Placental Physiology Flashcards
What are some differences between the early and late placenta?
Early:
- thick
- permeability low
- small SA
- total diffusion conductance is miniscule
Late:
- thin
- high permeability
- large SA
- large increase in placental diffusion
What is the oxygen pressure gradient for both the mother and fetus near the end of pregnancy?
PO2 mother: 50mm Hg
PO2 fetus: 30mm Hg
What are some reasons that adequate oxygenation can occur with such a low pressure gradient?
- fetal hemoglobin has a higher affinity for oxygen
- fetal blood hemoglobin concentration is about 50% greater than maternal
- Bohr effect
What is the Bohr effect? What can changes cause?
-hemoglobin can carry more oxygen at a low PCO2
Changes cause:
-increase in capacity of fetal blood to combine with oxygen
-decrease in capacity of maternal blood to combine with oxygen
What is the double Bohr effect?
Refers to double shift in the maternal blood and in the fetal blood
What secretes hCG? What is the timeline of the secretion?
- secreted by syncytial trophoblast cells into maternal fluids
- measurable secretion 8-9 days after ovulation
- max secretion during 10-12 week of pregnancy
- lower levels secreted 16-20 weeks
What are some 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 function of the placenta?
-diffusion of oxygen and CO2
+PCO2 of fetal blood= 2-3x higher than maternal blood
-diffusion of foodstuffs
+facilitated diffusion of glucose via trophoblast
+slower diffusion of FA into fetal blood
-excretion of waste products
+urea, uric acid, adn creatinine diffuse from fetus to maternal blood
What secrets estrogens during pregnancy? What are they formed from?
- syncytiotrophoblast cells of placenta
- placental estrogens are formed almost entirely from androgen steroid compounds -> fetal and maternal adrenal glands+converted by trophoblast cells into estradiol, estrone, and estriol
How many times higher is estrogen secretion toward the end of pregnancy?
30x more
What are the functions of estrogen?
- Breast and uterine enlargement
- growth of breast ductal structure
- enlargement of maternal external genitalia
- relaxation of pelvic ligaments
- may also affect aspects of fetal development
What secretes progesterone during pregnancy?
- small quantities by corpus luteum
- large quantities by placenta
What are the functions of progesterone during pregnancy?
- cas uses decidual cells to develop in the endometrium
- decreases contractile of pregnant uterus
- increases secretions of Fallopian tubes and uterus
- may work with estrogen to prepare breasts for lactation
What is human chorionic somatomammotropin?
- secreted by placenta beginning in 5th week of pregnancy
- causes decreased insulin sensitivity and decreased utilization of glucose by mother
- general metabolic hormone
What are some theories concerning placental immunology?
- lack of expression of major histocompatibility antigens by syncytiotrophoblast and cytotrophoblast (placental components)
- paralysis of mother’s immune system during pregnancy
- decidual immune barrier
- inactivation of mother’s immune system components by molecules formed on fetal placental surface
What is fetal alcohol syndrome?
- placenta is highly permeable to alcohol
- can result in poor growth rate, microcephaly, mental retardation, heart defects, and hypoplasia of facial structures
What is hydrops fetalis?
-water accumulation in the fetus with accompanying jaundice and brain damage and anemia
What is placenta previa?
- abnormal implantation site within the uterus
- can cover the birth canal
- can result in hemorrhage
