Lecture 36: Physiology of Pregnancy and the Fetus

Question 1

Major functions of the placenta

Answer 1

serves as fetal abdomen, lung, kidney and endocrine gland

Question 2

What are the characteristics of placental interface that ideal for maternal fetal blood flow?

Answer 2

• large surface area for exchange due to lots of villi
• maternal and fetal vasculatures are highly developed, both circulations are separate but really intimately close together

Question 3

What are the major features of the placenta and what are their functions?

Answer 3

1. Chorionic villi - functional unit, heavy branching for increased surface area
2. Intervillous space - maternal spiral arteries empty here, drained by maternal veins
3. Decidua basalis

Question 4

What is the pathway of maternal blood flow to the placenta?

Answer 4

Spiral arteries carry oxygenated maternal blood > empty into intervillous spaces > lots of surface area on the spaces slows the blood flow > increases nutrient exchange time with the placenta surface > blood drains to maternal veins

Question 5

What is the pathway of fetal blood flow to the placenta?

Answer 5

Umbilical arteries carry deoxygenated blood to placenta > branch into the chorionic villi capillary network to obtain the O2 from intervillous spaces > return to fetus via umbilical vein

*terminal dilations at the end of the capillary networks allow for slower exchange time

Question 6

Is the PO2 of blood flowing from placenta to fetus high or low?

Answer 6

30-35 mmHg, but compensated by fetal hemoglobin having higher O2 affinity, so O2 saturation for fetus is still ok

Question 7

What conditions allow the diffusion of CO2 from fetus to mom?

Answer 7

Higher partial pressure in umbilical arteries vs. intervillous space and fetal blood having lower affinity to CO2 compared to maternal blood > end result is diffusion of CO2 from fetus to mom

Question 8

Which substances are sent to the fetal circulation in the intervillous space via these mechanisms? 
Passive
Facilitated diffusion
Primary/secondary active transport
Receptor mediated endocytosis

Answer 8

1. non protein nitrogen wastes like urea, lipid soluble hormones
2. glucose
3. AAs, vitamins, minerals
4. large molecules (LDL, antibodies)

Question 9

hCG (human chorionic gonadotropin)

Trends in pregnancy levels and physiological functions:

Answer 9

Maternal levels: produced by syncytiotrophoblasts > double daily until 10 weeks, then falls

Function: stimulate LH receptors in corpus luteum to prevent luteolysis (degeneration) and to make progesterone to maintain pregnancy, some amount induces fetal Leydig cells to make testosterone, morning sickness

Question 10

hCS (human chorionic somatomammotropin)

Trends in pregnancy levels and physiological functions:

Answer 10

Maternal levels: produced by syncytiotrophoblasts at day 10 > diffuses to maternal serum at 3 weeks = increases gradually throughout pregnancy

Functions: fuel economy (glucose conversion to ketone/FAs, antagonize maternal insulin), lipolysis to use FAs for maternal energy, mammary gland develoipment

Question 11

Progesterone

Trends in pregnancy and physiological functions

Answer 11

Maternal levels: comes from CL > gradually increases throughout pregnancy

Functions: increase chances of implantation, pregnancy maintenance, inhibits uterine contractions, mammary gland growth

Question 12

Estrogen

Trends in pregnancy and physiological functions

Answer 12

Maternal levels: gradually increases in pregnancy

Functions: increase blood flow to placenta, increase in LDL receptor to enhance steroid production in placenta, increase in prostaglandin and oxytocin receptors (late pregnancy), mammary gland growth

Question 13

How does the maternal and fetal systems work together to maintain pregnancy?

Answer 13

Maternal Placental-fetal unit

Mother supplies cholesterol, fetal adrenal gland and liver supplies enzymes that the placenta lacks

Question 14

How is progesterone produced during pregnancy?

Answer 14

early preg: CL releases the progesterone
Week 8: progesterone production shifts to placenta

Syncytiotrophoblasts import cholesterol from maternal blood > release progesterone into maternal compartment = increase in progesterone levels during pregnancy

Question 15

How is estrogen produced during pregnancy?

Answer 15

Placenta does not have 17a hydroxylase and 17,20 desmolase to make estradiol

MPF unit works together (mom gives cholesterol, fetal adrenal gland and liver has the enzymes)

Question 16

What is preeclampsia?

Clinical symptoms?

Answer 16

• High BP and organ damage (kidneys and liver) during pregnancy, occurs after week 20
• proteinuria, generalized edema

Question 17

What are the complications of preeclampsia?

Answer 17

• Uterine arteries have decreased blood supply > —ischemia and endothelium damage with cytokine release
• can lead to eclampsia, HELLP (hemolysis, elevated liver enzymes, low platelets)

Question 18

Where does fetal hematopoiesis occur?

Answer 18

Yolk sac (early)
liver takes over (2nd trimester) 
bone marrow (end of pregnancy)