Endocrinology of Pregnancy and Parturition

Question 1

List 3 differences between lipid-based hormones and protein hormones.

Answer 1

1 - Lipid-based hormones are hydrophobic whereas protein hormones are hydrophilic.

2 - Lipid-based hormones act on receptors in the cytoplasm and nucleus, whereas protein hormones act on receptors at the cell membrane.

3 - Lipid-based hormones cause cellular changes by inducing gene transcription and translation directly, whereas protein hormones initiate second messenger signalling mechanisms.

Question 2

List 4 steroid hormones.

Answer 2

1 - Oestrogens.

2 - Progesterone.

3 - Cortisol.

4 - Androgens.

Question 3

List 9 protein hormones.

Answer 3

• Gonadotropins:

1 - FSH.

2 - LH.

3 - hCG.

• Somatomammotropins:

4 - Prolactin.

5 - Growth hormone.

6 - Human placental lactogen (HPL).

7 - Relaxin.

• Small peptides:

8 - GnRH.

9 - Oxytocin.

Question 4

List the phases of the menstrual cycle.

Answer 4

• The ovarian cycle and uterine cycle occur simultaneously:

1 - The ovarian follicular phase and the uterine proliferative phase

2 - Ovulation.

3 - The ovarian luteal phase and the uterine secretory phase.

Question 5

How does LH result in oestrogen production?

Answer 5

1 - LH stimulates the theca cells of the ovary to produce testosterone.

2 - Granulosa cells convert testosterone into oestrogen.

Question 6

What is common between FSH, LH and hCG?

Why is this important?

Answer 6

• FSH, LH and hCG all share the same alpha subunit.
• This is important because hCG can stimulate both FSH and LH receptors during pregnancy.
• They also share the same alpha subunit as TSH.

Question 7

List 2 functions of hCG.

Answer 7

1 - Maintains the corpus luteum.

2 - Stimulates testosterone production in males.

3 - Stimulates DHEA production in the foetal adrenal glands. DHEA is a precursor to testosterone and oestrogen.

Question 8

Where is hCG secreted?

Answer 8

hCG is secreted from the syncytiotrophoblast.

Question 9

How is hCG concentration tested?

Answer 9

The beta subunit of hCG can be measured using a urine sample.

Question 10

How long does the corpus luteum secrete progesterone before the placenta takes over?

Answer 10

The corpus luteum secretes progesterone for 6-8 weeks before the placenta takes over.

Question 11

List the functions of progesterone during pregnancy.

Answer 11

1 - Progesterone maintains the decidua.

2 - Progesterone relaxes the myometrium by downregulating the synthesis of contractile-associated proteins such as gap junctions and oxytocin receptors.

3 - Progesterone suppresses myometrial contractions, preventing birth.

Question 12

List the oestrogens.

What are the functions of the oestrogens?

Answer 12

1 - Oestrone (E1) - predominates in menopause.

2 - Oestradiol (E2) - regulates menstruation.

3 - Oestriol (E3) - specific to pregnancy.

Question 13

Why are pregnant women hypercoagulable?

Answer 13

Pregnant women are hypercoagulable due to the high oestrogen during pregnancy, which stimulates thrombosis.

Question 14

What is the function of placental growth hormone (PGH)?

Where and when is it secreted?

Describe the pattern by which it is secreted.

Answer 14

• There is no functional growth hormone receptor until birth, so PGH replaces the function of growth hormone in the foetus.
• Placental growth hormone modifies receptors which transport glucose across the foetal compartment.
• It also stimulates maternal gluconeogenesis and lipolysis.
• It is secreted from 15 weeks of gestation by the placenta.
• Its secretion is non-pulsatile, and the levels correlate with placental size.

Question 15

What is the function of human placental lactogen (HPL)?

Where is it secreted?

Answer 15

• Human placental lactogen controls maternal glucose metabolism by increasing insulin resistance, lipolysis and gluconeogenesis.
• It is secreted by the syncytiotrophoblast.

Question 16

What is the risk of suffering from diabetes during pregnancy?

Answer 16

• During pregnancy, HPL and placental GH increase both increases blood glucose.
• If glucose regulators are dysfunctional, such as in diabetes, the pancreas is likely to overproduce insulin.
• Insulin can cross the placental barrier, causing hypoglycaemia in the foetus.

Question 17

What is the function of relaxin?

Where is it secreted?

Answer 17

1 - Relaxin increases cardiac output and arterial compliance.

2 - Relaxin increases renal blood flow.

3 - Relaxin relaxes pelvic ligaments and softens the pubix symphysis, facilitating parturition.

• It is secreted by the corpus luteum, decidua and placenta.

Question 18

List 2 hormones that are not present in the foetal circulation that are involved in steroidogenesis.

What is the implication of this?

Answer 18

1 - The placenta lacks 17 alpha-hydroxylase, so cannot convert progesterone to DHEA.

2 - The fetal adrenal glands lack 3 beta-hydroxysteroid dehydrogenase, so cannot convert pregnenolone to progesterone.

• These modifications mean that the foetus must use an alternative pathway for oestrogen synthesis.

Question 19

What counteracts the anti-contractile effects of progesterone during pregnancy?

Answer 19

The anti-contractile effects of progesterone are counteracted by the pro-contractile effects of oestradiol.

Question 20

What is cervical effacement?

What causes cervical effacement?

Answer 20

• Cervical effacement is the first part of labour. It is characterised by:

1 - A reduction in collagen fibres.

2 - An increase in glycosaminoglycans.

3 - An increase in metalloproteinases.

4 - Shortening and thinning out (effacement) of the cervix.

• These changes facilitate parturition.
• Prostaglandins cause cervical effacement.

Question 21

What is the function of prolactin?

Where is it secreted?

When is it secreted?

What stimulates prolactin production?

Answer 21

1 - Prolactin stimulates milk synthesis within the alveolar cells of the breast.

2 - Prolactin causes hypertrophy and hyperplasia of the breast lobules.

3 - Prolactin aids in the final stages of foetal lung maturation.

• Prolactin is produced by the anterior pituitary.
• Prolactin rises during pregnancy but also in response to breastfeeding.
• It is stimulated by oestrogen, which acts directly on the anterior pituitary and also indirectly by suppressing dopamine, which antagonises prolactin release.
• Once secreted, prolactin maintains its own production by suppressing dopamine.

Question 22

What is the function of oxytocin?

Where is it secreted?

What stimulates oxytocin production?

Answer 22

1 - Oxytocin acts on the myometrium to increase the length, strength and frequency of contractions during labour. It does this by increasing intracellular calcium in the myometrium.

2 - Oxytocin maintains uterine contractions after birth to help the uterus shrink back to its original size.

3 - High levels of oxytocin in the mother and baby promote attachment and desire in the mother to protect the baby.

4 - Oxytocin promotes the let-down reflex, which enables the breasts to eject milk.

• Oxytocin is produced by the posterior pituitary.
• Oxytocin rises during labour.

Question 23

What stimulates prostaglandin production in pregnancy?

Answer 23

Prostaglandin production is stimulated by the mechanical action of the head of the foetus against the cervix.

Question 24

Describe the foetal contribution to the initiation of labour.

Answer 24

1 - Placental corticotropin-releasing hormone (placental CRH) increases with gestation.

2 - Placental CRH increases the production of DHEAS in the foetal adrenal gland.

3 - DHEAS passes into the placenta, where it is converted into oestradiol.

4 - Oestradiol has pro-contractile myometrial effects and is metabolised in the maternal liver.

Question 25

What is the difference between a miscarriage and stillbirth?

Answer 25

• Miscarriage occurs befroe 24 weeks of gestation.

- Stillbirth occurs after 24 weeks of gestation.