Fetal Circulation

Question 1

Describe postnatal circulation

Answer 1

• separate pulmonary and systemic circulations
• no mixing of oxygenated and deoxygenated blood
• oxygenation of blood occurs in the lungs
• extensive hepatic blood supply

Question 2

What limitations and special needs does a developing foetus have?

Answer 2

• Lungs are not functioning as in adults
• digestive system is not functioning as in adults
• Foetus has restricted hepatic circulation

Question 3

What are the 3 shunts/by-passes in foetal circulation to avoid the lungs and liver

Answer 3

• By-pass of hepatic cirulation
• By pass of the pulmonary circulation vua the foramen ovale
• By-pass of the pulmonary circulation by ductus arteriosus

Question 4

What travels across the placenta?

Answer 4

O₂ and nutrients diffuse across the placental barrier from mother to foetus while CO₂ and metabolic waste are removed via the placenta

Question 5

What is the placenta?

Answer 5

Interface between the foetus and mother

Question 6

Do maternal and foetal blood ever mix?

Answer 6

NO

Question 7

Where is the placenta located?

Answer 7

at the fundus of the uterus

Question 8

What surrounds the umbilical cord?

Answer 8

• Fetal membrane
• amnion
• contains Wharton’s Jelly

Question 9

What is embedded in Wharton’s jelly?

Answer 9

two umbilical arteries and a single umbilica vein

Question 10

What is another name given to the umbilical vein?

Answer 10

Ductus Venous

Question 11

What travels in the umblicial vein?

Answer 11

Oxygen- and nutrient-rich blood from the placenta

Question 12

What 2 branches does the umbilical vein divide into? And where do the branches go?

Answer 12

• Smaller branch, which goes to the liver
• Larger branch, ductus venosus by-passes the liver and drains into the inferior vena cava

Question 13

What occurs when the umbilical vein/ductus venosus merges with the IVC

Answer 13

arterial blood mixes with venous blood from the lower limbs

The amount of venous blood = insignficant

Question 14

Where does most of the blood coming through the IVC passes through

Answer 14

Passes from the RA into the LA through foramen ovale then onto the LV and aorta

Question 15

What is foramen ovale?

Answer 15

The shunt that connects the right atrium to the left atrium.

It means some oxygenated blood travels into the RA

Question 16

How does the valve of the IVC influence blood flow?

Answer 16

Causes blood to travel through FO with the correct trajectory

Question 17

Where does blood carried by the superior vena cava (de-oxygenated) travel to?

Answer 17

• RA
• RV
• Pulmonary Trunk
• Ductus Arteriosus (90%)
• Aorta

Question 18

What is the ductus arteriosus?

Answer 18

connection between the pulmonary trunk and aorta; 90% of the blood = shunted

Question 19

Where is one thrid of the blood carried in the descending aorta distributed to?

Answer 19

abdomen, pelvis and lower limbs

Question 20

Where does two thirds of the blood in the descending aorta travel to?

Answer 20

go to the placenta

Iliac artery ⇒ umbilical artery ⇒ placenta

Question 21

Draw a diagram of fetal circulation

Answer 21

Question 22

What occurs at birth that is vital to post natal circulation?

Answer 22

Shunts must be obliterated at birth when the pulmonary circulation comes on stream

Question 23

What occurs when the umbilical cord is tied and cut?

Answer 23

• Loss of blood flow through the placenta
• Increased systemic vascular resistance
• Increased aorta, LV and LA pressures

Question 24

What occurs when a child takes their first breath?

Answer 24

• Expansion of the lungs (alveoli)
• Decreased pulmonary vascular resistance
• Reduced pulmonary arterial, RV and RA pressures

Question 25

What occurs when pulmonary circulation is established?

Answer 25

• blood from the lungs is returned to the LA
• Pressure rises in the LA
• Valve of the foramen ovale is pushed rightward and closes the foramen
• This is the functional closure

Question 26

When does structural closure of the FO occur? And what does this form

Answer 26

4 months

Forms fossa ovalis and falx septi

Question 27

What is patent foramen ovale (PFO) and what can it cause?

Answer 27

• Consequence of non-closure
• usually asymptomatic
• May cause paradoxical emboli

Question 28

When does the functional closure of ductus arteriosus occur? And how does it occur?

Answer 28

first hour

constriction of smooth mucle on all of ductus arteriosus. O₂ stimulates the bradykinin which causes vessels to constrict. There is also a fall in prostaglandins which are usually repsonsible for vasodilation

Question 29

When does the structural obliteration of ductus arteriosus occur? And how?

Answer 29

Within 1 and 4 months

Anatomical closure by thickening of the tunica intima

Question 30

What does the obliterated ductus arteriosus become?

Answer 30

Ligamentus arterosium

Question 31

Patent Ductus Arteriosus

Answer 31

• Postnatally the aortic pressure i greater than in the pulmonary trunk
• Blood will flow back into the pulmonary circulation
  
  • left to right shunt
  • Increased pulmonary blood flow ⇒ pulmonary hypertension
  • Congetsive heart failure

Question 32

What occurs in the obliteration of the umbical vein?

Answer 32

forms the round ligament of the liver (ligament teres hepatis)

Question 33

What do the distal parts of the umblical arteries become?

Answer 33

Medical umbilical ligaments

Question 34

What occurs in obliteration of ductus venosus when blood flow through the umbilical vein ceases?

Answer 34

• Muscle wall of ductus venosus contracts
• Portal venous blood flows through hepatic sinuses
• Closes within 1 to 3 hours of birth
• becomes ligamentum venosum