical arteries

Question 7

What happens to blood in the placenta?

Answer 7

blood is oxygenated and picks up nutrients from maternal blood across the placental membrane

Question 8

What are the 2 adaptations of the foetal circulation?

Answer 8

• no need for pulmonary circulation since blood is oxygenated at the placenta
• no need for a hepatic circulation since nutrients already modified by maternal liver

Question 9

How does blood pass from the Right atrium to the left atrium in the foetal heart?

Answer 9

blood is directed by a valve through the foramen ovale

Question 10

what is the function of the foramen ovale?

Answer 10

bypasses the right ventricle and pulmonary trunk hence the pulmonary circulation

Question 11

What is the purpose of the Ductus Arteriosus?

Answer 11

bypass the pulmonary circulation, carries venous blood directly into the aorta after the arch and its branches

Question 12

where is the Ductus A. situated?

Answer 12

connects the pulmonary trunk to the inferior aspect of the arch of the aorta

Question 13

what happens to blood that reaches the foetal lungs?

Answer 13

10% of right ventricle blood passes into the pulmonary circulation to provide the developing lungs with oxygenated blood

Question 14

What is the purpose of the Ductus venosus?

Answer 14

oxygenated blood from the mother entering the foetus via the placenta must bypass the liver, this is done by the Ductus V.

Question 15

Where does the Ductus V. drain to?

Answer 15

Drains into the IVC

Question 16

What is the blood composition of the foetal IVC?

Answer 16

• oxygeanted, nutrient rich blood from Ductus V.

- deoxygenated blood with waste products returning from the foetal systemic circulation

Question 17

how is the pulmonary circulation established at birth?

Answer 17

• first breath pulls blood into the pulmonary circulation
• sudden increase in pressure in the Left atrium pulls the inter-ventricular septum shut closing the foramen ovale
• blood is returned from pulmonary circulation and Left A pressure=Right Atrium pressue

Question 18

How many phases is the ductus arteriosus destroyed in?

Answer 18

2

Question 19

what happens in the first phase of destruction of the Ductus A. ?

Answer 19

• due to smooth muscle contraction
• oxygen is a potent constrictor of Ductus A. and the oxygen tension of blood in aorta and PT increases after 1st breath
• drop in prostaglandins since no longer produced by placenta= Ductus A. closure

Question 20

What happens in the second phase of destruction of the Ductus A.?

Answer 20

-thickening of tunica intima that occurs over a period of 1-3 months

Question 21

What artefact is left behind from the Ductus A.?

Answer 21

ligamentum arteriosum

Question 22

What happens to the Ductus Venosus?

Answer 22

• with delivery of placenta the umbilical vessels contract and get obliterated over a period of days
• hepatic circulation becomes established and the Ductus Venosus becomes the Ligamentum Venosum

Question 23

What structure does the umbilical vein develop into?

Answer 23

Ligamentum teres

Question 24

what do the 2 umbilical arteries develop into?

Answer 24

medial umbilical ligaments