Spermatogenesis Flashcards
What is spermatogenesis?
The process whereby spermatozoa are formed, it consists of proliferation by mitosis, meiosis and differentiation.
Spermatogenesis take around 5-9 weeks depending on the species and certain endocrine requirements must be met before the sperm can be produced.
It takes place in the seminiferous tubules
Describe the divisions required for a spermatogonia to become a functioning spermatozoa
Spermatogonia divide by mitosis to produce primary spermatocytes, these PS then divide by meiosis 1 to produce secondary spermatocytes and then by meiosis 2 to produce spermatids which them mature and gain tails
Why is the primary spermatocyte the longest life stage in spermatogenesis?
Prophase 1 of the first meiotic division is the longest process (18-19 days in the bull)
Name the 4 stages of differentiation
Golgi Phase, cap phase, acrosomal phase and maturation phase
Describe the events in the golgi phase
The vesicles of golgi fuse to form acrosomic vesicles and acrosomic granules are formed.
The centrioles move to the base of the nucleus, the proximal centriole will anchor the tail to the nucleus and the distal centriole forms the central flagellum
Describe the events in the cap phase
The acrosome forms a cap and the golgi body migrates and disappears. The primitive flagella is starting to appear and there is an inner and outer acrosomal membrane
Describe the events of the acrosomal phase
The acrosome spreads and the nucleus elongates An annulus ( connection between the middle piece and principle piece) forms as do machette tubules
Describe the events of the maturation phase
The manchette tubules for the post nuclear cap which picks up from where the acrosomal cap stops. There is a gathering of mitochondria which forms a spiral assembly in the middle piece
The flagellum of a sperm consists of
Composed of the captilum (part of the middle piece that fits into posterior nucleus), middle piece, principle piece and the terminal piece.
Because there is no surge centre we have intermittent episodes of GnRH secretion from the hypothalamus, and this occurs throughout day and night.
What does the GnRH act on?
The GnRH acts on the anterior pituitary which stimulates the release of LH (luteinising hormone) and FSH (follicle stimulating hormone).
The LH surge is short, around 20 mins but because the half-life of FSH is longer you get a lower longer peak
What is the role of LH and FSH in the male?
LH binds to receptors on Leydig cells which stimulates them to produce testosterone
FSH binds to receptors on Sertoli cells enabling function (converting testosterone to oestradiol and producing inhibin)
Why is it important to have a pulsatile release of LH?
So each pulse of LH is followed by a pulse of testosterone leading to a pulsatile release of testosterone, this prevents prolonged secretion of LH which would shut off the Leydig cells to its stimulation (becomes refractory) and therefore shut down testosterone release.
What is the function of the pampiniform plexus?
The pampiniform plexus ensures there is a higher concentration of testosterone in the testis, if this didn’t happen too much testosterone could shut down release of GnRH.
How is GnRH release controlled?
Once the subsequent LH and FSH reach the testes, the LH which binds to Leydig cells and testosterone is released, some is converted to oestrogen and these feed back and inhibit GnRH release.
In the Sertoli cells the testosterone is converted to dihydrotestosterone which also inhibits GnRH. The Sertoli cells also releases inhibin which shuts down FSH release from the pituitary.
