Physiology of Labour

Question 1

Uterotropins (function and 4 examples)

Answer 1

Set the stage for contractions and cervical change (ripen the cervix)
Ex: estrogen, relaxin, Ca dependent phospholipases, arachidonic acid (to make prostaglandins)

Question 2

What hormone counteracts uterotropins?

Answer 2

Progesterone
Maintains uterine quiescence
Decreased progesterone is involved in cervical ripening

Question 3

Uterotonins (function and 3 examples)

Answer 3

Directly involved in contraction of myometrial smooth muscle cells
Increase intracellular Ca in myometrium
Ex: oxytocin, prostaglandins (PGF2a), endothelin 1

Question 4

Do we know what initiates parturition in humans?

Answer 4

Nope!

Question 5

Where are prostaglandins produced?

Answer 5

Interface of the amnion/chorion and myometrium

Question 6

Does progesterone activate or inhibit prostaglandin production?

Answer 6

Inhibit

Increases progesterone increases the amount of prostaglandin dehydrogenase

Question 7

PGE2 function

Answer 7

Cervical effacement
Highest levels of PGE2 are in amniotic fluid just below the presenting forewaters
Cause the breakdown of the rigid structure of collagen fibers (unwinds the fibers)
Softens the ECM

Question 8

How is PGF2a produced? What is its function?

Answer 8

The thinning of lower uterine segment during active labour causes an inflammatory response, which results in the release of arachidonic acid
This process is also stimulated by oxytocin
PGF2a causes an increase in intracellular Ca (and contraction)

Question 9

Oxytocin receptors

1. When do they increase
2. What are they increased by
3. What are they down regulated by

Answer 9

1. Near term
2. Estradiol
3. Progesterone

Question 10

What does oxytocin do?

Answer 10

Increases the amount of intracellular Ca, which helps with contraction

Question 11

How are gap junctions in the myometrium affected by

1. Estradiol
2. Progesterone

Answer 11

1. Increased

2. Decreased

Question 12

5 ways to induce labour

Answer 12

Amniotomy (artificially rupture the membranes)
Membrane sweeping
Prostaglandins
Foley catheter in cervix
Oxytocin

Question 13

3 meds to give to prevent labour

Answer 13

NSAIDs (but only for 2 days because dont want to close PDA)
Progesterone
Ca channel blockers

Question 14

Definition of labour

Answer 14

Progressive cervical dilation, effacement, or both, resulting from regular uterine contractions every 5 mins lasting 30-60s

Question 15

First stage of delivery

Answer 15

Onset of involuntary painful regular contractions to full dilation
Has latent and active phase

Question 16

Latent phase

Answer 16

Onset of regular painful contractions every 5 mins lasting 30-60 s
Cervix is less than 3 cm dilated
Extremely variable duration

Question 17

Active phase

Answer 17

Regular painful contractions every 2-3 mins lasting 45-60s
Cervix 3-4cm to fully dilated
A bit faster in women who had more than one pregnancy

Question 18

Second stage of delivery

Answer 18

Full cervical dilation to the delivery of fetus

Maternal pushing increases forces directing fetus downwards and outwards

Question 19

Third stage of delivery

Answer 19

Delivery of baby to delivery of placenta

Can take 0-30 mins (most deliver by 15 mins)

Question 20

4 signs of placental separation

Answer 20

Gush of blood
Lengthening of cord
Fundus rises up
Uterus becomes firm and globular

Question 21

3 ways to reduce the risk of postpartum hemorrhage in the third stage

Answer 21

Give uterotonics with delivery (oxytocin, misoprostol)
Gentle, controlled cord traction
Maybe early cord clamping

Question 22

Fourth stage

Answer 22

The 1-1.5 hours after the delivery of placenta
Bleeding slows
Uterus remains contracted
Maternal stabilization and bonding
First attempt at breastfeeding

Question 23

Puerperium phase

Answer 23

6 weeks following delivery
Most physiological changes return to non-pregnant state
Uterine bleeding stops by contraction of muscle around vessels and thrombus formation
Involution of uterus (gradual)
Cervix lengthens
Diuresis of increased circulatory volume

Question 24

How does milk produced after the delivery of the placenta?

Answer 24

Delivery of placenta
Decrease in the amount of estrogen and progesterone
Increase in prolactin from anterior pituitary
Milk production

Question 25

Suckling stimulates what hormone?

Answer 25

Oxytocin
Causes myoepithelial cells around alveoli in breast glands contract
Milk ejected

Question 26

A decrease in what hormone causes menses to resume?

Answer 26

Prolactin