Physiology of Pregnancy

Question 1

What happens on day 1?

Answer 1

fertilisation takes place

Question 2

Where does fertilisation take place?

Answer 2

Ampulla of fallopian tube

Question 3

What happens on day 3-5?

Answer 3

transport of the blastocyst into the uterus

Question 4

What is a blastocyst?

Answer 4

fertilised ovum on day 4

Question 5

How does a fertilised ovum divide?

Answer 5

zygote - 2 cell stage - 4 cell stage - 8 cell stage - morula - blastocyst (4 days)

Question 6

What occurs on day 5-8?

Answer 6

blastocyst attaches to lining of uterus

Question 7

What do the inner cells of the blastocyst become?

Answer 7

embryo

Question 8

What do the outer cells of the blastocyst become?

Answer 8

placenta

Question 9

What happens when the blastocyst adheres to the endometrial lining?

Answer 9

Cords of trophoblastic cells begin to penetrate the endometrium
Tunnel deeper into endometrium, creating hole for blastocyst

Question 10

By what day is implantation finished?

Answer 10

12 - blastocyst is completely buried in endometrium

Question 11

What is the placenta derived from?

Answer 11

Trophoblast and decidual tissue

Question 12

By what week is the placenta functional?

Answer 12

week 5

Question 13

What hormone signals the corpus luteum to continue to make progesterone?

Answer 13

human chorionic gonadotrophin (HCG)

Question 14

What increases the contact area between uterus and placenta?

Answer 14

Placenta extends villi into uterine wall - more nutrients and waste material can be exchanged

Question 15

Describe the oxygen transport between mother and fetus?

Answer 15

through placenta

• between maternal oxygen rich blood and umbilical oxygen poor blood (mixed arterial and venous)
• O2 diffuses from maternal to fetal circulation (PO2 maternal > PO2 fetal)
• CO2 follows reversed gradient (partial pressure increased in fetal blood)
• fetal oxygen saturated blood returns to fetus via umbilical vein

Question 16

What facilitates the supply of oxygen to the fetus?

Answer 16

1 - fetal Hb (increased ability to carry oxygen)
2 - higher Hb concentration in fetal blood
3 - Bohr effect -

Question 17

What is the Bohr effect?

Answer 17

fetal Hb can carry more oxygen in lower pCO2 than high pCO2

Question 18

Describe what happens to progesterone production during pregnancy.

Answer 18

HCG prevents breakdown of corpus luteum and stimulates progesterone production

Question 19

What does progesterone do during pregnancy?

Answer 19

Decreases smooth muscle excitability (uterus, gut, ureters)

and raises body temperature

Question 20

What do oestrogens do during pregnancy?

Answer 20

Mainly estriol

increase breast and nipple growth, water retention and protein synthesis

Question 21

What hormone decreases insulin sensitivity in mother? Why?

Answer 21

HCS (human chorionic somatomammotrophin)

More glucose for fetus

Question 22

What happens to cardiac output in pregnancy?

Answer 22

Increases and peaks at 24 weeks (due to demands of uteroplacental circulation)
Decreases in last 8 weeks

Question 23

What happens to heart rate in pregnancy?

Answer 23

Increases - up to 90/min

Question 24

What happens to blood pressure during pregnancy?

Answer 24

Falls during second semester

Rises to non pregnancy levels by term

Question 25

What are some haemodynamic changes that occur during pregnancy?

Answer 25

Plasma vol increases (proportional with CO) Increase in erythropoiesis Hb decreases (by dilution) Iron requirements increase

Question 26

What respiratory changes are made?

Answer 26

O2 consumption increases (to meet metabolic needs of mother fetus and placenta) Progesterone signals brain to decrease CO2 levels: - resp rate increases - tidal vol increases - pCO2 slightly decreases - vital capacity and Po2 stay the same

Question 27

What happens to the renal system in pregnancy?

Answer 27

Increased GFR Increased reabsorption of ions and water Increased urine formation

Question 28

When and what is the anabolic phase of pregnancy?

Answer 28

Weeks 1-20 - small nutritional demands of conceptus - normal or increased insulin sensitivity - lipogenesis and increased glycogen stores

Question 29

When and what is the catabolic phase of pregnancy?

Answer 29

Weeks 21-40 - increased metabolic fetal demands - maternal insulin resistance - increased transport of nutrients transplacentally - lipolysis

Question 30

How many extra calories does the mother need during pregnancy?

Answer 30

250-300 extra kcal/day