Lecture 5

Question 1

Prevention of Embryo-Fetus rejection

Answer 1

• the specialized implantation area is called the decidua
• The trophoblast cells produce Fas ligand that binds to the Fas
  receptors on the maternal CD8+ cells
• Causes apoptosis in the CD8+ cells, preventing immune
  rejection of the fetal cells
• the fetal part of the placenta produces indoleamine 2,3
  dioxygenase (IDO) which destroys tryptophan
  > tryptophane is critical in activation of CD8+ cells
• the maternal foreign tissue attack system is thus shut down
• Treg cells double and suppress CD8+ cells

Question 2

Gestation

Answer 2

• About 38 weeks from conception
• Physical changes within mother to meet demands of pregnancy
  Uterine enlargement
  Breasts enlarge and develop ability to produce milk
  Volume of blood increases 30%
  Weight gain
  Respiratory activity increases by about 20%
  Urinary output increases
  Kidneys excrete additional wastes from fetus
  Nutritional requirements increase

Question 3

The placenta and functions

Answer 3

Chorionic (fetal) tissue form the placental villi, which protrude into a pool of maternal blood

Decidual (maternal) capillary walls are broken down and maternal blood oozes through the spaces between the placental villi

Fetal placental capillaries branch off the umbilical arteries and project into the placental villi

Fetal blood flowing through these vessels is separated from the maternal blood by only the capillary wall and thin chorionic layer that forms the placental villi

Maternal blood enters through the maternal arterioles, then percolates through the pool of blood in the intervillus spaces

Here, exchanges are made between the fetal and maternal blood before the fetal blood leaves through the umbilical vein and maternal blood exits through the maternal venules

Amniotic fluid isgenerated from maternal plasma, and passes through the fetal membranes by osmotic and hydrostatic forces.

When fetal kidneys begin to function around week 16, fetal urine also contributes to the fluid

Question 4

The placenta and functions continued

Answer 4

Performs the functions of the digestive system, the respiratory system, and the kidneys for the “parasitic” fetus.

The fetus has these organ systems, but they do not need to function.

Nutrients and O2 move from the maternal blood across the thin placental barrier into the fetal blood

CO2 and other metabolic wastes simultaneously move from the fetal blood into the maternal blood

CO2 and wastes transferred into the maternal blood are eliminated by the mother’s lungs and kidneys.

O2, CO2, water, and electrolytes, cross by simple diffusion

Glucose crosses the placental barrier by special mediated transport systems in the placental membranes by facilitated diffusion

Amino acids cross the placental barrier by secondary active transport

Question 5

Human Chorionic GOnadotropin

Answer 5

The placenta secretes several hormones that prevent menstruation during pregnancy, including human chorionic gonadotropin, human chorionic somatomammotropin, oestrogen, and progesterone.

The corpus luteum remains active during early pregnancy because of human chorionic gonadotropin (hCG), a peptide hormone secreted by the chorionic villi and developing placenta.

Human chorionic gonadotropin is structurally related to LH, and it binds to LH receptors.
> it causes the corpus luteum to secrete even larger quantities
of progesterone and oestrogens for the next few month

hCG secretion is essential in the first 5 – 6 weeks when the placenta is immature

Home pregnancy tests work by detecting elevated hCG levels in the woman’s urine

hCG declines by the 10th week of pregnancy

Human chorionic gonadotropin production by the placenta peaks at three months of development, then diminishes. A second function of hCG is stimulation of testosterone production by the developing testes in male foetuses.

Question 6