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Spermatogenesis
Testis, spermatogenesis
| Term | Definition |
|---|---|
| What is cryptorchidism? | Maldescent of testis into scrotum prior to birth -> temp remains high -> associated w/ teratocarcinoma, reduced spermatogenesis, subfertility |
| What is the blood supply/drainage of the testis? | Countercurrent heat exchange -> highly tortuous testicular artery takes warm blood into testis -> cooled by adjacent venous blood in pampiniform plexus taking cool blood out of testis |
| What is the stimulation, function and location of Leydig cells? | Hypothalamic GnRH -> anterior pituitary LH -> testis -> continuous output of androgens and inhibin -> located outside of seminiferous tubule (outside basal lamina) |
| What are the testicular septae? | Divide testis into 250 lobules |
| What are the measurements of the seminiferous tubules? | Each testicular lobule has 1-4 seminiferous tubules, total 12000 tubules for length of 250m |
| What are the characteristics of sperm released from the seminiferous tubules? | Non-motile -> mvmt mediated by bulk fluid flow |
| What is the stimulation, function and location of Sertoli cells? | Make up wall of seminiferous tubules (inside basement membrane) -> 1 cell thick but appear multilayered -> tight junctions make up blood-testis barrier, stimulated by FSH to secrete fluid for seminiferous tubule lumen |
| What makes up the blood-testis barrier? | Tight junctions btwn Sertoli cells -> divide testis into basal/apical (adluminal) compartments |
| What happens in the basal compartment of the testis? | LH -> Leydig cells -> testosterone production, FSH -> Sertoli cells -> androgen binding protein production -> binds testosterone, contains spermatogonia |
| What happens in the adluminal compartment of the testis? | Immunologically privileged site -> spermatocyte meiosis introduces haploid cells -> new allele recombination/segregation -> foreign Ag from chiasmata on sperm surface are intolerised, contains primary spermatocytes and onwards |
| What happens if the blood-testis barrier breaks down? | Adluminal compartment no longer immunologically privileged -> autoimmune reaction to sperm haploid cells -> production of anti-spermatozoal Ab -> subfertility |
| What are the testicular interstices? | Space btwn tubules that have blood vessels and lymphatics -> blood flow (outside seminiferous tubule) separated from spermatogenesis (w/in seminiferous tubule) |
| What is the structure and function of the epididymis? | Sperm maturation and storage, rete testis -> epididymis head -> body -> tail -> vas deferens |
| What is the function of the vas deferens? | Carries mature sperm out of testis towards prostate gland and to ejaculatory duct |
| What is the appearance of the testis in the fetal period? | Developed during fetal period but inactive until puberty -> wk 24 epithelium -> not fully organised, no Sertoli tight junctions, spermatogonia not on basement membrane, inconspicuous Leydig cells |
| What is the apperance of the testis in puberty? | FSH/LH rises -> testis enlarges -> Leydig cells/seminiferous tubules expand -> Leydig cells produce testosterone, Sertoli cells begin spermatogenesis |
| What is spermiogenesis? | Cytodifferentiation -> post-meiotic haploid spermatids transform phenotype from round spermatid to elongated spermatid to spermatozoon -> controlled by FSH |
| What is spermatozoon? | Singular of spermatozoa -> fully matured spermatid -> head is expanded w/ nucleus/acrosomal cap, midpiece contains centrioles, tail contains axoneme (central flagellum strand) |
| What is spermiation? | Mature spermatids released luminally into testicular fluid of seminiferous tubules -> controlled by LH -> require maturation in epididymis |
| What cell types are involved in spermatogenesis? | Spermatogonium (basal) (46) -> blood-testis barrier -> 1 primary spermatocyte (adluminal) (46) -> 2 secondary spermatocyte (23) -> 4 spermatids (23) -> 4 spermatozoa (23) |
| What triggers mitotic proliferation in spermatogonium? | FSH/testosterone |
| What stimulates the 1st meiotic division? | Testosterone -> 1 primary spermatocyte (46) -> 2 secondary spermatocytes (23) |
| What stimulates the 2nd meiotic division? | Testosterone -> 2 secondary spermatocytes (23) -> 4 spermatids (23) |
| How do spermatids become spermatozoa? | Spermiogenesis (FSH) -> transform phenotype from round spermatid to long spermatide to spermatozoon, spermiation (LH) -> spermatozoon released into seminiferous tubule lumen |
| What is the cytoplasmic bridge? | Formed during meiosis due to incomplete cytokinesus -> allows X/Y haploid sperm cells to exchange proteins |
| What is the process of spermiogenesis? | Spermatid remodelling -> flagellum develops, acrosomal vesicle forms, xcs cytoplasm packaged into residual body (streamline) phagocytosed by Sertoli cells, chr condensation (histones -> protamines), cytoplasmic bridges separate (spermatozoa released) |
| How long is the spermatogenic cycle? | Stem cells divide asynchronously every 16 days, spermatogenesis takes 64 days (4 successive simultaneous spermatogenic processes) |
| What is the spermatogenic wave? | Poorly defined timescale for one spermatogenic cycle -> tubule circumference wedges differn in consecutive cycle phases |
| How are spermatozoa transported? | Seminiferous tubules -> rete testis -> vasa efferentia (12-20 ductules) -> head of epididymis -> body -> tail -> vas deferens |
| What happens in the vas deferens? | 90% fluid reabsorption -> [spermatids] rise, spermatozoa fully matured -> stiffening of tail outer dense fibres, addition of glycoproteins to surface, change in membrane lipid composition -> fully motile/some mvmt via muscular contractions |
| How many sperm are produced daily? | 30 million spermatozoa / day |
| What is considered oligospermic? | Reduced sperm count (<13 M/ ml), may be azoospermic (no detectable sperm) |
| What are the causes of reduced sperm count? | Cryptorchidism (failed descent), varicocoele (pampiniform plexus enlargement destroys countercurrent flow), drugs (antimitotic, alcohol), hyperprolactinaemia (inhibits hypothalamic GnRH -> hypogonadism), obstructive pathology (congenital/post-infection) |
| What are the causes of azoospermia? | Obstructive blockage of epididymis/vas deferens, non-obstructive (decreased testis spermatozoa production from hypophysectomy), vasectomy |
Created by:
vykleung
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