The Physiology of Parturition

Question 1

What causes the pain in pregnancy?

Answer 1

The pressure from contractions makes the myometrium ischemic, which is painful.

Question 2

During labor, the uterus can generate ____________ of pressure.

Answer 2

60 mm Hg

Question 3

The cervix is made of types ________ collagen.

Answer 3

I and III

Question 4

Dilation in contraction refers to the ____________.

Answer 4

internal os of the cervix (there is an external os, too, but that does not matter)

Question 5

What stimulates dilation of the cervix?

Answer 5

Proteases degrade the collagen of the cervix in response to uterine contractions. (This lecturer said “it goes from the consistency of your nose to the consistency of Jello.”)

Question 6

What are the four clinical stages of labor?

Answer 6

• 1: Effective contractions to complete dilation of the cervix
• 2: Complete cervical dilation to delivery of fetus
• 3: Delivery of the fetus to delivery of placenta
• 4: First six hours after delivery

Question 7

What is the difference between latent and active labor?

Answer 7

In latent labor, the cervix is not changing but the uterus is contracting. In active labor, the cervix is dilating up to 1 cm per hour.

Question 8

What occurs during stages 1, 2, and 3 of labor?

Answer 8

• 1: latent and active labor
• 2: complete dilation of the cervix
• 3: delivery of the fetus

Question 9

_______________ is an important uterine quiescence factor.

Answer 9

Progesterone

Question 10

_______________ is a uterine activation factor.

Answer 10

Estrogen

Question 11

Explain the progesterone switch at the end of pregnancy.

Answer 11

Progesterone is normally pro-gestational (I finally get the name), but toward the end of pregnancy the myometrium switches its kind of progesterone receptors such that it no longer gets activated by progesterone.

Question 12

What is Pitocin?

Answer 12

Synthetic oxytocin that stimulates contractions

Question 13

The uterus grows in pregnancy by ________________________.

Answer 13

hypertrophy and hyperplasia

Question 14

Toward the end of pregnancy, _____________ become connected.

Answer 14

myocytes (by connexins in gap junctions)

Question 15

Why don’t Braxton-Hicks contractions induce labor?

Answer 15

They are irregular and not coordinated.

Question 16

Prostaglandins stimulate ____________ in the uterus.

Answer 16

contraction

Question 17

Which uterine proteins get up-regulated during labor?

Answer 17

• Prostaglandin receptors
• Oxytocin receptors
• Calcium channels

Question 18

Prostaglandins act in a ____________ fashion.

Answer 18

paracrine

They are produced by the myometrium and placental membranes.

Question 19

_____________ is produced by the placenta and works in a way similar to progesterone. That is, it is a quiescent factor for most of pregnancy, but due to switching of receptor types it becomes stimulatory.

Answer 19

Corticotropin releasing hormone

Question 20

How does cortisol mediate labor?

Answer 20

Unlike the human hypothalamus, the placenta makes more CRH in response to cortisol. As the fetus gets bigger, more cortisol is sent back to the placenta and more CRH is made. This positive feedback cycle involves labor.

Question 21

True or false: prostaglandins and oxytocin can be quiescence factors.

Answer 21

False.

Question 22

By what cellular mechanism does progesterone promote quiescence?

Answer 22

NO and cGMP

Question 23

What does oxytocin do to the cell?

Answer 23

It stimulates the release of calcium from membrane channels and the sarcoplasmic reticulum. Also, it stimulates COX-2.

Question 24

Prostaglandins and oxytocin both bind to _____________ receptors.

Answer 24

Gq

Question 25

Prostacyclins are _______________.

Answer 25

relaxants

Question 26

Membrane prostaglandin dehydrogenase goes _________ during labor.

Answer 26

down

Question 27

The endometrium is divided into three parts during pregnancy. Where is each?

Answer 27

• Decidua capsularis: around the baby
• Decidua basalis: between the baby and the myometrium
• Decidua parietalis: the part of the uterus excluding the basalis and capsularis

Question 28

Describe the myometrial stages of labor.

Answer 28

• 1: Quiescence (prior to clinical stage 1)
• 2: Actvation (prior to clinical stage 1)
• 3: Stimulation (clinical stages 1, 2, and 3)
• 4: Involution (clinical stage 4)

Question 29

Explain the principle of mechano-transduction.

Answer 29

If one part of the uterus contracts, then it will pull on the other parts of the uterus and initiate stretch contraction.

Question 30

name the myometrium inhibitors

Answer 30

progesterone

corticotropin releasing hormone

Question 31

name the myometrial stuimulators

Answer 31

corticotropin releasing hormone
oxytocin
prostaglandins
calcium

Question 32

name the contraction activated proteins

Answer 32

oxytocin receptors
prostaglandin receptors
calcium channels
gap junctions

Question 33

explain the different effects of CRH

Answer 33

in early pregnancy = quiescence by blocking myosin light chain kinase
in late pregnancy = contraction by activating the protein kinase C pathway