Part 4: Pregnancy Steroids

Question 1

Implantation usually occurs how long after fertilization?

Answer 1

• 4-6 days following fertilization.

Question 2

hCG production usually begins how long after implantation?

Answer 2

8 days following implantation.

Question 3

Following implantation, what cells produce hCG, and in response to what?

Answer 3

• trophoblast cells secrete hCG in response to placental GnRH.

Question 4

hCG function:

Answer 4

• LH analog.
• hCG binds corpus luteum LH receptors and stimulates continued progesterone production.

Question 5

What causes the menstrual cycle to stop during the first few weeks of pregnancy?

Answer 5

• hCG stimulating the corpus luteum to produce high P4 levels via LH receptors.
• P4 inhibits LH/FSH secretion.
• menstrual cycle halts.

Question 6

What hormone in the urine is an early indicator of pregnancy?

Answer 6

• hCG.
• secreted by trophoblast cells in response to placental GnRH.

Question 7

Which estrogen is the main estrogen produced during pregnancy?

Answer 7

E3 (estriol).

Question 8

The three hormones produced inside the fetus:

Answer 8

1. ACTH
2. DHEAS
3. cortisol

Question 9

Hormones released by the fetal adrenal cortex and their function (2):

Answer 9

1. DHEAS (E3 precursor).
2. Cortisol (organ maturation).

Question 10

What stimulates the release of DHEA and cortisol from the fetal adrenal cortex (2)?

Answer 10

1. Fetal ACTH from the anterior pituitary.
2. Maternal progesterone.

Question 11

Fate of DHEAS released from the fetal adrenal cortex:

Answer 11

1. Transferred to placenta.
2. Placental steroid sulfatase converts DHEAS to DHEA.
3. DHEA converted into E3 (estriol) in placenta.

Question 12

Which structure is responsible for steroidogenesis during the first trimester?

Answer 12

• corpus luteum.
• maintained via trophoblast hCG.

Question 13

Which structures are responsible for steroidogenesis during the second and third trimester (2)?

Answer 13

1. placenta.
2. fetus adrenal cortex.

Question 14

hCG levels in the first, second, and third trimester:

Answer 14

• Only elevated in the first trimester to maintain corpus luteum steroidogenesis.

Question 15

Progesterone levels in the first, second, and third trimester:

Answer 15

• steadily increases throughout pregnancy.
• fall in the few weeks immediately preceding birth.

Question 16

E3 and E2 hormone levels in the first, second, and third trimester:

Answer 16

• E3 = E2 up until week 30.
• E3 > E2 at end of third trimester.

Question 17

Effect of high progestorone levels on the uterus throughout pregnancy:

Answer 17

• maintains relaxed myometrium.
• prevents myometrium contraction.

Question 18

Effect of E2 and E3 on the uterus in general:

Answer 18

• promotes myometrium contraction when in unequal proportions.

Question 19

Importance of the roughly equimolar ratio of E2:E3 during most of pregnancy:

Answer 19

• Equal E2 and E3 levels antagonizes activation of the estrogen receptor (ER).
• Myometrium contraction prevented.

Question 20

What occurs when E3 > E2 levels at the end of the third trimester?

Answer 20

• E3 activates endometrial estrogen receptor.
• Increased contractile protein expression in myometrium.
• Myometrium contraction promoted.

Question 21

CRH levels in the first, second, and third trimester:

Answer 21

• steadiy rise throughout pregnancy.
• promotes ACTH and cortisol secretion.