Week 3: Pregnancy and placenta physic

Question 1

early embryonic development and implantation

Answer 1

• Day 4: morula, mass of 16 cells arrives in uterus
• Day 5/6: cavity within cell mass. Blastocyst with blastocoele cavity. Outer cells are trophoblast, which will form placenta.
• Day 6/7: endometrium in secretory phase, glands secreting, large venous lakes, stroma loose and edematous. Blastocyst attaches via integrins, infiltrates endometrium, aided by proteases that degrade extracell. matrix.

Question 2

placenta development 1: 2 cell layers

Answer 2

• Day 8/9: trophoblast proliferates divides to 2 layers. Syncytiotrophoblasts-multinucleated, outer layer, no mitosis. Cytotrophoblast-inner layer, provides cells for outer. Both start producing hCG
• Day 10/11: lacunae and lacunar networks form within syncytiotrophoblast.

Question 3

placenta development 2: villi formation

Answer 3

• Day 13/15: lacunae enlarge and fill with maternal blood. Primary villi form: core of cytotrophoblast surrounded by suncytiotrophoblast, anchor to endometrium.
• Day 16/17: mesoderm invade cytotrophoblast cores to form blood vessels. Secondary villi form: core of mesoderm CT, basal lamina, surrounded by cytotrophoblast, and outer layer of synctiotrophoblast.
• after day 17: fibroids form along anchoring villi.placenta thins at top and expands at bottom, disc shaped.

Question 4

human chorionic gonadotropin

Answer 4

• endometrium must be maintained for pregnancy to develop
• CL needs signal to continue secreting estradiol and progesterone or else it will degenerate by 12th day after ovulation
• hCG synthesized and secreted by trophoblast. Similar to LH and stimulates CL to continue secreting hormones
• hCG detectable in blood by 8th day post ovulation (time of implantation)

Question 5

human chorionic sommatotropin

Answer 5

• aka human placental lactogen
• produced by trophoblast cells, increase in levels throughout pregnancy, peaks at the end of pregnancy, and falls to undetectable following parturition
• glucose sparing, makes glucose available from mother for fetus
• may also prepare for lactation

Question 6

relaxin

Answer 6

• similar to insulin structurally, secreted by CL
• highest conc. in first trimester
• inhibits uterine myometrial contractions to maintain pregnancy
• softens cervix and relaxes pubic ligament for vaginal delivery

Question 7

Estrogen and progesterone production during pregnancy

Answer 7

• initially CL is primary source
• trophoblast becomes major site of production by week 8
  1. progesterone
• production of steroidogenesis by trophoblast doesn’t require stimulation by tropic hormones.
• fxn: calm the uterus, inhibits SM contraction, blocks oxytocin receptors. Acts as immunosuppressant to block fetal rejection.
  2. Estrogens:
• pregnenolone made from LDL cholesterol in placenta, moves to fetus
• fetal adrenals make androgens (placenta can’t make)-sulfated DHEA from prenenolone
• placenta desulfates DHEA-makes estradiol and estrone. Estriol also made.

Question 8

Tertiary villi in early pregnancy and near term

Answer 8

1. early pregnancy ~3months
   - syncytiotrophoblast, cytotrophoblast, basal lamina, CT corecapillary basal lamina, fetal endothelium.
   - Hofbauer cell-macrophage within CT
2. near term
   - syncytiotrophoblast thinned, few cytotrophoblast cells (incorporated into syncytio), less CT
   - minimal exchange barrier-blood vessels enlarge and move closer to periphery.
   - Fetal capillaries dilated, basal lamina of capillary and syncytiotrophoblast may appear fused. Similar to gas exchange of alveoli.

Question 9

Decidua

Answer 9

• layer that is shed. maternal lining of uterus that is shed after delivery. equiv. to stratum functionalis.
• derived from endometrial stream cells in response to progesterone. Secrete prolactin, relaxin, and PGs.

Question 10

Initiation of labor

Answer 10

• Pgs and cytokines causes cervix to thin and dilate. Uterine contractions begin (unknown mechanism). Fetus head against cervix stretches cervix and stimulates synthesis and release of oxytocin
• more oxytocin means more stretching=positive feedback
• at end of pregnancy, myometrium very sensitive to oxytocin, but still inhibited by progesterone. Must have declining progesterone for contractions.

Question 11

Tocolytics

Answer 11

• used to relax uterus to delay preterm labor
  1. beta adrenergic agonist
• increase adenyl cyclase -> increase cAMP -> decrease myosin light chain kinase -> decrease Ca
  2. Cox inhibitors
• decrease PG production
  3. Mg sulfate
• blocks voltage activated Ca channels
  4. Nifedipine: L type Ca channel blocker

Question 12

Uterotonic agents

Answer 12

• to increase myometrial contractions
  1. Oxytocin (pitocin):
• increase Ca2+ release from sarcoplasmic reticulum, increase prostaglandin synthesis.
  2. Prostaglandin E (misoprostol, Cytotec): increase Ca2+ channel opening, induce cervical ripening
  3. Progesterone antagonist (mifepristone):relieves progesterone inhibition of contraction.
  4. Ergot alkaloids (ergonovine maleate):induces tonic contraction.