spermatogenesis and sperm deposition Flashcards
what is spermatogenesis?
the production of spermatozoa ( the male gamete).
this occurs in the seminiferous tubules
starts in the basement membrane (seminiferous epithelium)
proliferate and mature towards the lumen
what are the 3 phases that spermatogenesis is split into?
spematocytogenesis (proliferation)
meiosis
spermiogenesis (differentiation)
how many spermatozoa can a dairy bull produce?
7.5 x 10000000000 spermatozoa a day
what is spermatocytogenesis?
the first phase of spermatogenesis
spermatogonia (stem cells) undergo mitotic division
3 different spermatogonia:
A - divides by mitosis roughly 2 times then becomes an intermediate
I (intermediate) then divide via mitosis to become B
B then divides to become a primary spermatocyte
number of divisions depends on the species
e.g. ram has 6 stages = 64 primary
where as a stallion has 8 = 256 primary
many degenerate
what occurs during the phase of meiosis?
the spermatocytes made in the first phase undergo meiosis, making secondary spermatids
secondary spermatids = genetically unique (crossing over in meiosis 1)
primary spermatocytes = longes lived germ cell in the process
secondary spermatocytes = short-lived (less than 2 days)
what occurs in the 3rd phase, spermiogenesis?
differentiation occurs - no division occurs
spheroid spermatid undergoes:
condensation of nucleus
formation of: acrosome, tail (flagellum) and a mitochondrial helix
produces spermatozoa with the potential to be motile and able to fertilise
how long does spermatogenesis take?
the length varies between species.
bull = 61 days
ram = 47 days
boar = 39 days
stallion = 55 days
dog = 62 days
tom = 47 days
the process occurs throughout seminiferous tubules - this gives a continuous release of spermatozoa
different areas at different stages
what is spermiation?
spermiation = the release of spermatozoa from sertoli cells
what are the characteristics of sperm?
surrounded by permeable plasma membrane
have a head and tail
what are the characteristics of the sperm head?
contains the nucleus (n)
compact chromatin
nuclear membrane surrounds the head
has an acrosome which is membrane bound
the acrosome contains hydrolytic enzymes
there is also a postnuclear cap/ postacrosomal region
what are the characteristics of a sperm tail?
there is a neckpiece that acts as the middle section containing lots of mitochondria as energy is required to drive tail
the tail has a principal piece and an end piece
throughout the tail, there is an axoneme:
containing central filaments and microtubules
there are also coarse fibres
where does the sperm travel?
starting in the seminiferous tubules
to the rete testis
to the epididymis
then through the vas daferens
onto the accessory glands - ampulla, vesicular glands, prostate, bulbourethral glands (cowpers)
finally onto the urethra
how is sperm deposited?
sperm have matured in the epididymis
non- ejaculated sperm is senescent and broken down
deposition occurs in 3 stages
1) erection
2) emission - super through vas daferens, mixes with seminal plasma and is now called semen
3) ejaculation - semen expelled from the penis
how does ejaculation occur?
contraction of muscles in the:
epididymis
vas daferens
accessory glands
urethra
it is driven by testosterone
how is the erection caused?
it is activated by the central nervous system
causes increased blood flow to the erectile tissue
in the stallion/ tom/ dog = increase in diameter of penis
in the bull/ ram/ boar = small increase in diameter and relaxation of retractor muscle = sigmoid flexure straightens
