108 Parturition and lactation

Question 1

_________ are factors that transform the uterus in preparation for labour.
Their main action causes ________ withdrawal and _______activation.

Answer 1

Uterotrophins;
progesterone;
estrogen

Question 2

Phase 2 and 3 of human parturition are under the action of ____________, that are factors that directly stimulate the uterus to contract.

Answer 2

uterotonins

Question 3

Onset of labour is most likely triggered by an increased production of ________________ by intrauterine tissues together with placental production of ____________.

Answer 3

prostaglandins;

oxytocin

Question 4

Uterine production in uterus and oxytocin production in placenta increases the number and sensitivity of oxytocin receptors in uterine muscles.
What are the previous steps that contributes to this?

Answer 4

Fetal stress + placental CRH
> increase CRH in blood > increase fetal ACTH secretion > increase cortisol secretion and DHEA/DHEA-S (lung maturation) > placenta

(artificial/ spontaneous rupture of fetal membrane, sweeping of membrane too)

Question 5

What are the major roles of cortisol and DHEA/DHEA-S respectively?

Answer 5

Cortisol: stimulate fetal organ maturation (surfactant production in lungs), placental production of CRH, PGs, oxytocin

DHEA: provides precursors for estrogen synthesis by feto-placental unit > raise estrogen level to be against that of progesterone

Question 6

Functional progesterone withdrawal and functional estrogen activation:

A. Stimulate expression of oxytocin and prostaglandin receptors

B. Stimulate gap junction formation between myometrial smooth muscle cells

C. Increase myometrial smooth muscle cell excitability

D. Stimulate production of prostaglandins (PGF2a, PGE2) by intrauterine tissues

Answer 6

All of the above

Question 7

Oxytocin acts on receptors of the ___________ and ________. It causes the former to increase in intracellular Ca2+ levels; and causes the latter to increase in _________ synthesis and secretion.
Both of them results in increase in uterine contractions.

Answer 7

Myometrium; decidua ;

PGF2a (prostaglandins)

Question 8

Initiation of labour is mainly by:

Answer 8

increased production of prostaglandins by intrauterine tissues and placental production of oxytocin to start uterine contraction

Question 9

Propagation of labour is mediated by:

Answer 9

oxytocin released from the posterior pituitary through a neuroendocrine reflex and under positive feedback control. Oxytocin action is augmented by prostaglandins

Question 10

When labour begins, the cervix undergoes ______ and _______.

Answer 10

dilation; effacement (thinning)

Question 11

Cervical ripening:

A. is inflammation-like with leukocytes
B. involves lytic enzyme activity of fibroblasts, causing degradation of collagen
C. is stimulated by progesterone
D. is stimulated by NO, estrogen, CRH, relaxin and prostaglandins

Answer 11

all except C

inhibited by progesterone

Question 12

Uterotonins are agents that cause myometrium to contract.

State 4 examples of them and 3 uses of them.

Answer 12

Examples:
Oxytocin, 
Ergot alkaloids,
Prostaglandins,
(PGE2,1 for cervical ripening; PGF2a, PGE1,2 for uterine contraction)
Progesterone receptor antagonist 

Uses

1. Induction of labour
2. Control of postpartum uterine bleeding
3. Abortion

Question 13

State the function and therapeutic use of tocolytics.

Answer 13

Function: cause myometrium to relax
Use: delay premature labour

Question 14

Which of the following are tocolytics?

A. Magnesium sulphate
B. NO donor
C. inhibitors of prostaglandin (Indomethacin, COX-2 inhibitors)
D. Oxytocin receptor agonist 
E. Beta-mimetics (terbulatamine)
F. Ca2+ channel agonist

Answer 14

All except D and F
D: should be oxytocin receptor antagonist (atosiban)

F: should be Ca2+ blockers (nifedipine, nicardipine)

Question 15

Lactation:

Mammogenesis involves the following changes. List the hormone(s) involved in each change.

1. Growth of stromal and adipose tissue, growth of nipple, enlargement and increased pigmentation of areolar
2. Growth, elongation and branching of the ductal system (at the onset of puberty, menstrual cycle)
3. Development /budding of the lobulo-alveolar structures (or terminal ductal lobular units)

Answer 15

1. Estrogen
2. Estrogen and GH/IGF
3. Estrogen, prolactin, progesterone and thyroid hormone

Question 16

Lactation:

Lactogenesis stage 1
Begins around mid-pregnancy with secretory differentiation of lobulo-alveolar system under the effects of?

Answer 16

Prolactin/hPL and progesterone, and in the presence of estrogen, GH/IFG, cortisol and thyroid hormone

Question 17

High levels of ___________ prevent the progression of lactogenesis stage 1 into the next stage by:

• Limiting expression of prolactin receptors
• Competing for binding at glucocorticoid receptor

Answer 17

Progesterone

Question 18

______________ refers to the onset of copious milk secretion that begins following parturition.
___________ levels falls and remove their inhibition on _________ action.

Answer 18

Lactogenesis stage 2; progesterone and estrogen; prolactin

Question 19

In lactogenesis stage 3, suckling of breasts can attain 2 goals:

Answer 19

1. induce periodic surges of prolactin

2. remove milk (local control)

Question 20

Milk production is inhibited by:

A. Milk retention/ engorgement of breast

B. Dopamine agonist (bromocriptine)

C. Combined oral contraceptives

Answer 20

All of the above

A: reduced blood supply and hence delivery of prolactin; secretion of a milk protein known as feedback inhibitor of lactation (FIL) to downregulate PRL receptors; gland disruption from increased intramammary pressure, leading to involution

Question 21

Why will lactational amenorrhea occur?

Answer 21

suckling-induced release of inhibitory NT reduce pulsatile GnRH release,
prolactin from anterior pituitary also give rise to multiple inhibitory inputs to hypothalamic-pituitary-ovarian axis

Question 22

Other than contraction of myoepithelial cells surrounding the alveoli and mammary ducts to cause ejection of milk, what effect does oxytocin bring? (in the uterus)

Answer 22

Contraction (to limit postpartum hemorrhage) and involution of the uterus