Pregnancy Physiology Flashcards
How long is a nl pregnancy?
40 wks from onset of LMP (38 wks from last ovulation)
What happens to estrogen and progesterone during pregnancy? Why?
Rise steadily throughout
Maintain pregnancy, develop breasts, suppress further ovulation
What is the source of estrogen and progesterone?
1st trimester – corpus luteum
2nd/3rd trimester – placenta
How does fertilization occur?
within 24 hrs of ovulation
sperm penetrates ovum at ampulla –> 2nd polar body extruded, ovum divides –> blastocyst is formed and arrives at uterine cavity
How does implantation occur?
Blastocyst implants 5 days after ovulation
High progesterone from corpus luteum
Trophoblast (outer rim of cells on blastocyst) invades endometrium –> becomes fetal portion of placenta
What is the function of hCG and where does it come from?
Trophoblast secretes hCG 8 days after ovulation
LH analog
Signal of fertilization to corpus luteum –> prevents regression and stimulates estrogen and progesterone secretion
How is progesterone made?
Cholesterol brought into placenta –> LH stimulates cholesterol desmolase –> cholesterol converted to pregnenolone –> converted to progesterone
How is estriol made?
Pregnenolone (from cholesterol) enters fetal circulation –> converted to DHEA-S in fetal adrenal cortex –> hydroxylated in fetal liver –> crosses back to placenta and converted to estriol via aromatase (stimulated by FSH)
What are Braxton Hicks contractions?
Begin 1 mo before birth
Distension of uterus by fetus –> increased contractility
What is the role of cortisol in pregnancy?
Fetal adrenal cortex produces lots of cortisol near term –> increased estrogen production –> increased local production of prostaglandins –> increased Ca in uterine smooth muscle cells –> increased contractility
Role of oxytocin in pregnancy
Stimulant of uterine contraction
Stimulated by cervical dilation
Stages of labor
1st – downward uterine contractions move fetal head to cervix and widen and thin cervix
2nd – fetus is forced thru cervix
3rd – placenta separates from uterus and is delivered; uterine contractions allow for vasoconstriction (limits bleeding)
Role of estrogen and progesterone on breasts
Increase size
Stimulate prolactin
Inhibit action of PRL on breasts during pregnancy (levels fall off after birth –> allow for lactation)
How is lactation a method of birth control?
High PRL inhibits GnRH secretion –> decreased FSH/LH –> no ovulation
