8. Male Reproductive Physiology Notes (Lopez) Flashcards
What cells secrete estrogen in the male?
Sertoli cells, as well as peripheral tissues such as adipose tissue
What is the role of testosterone in spermatogenesis?
Testosterone stimulates Sertoli cells.
What is the function of androgen-binding protein?
Androgen-binding protein stores testosterone and concentrates it in the lumen of the seminiferous tubules.
What is secreted by the seminal vesicles?
Fluid rich in citrate, fructose, prostaglandins, and fibrinogen.
Beard growth is specific to which male androgen – DHT or testosterone?
DHT
What is the function of prostaglandin in semen?
Reacts with the cervical mucus to make it more receptive to sperm movement (less thick).
Causes reverse peristalsis in the uterus and fallopian tubes.
Differentiation of the epididymis, vas deferens, and seminal vesicles are very specific to which male androgen – DHT or testosterone?
Testosterone.
Presence or absence of testosterone during what period of time in embryonic life leads to the masculinization or feminization of the external genitalia?
During the second month of embryonic life.
What enzyme is responsible for the conversion of testosterone into dihydrotestosterone?
5α-reductase.
When does testosterone cause the dissent of the testes into the scrotum?
During the last 2-3 months of pregnancy.
What androgen is primarily responsible for the descent of the testes?
Testosterone.
What is the more common name for P450scc?
Cholesterol desmolase.
What process creates 2° spermatocytes?
The first round of meiotic division of 1° spermatocytes.
(One chromosome, duplicated.)
What is the function of 3β-hydroxysteroid dehydrogenase?
Conversion of dehydroepiandrosterone (DHEA) to androstenedione.
(Androstenedione will then be converted into testosterone by 17β-hydroxysteroid dehydrogenase.)
How is cholesterol obtained by the Leydig cells for testosterone synthesis?
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).
Meiotic division of 2° spermatocytes results in what type of cell?
Spermatids.
What is the function of sex hormone-binding globulin?
Acts as a reservoir for testosterone, and prevents it from influencing the hypothalamic-pituitary axis.
Is testosterone or DHT important for the formation of male external genitalia?
DHT is important for the formation of male external genitalia, testosterone does not serve that function.
What changes to the spermatozoa occur during capacitation in the uterine and fallopian tubes?
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.
What are the consequences of testosterone deficiency in the third trimester of pregnancy?
Failure of the testes to descend and micropenis.
What enzyme converts androstenedione to testosterone in the testis?
17β-hydroxysteroid dehydrogenase
What are the specific actions of DHT?
Fetal differentiation of the external genitalia.
Male hair distribution and male pattern baldness.
Sebaceous gland activity.
Growth of the prostate.
What is secreted by the prostate gland?
An alkaline aqueous solution rich in citrate, calcium, and enzymes.
What cells produce ABP?
Sertoli cells.
Is FSH or LH more prominent during childhood, adult reproductive period, and senescence respectively?
During childhood FSH is more prominent.
During the adult reproductive period LH is more prominent.
During senescence FSH is more prominent.
How many sperm cells per ejaculation is considered to be “infertile?”
<20 million.
What are the consequences of low testosterone post-puberty?
Decreased libido, erectile dysfunction, decreased facial and body hair growth, low energy, infertility.
What process creates 1° spermatocytes?
Several rounds of mitosis of the spermatogonia.
What is the role of growth hormone in spermatogenesis?
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.
Rhythmic contraction of which muscles cause ejaculation?
The bulbospongiosus and the ischiocavernosus muscle.
Which anterior pituitary hormone triggers the release of inhibin?
Which cell is affected, thereby releasing inhibin?
Follicle stimulating hormone triggers Sertoli cells to release inhibin.
Describe Kallman’s syndrome in men.
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.
Was the first step in testosterone synthesis?
Cholesterol -> (cholesterol desmolase) -> pregnenolone.
How does luteinizing hormone stimulate production of testosterone?
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.
What enzyme is responsible for the conversion of testosterone into estrogen?
CYP19 (more commonly called aromatase)
What is the consequence of testosterone deficiency during puberty?
Poor secondary sexual development and overall eunuchoid features.
What is the difference between the action of a pulsatile secretion of GnRH vs. a sustained secretion of GnRH?
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.
What is the cause of BPH?
Increased activity of DHT – recent evidence shows it may be due to ↑ DHT receptor presentation, rather than ↑ DHT levels.
What enzyme is lacking in the adrenal cortex which leads to the formation of androstenedione instead of testosterone?
17β-hydroxysteroid dehydrogenase
What is the target enzyme for medications that treat male pattern baldness and benign prostatic hyperplasia?
These medications inhibit 5α-reductase.
What is the function of inhibin?
Inhibin inhibits FSH at the level of the anterior pituitary (not the hypothalamus).
What are the consequences of testosterone deficiency in the second and third month of gestation?
Ambiguous genitalia to varying degrees.
Describe Klinefelter syndrome.
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.
What is the function of the epididymis in sperm maturation?
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..
