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Male Reproductive Physiology Flashcards

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1
Q

What is the general timeline of gonadal development in gestation?

A

weeks 1-5: bipotential

6-7: testes begin to develop

week 9: the ovaries begin to develop

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2
Q

What is Gonadotropin secretion like over the lifetime?

A

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

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3
Q

What initiates puberty?

A

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

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4
Q

What can delay onset of puberty?

A

extreme stress or caloric deprivation in girls

melatonin may be a natural inhibitor of GnRH release

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5
Q

What is the scrotum essential for?

A

maintaining lower temperature essential for spermatogenesis (1-2C below body temp)

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6
Q

What is the primary function of the epididymis?

A

location for the maturation and storage of sperm

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7
Q

Where do spermatogonia mature into spermatozoa?

A

seminiferous tubules

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8
Q

What is the general composition of an adult testis?

A

80% seminiferous tubules

20% CT w/ leydig cells

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9
Q

What are the androgens secreted by the testes?

A

testosterone (most abundant)

DHT

androstenedione

most T goes to DHT in target tissues

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10
Q

When enzymes do the testes have and lack?

A

Lack: 21beta-hydroxylase and 11beta-hydroxylase (no glucocorticoids or mineralcorticoids are made)

have: 17beta-hydroxysteroid dehydrogenase (androstenedione –> T)

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11
Q

What does 17B-hydroxysteroid dehydrogenase do?

A

converts androstenedione to testosterone

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12
Q

What occurs to T in the lumen of seminiferous tubules?

A

concentrated by binding to androgen-binding protein

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13
Q

When do Leydig cells do?

A

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

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14
Q

How is estrogen produced in the male?

A

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

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15
Q

What is 17,20 desmolase?

A

same as 17-alpha hydroxylase

converts 17alpha-hydroxyprogesterone to androstenedione

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16
Q

What is the rate limiting step in the synthesis of testosterone?

A

conversion of cholesterol to pregnenolone

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17
Q

What does LH do in a male?

A

increases affinity for cholesterol desmolase for cholesterol

stimulates synthesis of cholesterol desmolase

regulates overall rate of T synthesis by leydig cells

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18
Q

What is P450scc?

A

cholesterol desmolase

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19
Q

When does Testosterone production begin?

A

7-8 weeks gestation

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20
Q

What is the androgen receptor?

A

nuclear receptor that directs protein synthesis

found in prostate, testis, epididymis and seminal vesicles

also in non-repro tissue

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21
Q

what is the significance of DHT?

A

binds to AR w/ greater affinity than T alone

has important role in causing changes at puberty

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22
Q

How is T found in the blood?

A

60% bound to SHBG

38% bound to albumin

2% free T = bio active form

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23
Q

How is T excreted?

A

primarily in urine

50% of excreted androgens found as urinary 17-ketosteroids

remainder conjugated androgens or diol or triol

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24
Q

What are the fetal actions of T?

Study These Flashcards
A

present at 2nd month

differentiation of internal male genital tract

causes descent of testes during last 2-3 months of pregnancy

25
What are the specific actions of DHT?
fetal differentiation of external male genitalia hair distribution and baldness sebaceous gland activity growth of prostate
26
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
27
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
28
How does LH stimulate leydig cells?
Gs receptor --\> cAMP/PKA --\> steroidogenesis and T production
29
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
30
What stimulates ABP production?
FSH --\> sertoli cells --\> ABP into lumen of S tubules
31
What are the exocrine fxns of sertoli cells?
produce fluid ABP determination of release of sperm from seminiferous tubules
32
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
32
33
How long does spermatogenesis take?
64 days
34
What occurs to spermatogenesis at puberty?
mitotic divisions (spermatocytogenesis) increase to produce daughter spermatogonia
35
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
36
What is spermiogenesis?
spermatid maturation into spermatozoa
37
What is the residual body and how is it removed?
excess cytoplasm ejected during spermatid maturation phagocytized by sertoli cells
38
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
39
What is seen in sperm in pituitary dwarfs?
no GH --\> spermatogenesis is severely deficient or absent = infertile
40
What occurs when exogenous T is administered?
inhibits LH release --\> lowered intratesticular T levels --\> insufficient spermatogenesis
41
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
42
What is decapacitation?
adding molecules to membranes of sperm to prevent acrosomal reaction before contact w/ an egg
43
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
44
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
45
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
46
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)
47
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
48
What is ejaculation?
propulsion of semen out of male urethra rhythmic contraction of **bulbospongiosus and ischiocavernosus ms** striated muscles innervated by somatic motor nerves
49
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
50
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
51
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
52
What does T deficiency in puberty cause?
poor secondary sexual dev and overal eunuchoid features (prepubertal characteristics)
53
What does T deficiency in post-puberty cause?
decreased libido, erectile dysfunction, decreased facial and body hair growth, low energy, infertility
54
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
55
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
56
What can treat benign prostatic hypertrophy?
5alpha-reductase inhibitor
57
What do tumors of testis often cause?
interstitial tumors: large amounts of testosterone germinal epithelial tumors: produce no hormones
58
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

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