Embryology of circulatory system

Question 1

What are the functions of the placenta?

Answer 1

• fetal homeostasis
• gas exchange
• acid base balance
• nutrient transport to foetus
• waste product transport from foetus
• hormone production
• transport of IgG
• PGE2 (maintain ductus patency)

Question 2

How does life in foetus differ from adults?

Answer 2

• placenta is included in circulation
• lungs are filled with fluid and are unexpanded
• liver has little role in nutrition and waste management
• the gut is not in use

Question 3

How dies foetal circulation work?

Answer 3

blood comes from placenta to the heart. A little bit goes to the lung but most of it supplies the body and brain then goes back to placenta

Question 4

What is contained within the umbilical cord?

Answer 4

-2 arteries and 1 vein

Question 5

What differs about the blood in foetuses?

Answer 5

In foetal circulation veins have oxygenated blood and arteries have deoxygenated blood

Question 6

What are the three shunts specific to foetal life?

Answer 6

• ductus venosus
• formamen ovale
• ductus arteriosus

Question 7

What is the anatomy of the ductus venosus?

Answer 7

It connects the umbilical vein to the inferior vena cava

Question 8

What is the anatomy of the foramen ovale?

Answer 8

Opening in atrial septum connecting RA to LA. Allows blood to flow from right side of circulation to the left

Question 9

What is the anatomy of the ductus arteriosus?

Answer 9

Connects pulmonary bifurcation to the descending aorta. Specific to foetal development

Question 10

What is th role of the ductus venosus?

Answer 10

-carries most o the placental blood straight to the IVC bypassing th portal circulation

Question 11

What is the role of the formamen ovale?

Answer 11

• allows blood to pass from RA to LA through the pass of least resistance.
• Allows the best oxygenated blood to enter left atrium and then on to LV, ascending aorta and carotids

Question 12

What is the pressure gradient in foetal circulation?

Answer 12

• pressure in right side is greater than on left side

- It is the opposite in adults where the increased pressure causes the flap to close

Question 13

What is the function of the ductus arteriosus?

Answer 13

-A duct through which most of the RV output joins into the descending aorta

Question 14

How is patency of ductus arteriosus maintained?

Answer 14

Circulating prostaglandin E2 produced by the placenta

Question 15

What happens to the O2 stats from birth until a few hours later?

Answer 15

• low O2 at birth (~65%)
• increases rapidly in first couple minutes (transition from blue to pink)
• increases gradually then after until reaches normal sats values

Question 16

What are the circulatory changes that occur?

Answer 16

• pulmonary vascular resistance drops as soon as the baby starts to breath
• systemic vascular resistance increases once cord is clamped and cut as the low resistance flow is cut off

Question 17

Describe the mechanism of duct constriction

Answer 17

• duct will start to constrict
• unlike lung circulation where oxygen is a vasodilator, in duct the rising oxygen concentration is a vasoconstrictor causing it to shut
• the source of prostaglandin gets removed
• few days after birth the duct is still a vessel that can be reopened if needed

Question 18

What occurs when the duct fails to close?

Answer 18

You get excessive blood circulating to lungs which can cause a few different things including the restriction of blood to other areas of the body

Question 19

What can be used to close the duct?

Answer 19

• wait and see
• surgery (high risk)
• ibuprofen or other non steroidal anti inflammatory.

Question 20

Why do non steroidal anti inflammatory drugs work to close the duct?

Answer 20

They inhibit prostaglandin production

Question 21

What is a duct dependent circulation?

Answer 21

A circulatory defect that depends on the duct being open to keep the baby alive

Question 22

What is an example of a duct dependant circulation?

Answer 22

Interruption of aortic arch

• The aortic arch terminates prematurely therefore cannot supply the body with blood. Therefore the body is supplied by the ductus.
• need to maintain duct patency until definitive surgery can be carried out

Question 23

When is persistant pulmonary hypertension most common?

Answer 23

In sick babies ie those with sepsis, cold stress etc

Question 24

What occurs in persistant pulmonary hypertension of the newborn?

Answer 24

• resistance to flow in lung circulation doesn’t drop
• therefore pressure in the right side is still higher than the left
• therefore blood flows across the atrium via duct
• this causes mixing of blood

Question 25

What are the signs of PPHN?

Answer 25

• blue baby

- large difference between pre and post ductal O2 sats

Question 26

How can you treat PPHN?

Answer 26

• ventilation
• oxygenation
• high systemic blood pressure
• inhaled nitric oxide
• ECLS (life support)