Testis and spermatogenesis Flashcards
What are the compartments of the testis?
Seminiferous tubules -> spermatogenesis
Vascularised stroma -> contains Leydig cells
Which hormones does the testis produce?
androgens maintain reproductive + sexual function. testosterone synthesised from acetate + cholesterol by Leydig cells + secreted principally into blood vessels + lymph.
What happens to testosterone after it leaves the testis?
passes to seminiferous tubules, converted to dihydrotestosterone by 5a-reductase in Sertoli cells.
androgens required for spermatogenesis.
How does removal of the pituitary (hypophysectomy) affect the testis?
testes shrink, spermatogenesis arrests
What are the effects of LH?
stimulates Leydig cells to produce androgens for spermatogenesis
What are the effects of FSH?
stimulates Sertoli cells required for spermatogenesis
How are seminiferous tubules organised?
Peripheral myoid cells, then basement membrane.
Sertoli cells + spermatogenic cells within tubules.
Physiological barrier formed by gap- and tight-junctioned complexes between Sertoli cells.
Creates basal compartment + adluminal compartment.
Outline spermatogenesis
Mitotic proliferation produces lots of cells.
Meiotic division generates genetic diversity.
Cell modelling packages chromosomes for delivery to oocyte.
What occurs during the mitotic stage of spermatogenesis?
Germ cells of immature testis are reactivated at puberty to undergo rounds of mitosis in basal compartment of tubule.
A spermatogonia emerge which forms clone of cells. clone divide to form resting primary spermatocytes which inhabit cavities formed in Sertoli cell cytoplasm. primary spermatocytes linked by cytoplasmic bridges as cytoplasmic division isn’t complete.
What occurs during meiosis of spermatogenesis?
Resting primary spermatocytes push through sertoli cell junctions into adluminal compartment. enter meiotic prophase. paired homologous chromosomes form contacts at pachytene, break, swap segments and rejoin.
very sensitive to damage at this time.
first division ends with separation of homologous chromosomes to opposites ends of meiotic spindle, cytoplasm divides forming short-lived secondary spermatocytes. these quickly divide to form haploid spermatids.
How does packaging occur during spermatogenesis?
Cytoplasmic remodelling of spermatid: Tail for forward propulsion Midpiece with mitochondria for energy Nucleus with packaged chromosomes Cap region forms for sperm-oocyte fusion Acrosome forms to penetrate oocyte A small residual body is the dustbin for unwanted cytoplasm, later eaten by sertoli cell
What is the time for completion of spermatogenesis?
64 days. sperm generated from single spermatogonium. once it starts, new stem cells at same location don’t start generation of clones again for few days. interval is constant at around 16 days.
4 successive sets of clonal development.
How is spermatogenesis controlled?
If all spermatogonia were activated on 11th birthday, mature spermatozoa would be produced every 16 days,
result: episodic fertility.
If spermatogonia were activated randomly, continuous production could occur.
small regions seem to be activated together, in wedges + helices around tubule.
What is the spermatogenic wave?
If seminiferous tubules dissected longitudinally, adjacent synchronised clones of spermatogenesis seen
What occurs during the final stages of maturation?
Spermatozoa wash into rete through vasa efferentia into epididymis where fluid is absorbed + sperm concentrated. In rete they can twitch: by cauda epididymis they can swim.
process dependent on androgen stimulation.
