Exam 2 (Lecture 5) - Anterior Pituitary and Gonadotropin

Question 1

Name two anterior pituitary gonadotropins. What is their chemical nature? How do the hypothalamus and ovarian hormones control their secretion?

Answer 1

1) Luteinizing hormone (LH) and Follicle-stimulating hormone (FSH)

2) Protein hormones

3) Their secretion is controlled by GnRH

Question 2

Name phases of estrous cycle and describe the corresponding physiological changes in the ovary and uterus.

Answer 2

1) Proestrus
- build-up to estrus, luteolysis is completed, follicular growth and maturation (stimulated by FSH and LH)
- low progesterone
- HIGH ESTROGEN (produced by follicles); stimulates endometrial proliferation

2) Estrus
- HIGH ESTROGEN (stimulates LH surge); LH surge triggers ovulation

3) Metestrus
- CL secreted progesterone suppresses FSH and LH
- Stimulates endometrial secretion in preparation for implantation
- Supports pregnancy

4) Diestrus
- In pregnant female of some mammals, the CL is rescued from regression by placental hormone
- chorionic gonadotropin (or interferon tau in cattle)

5) Anestrus
- In the absence of pregnancy, the CL regresses as a consequence of uterine prostaglandin F2-alpha
- The resulting decrease of progesterone levels removes LH and FSH inhibition and the cycle can start again

Question 3

Which cells of ovary secrete estrogen and progesterone? Which cells produce androgens? Which pituitary hormones stimulate each of these two cell types?

Answer 3

1) Granulosa cells secrete estrogen and progesterone (stimulated by LH)

2) Theca cells produce androgens (stimulated by FSH)

Question 4

Which phase of the estrous cycle is dominated by ovarian secretion of estrogen? Which phase is dominated by ovarian secretion of progesterone? What are the effects of estrogen and progesterone on endometrium?

Answer 4

1) Proestrus

2) Diestrus

3) Estrogen stimulates endometrial proliferation; progesterone stimulates endometrial secretion in preparation for implantation

Question 5

Why is the change from the negative to the positive estrogen feedback effect on gonadotropin release important for ovarian physiology and what are the consequences of this process for mature follicles?

Answer 5

When the switch from the negative to positive estrogen feedback takes place, it causes a surge of LH which triggers ovulation

Question 6

How would you describe the dynamics of gonadotropin release in males? Which cells in testes are targets of pituitary gonadotropins? To which ovarian cells are these testicular cells analogs? Which cells in testes produce testosterone?

Answer 6

1) In males, FSH and LH are released in a steady fashion to stimulate secretion of testosterone and estrogen to support continuous spermatogenesis.

2) FSH targets Sertoli cells (analogous to granulosa cells in ovary); spermatogenesis
LH targets Leydig cells (analogous to theca cells in ovary); secretes testosterone and surrounds the seminiferous tubules

3) Leydig cells