Lect. 18 - Placental Physiology

Question 1

Functions of the Placenta

Answer 1

Diffusion of oxygen and CO2; diffusion of foodstuffs; excretion of waste products `

Question 2

What are the characteristics of the early placenta?

Answer 2

Thick, low permeability, small SA, miniscule total diffusion conductance

Question 3

Characteristics of the late placenta

Answer 3

Thin, high permeability, large SA, large increase in placental diffusion

Question 4

What is the oxygen pressure gradient near the end of pregnancy?

Answer 4

PO2 of mother = 50 mm Hg and PO2 of fetus = 30 mm Hg

Question 5

Why can adequate oxygenation occur w/ such a low pressure gradient?

Answer 5

Fetal Hg has a higher affinity for O2; fetal blood Hg concentration is about 50% greater than maternal; Bohr effect

Question 6

Bohr effect

Answer 6

Hg can carry more O2 at a low PCO2

Question 7

Characteristic of fetal blood coming into the placenta.

Answer 7

Carries more CO2

Question 8

Double Bohr effect

Answer 8

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))

Question 9

What is the method of secretion of HCG?

Answer 9

Secreted by the syncytial trophoblast cells into maternal fluids

Question 10

When is HCG secreted?

Answer 10

Measurable secretion 8-9 days after ovulation and maximal secretion during the 10th-12th week of pregnancy. Lower levels secreted 16th through 20th weeks

Question 11

Functions of HCG?

Answer 11

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

Question 12

What is the method of secretion of estrogens?

Answer 12

Secreted by syncytiotrophoblast cells of placenta

Question 13

Timing of estrogen secretion

Answer 13

Toward end of pregnancy, secretion level is 30x the mother’s normal level

Question 14

How are estrogens formed?

Answer 14

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.

Question 15

Functions of estrogens

Answer 15

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

Question 16

Method of secretion of progesterone?

Answer 16

Secreted in small quantities by corpus luteum early and secreted in large quantities by placenta

Question 17

Functions of progesterone

Answer 17

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

Question 18

Method of secretion of human chorionic somatomammotropin

Answer 18

Secreted by placenta beginning in 5th week of pregnancy

Question 19

Functions of human chorionic somatomammotropin

Answer 19

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