Male Reproductive Physiology Flashcards
What is the general timeline of gonadal development in gestation?
weeks 1-5: bipotential
6-7: testes begin to develop
week 9: the ovaries begin to develop
What is Gonadotropin secretion like over the lifetime?
high in fetus
low in childhood (FSH>LH)
starts to increase in puberty
plateau in men in adulthood, fluctuates in women (LH>FSH)
increases in senescense, moreso in women (FSH>LH
What initiates puberty?
pulsatile secretion of GnRH –> gonadal tesroud hormones
secondary sex characteristics bc of T and estrogen
pulses of GnRH are essential - if you administer long-acting, puberty not initiated
What can delay onset of puberty?
extreme stress or caloric deprivation in girls
melatonin may be a natural inhibitor of GnRH release
What is the scrotum essential for?
maintaining lower temperature essential for spermatogenesis (1-2C below body temp)
What is the primary function of the epididymis?
location for the maturation and storage of sperm
Where do spermatogonia mature into spermatozoa?
seminiferous tubules
What is the general composition of an adult testis?
80% seminiferous tubules
20% CT w/ leydig cells
What are the androgens secreted by the testes?
testosterone (most abundant)
DHT
androstenedione
most T goes to DHT in target tissues
When enzymes do the testes have and lack?
Lack: 21beta-hydroxylase and 11beta-hydroxylase (no glucocorticoids or mineralcorticoids are made)
have: 17beta-hydroxysteroid dehydrogenase (androstenedione –> T)
What does 17B-hydroxysteroid dehydrogenase do?
converts androstenedione to testosterone
What occurs to T in the lumen of seminiferous tubules?
concentrated by binding to androgen-binding protein
When do Leydig cells do?
synthesize cholesterol de nove and also aquire it from LDL receptors
store cholesterol esters – HSL –> free cholesterol for androgen production
cholesterol – StAR –> mitochondrial membranes –> pregnolone
How is estrogen produced in the male?
In sertoli cells: T – aromatase –> estradiol
concentration of E is high in seminiferous tubule fluid - potential role in spermatogenesis
most of E is produced in other tissues
What is 17,20 desmolase?
same as 17-alpha hydroxylase
converts 17alpha-hydroxyprogesterone to androstenedione
What is the rate limiting step in the synthesis of testosterone?
conversion of cholesterol to pregnenolone
What does LH do in a male?
increases affinity for cholesterol desmolase for cholesterol
stimulates synthesis of cholesterol desmolase
regulates overall rate of T synthesis by leydig cells
What is P450scc?
cholesterol desmolase
When does Testosterone production begin?
7-8 weeks gestation
What is the androgen receptor?
nuclear receptor that directs protein synthesis
found in prostate, testis, epididymis and seminal vesicles
also in non-repro tissue
what is the significance of DHT?
binds to AR w/ greater affinity than T alone
has important role in causing changes at puberty
How is T found in the blood?
60% bound to SHBG
38% bound to albumin
2% free T = bio active form
How is T excreted?
primarily in urine
50% of excreted androgens found as urinary 17-ketosteroids
remainder conjugated androgens or diol or triol
What are the fetal actions of T?
present at 2nd month
differentiation of internal male genital tract
causes descent of testes during last 2-3 months of pregnancy
What are the specific actions of DHT?
fetal differentiation of external male genitalia
hair distribution and baldness
sebaceous gland activity
growth of prostate
What are the anabolic actions of androgens?
stimulation of EPO
stimulation os sebaceous glands
control of protein anabolic effects (N retention)
linear body growth, bone growth, and closure of epiphyses
ABP synthesis
behavioral effects, including libido
How is DHT involved in BPH?
concentrations of DHT in prostatic tissue not higher in men w/ BPH –> might have more DHT receptors on prostates
How does LH stimulate leydig cells?
Gs receptor –> cAMP/PKA –> steroidogenesis and T production
How does do FSH and T stimulate sertoli cells?
FSH –> Gs –> new protein synthesis and production of inhibin (inhibits FSH release)
Testosterone contributes to this too by diffusing freely from leydig to sertoli cells
What stimulates ABP production?
FSH –> sertoli cells –> ABP into lumen of S tubules
What are the exocrine fxns of sertoli cells?
produce fluid
ABP
determination of release of sperm from seminiferous tubules
What are the endocrine fxns of sertoli cells?
expression of ABP, T, and FSH
production of AMH
aromatization of T –> estradiol-17B
production of inhibin to regulate FSH
How long does spermatogenesis take?
64 days
What occurs to spermatogenesis at puberty?
mitotic divisions (spermatocytogenesis) increase to produce daughter spermatogonia
What occurs in the meiosis phase of spermatogenesis?
primary spermatocytes undergo 2 meiotic divisions:
1st: 2 secondary spermatocytes, 1n, 2d
2nd: spermatocytes enter 2nd div, producing 2 spermatids, 1n, 1d
What is spermiogenesis?
spermatid maturation into spermatozoa
What is the residual body and how is it removed?
excess cytoplasm ejected during spermatid maturation
phagocytized by sertoli cells
What are the hormonal factors that stimulate spermatogenesis?
LH –> leydig cells make T
FSH –> sertoli cells nurse and form sperm
GH –> necessary for background metabolic fxns of testes; promotes early div of sperm
T –> growth and div of germinal cells
Estrogens –> might be essential
What is seen in sperm in pituitary dwarfs?
no GH –> spermatogenesis is severely deficient or absent = infertile
What occurs when exogenous T is administered?
inhibits LH release –> lowered intratesticular T levels –> insufficient spermatogenesis
What occurs to sperm in the epididymis?
sperm spend about a month here further maturing after release from rete testis
weakly motile upon entering, strongly motile when exiting
decapacitation
storage site for mature sperm for several months
What is decapacitation?
adding molecules to membranes of sperm to prevent acrosomal reaction before contact w/ an egg
What are plasma testosterone and sperm production like throughout a male’s life?
no sperm production until puberty; high through adulthood and decreases in old age
T high fetally, dips at birth, high neonatally
low in childhood
increases during puberty and stays high throughout adulthood, decreases in old age
What do prostaglandidns do and where are they secreted?
from seminal vesicles
react w/ female cervical mucus to make it more receptive to sperm movement (less thick)
cause backward peristaltic contractions in uterus and fallopian tubes to move sperm to ovaries
When does the prostate gland secrete, and what is in its secretion?
secrete during emission
thin fluid w/ Ca, citrate ion, Pi, clotting enzyme, and profibrinolysin
fxns for pH adjustment
How long can sperm live once ejaculated?
How many sperm are in each ejaculation?
24-48 hrs at body temp
2-6 mL, 20-200 million sperm (<20 million = infertile)
What is emission?
movement of semen from epididymis, vas deferens, seminal vesicles, and prostate to ejaculatory ducts
under Sympathetic control
peristaltic contraction of SM of vas deferens –> closes internal sphincter of bladder to prevent retrograde ejaculation
usually precedes ejaculation
What is ejaculation?
propulsion of semen out of male urethra
rhythmic contraction of bulbospongiosus and ischiocavernosus ms
striated muscles innervated by somatic motor nerves
What occurs in capacitation?
changes occur when sperm come in contact w/ fluids of female tract
uterine tubes wash away inhibitory factors
loss of cholesterol built-up on acrosome
membrane more permeable to Ca –> increased motility
What is the acrosome reaction?
large quantities of hyaluronidase and proteolytic enzymes stored in acrosomal head
hyaluronidase –> depolymerizes hyaluronic acid polymers in intercellular cement that hold ovarian granulosa cells together
proteolytic enzymes –> digest proteins in structural elements of tissue cells that adhere to ovum
What does T deficiency in 2-3rd mo of gestation cause?
3rd trimester?
2-3rd mo: varying degrees of ambiguity in male genitalia, DSD
3rd trimester: problems in testicular descent, micropenis
What does T deficiency in puberty cause?
poor secondary sexual dev and overal eunuchoid features (prepubertal characteristics)
What does T deficiency in post-puberty cause?
decreased libido, erectile dysfunction, decreased facial and body hair growth, low energy, infertility
What is Kallman’s syndrome?
genetic disorder
GnRH neurons fail to migrate into hypothalamus during embryo
delayed/absent puberty and impaired sense of smell
hypogonadotropic hypogonadism
What is Klinefelter syndrome?
male w/ extra X chromosome
at puberty, increased gonadotropins fail to induce normal testicular growth and spermatogenesis
androgen production is low = primary hypogonadism
seminiferous tubules destroyed –> infertility
What can treat benign prostatic hypertrophy?
5alpha-reductase inhibitor
What do tumors of testis often cause?
interstitial tumors: large amounts of testosterone
germinal epithelial tumors: produce no hormones
What occurs in “andropause”?
as men age, gonadal sensitivity to LG decreases and androgen production drops
serm LH and FSH rise (FSH>LH)
T production decreases slowly after age 40
sperm production drops after age 50, but many men can maintain repro fxn and spermatogenesis throughout life
