W9.0 - fetal physiology

Question 1

Which fetal vessel carries oxygenated blood from the mother?

Answer 1

-Umbilical vein

Question 2

Which fetal vessel(s) carries deoxygenated blood from the mother?

Answer 2

-Umbilical arteries

Question 3

Regarding the placenta, where are the fetal capillaries?

Answer 3

-Within the chorionic villi

Question 4

What happens to the placental barrier as pregnancy progresses?

Answer 4

-Gets thinner until it comprises only fetal capillary endothelium and syncytiotrophoblast

Question 5

Why is a gradient of partial pressure required at the placental barrier?

Answer 5

-Allow O2 to pass into fetal blood and CO2 to pass into maternal blood

Question 6

What 3 factors establish the pO2 gradient between mother and fetus?

Answer 6

• Increased production of 2,3-BPG in the mother
• Fetal haemoglobin variant
• Double bohr effect?

Question 7

How does an increase in 2,3-bpg in the mother help create the pO2 gradient?

Answer 7

-Promotes the T state and thus more O2 is given up into the blood, thus more is available to cross the diffusion barrier

Question 8

How does fetal Hb help create the pO2 gradient?

Answer 8

-Fetal Hb has 2 a and 2 g chains. g chains have a lower affnity for 2,3-bpg and this promotes the R state of Hb, thus there is a higher affinity of fetal Hb for O2

Question 9

What is the double bohr effect and how does it help create the pO2 gradient?

Answer 9

• A process which helps to speed up O2 transfer
• As CO2 passes into intervillous blood, there is a decrease in pH causing promotion of the T state and thus more O2 is given up
• As CO2 leaves fetal blood, there is an increase in pH causing promotion of the R state which has a higher affinity for oxygen

Question 10

What 2 factors promote CO2 transfer between fetus and mother?

Answer 10

• Progeterone-driven hyperventilation causing more acid to be blown off producing a physiological respiratory alkalosis -> This generate a concentration gradient between mother and fetus
• Double haldane effect -> As maternal Hb gives up O2 it can accept more CO2 and as fetal hb accepts more O2 it gives up more CO2

Question 11

How does oxygenated blood from the umbilical vein bypass the lungs?

Answer 11

• Enters right atrium and streams across into left atrium through foramen ovale
• If pumped into right vetricle-> leave pulmonary trunk through ductus arteriosus into aorta

Question 12

What is ductus venosus? Why is it important?

Answer 12

• Bypass of liver between umbilical vein to IVC

- Allows oxygenated blood to enter the right atrium and go to the brain without being desaturated by the liver

Question 13

Why is it significant that ductus arteriosus joins after the supply to the head and the heart?

Answer 13

-Blood from DA is highly deoxygenated as it mixed into the RV with the blood returning via the SVC -> therefore by joining after supply to the head/heart it makes sure that they recieve oxygenated blood.

Question 14

Describe the fetal response to hypoxia

Answer 14

• HbF and Hb conc increases
• Redistribution of flow to protect vital organs cuah as head and heart (GIT, renal and limbs reduced)
• Slowing of fetal HR due to vagal stimulation via chemoreceptors detecting drop in O2 or rise in CO2

Question 15

What is the result of chronic hypoxaemia on the fetus?

Answer 15

• Growth restriction

- Behavioural changes

Question 16

Name the hormones important for fetal growth and state when they are most dominant

Answer 16

-Insulin
-IGFI -> dominant in T2 and T3
-IGFII -> dominant in T1
-Leptin
(EGF and TGF-a)

Question 17

Which hormone required for fetal growth is nutrient dependent? What does this mean?

Answer 17

• IGF 1

- The ability for growth is dependent upon the utrient status of the mother

Question 18

When does symmetrical growth restriction occur and why?

Answer 18

• Malnutrition upto 28 weeks

- Growth is affected in a symmerrical way as hyperplasia is the most significant growth mechanism

Question 19

When does asymmetrical growth restriction occur and why?

Answer 19

-28+ weeks as the dominant growth mechanism is hypertrophy

Question 20

What are the 2 main functions of amniotic fluid?

Answer 20

• Protection

- Development of lungs

Question 21

State the approximate volumes of amniotic fluid at 8 weeks and 38 weeks?

Answer 21

• 10 ml at 8 weeks

- 1L at 38 weeks

Question 22

What happens to the amniotic fluid post EDD?

Answer 22

-Falls away due to placental senescence

Question 23

What is the main system in the production of amniotic fluid? Why?

Answer 23

• Urinary system

- Urine makes up the majority of amniotic fluid

Question 24

What systems/tissues are involved in the recycling of the amniotic fluid and how?

Answer 24

• Recycled by the baby through breathing into the lungs and swallowing into the GI tract -> returned to the amniotic sac by the urinary system
• Placental and fetal membranes also recycle the amniotic fluid by the intramembranous pathway

Question 25

Describe the composition of amniotic fluid

Answer 25

• 98% water

- Urea, electrolytes, creatinine, bile pigments, renin, glucose

Question 26

What is lanugo?

Answer 26

-Fine hair which covers the fetus duing development

Question 27

what is vernix caseosa?

Answer 27

-White liquid which covers the baby to prevent the skin drying out on contact with air

Question 28

What is meconium?

Answer 28

• Debris from amniotic fluid and intestinal secretions which accumulates in the gut -> first baby faeces
• Can pass on delivery id baby is under stress eg hypoxia

Question 29

What is amniocentesis?

Answer 29

• Sampling of amniotic fluid allowing collection of fetal cells
• Used for diagnostic testing eg fetal karyotyping

Question 30

What happens to the bilirubin metabolism in utero?

Answer 30

-Bilirubin is handled suffieicntly by the placenta as the liver is immature and lacks enzymes for conjugation and excretion

Question 31

Why is physiological jaundice common in pre-term baby?

Answer 31

-Physiological processes to deal with bilirubin occur late in development and thus the liver is too imature to handle bilirubin