Physiology of Pregnancy and the Fetus Flashcards
How does the placenta act like an endocrine gland?
it synthesizes steroids and proteins that affect both maternal and fetal metabolism
what are the three major features of the placenta?
the chorionic villi, the intervillous space, and the decidua basalis
what represent the functional unit of the placenta?
the chorionic villi
Why is the branching of the chorionic villi important?
it increases the surface area for exchange to happen
what empties into the intervillous space?
spiral arteries from the maternal side
why is it important to have a slowing of blood flow into the intervillous space?
it allows adequate time for exchange of nutrients
how does the fetal blood travel from the fetal circulation to the placenta?
via the umbilical arteries and into the chorionic villi (2)
what do the two umbilical arteries carry?
deoxygenated blood
How can the terminal umbilical arteries be described?
they have terminal dilations to slower blood flow and allow for exchange of nutrients
how does blood travel from the placenta back to the fetus?
via the single umbilical vein
diffusion of O2 into the chorionic villi has what affect on the Po2?
it causes the Po2 of blood in the intervillous space to fall to 30-35 mmHg and lower in the umbilical vein of the fetus
How does fetal hemoglobin and adult hemoglobin differ?
fetal hemoglobin has a much higher affinity for O2 than adult hemoglobin
what drives CO2 transfer?
concentration gradient differences
what is the Pco2 in the umbilical arteries near term? and in the intervillous space?
it is 48 mmHg in the umbilical arteries and 43mmHg in the intervillous space; all factors favor transfer of Co2 from fetus to mother
what things cross the placenta via passive exchange?
non-protein nitrogen wastes (urea/creatinine) from fetus to mother; lipid soluble hormones
how does glucose get from the mother to the fetus?
facilitated diffusion
what things get to the fetus via primary and secondary active transport to support growth?
amino acids, vitamins, and minerals
what things get from the mother to the fetus via receptor mediated endocytosis?
large molecule exchange- LDL, hormones like insulin, and antibodies (IgG)
how does the placenta regulate in a paracrine fashion?
it releases local placental hormones, it releases hormones into fetal or maternal circulations
what effect do the placental hormones have on the breasts?
they stimulate lobuloalveolar growth and function of maternal breasts
what is hCG produced by?
syncytiotrophoblasts
what does hCG bind with high affinity to?
LH receptors (it is structurally related to LH)
what is the primary function of hCG?
to stimulate LH receptors in the corpus luteum
what happens when hCG stimulates LH receptors in the corpus luteum?
it prevents luteolysis and it maintains high levels of luteal-derived progesterone
what effect does the small amount of hCG that enter fetal circulation have on the fetus?
it stimulates fetal leydig cells to produce testosterone
why does hCG have a much longer half life than LH?
due to glycosylation (the longer half life allows it to quickly accumulate in maternal circulation
what hormone does the placenta secrete that is structurally related to growth hormone and prolactin?
hPL (aka hCS)
what part of the placenta produces the hPL aka hCS?
the syncytiotrophoblast
what effect does hPL aka hCS have on mother?
causes maternal blood glucose levels to increase (there is an inhibition of peripheral glucose uptake in the mother), but it helps contribute to the nutrition of the fetus
what effect does hPL have on the mother’s insulin levels?
she will have a resistance to endogenous insulin
when does the placenta take over progesterone secretion from the corpus luteum?
about the 8th week of pregnancy
why is progesterone needed all throughout pregnancy, not just for the initial implantation?
it reduces uterine motility, inhibits propagation of uterine contractions. (by inhibiting the oxytocin receptor), induces mammary growth and differentiation
what effect does estrogen secreted from the placenta have on pregnancy?
it increases uteroplacental blood flow, increases LDL receptor expression in syncytiotrophoblasts, induces prostaglandins and oxytocin receptors necessary for parturition
How does the mother contribute to the high maternal levels of progesterones and estrogens?
the mother supplies cholesterol (used as a precursor to steroid hormone production)
How does the fetus contribute to high maternal levels of progesterone and estrogens?
the fetal adrenal gland and liver supply enzymes the placenta lacks for the conversion of intermediate products in steroid hormone synthesis
how is progesterone production regulated?
it is largely unregulated
how does the placenta produce progesterone?
the syncytiotrophoblasts import cholesterol from the maternal blood, and they will use CYP11A1 and 3beta-HSD1 to convert it into progesterone and then release it back into the maternal blood
how does the placenta produce estrogen if it doesn’t have cholesterol or 17-alpha hydroxylase, 17,20 desmolase, or 16-alpha hydroxylase?
the fetal adrenal gland and liver supply the enzymes needed; the mother supplies the cholesterol
the fetal circulatory system uses 3 shunts, what are they?
ductus venosis, foramen ovale, and ductus arteriosis
what is the ductus venosis for?
to bypass the fetal liver (not fully functional until late pregnancy/just after birth)
what is the foramen ovale used for?
it moves blood from the right atrium to the left atrium
what is the ductus arteriosis used for?
it moves blood from the pulmonary artery to the aorta
what does the ductus venosus provide?
a direct route from the placenta to the inferior vena cava and then to the right atrium
what is the foramen ovale and where is it?
it is a hole in the septum dividing the right and left atria- it is on the posterior aspect of the right atrium
what does the foramen ovale allow bypass of?
the right ventricle
what does the ductus arteriosus allow bypass of?
the lungs
which duct closes rapidly- within taking the first few breaths of air?
the ductus arteriosus
what causes the ductus arteriosus to close?
there is a major reduction in pulmonary pressure and an increase in aortic pressure
what is a clinical finding of a patent ductus arteriosis (PDA)?
it can be heard as a heart murmur
what can result from patent ductus arteriosus?
it puts a strain on the heart and it increases the pulmonary blood pressure
what causes the foramen ovale to close?
this closure results from changes in pressure across the atrium; there is increased venous return to the left atrium and elevated left arterial pressure
what does closure of the foramen ovale establish?
left and right circulatory system
what causes a patent foramen ovale?
increased right atrial pressure can push the flap open
what is the effect of a patent foramen ovale?
sustained pulmonary hypertension or transient increases
what causes the ductus venosus to close?
within 1-3 hours after birth, the muscle wall of the ductus venosus contracts and closes due to decreased blood flow and pressure changes; the portal venous pressure rises, which forces venous blood through liver sinuses
