L12 - Endocrinology of Pregnancy & Parturition

Question 1

What is common between FSH, LH and hCG?

Why is this important?

Answer 1

• 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 2

What are the functions of hCG?

Answer 2

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 3

From where is hCG secreted?

Answer 3

The syncytiotrophoblast

Question 4

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

Answer 4

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

Question 5

What are the functions of progesterone during pregnancy?

Answer 5

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 6

What are the functions of the different oestrogens?

Answer 6

1 - Oestrone (E1) - predominates in menopause (least potent)

2 - Oestradiol (E2) - regulates menstruation (most potent)

3 - Oestriol (E3) - specific to pregnancy

Question 7

Why are pregnant women hypercoagulable?

Answer 7

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

Question 8

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

Where and when is it secreted?

Answer 8

• 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 9

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

Where is it secreted?

Answer 9

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

Question 10

What is the function of relaxin?

Where is it secreted?

Answer 10

• Primarily corpus luteum secretion
• Increases CO, arterial compliance, renal blood flow
• Relaxes pelvic ligs, softens pubic symphysis & ‘cervical ripening’

Question 11

What is cervical effacement?

What causes cervical effacement?

Answer 11

• Collagen fibres reduce -> keratan sulphate (doesn’t bind collagen) reduces & dermatan sulphate (binds collagen tightly) increases
• Shortening & thinning of cervix

Question 12

What is the function of prolactin?

Answer 12

• Produced by ant pituitary & involved in continuous production of milk throughout pregnancy -> acts on alveolar cells in breast
• Following parturition, prolactin levels decline but basal conc remain high
• Prolactin also released episodically at each feed via suckling-induced reflex -> maintains milk production

Question 13

What is the function of oxytocin?

Answer 13

• Released in response to suckling via let-down reflex

- Acts on myoepithelial cells in breast -> SM contraction -> milk ejection

Question 14

What stimulates prostaglandin production in parturition?

Answer 14

Pressure of the foetal head on the cervix

Question 15

Describe the foetal contribution to the initiation of labour.

Answer 15

• Pressure of baby’s head pushing on cervix induces oxytocin release
• Oxytocin induces Ca2+ entry into myometrial cells via VG-Ca2+ channels & release of Ca2+ from SR -> myometrial contraction -> parturition initiation