Physiology of Pregnancy, Parturition, and Lactation Flashcards
What is the functional unit of the placenta?
chorionic villus
*extensive branching increases SA for maternal-fetal exchange
Where do spiral arteries empty?
directly into the intervillous space
How does maternal blood flow to and from baby?
enters in pulses to wall of uterus –> inter-villous space –> bathes chorionic villi –> drains through venous orifices in basal plate –> enters maternal placental veins –> into pelvic Vs
*intervillous space is functional capillary bed
How do uterine contractions affect maternal blood flow?
attenuate arterial inflow and completely interrupt venous drainage –> volume of blood in IVS increases so there is continual exchange
What are 2 important functions of the amniotic fluid in relation to blood flow?
mechanical buffer to protect fetus from external damage
excretes waste products through it
How does the Pressure of O2 change across the placenta?
maternal blood coming into IVS has arterial blood gas = PO2 of 100 mmHg
diffusion into chorionic villi causes PO2 of blood in IVS to fall = 30-35 mmHg
PO2 of blood in umbilical V is even less
How does the fetus overcome the low PO2 in the IVS?
fetal Hb has much higher affinity for O2 than maternal Hb
fetus has relatively high CO per unit body weight –> increases O2 carrying capacity of fetal blood –> Hb rises to 50% higher in fetus
What things move across the placenta passively?
waste products
lipid-soluble steroid hormones
How does glucose move across the placenta?
facilitated diffusion
What things move across the placenta via active transport?
amino acids
vitamins and minerals
What molecules move across the placenta via receptor-mediated endocytosis?
LDL
transferrin
some hormones and Abs
*uptake of these increases throughout gestation until just before birth
What part of the placenta produces hormones?
syncytiotrophoblasts
What is hCG secretion like throughout pregnancy?
first hormone produced by syncytiotrophoblasts
rapidly accumulates in maternal circulation, detectable w/in 24 hrs of implantation
doubles every 2 days for 1st 6 weeks –> peak at 10 weeks, then declines to constant level
What is the action of hCG?
binds w/ high affinity to LH receptor –> stimulates corpus luteum to keep making progesterone in first 10 weeks
causes nausea of morning sickness
What is human placental lactogen (hPL) secretion like throughout pregnancy?
1st made 10 days after conception –> in maternal serum by 3 weeks
rise progressively throughout remainder of pregnancy
What are the actions of hPL?
structurally similar to GH and prolactin
antagonistic to insulin –> diabetogenicity
inhibits maternal glucose uptake –> more for baby
helps mother shift to use of FFAs for energy
What is placental progesterone secretion like throughout pregnancy?
production is largely unregulated - produces as much as the supply of cholesterol, desmolase, and 3beta-HSD will allow
levels increase throughout pregnancy
What is estriol production dependent on?
a healthy fetus
levels can be used to assess fetal well-being
What are the functions of estrogens in pregnancy?
increase uteroplacental blood flow
enhance LDL receptor expression in syncytiotrophoblasts
induce prostaglandin and oxytocin receptors
increase growth and development of mammary glands
What major hormone can the fenal adrenal cortex synthesize and how is it dealt with?
cortisol –> may be fetal signal for contractions, other things late in pregnancy
11B-HSD converts it to cortisone in syncytiotrophoblasts = weaker, so not too much floating around
On what day of the menstrual cycle does implantation usually occur?
~ day 21
What are the major functions of progesterone in early pregnancy?
stimulates secretion from uterine glands –> provides nutrients to embryo = histotrophic nutrition
inhibits myometrial contraction and release of paracrine factors that lead to menstruation
What does progesterone due in the indow of receptivity?
increases adhesivity of endo epithelium
formation of cellular extensions on apical surface of epithelia
What is important about the extensive blood supply in the endometrium during receptive window/implantation?
critical role in capturing embryonic hCG and taking it to ovary to maintain pregnancy
also allows for good delivery of progesterone back to endo
When does the source of progesterone and estrogens in pregnancy switch?
8 weeks
from corpus luteum –> placenta
What 3 enzymes are in the placenta and not in the fetus, and what do they do?
sulfatase: converts DHEA-S –> DHEA
aromatase and 3beta-HSD: involved in converting DHEA –> Estradiol
What 3 enzymes are in the fetus, but not in the placenta and what do they do?
17 alpha-hydroxylase/17,20 desmolase: progesterone –> 17alpha-hydroxyprogesterone
16alpha-hydroxylase: in fetal liver; DHEA-S –> 16alpha-OH DHEA-S
What does the mother do to help the placenta create hormones?
How does the fetus help?
mother: supplies it with LDL = cholesterol
fetus: supplies placenta w/ lacking enzymes
What hormone should the fetus NOT create?
estrogens - if so, fetus would be exposed to dangerous levels of E
*can’t make E bc no 3B-HSD and aromatase
How does the fetus reduce the activity of steroid intermediates?
sulfates them
does this to pregnenolone, DHEA, and 16A-OH-DHEA
(sulfate removed in placenta)
What occurs to maternal blood volume during pregnancy and how?
blood volume increases - starts during 1st trimester, grows rapidly in second, evens out in 3rd
mediated by increases in aldosterone
What occurs to mean arterial pressure of the mom during pregnancy?
increased plasma volume, but decreased peripheral vascular resistance –> MAP usually decreases during mid-pregnancy, then rises in 3rd trimester
What occurs to maternal cardiac output in pregnancy?
increases a lot in 1st trimester (35-40%) –> only slight increase during 2nd and 3rd
reflects increase in stroke volume and HR
How does progesterone affect maternal lungs?
increase alveolar ventilation via increased tidal volume
What are the main maternal GI tract changes in pregnancy?
morning sickness resolved by 14-16 wks
prolonged gastric empty time
decreased GE sphincter toen –> acid reflux
decreased colon motility –> constipation
What is the obstetric definition of labor?
series of regular, rhythmic, and forceful contractions that develops to facilitate thinning and dilation of cervix
What are the stages of labor?
0 = tranquility
1 = uterine awakening, initiation of parturition, extending to complete cervical dilation
2 = active labor, from complete dilation to delivery
3 = from delivery to expulsion of placenta and final contraction
What physiological change occurs in the uterus during labor?
increased number of gap jxns btw myometrial cells
increase in oxytocin receptors
What is fetal station?
where the baby is in the pelvis
presenting part = part leading way through canal
0 station = when head is even w/ ischial spines
- numbers = superior to spines
+ numbers = inferior to spines
What does estrogen do to induce labor?
increases degree of uterine contractility
stimulates synthesis of oxytocin receptors
What do prostaglandins do to induce labor?
initiate labor
uterine stretch, estrogen, and oxytocin induce synthesis
PGF 2a and PGE 2 –> increase uterine motility
levels increase in uterus, placenta, amniotic fluid, and fetal membranes before onset of labor
What occurs to the uterus’s sensitivity to oxytocin close to labor?
insensitive to oxytocin until 20 weeks –> receptors increase 80x –> baseline at 36 weeks –> rises 200x during early labor
*uterus only susceptible to oxytocin at end of pregnancy vs prostaglandins throughout pregnancy
What hormone is thought to initiate rhythmic uterine contractions?
prostaglandins
(increased oxytocin does NOT do this)
What does oxytocin bind to stimulate prostaglandins?
receptors on decidual cells –> prostaglandins
*because it can stim prostaglandins, oxytocin may play role in expulsion of fetus during 2nd stage of labor
What 2 things stimulate oxytocin response?
estrogen –> more oxytocin receptors
cervix stretch –> increased oxytocin release
What does OT do after fetus is expelled?
causes uterus to contract immediately after birth –> limits blood flow and blood loss
basal maternal OT levels unchanged after delivery
fetal OT higher after vaginal delivery than C section
What is relaxin?
produced by corpus luteum, placenta, and decidua
keeps uterus quiescent during pregnancy
production and release increases during labor
may soften and dilate cervix during labor
How do the fetal pituitary, adrenals, and placental membrane affect the uterus during labor?
pit: oxytocin
adrenals: cortisol –> may be uterine stimulant
placental membranes –> prostaglandins –> increase intensity of contractions
What is significant about fetal movements and labor?
fetal movements –> stretch uterus –> increases its contractility
twins are born on avg 19 days earlier than single child
What are Braxton Hicks contractions?
weak and slow rhythmic contractions that occur throughout pregnancy
How are labor contractions mediated?
by positive feedback:
stretch –> oxytocin and prostaglandins –> contraction –> stretch
loop that keeps going
What is effacement?
cervix prepares for delivery
becomes soft, short, and thinner
100% effaced = paper-thin, labor about to occur
Describe descent and expulsion.
cervix fully dilated: 10 cm
contractions strongest at top pushing fetus down
avg 20-50 min in duration
What is considered prolonged labor?
lasting more than 18-24 hrs
2 types: early labor > 8hrs or active phase is > 12 hrs
What is the other word for obstructed labor?
labor dystocia
What is considered preterm labor?
before 37th week
12% of all pregnancies
uterine contractions cause cervix to open earlier than normal
risk factors: uti, uterin/cervical abnormalities, chronic illness, smoking drinking, EtOH, etc.
What are risk factors for a ruptured uterus?
uterine scar from previous C section
dysfunctional/prolonged labor
labor augmentation by OT or PG
excessive manual pressure applied by fundus during delivery
What are the leading and cardinal signs of a ruptured uterus?
leading = deterioration of fetal heart rate
cardinal = loss of fetal station on manual vaginal exam
What is preeclampsia?
high blood pressure and signs of damage to another organ sys, often kidneys
proteinuria and generalized edema seen
occurs after week 20 of pregnancy
5-8% of pregnancies
What is a proposed cause of preeclampsia?
disease of placenta:
associated w/ limited blood supply to uterine As –> ischemia and endothelial damage w/ release of cytokines
placenta of women w/ preE has poor trophoblastic invasion
What endothelial things are thought to be changed during preeclampsia?
increased: ET-1, TBx, ANGII (due to autoAb)
decreased: NO, PG2
What is the general organization of the breast?
alveoli –> lobule –> drains to ductule –> widens into ampulla
What makes up a lactation alveolus?
secretory epithelial cells (alveolar cells)
contractile myoepithelial cells
surrounded by adipose tissue
What does breast development at puberty and pregnancy depend on?
puberty: estrogens and progesterone
pregnancy: PRL and hPL and very high E and P –> full development
What are mammogenic hormones?
promote proliferation of alveolar and duct cells
Estrogen
GH
Cortisol
Prolactin
Relaxin?
What are lactogenic hormones?
promote initiation of milk production by alvelar cells
Prolactin
hCS
Cortisol
Insulin
Thyroid Hormones
withdrawal of E and P
What are galactokinetic hormones?
promote contraction of myoepithelial cells and thus milk ejection
Oxytocin
Vasopressin
What are galactopoietic hormones?
maintain milk production after it has been established
prolactin (primary)
cortisol and others
What are the 5 main routes of milk secretion?
- secretory path
- transcellular endocytosis/exocytosis
- lipid path
- trancellular salt and water transport
- paracellular path
What is the secretory pathway of milk secretion?
milk proteins lactalbumin and casein synth in ER –> golgi
alveolar cells add Ca and Pi to golgi
lactose synthesized
water enters secretory vesicles by osmosis
exocytosis
What is the transcellular endocytosis/exocytosis path of milk secretion?
maternal immunoglobulins (IgA) taken up by endocytosis on basolateral side
secreted via exocytosis –> absorbed in baby’s GI
What is the lipid pathway of milk secretion?
FAs form lipid droplets in alvelar cells –> secreted in membrane-bound sacs
What is the transcellular salt and water path of milk secretion?
salts go in cells (not between them) and are moved into lumen –> water follows via osmotic gradient
*gradient formed primarily by lactose
What is the paracellular pathway of milk secretion?
salt and water move btw cells through tight jxns
cells (primarily leukocytes) can squeeze in too
How is lactation controlled during pregnancy?
PRL is inhibited by high E and P
human placental lactogen is also lactogenic
only colostrum secreted = thin, yellowish substance with a lot of IgA
What controls lactation after birth?
prolactin increases
E and P decrease
suckling is most powerful physiological stimulus for PRL release (inhibits domaminergic neurons)
How does oxytocin affect lactation?
enhances milk ejection by stimulating contraction of myoepithelial cells
+ feedback by suckling causes more OT to be synthesized and released
How does lactation affect ovarian cycle?
increased PRL –> inhibits GNRH production –> decreased LH and FSH –> no ovarian cycle
