Male Reproductive System Flashcards
What are the functions of Sertoli cells? What hormone do they produce?
Support, protect, and nourish spermatogonia; produce inhibin B
Which testis cells produce testosterone?
Leydig cells
What is secreted by the epididymis? Cowper glands?
H+; Mucus
What is secreted by the prostate?
Acid phosphatase, protease, prostate-specific antigen
What is secreted by the seminal vesicles?
Fructose-rich product, prostaglandins, ascorbic acid, fibrinogen, and thrombin-like proteins
Which hypophysiotropic hormone stimulates LH and FSH release?
Gonadotropic-releasing hormone
How is the ratio of FSH to LH regulated?
The anterior pituitary determines how many beta subunits of each to make based on feedback signals
To what cells does FSH bind in males? What is the effect?
Sertoli cells; stimulation of spermatognesis, testicular development, Sertoli proliferation, seminiferous tubule growth, production of inhibin B and androgen-binding protein
To what cells does LH bind? What are the effects?
Leydig cell; Stimulates testosterone synthesis and release?
What inhibits release of FSH and LH? Release of GnRH?
Testosterone, estradiol, and inhibin B; Beta endorphin, IL-1, prolactin, GABA, dopamine
What is the effect of activin?
Stimulation of FSH release
To what kind of receptor do LH and FSH bind?
GsPCR
What is the effect of FSH binding on testicular size?
Increases
How is testosterone synthesized?
Cholesterol is cleaved and transported to the inner mitochondrial membrane where it is converted to pregnenolone which can be converted to progesterone and then androstenedione and finally to testosterone in the testes
How can testosterone be further metabolized once it is released from Leydig cells?
Converted to 17-beta-estradiol by aromatase (and then to estriol and 2-methoxyestrone) OR conversion to dihydrotestosterone by 5-alpha-reductase
What is the biological potency of dihydrotestosterone relative to testosterone’s? Why?
DHT is much more active than testosterone because it has a higher affinity for the androgen receptor
How does testosterone circulate in the blood?
Mostly circulates bound to sex hormone binding protein or albumin
How are high concentrations of testosterone in the testes maintained?
Testosterone is made by the Leydig cells of the testis and then is sequestered by androgen binding protein.
Which enzyme catalyzes the conversion of androgen to estrogen? In which tissues is this enzyme expressed in males?
Aromatase; Expressed in brain, prostate, breast, bone, liver, and adipose
What is the function of estradiol in the male brain? In bone?
At the brain it is critical for negative feedback inhibition of FSH and LH release and in bone it is important for growth and closure of the epiphyseal plate
What results from lack of aromatase or estrogen receptor expression in men?
No linear growth spurt in puberty, no epiphyseal closure- continued growth, osteopenia
What tissues mainly form the estrogens found in circulation?
Liver and adipose
What enzyme converts androstenedione to testosterone?
17beta-hydroxysteroid dehydrogenase
Measurement of what hormone gives a good index of spermatogenesis?
Inhibin B
To what kind of receptor does testosterone or dihydrotestosterone bind? How does it mediate cellular change?
Binds to intracellular androgen receptor in the cytosol, translocates into the nucleus where it dimerizes and binds to hormone response elements to affect gene transcription
What are the in-utero effects of testosterone on the male fetus?
Leydig cell proliferation, steroidogenic enzyme and androgen receptor expression, and masculinization of the embryo
How do Wolffian ducts develop? Into what structures do the wolffian ducts become?
Sertli cells secrete mullerian inhibitory factor causing regression of the mullerian ducts and leydig cells produce testosterone which favor the formation of the wolffian ducts which develop into the vas deferens, epididymis, and seminal vesicles
What in-utero developmental events are mediated specifically by dihydrotestosterone?
Growth of the penis and fusion of the labio-scrotal folds
What is adrenarche?
A period chacterized by increased adrenal production of DHEA and androstenedione at around 6-8 years of age, not associated with increased production of ACTH or cortisol
What triggers the onset of male puberty? Which hormone acts in a permissive fashion to allow initiation of pulsatile GnRH release?
Increased pulsitile secretion of GnRH by the hypotalamus; Leptin
What is responsible for producing the normal pubertal growth?
The increase in growth hormone and sex hormone release
What are the four steps of spermatogenesis?
Proliferation of spermatogonia, meiosis (spermacytes–> spermatids), spermiogenesis (maturation and development), and spermiation (release of mature sperm)
How does FSH affect the process of spermiogenesis? Testosterone?
FSH stimulates the proliferation and secretory activity of Sertoli cells; Testosterone stimulates spermatogenesis through receptor-mediated events in the sertoli cells and production of androgen-binding protein in the Sertoli cells
How is testosterone transported to developing sperm?
Androgen binding protein
What are the anabolic effects of testosterone?
Stimulates muscle protein synthesis, helping to build muscle mass; Supresses lipid uptake and increased lipolysis; converted into estradiol in bone which increases osteoblast lifespan and proliferation
At what point in the male’s life does a gradual decline in testosterone begin? What other events in the male reproductive cycle are affected by senescence?
About 40; Decreased LH and testosterone release, loss of diurnal rhythm of testosterone secretion, decreased spermatogenesis, and increased sex-hormone-binding protein (decreasing bioavailability of testosterone)
What physiologic effects are mediated specifically by dihydrotestosterone?
Prostate development and growth, phallic growth, male-pattern balding, pubic and underarm hair, and sebaceous gland activity
How does parasympathetic stimulation elicit an erection?
ACh is released, binding to endothelial receptors in the helicine aa, triggering production and release of nitric oxide, which enters smooth muscle and stimulates guanylate cyclase, creating cGMP and activating PKG, which suppresses Ca++ influx and increases vasodilation
What are the potential causes for androgen excess?
Central- hypothalamic and pituitary tumors, Peripheral- LH receptor activating mutations, CAH, androgen-producing tumors, pharmacological
What are the potential causes of androgen deficiency?
Mutations in the GnRH receptor or LH or FSH subunits, prolactinoma, trauma, surgery, testicular dysfunction, leydig cell tumors, cryptorchidism, adrenal hypoplasia, XXY
How does a testosterone excess present in boys and adult males?
Kids- precocious puberty, increased growth of penis, testicles, pubic, underarm, and facial hair, spontaneous erections, acne, deepening of ; In adults- behavioral changes and increased muscle mass
How does a testosterone deficiency present in boys and adult males?
Kids- decreased growth, no change in voice, anemia, decreased growth of muscles and genitalia, decreased spermatogenesis and sexual function; Adults- decreased bone and muscle mass, anemia, changes in mood and cognition, decreased sexual function and spermatogenesis
