11: Male Reproductive Physio Flashcards
Genetic sex in embryos week 5, 6, ad 9
Week 5: gonads are bipotential
Week 6: testes begin to form in males
Week 9: ovaries begin to form in females
What determines phenotypic sex?
Hormonal output of gonads
What initiates puberty?
Pulsatile secretion of GnRH causing a pulsatile secretion of FSH and LH to stimulate gonadal steroid hormones
Regulating puberty: GnRH analogue in pulses vs long-acting
GnRH analogue in pulses: puberty is initiated, reproductive function is established
GnRH long-acting: puberty is not initiated
P450scc
Aka desmolase, cholesterol -> pregnenolone
Three androgens secreted by testes
T, DHT, androstenedione
Most abundant androgen secreted by testes
Testosterone
End product of steroid synthesis in testes vs adrenal gland
Testes: T
Adrenals: DHEA and androstenedione
Two enzymes lacking in the testes and the outcome of this
Lacks: 21B-hydroxylase & 11B-hydroxylase -> no mineralocorticoids or glucocorticoids
Three big androgenic actions of androgens
- Differentiation of male internal and external genitalia in fetus
- Stimulate secondary sexual characteristics at puberty
- Maintain reproductive tract and production of semen and sperm
7 Anabolic actions of androgens
- Erythropoeitin synthesis
- ABP synthesis
- Control protein anabolic effects (N retention)
- Maintain sex gland secretions
- Sebaceous gland secretions
- Regulate behavior
- Regulate libido
Three forms of circulating T
- 60% bound to SHBG
- 38% bound to albumin
- 2% free (most important biologically)
What will not occur without FSH?
Spermiogenesis
What happens with no GH?
Spermatogenesis is severely deficient or absent -> pt is infertile
Sperm maturation in epididymis
Spend about 1 month (can spend several) in epididymis becoming more mature and becoming strongly motile
Decapacitation in epididymis
Adding moleucles to sperm membrane to prevent acrosomal reaction before contact with egg
Final pH of semen
7.5
Lifespan of sperm once ejaculated
24-48 hours at body temp
Ml of semen per ejaculate
2-6ml
Sperm count to be considered infertile
Less than 20 million
Two differences between male and female tracts
- Males have continuous lumen from seminiferous tubule to end of male tract
- Male tract connects to distal urinary tract
Helicine arteries
Supply blood to cavernous spaces of penis
Pathway for erection
- Parasymp nerves stimulate helicine arteries
- NO released -> guanylate cyclase -> increased cGMP -> vasodilation
- Blood flows into spaces -> erection
How erection is maintained
Engorged tissues press dorsal veins against outer fascia (tunica albuginea) -> reduced drainage
How does somatic stimulation help maintain erection?
Increased contraction of muscles at base of penis -> further promote erection
Emission of sperm control
Sympathetic
Internal sphincter of bladder
Closed during emission to prevent retrograde ejaculation into bladder
Process that causes ejaculation
- Rhythmic contraction of bulbospongiosus + ischiocavernosus innervated by somatic motor nerves
Why penis becomes flaccid after ejaculation
Sympathetics constrict helicine arteries -> decreased blood flow -> veins drain most of the blood
What enzyme converts androstenedione to testosterone?
17B-hydroxysteroid dehydrogenase
What does aromatase do?
Testosterone -> estradiol
