Lecture 7

Question 1

Synthesis of arachidonic acid: direct pathway

Answer 1

Agonist binds to G-protein coupled receptor -> PLA2 -> arachidonic acid is released from membrane phospholipid.

Question 2

Synthesis of arachidonic acid: indirect pathway

Answer 2

Agonist binds to G-protein coupled receptor -> PLC cascade.
DAG lipase releases arachidonic acid from DAG.
IP3 -> Ca2+ -> PLA2 (direct pathway).
MAPK also activates PLA2.

Question 3

NSAIDs and childbirth:

Answer 3

NSAIDs block COX, so pregnant lady will be unable to enter labour.

Question 4

20-HETE:

Answer 4

Most powerful vasoconstrictor in the body.

Question 5

EET:

Answer 5

A powerful vasodilator.

Question 6

Why is the uterus quiescent for most of pregnancy?

Answer 6

Shushed by progesterone and relaxin.

Question 7

Initiation of labour: in rabbits

Answer 7

Withdrawal of placental progesterone evacuates the uterus.

Administering progesterone delays labour.

Question 8

Initiation of labour: in humans

Answer 8

Different from rabbits, but progesterone is definitely involved in gestation length.

Question 9

Stages of labour:

Answer 9

Stage 0: uterus is sleeping.
Stage 1: uterine awakening, initiation of parturition, complete cervical dilation.
Stage 2: activate labour, dilation to delivery.
Stage 3: delivery to expulsion of placenta, final uterine contraction.

Question 10

Physiological changes during labour:

Answer 10

In stage 1: increased number of gap junctions between myometrial cells, increased number of oxytocin receptors.

Question 11

Uterine contraction hormones:

Answer 11

Prostaglandins cause uterine smooth muscle contraction. Also cause softening, dilation, and thinning of cervix in early labour.
Oxytocin stimulates decidual cells to make more cells that produce prostaglandins.
Both (and estradiol) increase the number of gap junctions between uterine smooth muscle cells for synchronizing contractions.

Question 12

Inducing labour:

Answer 12

Administer prostaglandin. Doesn’t care about stage of gestation or route of administration.

Question 13

Oxytocin’s family:

Answer 13

Closely related to vasopressin. Probably evolved from vasotocin, the only neurohypophyseal hormone in nonmammalian nonvertebrates.

Question 14

Oxytocin’s involvement in uterine contraction:

Answer 14

PLC cascade.
Ca2+ -> calmodulin -> myosin light-chain kinase.
Myosin light-chain kinase phosphorylates regulatory light chain and contraction begins.

Question 15

Uterine sensitivity to oxytocin:

Answer 15

Insensitive until 20 weeks. Estrogen increases number of oxytocin receptors.

Question 16

Oxytocin timeline in labour:

Answer 16

Fetal OT initiates labour.
Maternal OT maintains labour.
OT is released in bursts in stage 1 of labour.

Question 17

Ferguson reflex:

Answer 17

Distention of cervix causes release of maternal OT.

Question 18

Synergistic role of OT in labour:

Answer 18

In second stage, OT stimulates prostaglandin release.

Question 19

Agents involved in sustaining labour: relaxin

Answer 19

Produced by corpus luteum, placenta, decidua.

Shushes uterus. Production increases during labour to soften cervix.

Question 20

Agents involved in sustaining labour: mechanical factors

Answer 20

Stretch stimulates contractions.

Question 21

Agents involved in sustaining labour: positive feedback

Answer 21

Contractions stimulate prostaglandin to increase intensity of contractions.
Stretch stimulates OT by Ferguson reflex. OT stimulates contractions.

Question 22

Breast development at puberty depends on:

Answer 22

Progesterone and estrogens.

Question 23

Full development of breasts at pregnancy requires:

Answer 23

Gradual increases in PRL, hPL.

High levels of estrogens and progesterone.

Question 24

Kinds of hormones affecting breasts:

Answer 24

Mammogenic: proliferation of alveolar and duct cells.
Lactogenic: initiation of milk production.
Galactopoietic: maintaining milk production.
Galactokinetic: milk ejection.

Question 25

Pathways for secreting milk components: secretory

Answer 25

Proteins synthesized in nucleus and sent out in vesicles.

Question 26

Pathways for secreting milk components: transcellular endo/exocytosis

Answer 26

Proteins synthesized in nearby cells and sent out in vesicles.

Question 27

Pathways for secreting milk components: lipid pathway

Answer 27

Lipids from nucleus travel freely through cell, then get exocytosed.

Question 28

Pathways for secreting milk components: transcellular salt/water transport

Answer 28

Through cells using channels and transporters.

Question 29

Pathways for secreting milk components: paracellular ion/water transport

Answer 29

Between cells.

Question 30

Composition of milk:

Answer 30

Milk is an emulsion of fats in aqueous solution.
Sugar: lactose
Proteins: lactalbumin and casein
Cations: K, Ca, Na
Anions: Cl, phosphate

Question 31

Mammogenic hormones: list

Answer 31

Estrogen, IGF-1, cortisol, prolactin, relaxin

Question 32

Lactogenic hormones: list

Answer 32

Prolactin, hPL, cortisol, IGF-1, thyroid hormones, withdrawal of estrogens and progesterone.

Question 33

Galactokinetic hormones: list

Answer 33

OT, slightly vasopressin

Question 34

Galactopoietic hormones: list

Answer 34

Prolactin, slightly cortisol and other metabolic hormones.

Question 35

Suckling response:

Answer 35

Sensory afferents synapse in SC.
Arcuate nucleus of hypothalamus disinhibits PRL by inhibiting dopamine.
In supraoptic and paraventricular nuclei of hypothalamus, afferent input triggers OT in post pit.
In preoptic area and arcuate nucleus, afferent input inhibits GnRH, leading to inhibition of FSH/LH.