12. Male Reproductive Physiology Flashcards
What distinguishes gonadal sex and phenotypic sex
Gonadal- testes or ovaries
Phenotypic- physical characteristics of internal genital tract and external genitalia
What are the main gonadotropin hormones
FSH and LH
How do levels of FSH and LH compare in childhood and puberty/adulthood and senescence
Childhood- FSH > LH
Puberty/Adulthood- LH > FSH
Senescence- FSH > LH
What initiates puberty
Pulsatile secretion of GnRH which drives the pulsatile secretion of FSH and LH
What happens if a long-acting GnRH analogue is administered
Puberty is not initiated
-If a GnRH analogue is administered in intermittent pulses puberty is initiated and reproductive function is established
What are the main general functions of the testes, scrotum and epididymis
Testes- spermatogenesis and secretion of testosterone
Scrotum- lower temperature below body temperature
Epididymis- primary location for maturation and storage of sperm
What are the main general functions of the Vas deferens and the Prostate gland
Vas Deferens- storage for sperm, nourish sperm (fructose), seminal vesicles (adds 2/3 fluid)
Prostate Gland- secrete milky aqueous solution rich in citrate, calcium and enzymes
What makes up seminiferous tubules
Epithelium formed by the Sertoli cells with interspersed germ cells
- Spermatogonia (immature) are in the periphery
- Spermatozoa (mature) are near the lumen
What makes up the testis
80% seminiferous tubules
20% CT with Leydig cells
What is the general function of Sertoli cells
‘Nursing Cells’
- Form tight junctions to control sperm environment
- Provide nutrients to the sperm
- Helps transport sperm through tubules into epididymis
What is the general function of Leydig cells
Synthesis and secretion of testosterone
What is the function of 17B-Hydroxysteroid in male physiology
-Converts androstenedione to testosterone
In the periphery what activates testosterone in target tissue
5a-reductase converts T to DHT
lack of enzyme results in ambiguous external genitalia
What is responsible for steroid synthesis in the testis
Leydig cells synthesize cholesterol de novo and store cholesterol as esters
- generated via Hormone-Sensitive Lipase (HSL)
- cholesterol is transferred via StAR
- cholesterol converted to pregnenolone
How do males get estrogen
- Aromatase (CYP19) converts testosterone to estradiol in sertoli cells
- Most estrogen made in adipose tissue
What is the rate-limiting step in synthesis of testosterone
Conversion of cholesterol to pregnenolone by P450SCC
How is testosterone concentrated in seminiferous tubules
binding to ABP
What role does LH play in testosterone synthesis
Promotes pregnenolone synthesis via
- increasing affinity of P450SCC for cholesterol
- stimulate synthesis of P450SCC
How does most of testosterone circulate
60% bound to sex hormone-binding globulin (SHBG)
38% bound to albumin
2% free
What does DHT due embryologically
External Genitalia (penis prostate and scrotum)
What are some anabolic actions of androgens
- Stimulation of erythropoietin synthesis
- Stimulation of sebaceous gland secretion
- Stimulation of ABP synthesis
- Nitrogen retention
What is Benign Prostastic Hyperplasia (BPH)
- Patients might have more DHT receptors on prostates but do not have more DHT in prostastic receptor
- Patients have prostate peeing issues
What are the intracellular mechanism of action of testosterone
cAMP-PKA pathway for both LH and FSH
FSH- uses pathway to synthesize ABP and aromatase
What are the three stages of Spermatogenesis
- Mitotic divisions
- Meiotic divisions
- Spermiogenesis
Describe the mitotic division phase of Spermatogenesis *spermatocytogenesis)
- Proliferative phase
- At puberty, mitotic cycles increase and spermatogonia or stem cells divide to produce daughter spermatogonia
- After last division the resulting cells are called primary spermatocytes
Describe the meiosis phase of Spermatogenesis
- Production of the haploid gamete
- Primary spermatocytes undergo two meiotic divisions
- First division produces two secondary spermatocytes, each with a haploid number of duplicated chromosomes
- Secondary spermatocytes enter second meiotic division, producing two spermatids, each with a haploid number of unduplicated chromosomes
Describe the spermiogenesis phase of Spermatogenesis
- Spermatids undergo spermiogenesis and mature into spermatozoa
- Nuclear and cytoplasmic changes to produce mature spermatozoa
- Ends in testis with release of spermatozoa from Sertoli cells
What are the three major hormonal factors that stimulate spermatogenesis
LH
FSH
GH
What are the two main differences the male reproductive tract has
- Continuous lumen from seminiferous tubule to the end of the male tract
- Male tract connects to the distal urinary tract
What role do parasympathetics play in erection
- Innervates vascular SM of the helicine arteries that supply blood to the cavernous spaces release NO
- Vasodilation allows blood to flow into spaces, causing engorgement and erection
- Engorged tissue presses the veins against a noncompliant outer fascia, reducing venous drainage
How does Viagra work
- NO activates guanylyl cyclase to make cGMP
- cGMP prolongs the erection so viagra inhibits Type 5 phosphodiesterase which degrades cGMP to GMP
What is the male sexual response of Emission
Movement of semen from the epididymis, vas deferens , seminal vesicles and prostate to the ejaculatory ducts
What happens when there is a lack of testosterone (gonadal dysfunction) in the 2-3rd months of gestation vs 3rd trimester of pregnancy
2-3 months = ambiguity in male genitalia
3rd trimester = problems with testicular descent (cryptorchidism) and micropenis
What happens when there is a lack of testosterone (gonadal dysfunction) in puberty vs post-pubery
Puberty = poor secondary development and overall eunuchoid features Post-Puberty = decreased libido, ED, low hair and energy, infertility
What is Kallman’s Syndrome
Genetic disorder where GnRH neurons fail to migrate into the hypothalamus during embryological development
- Delayed or absent puberty and an impaired sense of smell
- Form of hypogonadotropic hypogonadism (SECONDARY)
What is Klinefelter Syndrome
Seminiferous tubular dysgenesis- male with an extra X chromosome
- at puberty gonadotropins levels fail to induce normal testicular growth and spermatogenesis
- low androgen production but high gonadotropins indicating PRIMARY HYPOGONADISM
What does Hyperprolactinemai do
suppresses FSH and LH secretion
