Spermatogenesis Flashcards
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
an erection causes what?
vasodilation of corpus cavernosum
-under parasympathetic control
partial constriction of the venous return
what does the autonomic nervous system cause?
co-ordinated smooth muscle contractions of vas deferens, glands and urethra
role of sympathetic nervous system in ejaculation?
movement of sperm into epididymis, vas deferens, penile urethra (emission)
role of somatic nervous system in ejaculation?
expulsion of the glandular secretions
& evacuation of urethra
what is the initial portion of the ejaculate?
sperm rich
what happens to the initial portion of the ejaculate?
90% lost before it reaches the ampulla of the uterine tube
what is seminal fluid?
consists of secretions from:
seminal vesicles, prostate, bulbo-urethral gland combined with epididymal fluid
role of Bulbo-Urethral Gland in seminal fluid?
- this gland secretes before ejaculation
- produces a clear viscous secretion high in salt, known as pre-ejaculate
- lubricates the urethra for spermatozoa to pass through, reduces risk of sperm being damaged by friction
- neutralises traces of acidic urine
role of seminal vesicles in seminal fluid?
- comprise 50-70% of the ejaculate
- contains proteins, enzymes, fructose, mucus, vitamin C and prostaglandins
- high fructose concentrations provide energy source
- high pH protects against acidic environment in vagina
- smooth muscle contractions moving the sperm up.
role of prostate in seminal fluid?
- secretes milky or white fluid, 30% of the seminal fluid
- protein content is less than 1% and includes proteolytic enzymes, prostatic acid phosphatase and prostate-specific antigen - involved in liquefaction
- high zinc concentration, antibacterial
structure of the spermatozoa
end piece, principal piece and midpiece
- nucleus has the DNA – most important bit
- hardly any cytoplasm
- mitochondrial sheath – needs lots of mitochondria producing ATP for movement
- 9 pairs of tubules, with a pair in the center – this is the pattern all the way down the tail
do fresh sperm fertilise the egg?
Fresh sperm will never fertiliise the egg, they need to undergo a process called capacitation which involves changes in the membrane over the head of the sperm, takes between 4-18 hours.
what receptor to the sperm bind to on the zona pellucida?
zp3
