Part 4: Pregnancy Steroids Flashcards
Implantation usually occurs how long after fertilization?
- 4-6 days following fertilization.
hCG production usually begins how long after implantation?
8 days following implantation.
Following implantation, what cells produce hCG, and in response to what?
- trophoblast cells secrete hCG in response to placental GnRH.
hCG function:
- LH analog.
- hCG binds corpus luteum LH receptors and stimulates continued progesterone production.
What causes the menstrual cycle to stop during the first few weeks of pregnancy?
- hCG stimulating the corpus luteum to produce high P4 levels via LH receptors.
- P4 inhibits LH/FSH secretion.
- menstrual cycle halts.
What hormone in the urine is an early indicator of pregnancy?
- hCG.
- secreted by trophoblast cells in response to placental GnRH.
Which estrogen is the main estrogen produced during pregnancy?
E3 (estriol).
The three hormones produced inside the fetus:
- ACTH
- DHEAS
- cortisol
Hormones released by the fetal adrenal cortex and their function (2):
- DHEAS (E3 precursor).
- Cortisol (organ maturation).
What stimulates the release of DHEA and cortisol from the fetal adrenal cortex (2)?
- Fetal ACTH from the anterior pituitary.
- Maternal progesterone.
Fate of DHEAS released from the fetal adrenal cortex:
- Transferred to placenta.
- Placental steroid sulfatase converts DHEAS to DHEA.
- DHEA converted into E3 (estriol) in placenta.
Which structure is responsible for steroidogenesis during the first trimester?
- corpus luteum.
- maintained via trophoblast hCG.
Which structures are responsible for steroidogenesis during the second and third trimester (2)?
- placenta.
- fetus adrenal cortex.
hCG levels in the first, second, and third trimester:
- Only elevated in the first trimester to maintain corpus luteum steroidogenesis.
Progesterone levels in the first, second, and third trimester:
- steadily increases throughout pregnancy.
- fall in the few weeks immediately preceding birth.
E3 and E2 hormone levels in the first, second, and third trimester:
- E3 = E2 up until week 30.
- E3 > E2 at end of third trimester.
Effect of high progestorone levels on the uterus throughout pregnancy:
- maintains relaxed myometrium.
- prevents myometrium contraction.
Effect of E2 and E3 on the uterus in general:
- promotes myometrium contraction when in unequal proportions.
Importance of the roughly equimolar ratio of E2:E3 during most of pregnancy:
- Equal E2 and E3 levels antagonizes activation of the estrogen receptor (ER).
- Myometrium contraction prevented.
What occurs when E3 > E2 levels at the end of the third trimester?
- E3 activates endometrial estrogen receptor.
- Increased contractile protein expression in myometrium.
- Myometrium contraction promoted.
CRH levels in the first, second, and third trimester:
- steadiy rise throughout pregnancy.
- promotes ACTH and cortisol secretion.
