Lect. 18 - Placental Physiology Flashcards Preview

Embryo Exam II > Lect. 18 - Placental Physiology > Flashcards

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


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


Functions of human chorionic somatomammotropin

Causes decreased insulin sensitivity and decreased utilization of glucose by mother; general metabolic hormone