Lecture 14 - Endocrinology of Pregnancy, Labor, and Lactation

Question 1

Effect of hCG on male fetus?

Answer 1

Stimulates testosterone production by the testes of male fetus (development and decent of testes)

Question 2

How do hCG and LH differ?

Answer 2

Few extra AAs on beta subunit of hCG

Question 3

Is there a specific receptor for hCG?

Answer 3

NOPE, it binds to the LH receptor

Question 4

Purpose of progesterone secretion by CP being stimulated by hCG?

Answer 4

Progesterone favors the maintenance of pregnancy because it maintains a non-contractile quiescent uterine myometrium (suppresses smooth muscle contractions of the uterus)

Question 5

Why do hCG levels decrease back to 0 at week 10-12?

Answer 5

Because progesterone production shift from CP to placenta

Question 6

Estrogen produced by placenta?

Answer 6

Estriol

Question 7

Changes involving estrogen/progesterone in the last week of pregnancy?

Answer 7

1. Progesterone levels start decreasing and # of myometrial receptors decreases
2. Estrogen increases so larger effect than progesterone => favors uterine contractions

Question 8

How does estrogen contribute to myometrium contractility during parturition?

Answer 8

CRH produced by placenta => fetal pituitary produces ACTH => fetal adrenal gland produces DHEA => DHEA diffuses through the placenta => placenta aromatase converts DHEA to local estrogen => increase in local estrogen/progesterone ratio => stimulation of prostaglandin synthase => production of prostaglandins PGF2-alpha => uterine contractions

Question 9

What does DHEA stand for? What is it?

Answer 9

Dehydroepiandrosterone: androgen steroid hormone

Question 10

What 4 factors stimulate uterine contractions?

Answer 10

1. Oxytocin from mother’s posterior pituitary
2. Catecholamines (NE and EPI) released by mother in response to pain/stress
3. PGF2-alpha
4. High local estrogen/progesterone ratio

Question 11

Describe the feedforward regulation during parturition?

Answer 11

Uterine contractions => cervical stretch => stretch sensory receptors communicate through spinal cord synaptic relays to the oxytocin secreting centers of the hypo => increased oxytocin secretion by post pit + prostaglandins => uterine contractions => cycle

Question 12

What is the functional unit of the breast allowing for milk production? Describe it.

Answer 12

Alveolus at the end of duct system

1. Lumen: space into which breast milk is deposited
2. Secretory columnar epithelial cells with prolactin receptors
3. Layers of smooth muscle cells (myoepithelial cells) surrounding secretory cells with oxytocin receptors

Question 13

How is milk secreted into the lactiferous ducts of the breast? What is this called?

Answer 13

Prolactin stimulates secretory cells to produce milk => milk is deposited into lumen => oxytocin stimules myoepithelial cells to contract => milk ejected into lactiferous ducts

= milk let-down reflex

Question 14

Is there milk production during pregnancy? Why? What happens after delivery?

Answer 14

NOPE

Although estrogen stimulates prolactin, both estrogen and progesterone block the ability of prolactin to stimulate milk synthesis by the breast lobules

Delivery of placenta => decrease in estrogen/progesterone => ability of prolactin to stimulate milk production

Question 15

Effect of estrogen on breasts during pregnancy?

Answer 15

Growth of ductile system

Question 16

Effect of progesterone on breasts during pregnancy?

Answer 16

Development of lobule-alveolar system

Question 17

Describe the regulation of prolactin secretion after birth.

Answer 17

Suckling stimulus => spinal afferent relays from nipple to spinal cord to hypo => dopaminergic neurons in the arcuate nucleus are shut off temporarily => prolactin release

Question 18

Most important substance secreted by hypo regulating prolactin secretion? 2 names?

Answer 18

Dopamine inhibits it

= prolactine inhibiting factor (PIF)

Question 19

What are prolactin releasing factors? What to note?

Answer 19

1. GnRH
2. Oxytocin
3. Vasoactive intestinal peptide

Note: minor effects compared to dopaminergic ones

Question 20

Other role of dopamine secreting neurons in the arcuate nucleus of the hypo? What to note?

Answer 20

Make synaptic connections with LHRH neurons in the arcuate nucleus and inhibits its release => low estrogen/progesterone secretion by ovaries => decreased reproductive capacity

During early breast-feeding the high levels of prolactin secreted form short loop negative feedback loops with the dopaminergic neurons => increased inhibition of LHRH secretion => infertility

As time goes by after birth, the rise in prolactin that is associated with breast-feeding is not as high due to decreased contact with infant => fertility returns

NOTE: in poor countries state of infertility may last longer because higher breast-feeding frequency and length

Question 21

Does pumping milk provide same prolactin rise as infant sucking?

Answer 21

NOPE, no psychogenic effects

Question 22

What is Sheehan’s syndrome?

Answer 22

Blood loss and hypovolemic shock during and after childbirth => decreased blood to the anterior/posterior pituitary (especially cause it receives a low pressure venous blood supply) => postpartum hypopituitarism or postpartum pituitary gland necrosis caused by ischemic necrosis => no breast milk production because no prolactin + no body hair because no adrenal androgens because no ACTH