Regulation of the stimulation of Sex Steroids

Question 1

What are the primary sex organs in males?

Answer 1

testes

Question 2

What are the primary sex organs in females?

Answer 2

ovaries

Question 3

What are the function of gonads/sex organs?

Answer 3

1. produce sex cells - gametes

2. secrete sex hormones

Question 4

What are accessory reproductive organs?

Answer 4

ducts, glands, and external genitalia

Question 5

What are the sex hormones secreted by males?

Answer 5

androgens

Question 6

What are the sex hormones secreted by females?

Answer 6

estrogen and progesterone

Question 7

Sex hormones play roles in?

Answer 7

1. The development and function of the reproductive organs
2. Sexual behavior and drives
3. The growth and development of many other organs and tissues

Question 8

What is the function of testosterone?

Answer 8

1. stimulate development of male sex organs, secondary sexual characteristics, and behavioral features
2. Participates in feedback loop involving GnRH.
3. Also inhibits secretion of LH

Question 9

What cells secrete testosterone and where are they found?

Answer 9

Between seminiferous tubules are clusters of endocrine cells called LEYDIG CELLS or INTERSTITIAL ENDOCRINOCYTES

Question 10

Function of GnRH in the hormonal regulation in males?

Answer 10

stimulates secretion of FSH and LH

- This happens when there is a low concentration of testosterone

Question 11

Describe the function of FSH and LH in hormonal regulation in males?

Answer 11

1. stimulating spermatogenesis
2. testosterone secretion
   - both produced by anterior pituitary.

Question 12

Describe the function of inhibin in hormonal regulation in males?

Answer 12

Inhibits secretion of FSH

- secreted by sustentacular cells

Question 13

Describe the hormonal regulation in non pregnant females (uterine cycle)?

Answer 13

1. HYPOTHALAMUS RELEASES GONADOTROPIN-RELEASING HORMONE (GnRH). This stimulates the anterior pituitary to release FSH and LH
2. FSH STIMULATES MATURATION OF PRIMARY OOCYTE IN AN IMMATURE FOLLICLE
3. FOLLICLE PRODUCES ESTROGEN. Estrogen: (A) builds the uterine wall (the endometrium); (B) inhibits secretion of FSH
4. HIGH LEVELS OF ESTROGEN FURTHER STIMULATE SECRETION OF LH BY ANTERIOR PITUITARY. This plus FSH also causes ovulation of the secondary oocyte – leaving follicle without egg (the corpus luteum). (Approximately day 15.)
5. CORPUS LUTEUM SECRETES ESTROGEN AND PROGESTERONE. This maintains the endometrium for 15-16 days and inhibits LH
6. (If oocyte is not fertilized and implanted in the uterine wall) CORPUS DEGENERATES (TO CORPUS ALBICANS) AND STOPS PRODUCING ESTROGEN AND PROGESTERONE
7. WITHOUT ESTROGEN AND PROGESTERONE, ENDOMETRIUM BREAKS DOWN – MENSTRUATION OCCURS. Menstruation is the sloughing off of the enlarged endometrial wall along with blood and mucous
8. DECREASE IN PROGESTERONE AND LH. Low LH causes secretion of FSH by pituitary again. The cycle repeats

Question 14

Describe the hormonal regulation in a nonpregnant female?

Answer 14

Hypothalamus releases GnRH that stimulates the anterior pituitary to release FSH and LH.

FSH stimulates maturation of primary oocyte in an immature follicle

Follicle produces estrogen:

 (a) builds the uterine wall (the endometrium); 
 (b) inhibits secretion of FSH.

High levels of estrogen further stimulate secretion of LH by anterior pituitary

This plus FSH also causes ovulation of the secondary oocyte – leaving follicle without egg (the corpus luteum).
Corpus luteum secrets estrogen and progesterone

This maintains the endometrium for 15-16 days and inhibits LH.

If oocyte is not fertilized and implanted in the uterine wall corpus degenerates (corpus albicans) and stops producing estrogen and progesterone

Without estrogen and progesterone, endometrium breaks down – menstruation occurs

Decrease in progesterone and LH

Low LH causes secretion of FSH by pituitary again - the cycle repeats.

Question 15

When can fertilization take place?

Answer 15

From point of ovulation (about day 15) to the point where the corpus luteum begins to degenerate (about day 25)
- The potential for fertilization is highest during the first three days of this 10-day period

Question 16

What sperm is the most robust?

Answer 16

Sperm with X-chromosome tend to be more robust, and can last longer than those with Y-chromosome.

Question 17

Is it possible to get pregnant if you have intercourse shortly before pregnancy?

Answer 17

if intercourse takes place a bit before ovulation and more robust sperm (with X-chromosome) are stored while weaker (Y-chromosome) sperm die off waiting for ovulation, the chance of having a baby girl increases
Note: females can be capable of sperm storage

Question 18

Describe sperm storage in the female?

Answer 18

Apparently, females can store sperm up to four days
- This explains in part why the “rhythm method” works poorly to avoid pregnancy.

(Also, it turns out that unused oocytes are actively scavanged.)

With sex before ovulation, sperm can be stored for use. So, even though ovulation hasn’t occurred, pregnancy can occur because the female is holding on the sperm.

Sex AFTER ovulation actually has a slightly lower chance for inducing pregnancy, as the egg could have been scavanged

Question 19

Describe the hormonal regulation in pregnant women?

Answer 19

The developing embryo has extra-embryonic membranes: chorion, amnion, yolk sac, and allantois.

Chorion and allantois are embryonic contribution to placenta.

Chorionic portion secretes human chorionic gonadotropin (hCG).

hCG prevents corpus luteum from degenerating – thus it continues to secrete progesterone and estrogen.

This maintains integrity of uterine wall and inhibits subsequent ovulation (due to lack of FSH or LH).

Birth-control pills mimic the high estrogen/progesterone levels to trick the body into thinking it is pregnant and thus inhibiting ovulation