Fetal Circulation

Question 1

Placenta features:

Answer 1

• discoid in shape
• approximately 20cm diameter
• has a maternal and fetal surface

Question 2

Features of maternal surface of placenta:

Answer 2

• dark red
• made up of 40 cotyledons
• cotyledons made up of lobules, each containing a single villus
  -cotyledons separated by sulci

Question 3

Features of fetal surface:

Answer 3

• shiny due to amnion covering it
• umbilical veins and arteries are visible, branching from the centre where umbilical cord is

Question 4

Purpose of placenta:

Answer 4

-exchange of substance between maternal and fetal circulatory system without mixing
-establishes a diffusion gradient
- placenta releases hormones

Question 5

Features of umbilical cord:

Answer 5

-about 50cm long
- has 2 arteries and 1 vein
-wrapped in soft connective tissue and surrounded by whartons jelly

Question 6

How does o2 diffuse to the fetus?

Answer 6

• o2 diffuses through the wall of the villi and binds to fetal haemoglobin
• fetal haemoglobin has a higher o2 affinity

Question 7

Metabolism and the placenta:

Answer 7

• placenta can metabolise proteins, fats and carbs into simple molecules
• fats can cross the placenta easily
• placenta stores glycogen

Question 8

Excretion of waste and the placenta:

Answer 8

• waste products of metabolism (co2) diffuse from fetus to mother

Question 9

Placenta and protection:

Answer 9

• protection against most bacteria
• smaller microorganisms can pass (HIV, syphilis)
• placenta transfers igG antibodies and rhesus antibodies to fetus

Question 10

What produces hCG and what is its function:

Answer 10

• trophoblast produces hCG
• maintains corpus luteum

Question 11

What produces progesterone?

Answer 11

-corpus luteum
- provides a nourishing environment

Question 12

What is the purpose of there being high concentrations of oestrogen and progesterone?

Answer 12

To maintain the pregnancy

Question 13

How does the pregnant body become insulin resistant?

Answer 13

-human placental lactogen hormone produced
- regulates metabolism and frees up glucose

Question 14

How is the fetus protected from immune rejection?

Answer 14

The trophoblast has unique immunological properties

Question 15

Placenta and stem cells:

Answer 15

• placenta tissue and whartons jelly and cord blood has potential stem cells

Question 16

Features of fetal circulation:

Answer 16

• fetal lungs are filled with fluid and play no role in gaseous exchange as this happens at the placenta
• fetal blood is circulated around organs that require it as gastrointestinal and kidneys do not function until after birth

Question 17

Three shunts and their function:

Answer 17

• directs o2 blood to essential areas
• ductus venousus
• foramen ovals
• ductus arteriosus

Question 18

What is the ductus venosus and what is its function?

Answer 18

• continuation of umbilical vein
• shunts portion of umbilical vein blood flow to the inferior vena cava
• allows o2 blood from placenta to bypass liver

Question 19

What is foramen ovale?

Answer 19

-opening in the septum that separates two atria
-covered by tissue acting as a valve
-blood flows from right to left atria
-bypasses lungs

Question 20

What is the ductus arteriosus and what does it do?

Answer 20

-connects pulmonary artery to descending thoracic arch
- diverts blood so very little passes through the lungs

Question 21

Path of fetal blood:

Answer 21

• umbilical vein has o2 blood
  -vein carries o2 blood through D.V and joins the I.V.C
  -to the R.A and through the F.O to the L.A
  -to the L.V and then the aorta to the brain and body
• umbilical artery brings blood back to the placenta for oxygen

Question 22

Why is it important that fetus’ chest is squeezed on descent though the vagina?

Answer 22

Fluid is squeezed out of the lungs so breathing can begin with inflation

Question 23

Stimuli that initiate breathing:

Answer 23

1) thermal- being cold
2) tactile- physical stimulation
3) chemical- cortisol and ADH increase

Question 24

What happens when the lungs inflate for the first time?

Answer 24

• increase in thoracic pressure
• remaining fluid in lungs is absorbed into bloodstream

Question 25

What happens to the cord after birth?

Answer 25

Whartons jelly constricts as temperature falls

Question 26

How does the foreman ovale close?

Answer 26

Pressure in left atria becomes higher than the right