Flashcards in Lect. 18 - Placental Physiology Deck (19):
Functions of the Placenta
Diffusion of oxygen and CO2; diffusion of foodstuffs; excretion of waste products `
What are the characteristics of the early placenta?
Thick, low permeability, small SA, miniscule total diffusion conductance
Characteristics of the late placenta
Thin, high permeability, large SA, large increase in placental diffusion
What is the oxygen pressure gradient near the end of pregnancy?
PO2 of mother = 50 mm Hg and PO2 of fetus = 30 mm Hg
Why can adequate oxygenation occur w/ such a low pressure gradient?
Fetal Hg has a higher affinity for O2; fetal blood Hg concentration is about 50% greater than maternal; Bohr effect
Hg can carry more O2 at a low PCO2
Characteristic of fetal blood coming into the placenta.
Carries more CO2
Double Bohr effect
Refers to the double shift in the maternal blood and in the fetal blood. (Fetal blood becomes more alkaline (low CO2) and maternal blood becomes more acidic (high CO2))
What is the method of secretion of HCG?
Secreted by the syncytial trophoblast cells into maternal fluids
When is HCG secreted?
Measurable secretion 8-9 days after ovulation and maximal secretion during the 10th-12th week of pregnancy. Lower levels secreted 16th through 20th weeks
Functions of HCG?
Prevents involution of corpus luteum; causes CL to increase secretion of progesterone and estrogens; causes increased growth in CL; exerts interstitial cell-stimulating effect on testes of male fetus - results in production of testosterone until birth
What is the method of secretion of estrogens?
Secreted by syncytiotrophoblast cells of placenta
Timing of estrogen secretion
Toward end of pregnancy, secretion level is 30x the mother's normal level
How are estrogens formed?
Placental estrogens are formed almost entirely from androgenic steroid compounds: found in mother's and fetal's adrenal glands; converted by trophoblast cells into estradiol, estrone, and estriol.
Functions of estrogens
Uterine and breast enlargement; growth of breast ductal structure; enlargement of maternal external genitalia; relaxation of pelvic ligaments; may also affect aspects of fetal development
Method of secretion of progesterone?
Secreted in small quantities by corpus luteum early and secreted in large quantities by placenta
Functions of progesterone
Causes decidual cells to develop in the endometrium; decreases contractility of pregnant uterus; increases secretions of Fallopian tubes and uterus; may work w/ estrogen to prepare breasts for lactation
Method of secretion of human chorionic somatomammotropin
Secreted by placenta beginning in 5th week of pregnancy