Physiology of Pregnancy and the Fetus Flashcards
What are the main fxns of the placenta?
- supply nutrients
- exchange O2 and CO2
- regulates fluid volumes and disposal of wastes/metabolites
- synthesizes steroids and proteins that affect maternal and fetal metabolism
What organs does the placenta take function over until birth?
lungs
kidney
gut
endocrine
What about the placenta is organized to facilitate exchange b/t mother and fetal circulation?
-large surface area for exchange
- highly developed vasculature in maternal and fetal components
- –>physically separate
What are the 3 main features of the placenta?
chorionic villi
intervillous space
decidua basalis
What is the functional unit of the placenta?
chorionic villi
–>extensive branching for increased surface area for exchange
What arteries empty from the mother into the intervillous space?
spiral arteries from maternal side, drained by maternal veins
Describe maternal blood flow in the placenta
Spiral A discharge in spurts into intervillous space
Filling dissipates force and velocity–>allows time for adequate exchange to villi
Blood drains through venous orifices, etners placental vein–>maternal veins
Are there capillaries in the maternal blood flow of the placenta?
NO
What do the 2 umbilical arteries carry?
deoxygenated blood
Where does fetal blood flow originate?
umbilical As
–>branch, penetrate chorionic plate to form chorionic villi capillary network
How does the umbilical vein receive oxygenated blood?
umbilical As from the fetus branch to the capillary network in the villi–> exchange with blood flowing from spiral As of mother–> taken up in single umbilical vein that is carried back to the fetus
What are the functions of the terminal dilations in the capillary network of villi?
has slower blood flow so it can exchange nutrients efficiently
Explain the PO2 change as oxygen flows from maternal blood–> intervillous space–> umbilical vein.
PO2 100mmHg in mother
Drops to 30-35 mmHg as it diffuses into villi
Drops further as it flows to umbilical vein
Fetal Hb able to get sufficient O2 saturation
Why is fetal Hb able to pick up more O2 c/t maternal Hb?
The PO2 is very low once it diffuses to the fetus, so needs to be able to pick up O2 efficiently
What factors cause CO2 to be transferred from the fetus to the mother?
Fetal blood has lower affinity for CO2 c/t mother
–>PCO2 is around 48 in umbilical As
–> PCO2 is around 43 in intervillous space
**CO2 flows down concentration gradient to mother
What are examples of passive exchange in the placenta?
- non-protein nitrogen wastes (urea, creatine) from fetus to mother
- lipid soluble hormones transfer between mother, placenta and fetus
What is an example of facilitated diffusion in the placenta?
glucose to fetus
What are examples of primary and secondary active transport to the fetus?
amino acids
vitamins
minerals
What are examples of receptor mediated endocytosis in the placenta?
Large molecule exchange
–> LDL, hormones (insulin), antibodies (IgG)
Describe the endocrine functions of the placenta
- Manufactures hormones
- —–>steroid, amines, polypeptides
- Regulates via paracrine
- –> releases local placental hormones into fetal or maternal circulations
What are the general functions of placental hormones in pregnancy?
- maintain pregnant state of uterus
- stimulate lobuloalveolar growth and function of maternal breasts
- adapt maternal metabolism and physio to support growing fetus
- regulate fetal development
- regulate timing and progression of childbirth
What produces hCG?
syncytiotrophoblasts
What binds with high affinity to LH receptors and rapidly accumulates in maternal circulation?
hCG
What is the primary fxn of hCG?
stimulate LH receptors in corpus luteum
- -> maintain high levels of corpus luteum progesterone
- -> prevent lysis of corpus luteum
What does the small amount of hCG that enters the fetus do?
stimulates Leydig cells to produce testosterone
What is thought to be responsible for nausea and morning sickness in pregnancy?
hCG
Describe serum levels of hCG
double daily up to 10 weeks
What produces hCS?
syncytiotrophoblasts
When is hCS detected?
day 10 syncytiotrophoblasts
3 weeks maternal serum
What is hCS?
human chorionic somatomammotropin
What is hCS structurally related to?
growth hormone and prolactin
–>type of human placental lactogen
What is the fxn of hCS?
coordinates fuel economy of fetoplacental unit
–> converts glucose to FA and ketones
–> promote development of mammary glands
–> lipolytic actions help mother shift to FFA use for energy
What can contribute to diabetogenicity of pregnancy?
hCS
–>antagonistic action to maternal insulin
What hormone is required for implantation and early maintenance of pregnancy?
progesterone via corpus luteum
What is window of receptivity?
increased adhesion proteins in endometrium
–> activated via progesterone
What stimulates endometrial gland secretions for early nutrient transfer?
progesterone
What hormone reduces uterine motility, inhibits uterine contractions and induces mammary growth?
progesterone
Describe serum levels of progesterone during pregnancy
High levels throughout pregnancy
–> from 20 to 120 ng/mL
Describe serum levels of hCS during pregnancy
steadily increases until birth
–> 2 to 10 ug/mL
What are the functions of estrogen in pregnancy?
- induces endometrial growth
- induces progesterone receptor expression
- induces LH surge prior to ovulation
- increases uteroplacental blood flow
- increases LDL receptor expression in syncytiotrophoblasts
- induces prostaglandins and oxytocin receptors for parturition
- increases growth and development of mammary glands
What are the concentrations of estrogen in serum during pregnancy?
Estradiol > estriol > estrone
Describe the need for the maternal-placental-fetal unit
progesterone and estrogens increase way higher c/t nml menstrual cycle
placenta can’t produce them by itself
Describe the maternal-placental-fetal unit
How it overcomes placental shortcomings:
- Mother provides cholesterol
- Fetal adrenal gland and liver supply enzymes that the placenta lacks
When does the luteal-placental shift of progesterone occur?
week 8
–>placenta starts producing majority of progesterone
Is progesterone production regulated in pregnancy?
NO
How is progesterone formed in pregnancy?
Syncytiotrophoblasts import cholesterol from maternal blood
Express CYP11A1 and 3B-HSD1
- -> released into maternal compartment
- —–>causes consistent rise in maternal serum levels throughout pregnancy
Can the placenta produce cholesterol?
NO- must get from mother
How does MPF unit overcome placental shortcoming regarding estrogen production?
mother–> cholesterol
fetal adrenal gland and liver–> production of DHEAS and 16-OH DHEAS (weak androgens)
Why can’t the placenta make estrogen by itself?
- can’t make cholesterol
- lacks 17a hydroxylase and 17, 20 desmolase
- —> to make estrone and estradiol
- lacks 16a hydroxylase
- –>to make estriol
When does preeclampsia occur?
after 20 weeks
5-8% of pregnancies
What are the sx of preeclampsia?
HTN, signs of damage to kidney or other organ
—>proteinuria, generalized edema
What is the cause of preeclampsia?
Unknown
–> existing maternal pathology, obesity, abnormal placentation, immunologic factors
What can occur if preeclampsia is left untreated?
Eclampsia
Death (m and fetus)
HELLP
–> Hemolysis, Elevated Liver enzymes, Low Platelet count
What happens to the fetus with preeclampsia?
limited blood supply to uterine arteries–> ischemia and endothelial damage
***release of cytokines
Describe the placental of women with preeclampsia
abnormal, poor trophoblastic invasion
Where is blood formed in the fetus?
yolk sac
liver
bone marrow
