The Physiology of Parturition Flashcards
What causes the pain in pregnancy?
The pressure from contractions makes the myometrium ischemic, which is painful.
During labor, the uterus can generate ____________ of pressure.
60 mm Hg
The cervix is made of types ________ collagen.
I and III
Dilation in contraction refers to the ____________.
internal os of the cervix (there is an external os, too, but that does not matter)
What stimulates dilation of the cervix?
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.”)
What are the four clinical stages of labor?
- 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
What is the difference between latent and active labor?
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.
What occurs during stages 1, 2, and 3 of labor?
- 1: latent and active labor
- 2: complete dilation of the cervix
- 3: delivery of the fetus
_______________ is an important uterine quiescence factor.
Progesterone
_______________ is a uterine activation factor.
Estrogen
Explain the progesterone switch at the end of pregnancy.
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.
What is Pitocin?
Synthetic oxytocin that stimulates contractions
The uterus grows in pregnancy by ________________________.
hypertrophy and hyperplasia
Toward the end of pregnancy, _____________ become connected.
myocytes (by connexins in gap junctions)
Why don’t Braxton-Hicks contractions induce labor?
They are irregular and not coordinated.
Prostaglandins stimulate ____________ in the uterus.
contraction
Which uterine proteins get up-regulated during labor?
- Prostaglandin receptors
- Oxytocin receptors
- Calcium channels
Prostaglandins act in a ____________ fashion.
paracrine
They are produced by the myometrium and placental membranes.
_____________ 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.
Corticotropin releasing hormone
How does cortisol mediate labor?
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.
True or false: prostaglandins and oxytocin can be quiescence factors.
False.
By what cellular mechanism does progesterone promote quiescence?
NO and cGMP
What does oxytocin do to the cell?
It stimulates the release of calcium from membrane channels and the sarcoplasmic reticulum. Also, it stimulates COX-2.
Prostaglandins and oxytocin both bind to _____________ receptors.
Gq
Prostacyclins are _______________.
relaxants
Membrane prostaglandin dehydrogenase goes _________ during labor.
down
The endometrium is divided into three parts during pregnancy. Where is each?
- 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
Describe the myometrial stages of labor.
- 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)
Explain the principle of mechano-transduction.
If one part of the uterus contracts, then it will pull on the other parts of the uterus and initiate stretch contraction.
name the myometrium inhibitors
progesterone
corticotropin releasing hormone
name the myometrial stuimulators
corticotropin releasing hormone
oxytocin
prostaglandins
calcium
name the contraction activated proteins
oxytocin receptors
prostaglandin receptors
calcium channels
gap junctions
explain the different effects of CRH
in early pregnancy = quiescence by blocking myosin light chain kinase
in late pregnancy = contraction by activating the protein kinase C pathway
