Physiology of Pregnancy

Question 1

What is the range of a normal pregnancy in humans?

Answer 1

37 - 42 weeks in humans, with 40 weeks being the average

Question 2

What is the span in weeks of each Trimester?

Answer 2

T1: 01 - 12
T2: 13 - 26
T3: 27 - 40

Question 3

When does a pregnancy officially start?

Answer 3

From the day of the Last Menstrual Period

Question 4

If the Pregnancy starts from the Last Menstrual Period, when does conception and implantation occur?

Answer 4

Conception is at Week 3

Implantation is at Week 4

Question 5

Braxton-Hicks contractions are experienced in which trimester(s)?

Answer 5

Third trimester

Question 6

The maternal heartbeat increases by how much during pregnancy?

Answer 6

60 to 76 beats per minute

Question 7

The maternal blood pressure changes how, during a pregnancy?

Answer 7

BP remains unchanged, however mother may become hypervolaemic. There may however be a small drop in blood pressure mid gestation

Question 8

Although the mother may become Hypervolaemic during a pregnancy - why is there a fall in Haematocrit?

Answer 8

The RBCs do not increase as much as the plasma, hence the fall in Haematocrit

Question 9

How does the Foetal heartbeat change during a pregnancy?

Answer 9

It rises up until the first trimester, then falls to a steady 140 bpm

Question 10

During which trimester is there the greatest foetal growth?

Answer 10

During the second trimester

Question 11

The Luteal Phase of the Ovarian cycle is analogue to what phase of the Uterine cycle?

Answer 11

Secretory Phase

Question 12

During what phase of the Ovarian cycle, does Implantation occur?

Answer 12

Luteal Phase

Question 13

Describe what happens during Implantation to the point where Histrotrophic support is established

Answer 13

1. The Blastocyst hatches from the Zona Pellucida, and the glycolayx of the Uterus is lost
2. The trophoblast interdigitate with cells of the epithelia, allowing integrin binding to occur
3. Cells of the epithelia change morphology, with the nuclei moving to basolateral surface to accomodate implantation
4. The trophoblast interdigitates the epithelia, destroying the stromal cells beneath -(decidualisation)
5. Trophoblast differentiates into syncytotrophoblast and cytotrophoblast
6. Within the syncytotrophoblast, lacunae form which provides histrotrophic support

Question 14

The epiblast becomes the…?

Answer 14

Ectoderm

Question 15

The hypoblast becomes the…?

Answer 15

Endoderm

Question 16

What forms between the ectoderm and endoderm?

Answer 16

Mesoderm

Question 17

Describe what happens when there is Cessation of Histrotrophic support and Haemotrophic support begins

Answer 17

1. Maternal spiral arteries will terminate at the Lacunae
2. Primary villi begin forming from conceptus extending into the syncytiotrophoblast
3. The villi grow into the lacunae
4. Maternal spiral arteries remodel, allowing blood to pool into the lacunae of the syncytiotrophoblast

Question 18

The villi of chorionic syncytiotrophoblast penetrate the uterus by which week?

Answer 18

Week 5

Question 19

Is the Placenta, fetus or maternal derived?

Answer 19

Fetus derived

Question 20

How does foetal blood carry 20-50% more oxygen than maternal blood?

Answer 20

Foetal haemoglobin (alpha2, gamma2) has a higher affinity for oxygen than Adult haemoglobin

Question 21

How does the placenta transport fats and sugars across to the foetus?

Answer 21

Glucose: via GLUT 1, 3, 4, 12 transporters
Fats: via LPL

Question 22

What is the precursor for Progesterone?

Answer 22

Pregnolone

Question 23

How much does the heart increase in size by during pregnancy?

Answer 23

12%

Question 24

What is Chadwick’s sign?

Answer 24

Blue-ish hue of vagina / labia, due to increased vascularisation

Question 25

During pregnancy, what respiratory changes are there?

Answer 25

• 4cm elevation of diaphragm
• 16-20% more oxygen consumed
• Thoracic breathing

Question 26

How does Progesterone stimulate the breast during pregnancy?

Answer 26

Growth of alveoli / lobules

Question 27

How does Oestrogens stimulate the breast during pregnancy?

Answer 27

Stimulates growth of milk ducts

Question 28

How does HPL (Human Placental Somatomammotropin) stimulate the breast during pregnancy?

Answer 28

Mimics prolactin and GH, causing breast / nipple / aerola to enlarge