55. the placenta

Question 1

when is placental circulation established?

Answer 1

By the 17th day, both fetal and maternal blood vessels are functional
placenta continues to adapt over the 2nd and 3rd trimesters

Question 2

when does the placenta become the primary producer of steroid hormones?

Answer 2

after the 7th week of gestation

Question 3

is there direct mixing of maternal and fetal blood?

Answer 3

no
Transfer of materials between mother and fetus is via maternal blood coming in contact with placental villi.

Question 4

what are the fetal and maternal components of the placenta?

Answer 4

Fetal: cytotrophoblasts (inner layer of chorionic villi), syncytiotrophoblasts (outer layer of chorionic villi; synthesizes and secretes hormones).

Maternal: decidua basalis.

Question 5

what are the roles of the placenta in maternal-fetal physiology?

Answer 5

1. Implantation: the syncytiotrophoblasts facilitate implantation by directly invading the wall of the endometrium in the uterus.
2. Maternal recognition and maintenance of pregnancy: hCG is synthesized and released from the syncytiotrophoblasts to stimulate luteal progesterone production to maintain the pregnancy.
3. Nutrients and gas exchange: Mother’s blood provides oxygen, water, electrolytes, hormones, and other nutrients. In exchange, the fetus excretes carbon dioxide, water, urea, hormones, and other waste products.
4. Immunologic fetal protection: provides a physical barrier as well as a functional platform for both the innate and adaptive immune systems.
5. Metabolic functions: glycogen synthesis, cholesterol synthesis, protein metabolism.
6. Endocrine functions: synthesis and release of various hormones and local mediators (hCG, hPL, progesterone, estrogen, cytokines, placental growth hormones, IGF, CRH, VEGF).
7. Metabolism of numerous hormones, substances, drugs, and potential toxins.

Question 6

what is the functional unit at which maternal-fetal exchange of nutrients and gases occur?

Answer 6

placental terminal villi