Lect 25 Flashcards
what is spermatogenesis
production of sperm
- undifferentiated diploid primordial germ cells (spermatogonia) are converted into haploid spermatozoa (sperm)
descent of testes is usually complete by what month of gestation
7th month
Why do testes descend into the scrotum
- provides cooler environment (1-2 C below body temperature) essential for spermatogenesis
testes perform what two functions
- produce sperm
- secrete testosterone
where is sperm produced
seminferous tubules
testosterone is produced in what cells
Leydig (interstitial) cells
- found in connective tissue of testes
Seminiferous tubules contain what two cell types
- germ cells (spermatogonia)
- sertoli cells
- provides nutrients to germ cells
function of sertoli cells
- form tight junctions: blood-testes barrier
- protect sperm and provide nourishment for sperm
- phagocytize bad germ cells
- secrete seminferous tubule fluid
sertoli cells secrete what three hormones? what is each’s function
- Inhibin: inhibit FSH release
- Andorgen Binding protein: maintains high level of testosterone in tubular fluid
- Anti-Mullerian hormone: development
Spermatogenesis is mediated by
testosterone
List the three major stages of Spermatogenesis
- Mitosis: daughter cell -> 4 identical primary spermatocytes
- Meiosis: each primary spermatocytes -> 4 spermatids
- Spermiogenesis
- packaging process in which spermatids transform into mature spermatozoa
When is a cell considered a primary spematocyte
has finished mitotic division: four identical diploid (4N DNA) cells
when is cell considered a secondary spermatocyte
after it has undergone meitoic division once
secondary spermatocyte enters the second meiotic division, producing two what
spermatids
what is the name of mature sperm
spermatozoa
full cycle of spermatogenesis takes how long
60-70 days
describe the spermatogenic wave
- production of spermatogenesis happens in waves throughout the entire seminiferous tubule
- guarentees a continuous supply of sperm
what is spermiogenesis? what is it mediated by?
- process by which spermatids mature into spermatozoa
- testosterone
what goes on during spermiogenesis
- packaging and elongation into mature spermatozoa
- remodeling of nucleus
- condensation of chromatin
- most of cytoplasm is lost
- formation of acrosome
What is Spermiation
process by which mature spermatozoa are extruded from Sertoli cells into the lumen of semineferous tubules
contraction of myoepithelial cells propels spermatozoa into
vas deferens
Where are sperm under final maturation prior to storage
epididymus
where are sperm stored
vas deferens
What is the effect of temperature on spermatogenesis
- lysosomal destruction prevented by cooler temperature
- testes kept cooler by
- air around scrotum, contraction/relaxation of muscles, venous blood flow
- interference with ability of scrotum to stay cool -> low sperm counts
- hot tubs, tight clothing, sitting too long
What is Criptorchidism
- undescended testes
- affected individuals are unable to produce viable sperm
Describe hormonal control of spermatogenesis
- hypothalamus releases gonadotropin-releasing hormones which acts on anterior pituitary to release FSH-secreting cells and LH secreting cells -> FSH and LH
- FSH sensitizes sertoli cells to testosterone and promotes secretion of inhibin and ABP from sertoli cells
- LH stimulates Leydig cells to produce testosterone by increasing activity of cholesterol desmolase
LH stimulates Leydig cells to produce testosterone by increasing activity of
cholesterol desmolase
function of androgen binding protein (ABP)
keeps high levels of testosterone within gonads
Describe negative feedback mechanisms of spermatogenesis
- testosterone causes negative feedback on anterior pituitary to inhibit FSH and LH
- Inhibin acts on anterior pituitary to inhibit FSH
testosterone can be sequestered within the seminiferous tubules by binding to
androgen binding protein by sertoli cells
testosterone can circulate within the peripheral circulation bound to
sex-hormone binding globulin (SHBG)
testosterone can be peripherally converted to what two things in target tissues
- dihydrotestosterone (DHT)
- estradiol
List the actions of testosterone on target tissues
- differentiation of epididymis, vas deferens, and seminal vesicles
- increased muscle mass
- pubertal growth spurt
- growth of penis seminal vesicles
- deeping of voice
- libido
List the actions of dihydrotestosterone on target tissues
- differentiation of penis, scrotum and prostate
- male hair pattern/pattern baldness
- sebaceous gland activity
- growth of prostate
which is more potent: dihydrotestosterone or testosterone
dihydrotestosterone
What are the primary effects of exogenous testosterone (steroid) use
- decrease LH and FSH release
- decrease sperm production
- increase in free estrogens (will free estrogens from binding proteins)
