Lecture 24 - Pregnancy, Labour, Delivery, and Lactation

Question 1

Name the 6 elevated hormones during mid- to late pregnancy

Answer 1

1. Progesterone - maintains endometrium, inhibits labour and lactation
2. Oxytocin - enhances uterine contractions
3. Oestrogen - regulates uterus and other organs, induces receptors for other hormones (ex. PRL and OT)
4. Prolactin - promotes mammary gland development
5. Relaxin - alters blood flow, promotes ligament loosening
6. Human Chorionic Gonadotropin (hCG) - promote immune tolerance of fetus

Question 2

6 examples of anatomical stress on the body due to pregnancy

Answer 2

1. Restriction of lung expansion
2. Compression of digestive organs
3. Weight misalignment with body axis and skeleton
4. Bladder is compressed to smaller volumes
5. Pressure on the rectum compresses blood vessels
6. Diastasis recti (left and right abdominals separate during pregnancy)

Question 3

7 examples of physiological stress on the body due to pregnancy

Answer 3

1. Increased respiration rate
2. Fully developed mammary glands
3. Increased urination
4. Blood volume increase by ~50% by the end of pregnancy
5. Nutrient requirements increases by 30%
6. Uterus expansion via hypertrophy of existing cells
7. Glomerular filtration rate (GFR) increases by ~50%

Question 4

Describe the three stages of labour

Answer 4

1. Dilation stage - cervix dilates to ~10cm in diameter
2. Expulsion stage - uterine contractions, supplemented by voluntary pelvic and abdominal contractions
3. Placental stage - continued uterine contractions dislodge the placenta

Question 5

How does the myometrium layer change during late pregnancy?

Answer 5

The uterine smooth muscle cells switch to single-unit (gap junction coupled) organization and begin to express oxytocin receptors

Question 6

Why does the myometrium layer change?

Answer 6

It’s due to prolonged exposure to elevated estrogen (secreted by the placenta). The single-unit organization allows the myometrium to contract and relax in synchronized waves

Question 7

How does the myometrium produce labour contractions?

Answer 7

Regular, rhythmic contractions of the uterine myometrial layer. Synchronized wave contractions are stronger and more effective at producing pressure on the cervix

Question 8

Placental factors of labour

Answer 8

Placental estrogen:

• inc. the sensitivity of the smooth muscle cells of the myometrium and make contractions more likely
• inc. the sensitivity of smooth muscle fibres to oxytocin

Production of estrogens accelerates closer to birth

Question 9

Fetal factors of labour

Answer 9

Growth and increase in fetal weight stretch the myometrium

The fetal pituitary gland releases oxytocin in response to estrogens

Question 10

What is the key event for triggering the onset of labour?

Answer 10

Prostaglandin production - estrogens and oxytocin stimulate the production of prostaglandins in the endometrium, which further stimulate smooth muscle contractions

Question 11

How does positive feedback play a role in labour?

Answer 11

Mechanical stimulation of cervical tactile neurons triggers maternal oxytocin release, which further enhances contraction and thus pressure on the cervix, increasing cervical dilation

Question 12

Name 2 medical interventions that assist or circumvent labour

Answer 12

1. Forceps or suction (assist)
2. Caesarean section (circumvent)

Question 13

Name 3 examples of Medical Induction Methods to induce labour

Answer 13

1. Artificial rupture of membranes
2. Balloon catheter
3. Prostaglandin gel

Question 14

Name a method to accelerate labour

Answer 14

Intravenous oxytocin (only given after regular contraction have begun)

Question 15

Why do the hormones of an ex-pregnant person rapidly change after parturition? What is the physiological consequence of this?

Answer 15

Without the placenta, estrogen and progesterone levels in a recently pregnant person decline, noticeable around day 3 postpartum

Progesterone inhibits the rise in prolactin from stimulating milk production in late pregnancy, but when the placenta is removed, milk production can start

Question 16

2 physiological components to lactation

Answer 16

1. Secretion - production/synthesis of milk within lobules
2. Ejection - milk ejects from the lobules through the nipple

Question 17

How does mammary stimulation play a role in milk production?

Answer 17

Mammary stimulation -> increases prolactin levels -> triggers milk production

Regular sucking/stimulation is necessary to keep PIH (prolactin-inhibited hormone) inhibited

Question 18

Difference between colostrum and breastmilk

Answer 18

Colostrum - nutrient poor, but rich in antibodies, which can provide immune protection for neonates or pre-term babies

Breastmilk - has fewer immune molecules, but is nutrient rich (fat and lactose)

NOTE: mammary secretions begin with colostrum, then gradually switch to breast milk

Question 19

Purpose of infant formula

Answer 19

It matches the nutrients in breastmilk (and adds essential minerals and vitamins), but doesn’t contain antibodies or other immune molecules

Breastmilk tends to be low in iron and lacks vitamin D, so liquid supplements are recommended

Question 20

How does oxytocin lead to milk ejection?

Answer 20

Oxytocin causes myoepithelial tissue contraction (related to smooth tissue) and leads to milk ejection