1.2 - origin of the gametes - males Flashcards
how many gametes does the male system produce?
hundreds of million a day
where do germ cells colonise?
the seminiferous cords in the medulla of the primordial gonad
what do the seminiferous cords in the medulla of primordial gonad connect with?
rete testis, epididymis and vas deferens
what is the speed of post-natal growth of testis
slow
when do germ cells begin meiosis
AT puberty, NOT before
what happens at puberty to allow germ cells to begin meiosis?
hollow seminiferous tubules form from the seminiferous cords
how many tubules does each testis have? where do they empty into?
250-750 tubules
empty into the rete testis
into a single convoluted tube - epididymis
where does spermatozoa develop? in association with what?
within seminiferous tubules in association with Sertoli cells
what are the tubules separated from the surrounding interstitial tissue by?
blood testis barrier
Where is testosterone secreted?
Leydig cells in the interstitial tissue
what do the germ cells form?
spermatogonia stem cells
How do the spermatogonia stem cells maintain their population? what does this allow for
begin mitosis to maintain a population of self-regenerating stem cells that remain avaliable up to and beyond the age of 70
allowing for continuous sperm production at a high rate
what marks the beginning of spermatogenesis in a particular part of the tubule?
at intervals, groups of distinct cells: ‘A1 spermatogonia’ emerge
what happens to the A1 spermatogonia?
undergo differentiation to produce further A type (stem cells) and type B cells - committed to differentiation to spermatozoa
what happens to each type B sermatogonium?
then undergoes a fixed number of mitotic divisions to produce a clone (normally 64) of primary spermatocytes
what are all primary spermatocytes linked together by?
cytoplasm bridge
how do primary spermatocytes begin meiosis?
push their way towards the lumen of the tubule
what does the first division of meiosis produce?
2 haploid secondary spermatocytes
what happens to the 2 haploid secondary spermatocytes?
each divides again to form spermatids
how many spermatids does each A1 spermatogonium yields up to?
256 spermatids
what happens to the spermatids?
re-modelled to form sperm by spermiogenesis
what happens once the spermatozoa are produced?
the cytoplasmic bridges break down and the sperm are released into the lumen to be washed down to the rete testis
what washes down the sperm to the rete testis?
fluid secreted from Sertoli cells
how long does spermatogenesis take in a man?
70 days
how often do new groups of A1 spermatogonia arise?
every 16 days (so 4 spermatogenic processes are going simultaneously)
how is production continuous?
because different sections along the length of a tubule begin the process at different times, so some part is always releasing sperm
(if happened over whole testis at same time, sperm only produced intermittently)
what sweeps along the length of tubule?
a spermatogenic ‘wave’ of production
when does spermatozoa finally mature?
during progress through the epididymis
what is ‘emission’?
during copulation contractions of the vas deferens sweep sperm to be mixed with other components of semen from the seminal vesicles (60% volume) and prostate (20% volume)
what is emission controlled by?
sympathetic nervous system
what is the purpose of emission?
to ejaculate semen into the female
what is the volume of a typical ejaculation? how many sperms does it contain?
3.5ml contains about 350 million sperm
how many sperms from ejaculation will reach the site of fertilisation?
fewer than 50
what is the site of fertilisation?
ampulla of uterine tube in the female tract
