function of the testis
- produce and store sperm
- produce hormones with regulate spermatogenesis
overheating of the testes has what effect?
reduces sperm count
where are the testes located and why?
in the scrotum, outside of the body cavity
-optimum temp for sperm production
what are the testis made up of?
90% seminiferous tubules, site of spermatogenesis
where do the seminiferous tubules meet?
tightly coiled tubules all meet at the rete testis, then go to epididymus
- stored in epididymus for a few days
- upon ejaculation, move through vas deferens
what do sperm start as?
spermatogonia
why can men always reproduce throughout their lifetime?
mitotic proliferation of spermatogonia means they have a lifetime supply of sperm
where are the spermatogonia located?
on the basement membrane
where are Sertoli cells located?
they lie along the seminiferous tubules
what are adluminal compartments and what do they do?
tight junctions between the sertoli cells
- protected from the immune system and toxic agents
- specific enclosed environment for spermatogenesis which is filled with Sertoli cell secretions
movement of sperm in tubules
Sperm start to be made on the edge, and as they form they start to move to the lumen. Once they reach they lumen they are fully fledged sperm
what are the spaces between the tubules filled with?
blood and lymphatic vessels
Leydig cells
interstitial fluid
Sperm stages during spermatogenesis
Spermatogonia Primary spermatocytes Secondary spermatocytes Spermatids Spermatozoa
Spermatogonia
diploid
germ cell on the basement membrane, capable of dividing to produce more spermatogonia, or producing primary spermatocytes
Primary spermatocytes
46 XY diploid
move into the adluminal compartment
chromosome replication, production of sister chromatids which exchange DNA (recombination) before meiosis 1
Secondary spermatocytes
have undergone meiosis 1
haploid, 23X and 23Y
Spermatids
meiosis 2
haploid, 4 spermatids
spermatid differentiation from round to elongated
loss of cytoplasm
Spermatozoa
Mature sperm extruded into the lumen.
how often is there a new cycle in spermatogenesis?
every 16 days
are the sperm cell divisions complete, and what happens as a result of this?
no, each cell division from a spermatogonium to a spermatid is incomplete
- the cells remain connected to one another by cytoplasmic bridges forming a syncytium allowing synchronous development
- waves of cells at different stages moving down the tubule
Oogonia v Spermatogonia
oocytes begin meiosis before birth, spermatocytes begin meiosis after puberty
lifetime supply of spermatocytes, limited supply of oocytes
Leydig cells
- have LH receptors, convert cholesterol into androgens
- LH binding stimulus testosterone production contributes to the male sexual characteristics
- testosterone also binds to the sertoli cell, stimulating spermatogenesis
sertoli cells
- FSH receptors, converts androgens to oestrogen
- FSH binding maintains Sertoli cell health and population
- Sertoli cell is in control of all the secretions into the adluminal compartment to maintain spermatogenesis
action of anabolic steroids
interfere with negative feedback, reducing FSH and LH and causing testicular atrophy
