8. Male Reproductive Physiology Notes (Lopez)

Question 1

What cells secrete estrogen in the male?

Answer 1

Sertoli cells, as well as peripheral tissues such as the liver.

Question 2

What is the role of testosterone in spermatogenesis?

Answer 2

Testosterone stimulates Sertoli cells.

Question 3

What is the function of androgen-binding protein?

Answer 3

Antigen-binding protein stores testosterone and concentrates it in the lumen of the seminiferous tubules.

Question 4

What is secreted by the seminal vesicles?

Answer 4

Fluid rich in citrate, fructose, prostaglandins, and fibrinogen.

Question 5

Beard growth is specific to which male androgen – DHT or testosterone?

Answer 5

DHT

Question 6

What is the function of prostaglandin in semen?

Answer 6

Reacts with the cervical mucus to make it more receptive to sperm movement (less thick).

Causes reverse peristalsis in the uterus and fallopian tubes.

Question 7

Differentiation of the epididymis, vas deferens, and seminal vesicles are very specific to which male androgen – DHT or testosterone?

Answer 7

Testosterone.

Question 8

Presence or absence of testosterone during what period of time in embryonic life leads to the masculinization or feminization of the external genitalia?

Answer 8

During the second month of embryonic life.

Question 9

What enzyme is responsible for the conversion of testosterone into dihydrotestosterone?

Answer 9

5α-reductase.

Question 10

When does testosterone cause the dissent of the testes into the scrotum?

Answer 10

During the last 2-3 months of pregnancy.

Question 11

What androgen is primarily responsible for the descent of the testes?

Answer 11

Testosterone.

Question 12

What is the more common name for P450scc?

Answer 12

Cholesterol desmolase.

Question 13

What process creates 2° spermatocytes?

Answer 13

The first round of meiotic division of 1° spermatocytes.

(One chromosome, duplicated.)

Question 14

What is the function of 3β-hydroxysteroid dehydrogenase?

Answer 14

Conversion of dehydroepiandrosterone (DHEA) to androstenedione.

(Androstenedione will then be converted into testosterone by 17β-hydroxysteroid dehydrogenase.)

Question 15

How is cholesterol obtained by the Leydig cells for testosterone synthesis?

Answer 15

LDL and HDL receptors pull cholesterol into the Leydig cells where it is stored as cholesterol esters.

When more cholesterol is required, it is cleaved from the ester by hormone sensitive lipase (HSL).

Question 16

Meiotic division of 2° spermatocytes results in what type of cell?

Answer 16

Spermatids.

Question 17

What is the function of sex hormone-binding globulin?

Answer 17

Acts as a reservoir for testosterone, and prevents it from influencing the hypothalamic-pituitary axis.

Question 18

Is testosterone or DHT important for the formation of male external genitalia?

Answer 18

DHD is important for the formation of male external genitalia, testosterone does not serve that function.

Question 19

What changes to the spermatozoa occur during capacitation in the uterine and fallopian tubes?

Answer 19

The uterine fallopian tubes wash away spermatic inhibitory factors.

Cholesterol is shed which weakens the head of the sperm.

The sperm’s membrane increases permeability to Ca2+, resulting in increased motility.

Question 20

What are the consequences of testosterone deficiency in the third trimester of pregnancy?

Answer 20

Failure of the testes to descend and micropenis.

Question 21

What enzyme converts androstenedione to testosterone in the testis?

Answer 21

17β-hydroxysteroid dehydrogenase

Question 22

What are the specific actions of DHT?

Answer 22

Fetal differentiation of the external genitalia.

Male hair distribution and male pattern baldness.

Sebaceous gland activity.

Growth of the prostate.

Question 23

What is secreted by the prostate gland?

Answer 23

An alkaline aqueous solution rich in citrate, calcium, and enzymes.

Question 24

What cells produce ABP?

Answer 24

Sertoli cells.

Question 25

Is FSH or LH more prominent during childhood, adult reproductive period, and senescence respectively?

Answer 25

During childhood FSH is more prominent.

During the adult reproductive period LH is more prominent.

During senescence FSH is more prominent.

Question 26

How many sperm cells per ejaculation is considered to be “infertile?”

Answer 26

<20 million.

Question 27

What are the consequences of low testosterone post-puberty?

Answer 27

Decreased libido, erectile dysfunction, decreased facial and body hair growth, low energy, infertility.

Question 28

What process creates 1° spermatocytes?

Answer 28

Several rounds of mitosis of the spermatogonia.

Question 29

What is the role of growth hormone in spermatogenesis?

Answer 29

Promotes early division of the sperm themselves and is necessary for controlling background metabolic functions of testis.

Spermatogenesis is severely deficient in the absence of growth hormone.

Question 30

Rhythmic contraction of which muscles cause ejaculation?

Answer 30

The bulbospongiosus and the ischiocavernosus muscle.

Question 31

Which anterior pituitary hormone triggers the release of inhibin?

Which cell is affected, thereby releasing inhibin?

Answer 31

Follicle stimulating hormone triggers Sertoli cells to release inhibin.

Question 32

Describe Kallman’s syndrome in men.

Answer 32

Kallman’s syndrome occurs when gonadotropin releasing hormone (GnRH) neurons fail to migrate to the hypothalamus during embryonic development.

We see delayed or absent puberty, as well as an impaired sense of smell.

Occurs more often in males than females, although it is possible to affect females as well.

Question 33

Was the first step in testosterone synthesis?

Answer 33

Cholesterol -> (cholesterol desmolase) -> pregnenolone.

Question 34

How does luteinizing hormone stimulate production of testosterone?

Answer 34

It upregulates cholesterol desmolase, which converts cholesterol into pregnenolone and is the rate limiting step in testosterone synthesis.

It does this by increasing the affinity of cholesterol desmolase for cholesterol, and increasing the synthesis of cholesterol desmolase the long-term.

Question 35

What enzyme is responsible for the conversion of testosterone into estrogen?

Answer 35

CYP19 (more commonly called aromatase)

Question 36

What is the consequence of testosterone deficiency during puberty?

Answer 36

Poor secondary sexual development and overall eunuchoid features.

Question 37

What is the difference between the action of a pulsatile secretion of GnRH vs. a sustained secretion of GnRH?

Answer 37

Pulsatile secretion of GnRH stimulates follicle stimulating hormone and luteinizing hormone, and can initiate puberty.

Sustained secretion of GnRH decreases the sensitivity and presentation of GnRH receptors, and can be used to decrease FSH and LH production in certain tumors.

Question 38

What is the cause of BPH?

Answer 38

Increased activity of DHT – recent evidence shows it may be due to ↑ DHT receptor presentation, rather than ↑ DHT levels.

Question 39

What enzyme is lacking in the adrenal cortex which leads to the formation of androstenedione instead of testosterone?

Answer 39

17β-hydroxysteroid dehydrogenase

Question 40

What is the target enzyme for medications that treat male pattern baldness and benign prostatic hyperplasia?

Answer 40

These medications inhibit 5α-reductase.

Question 41

What is the function of inhibin?

Answer 41

Inhibin inhibits FSH at the level of the anterior pituitary (not the hypothalamus).

Question 42

What are the consequences of testosterone deficiency in the second and third month of gestation?

Answer 42

Ambiguous genitalia to varying degrees.

Question 43

Describe Klinefelter syndrome.

Answer 43

Also called seminiferous tubular dysgenesis, Klinefelter syndrome occurs when a male is born with an extra X chromosome.

Individuals are phenotypically male, but have increased levels of gonadotropins during puberty which fail to induce normal testicular growth and spermatogenesis.

Androgen production is usually, but not always, low – whereas the levels of gonadotropins are elevated (FSH, LH). This indicates 1° hypogonadism.

Seminiferous tubules are destroyed, resulting in infertility.

Question 44

What is the function of the epididymis in sperm maturation?

Answer 44

Serves as a location force berm to increase their motility.

Causes “decapitation” – which involves adding molecules to the membranes of sperm to prevent the acrosomal reaction before contact with an egg..