Physiology of Pregnancy Flashcards
What is the functional unit of the placenta?
Chorionic villi
What functions does the placenta provide between the mother and fetus?
Gut - supplies nutrients
Lung - exchanges O2 and CO2
Kidney - regulates fluid volumes and disposes of waste metabolites
Endocrine gland - synthesizes steroids and proteins that affect maternal and fetal metabolism
What is the purpose of pulsatile maternal blood flow into intervillous spaces?
Dissapates the force of the blood and reduces blood velocity so the placental tissues do not separate
Allows adequate time for exchange of nutrients
What is the flow of the maternal blood from the intervillous spaces back to the mom?
Venous orifices in basal plate => maternal placental veins => Uterine and pelvic veins
What acts as the functional capillary of the placenta?
Intervillous space
What is the effect of uterine contractions on maternal blood flow?
Attenuate arterial inflow and interrupt venous drainage
Increased volume for continual exchange
What umbilical vessel carries the highest O2 and nutrient content?
Umbilical vein
What umbilical vessel carries deoxygenated blood?
Umbilical A.
Partial pressure O2 is __ on maternal side vs fetal side?
Higher
(opposite for PCO2)
What causes the low PO2 of blood in intervillous space?
Diffusion of O2 from maternal blood into chorionic villi of fetus
Why does the fetus not suffer from the low PO2 of maternal blood in the intervillous space?
Fetal Hb has higher affinity for O2 than maternal Hb
Also: high CO in the fetus, rise in Hb concentration late in pregnancy
How are waste products transported across the placenta?
Passive movement from fetus to mother
How are lipid-soluble hormones transported across the placenta?
Simple diffusion b/w mother, placenta, and fetus
How is glucose transported across the placenta?
Facilitated diffusion from mother to fetus
How are AAs transported across the placenta?
Secondary active transport
How are vitamins and minerals transported across the placenta?
Active transport
How are LDLs, transferrin, hormones, and antibodies transported across the placenta?
Placenta takes up large molecules from the mother, increases throughout gestation until birth
What is the endocrine function of the placenta?
Maintain pregnancy
Stimulate breast development
Regulate timing and progression of parturition
Antibodies used to detect hCG are designed to detect what part?
B-subunit
What is the affinity of hCG for the LH receptor?
High
The primary action of hCG is to stimulate LH receptors on corpus luteum
When is hCG detectable in the maternal serum?
Within 24 hours of implantation (rapid accumulation in week 1)
Where is human placental lactogen (hPL) produced?
Syncytiotrophoblast
When can hPL be detected in maternal serum?
3 weeks gestation
What is hPL’s contribution to pregnancy?
Antagonistic action to insulin
Increase glucose availability by inhibiting maternal glucose uptake (diabetogenic)
Protein anabolic and lipolytic
What is the rate limiting step of progesterone synthesis by the placenta?
Conversion of cholesterol by desmolase and 3B-HSD
What product of DHEAs can be used to detect fetal well-being?
Estriol
What are the 3 products of DHEAs from the fetal zone?
Estradiol-17B
Estrone
Estriol
What are the functions of estrogen during pregnancy?
Increase uteroplacental blood flow
Enhance LDL receptor expression in syncytiotrophoblasts
Induce prostaglandin and oxytocin receptors
Increase growth and development of the mammary glands
What is histotrophic nutrition? How long does it occur?
Stimulation of uterine gland secretion by progesterone to provide nutrients to embryo
Occurs during the first trimester, replaced with hemotrophic nutrition
What is the “window of receptivity”? When does it occur?
Progesterone-induced phase of increased adhesivity of endometrial epithelium
Day 20-24
What happens to maternal levels of progesterone and estrogen during pregnancy?
Increase substantially higher than during a normal menstrual cycle
What is progesterone’s effect on uterine motility?
Inhibitory, prevents contractions
At what point does placenta become the main source of progesterone and estrogens?
8 weeks
What steroidogenic enzymes does the placenta lack?
17a-hydroxylase
17, 20 desmolase
16a-hydroxylase
What steroidogenic enzymes does the fetus lack?
3B-HSD
Sulfatase
Aromatase
What steroidogenic enzyme do both the fetus and placenta utilize?
17B HSD
What steroidogenic reactions are occuring in the liver of the fetus?
DHEA-S => 16a-OH DHEA-S via 16a hydroxylase
What steroidogenic reactions are occurring in the adrenal gland of the fetus?
LDL Cholesterol => Prenenolone sulfate
Pregnenolone sulfate => DHEA-S via 17a hydroxylase and 17,20 Desmolase
What is the purpose of sulfatating androgens within the fetus?
Reduces biological activity of steroid hormones to protect the fetus from active androgens and premature/abnormal sexual development (primarily masculinization of female fetuses)
What hormone mediates the increase in maternal blood volume?
Increased aldosterone
During which trimester is the increase in blood volume most significant?
2nd trimester
When does the blood volume plateau during pregnancy?
Last few weeks of 3rd trimester
By how much does the maternal blood volume increase during pregnancy?
40-50%
What is the cause of the initial fall in mean arterial pressure (MAP) during pregnancy?
Progesterone and estradiol act as vasodilators => Decreased peripheral resistance => Decreased MAP
When is cardiac output the most significantly increased during pregnancy?
1st trimester (reflects increase in SV and HR)
What is the effect of pregnancy on respiration?
Increased tidal volume => Increased alveolar ventilation
How long does morning sickness last?
14-16 weeks
What effects does pregnancy have on the GI tract?
GERD - prolonged gastric empty time, decreased GE tone
Constipation - decreased colonic motility and increased water absorption
Increased demand for protein, iron, and folic acid
What hormones contribute to uterine quiescence during pregnancy?
Progesterone
Relaxin
How many weeks after fertilization does parturition occur?
38 weeks (fetal age)
How many weeks after the last menstrual period does parturition occur?
40 weeks
What characterizes stage 0 of labor?
Uterine tranquility and refractoriness to contraction
What characterizes stage 1 of labor?
Uterine awakening, initation of parturition, extending to complete cervical dilation
Physiological changes: increased # of gap jxns b/w myometrial cells, increased # of oxytocin receptors
What characterizes stage 2 of labor?
Active labor, from complete cervical dilation to delivery of the newborn
What characterizes stage 3 of labor?
Delivery of fetus to expulsion of placenta and final uterine contraction
What is the 0 station of the fetal station?
When the baby’s head is even with the ischial spines (narrowest part of the pelvis)
What happens to progesterone in the 7th month of pregnancy?
Plateaus and remains constant
What stimulates the production of prostaglandins in the fetal membranes?
Estrogen
What stimulates the production of prostaglandins in the uterine cells?
Oxytocin
What are prostaglandins synthesized from?
Arachidonic acid
What is the role of prostaglandins in parturition?
Initiates labor by enhancing motility/contraction of uterine smooth muscle cells
(Can induce abortion with large doses of PGF2a and PGE2)
When are prostaglandin levels the highest? Where?
Just before onset of labor
Uterus, placenta, amniotic fluid, fetal membranes
What stimulates uterine prostaglandin production?
Uterine stretch
What is the Ferguson reflex?
Stretch of the cervix that initiates oxytocin release and causes uterine contraction
How long does the uterus remain insensitive to oxytocin? What changes?
20 weeks gestation
After 20 weeks, # oxytocin receptors increases to 80x higher then 200x higher during early labor
What is the function of oxytocin during stage 1 of labor?
Stimulates powerful uterine contractions that sustain labor
(Does NOT initiate labor)
Stimulates PGF2a production (synergy)
Once stage 1 of labor is initiated, how is oxytocin released?
In bursts, with frequency increasing as labor progresses
What is the function of oxytocin during the 2nd stage of labor?
Binds receptors on decidual cells => stimulates PGF2a production
What is the function of oxytocin during the 3rd stage of labor?
Causes uterus to contract immediately after fetus is expelled to limit blood flow/loss
Why are fetal plasma oxytocin levels higher after vaginal delivery than by cesarean section?
Maternal oxytocin triggered by Ferguson reflex crosses placenta into fetus
What is the function of relaxin during parturition?
Softens and dilates cervix
What is the effect of cortisol on the uterus? Where is it produced during during pregnancy?
Uterine stimulant
Produced in the fetal adrenal glands
What is the mechanical reason for twins being born 19 days earlier than the average single child?
Increased fetal movement which elicits smooth muscle contraction
What are Braxton Hicks contractions? When do they become labor contractions?
Periodic episodes of slow, rhythmic contractions
Changes when contractions start to stretch the cervix and push the baby through the birth canal
What are the phases of delivery?
Dilation and effacement
Descent and Expulsion - fetus
Expulsion - placenta
What is the effacement phase of delivery?
Cervical thinning in preparation for delivery
100% when cervix is paper-thin
Contractions <10 min apart
What phase of delivery are the contractions the strongest?
Descent and Expulsion
How long does the dilation and effacement phase of delivery last?
7-12 hours
How long does the descent and expulsion phase of delivery last?
20-50 min
How long does the expulsion of the placenta phase of delivery last?
15 min
What are the two main types of prolonged labor?
Latent (early) phase of labor >8 hours
Active phase >12 hours
What can cause prolonged labor?
Poor uterine contractions
Abnormal fetus position/size
Issues w/ birth canal
What is labor dystocia?
Obstructed labor
Normal uterine contractions, but childbirth physically blocked
Can be fatal, increased risk of infection to mom
What classifies preterm labor?
Labor before 37th week of pregnancy
What classifies a ruptured uterus?
Failed integrity of the myometrial wall
What is the leading sign of a ruptured uterus?
Deterioration of fetal heart rate
What is the cardinal sign of a ruptured uterus?
Loss of fetal station on a manual vaginal exam
What can cause ruptured uterus?
Uterine scar from previous C-Section (failed integrity of myometrium)
Dysfunctional/prolonged labor
Labor augmentation with exogenous oxytocin/prostaglandins
Excess manual pressure to uterine fundus
When does preeclampsia normally present?
After week 20
What is preeclampsia characterized by?
High blood pressure and signs of damage to another organ system (kidneys)
Abnormal placenta (poor trophoblastic invasion)
What structure of the breast carries secretions to the outside?
Lactiferous duct
What is the fundamental secretory unit of the breast?
The alveolus
What do the alveoli of the breast contain?
Secretory alveolar cells surrounded by contractile myoepithelial cells surrounded by adipose cells
During pregnancy, what hormones contribute to lobuloalveolar growth of the breast?
Prolactin
Estrogen
Growth hormone
Cortisol
During pregnancy, what hormones contribute to ductal growth of the breasts?
Estrogen
Growth hormone
Cortisol
Relaxin
What hormones are lactogenic?
Prolactin**
hPL**
Cortisol
Insulin
Thyroid hormones
Withdrawal of estrogen and progesterone
What are galactokinetic hormones?
Promote contraction of myoepithelial cells and milk ejection
Oxytocin and vasopressin
What are galactopoietic hormones?
Maintain milk production after it has been established
Prolactin
Cortisol
What occurs during the secretory pathway of milk production?
Milk proteins lactalbumin and casein are sythesized into a vesicle with water
Vesical is exocytosed into the alveolar lumen
What occurs during the transcellular pathway of milk production?
Maternal IgG endocytosed into alveolar lumen and secreted via exocytosis
What occurs during the lipid pathway of milk production?
LCFAs from maternal diet secreted into alveolar lumen in membrane-bound sac
What occurs during the transcellular salt and water transport route of milk production?
Electrolytes transported from interstitial fluid to alveolar lumen followed by water via osmotic gradient (generated by lactose)
What occurs during the paracellular pathway of milk production?
Salt and water move into lumen of alveolus through tight junctions into the milk
What is colostrum?
Thin, yellow milk-like substance secreted the first few days after parturition
High concentration of immunoglobulins
What hormones inhibit prolactin during pregnancy?
High estrogen and progesterone
What is the biochemical stimulus of lactation?
Increased levels of prolactin
Decreased estrogen and progesterone
What is THE physiological stimulus of prolactin release?
Suckling
What is the pathway of hormone release stimulated by suckling?
- Suckling stimuli activates afferent neural pathway to hypothalamus
- DA release inhibited => inhibit lactotrophs => release prolactin
- Spinal cord neurons stimulate production and release of oxytocin from posterior pituitary => stimulate myoepithelial cells to contract
- Spinal cord neurons inhibit hypothalamus production of GnRH => inhibits ovarian cycle
