Physiology of Pregnancy & the Fetus

Question 1

What are the main functions of the placenta

Answer 1

1. Endocrine gland function: synthesizes steroids and proteins that affect both maternal and fetal metabolism
2. Serves as the fetal gut, lung & kidney

Question 2

What are the 3 major features of the placenta & their function?

Answer 2

1. Chorionic Villi: Functional unit of the fetal side of the placenta

2. Intervillous Space: Place where spiral arteries from maternal side empty in the placenta, forming a “pool” of blood

3. Decidual basalis: part of the endometrium in the pregnant human female that participates with the chorion in the formation of the placenta.

Question 3

Explain blood flow in the fetus

Answer 3

• 2 Umbilical arteries that carry deoxygentaed blood away from the fetus
• 1 umbilical vein that carries oxygenated blood to the fetus

Question 4

Why is blood flow slow in the fetus

Answer 4

Allows for exchange of nutrients

Question 5

How does oxygen flow from the mother to the fetus

Answer 5

Oxygen has a higher affinity for the fetal Hb so it will move from the mother to the fetus through the placenta

Question 6

How does CO₂ flow between the mother and the fetus

Answer 6

Driven by concentration gradient

CO₂ has a higher affinity for the mother’s blood so it’ll diffuse from the fetal blood to the pool of maternal allowing waste to be removed from the fetus

Question 7

What main hormones were discussed in lecture

Answer 7

1. Human Chorionic gonadotropin (hCG)
2. Human placental lactogen (hPL or hCS)
3. Progesterone
4. Estrogen

Question 8

What are some general functions of placental hormones in pregnancy

Answer 8

• Maintaining the pregnant state of the uterus
• Stimulating milk production of maternal breasts
• Adapting aspects of maternal metabolism and physiology to support a growing fetus
• Regulating aspects of fetal development
• Regulating timing and progress of parturition

Question 9

What cells secrete hCG

Answer 9

Syncytiotrophoblasts

Question 10

What is the function of hCG

Answer 10

Stimulates LH receptors in corpus luteum to maintain high levels of luteal-derived progesterone

Question 11

hCG facts you should probably know

Answer 11

• Structurally related to LH & binds LH receptors with high affinity
• Glycosylation increases it’s half-life
• Rapidly accumulates in maternal circulation. SERUM LEVELS DOUBLE UP DAILY UP TO ~10 WEEKS
• Thought to be responsible for nausea associated with morning sickness
• Enters fetal circulation & stimulates fetal Leydig cells to produce testosterone

Question 12

What cells produce Human placental lactogen (hPL) aka Human chorionic somatomammotropin (hCS)

Answer 12

Syncytiotrophoblast

Question 13

What is the function of hPL/hCS

Answer 13

Role in coordinating fuel economy from mom to fetus

• Conversion of glucose to fatty acids and ketones
• lipolytic actions help mother shift to free-fatty acid use for energy

Question 14

What are some thing you should probably know about hPL/hCS

Answer 14

• Structurally related to Growth Hormone & Prolactin
• Can have antagonistic action to maternal insulin, contributing to diabetogenicity of pregnancy
• Promote development of maternal mammary glands during pregnancy
• Detected at day 10 in synchiotrophoblast and in maternal serum at 3 weeks

Question 15

What hormone is required in high levels throughout pregnancy

Answer 15

Progesterone

Question 16

Why is progesterone required throughout pregnancy

Answer 16

• Required for implantation & early maintenance of pregnancy
• Reduced uterine motility
• Inhibits propagation of uterine contractions
• Induces mammary growth and differentiation

Question 17

What secretes progesterone

Answer 17

Corpus luteum during early pregnancy

Placenta takes over

Question 18

What are the functions of Estrogen

Answer 18

• Induces endometrial growth, progesterone receptor expression & LH surge just prior to ovulation
• Increases blood flow from uterus to placenta
• Increases LDL rceptor expression in syncytiotrophoblasts
• Induces prostaglandins & oxytocin receptors necessary for parturition (birth)
• Increases the growth and development of mammary glands

Question 19

What shunt bypasses the fetal liver

Answer 19

Ductus venosus

Question 20

Explain fetal blood flow using the ductus venosus

Answer 20

Oxygenated blood from the placenta travels to the right atrium of the heart.

Umbilical veins –> ductus venosus –> inferior vena cava –> right atrium

Bypasses liver

Question 21

What does the foramen Ovale do

Answer 21

Moves blood from the right atrium to the left atrium in the fetus

Question 22

What shunt moves blood from the pulmonary artery to the aorta

Answer 22

Ductus Arteriosus

Question 23

Explain how the ductus arteriosus works

Answer 23

The ductus arteriosus is a normal fetal artery connecting the main body artery (aorta) and the main lung artery (pulmonary artery). The ductus allows blood to detour away from the lungs before birth. Every baby is born with a ductus arteriosus.

Question 24

What is Patent Ductus Arteriosus (PDA)

Answer 24

Heart problem caused by failure of the ductus arteriosus to close. Leads to oxygenated blood in aorta mixing with deoxygenated blood in pulmonary atery which puts strain on the heart & increases pulmonary blood pressure.

Question 25

What causes the closure of foramen ovale

Answer 25

After birth there is a reversal of pressure gradient across the atria:

• Increased venous return to left atrium & elevated left atrial pressure
• Decreased right atrial pressure

Question 26

What is patent foramen ovale

Answer 26

Failure of Foramen Ovale to close permanently due to increased right atrial pressure which can push open flap. Can be caused by sustained pulmonary hypertension or transient increases.