Functions of male
Reproductive System:
• produce gametes
• deliver gametes
• protect and support
gametes
Spermatogenesis occurs in the testes
after puberty.
From the testes they are deposited into
the epididymas where they are stored.
and then vas deferens to begin
swimming and prepare to be deposited
into the female.
Sperm cells are haploid and are produced
in the tubules within the testes.
Spermatogenesis occurs in the seminiferous tubules. Here
spermatogonia cells (diploid) start to undergo meiosis. Sertoli cells
nourish the developing sperm. Interstitial cells outside the tubules
produce the hormone testosterone.
A microscopic image shows the Seminiferous Tubules.
Identify the structures that are shown here.
•A. Spermatogonia
B. Sperm
•C. Interstitial cells
D. Center of seminiferous tubules
C
•E. Sertoli cells
A
E
D
B
Sperm
Millions of sperm are produced in an average male every day. If
they are not ejaculated, they are reabsorbed after a couple of weeks
by the body and recycled.
Sperm are very stream-lined for what they do. They don’t have
any extraneous “gear.” No food for the trip and no proteins on
their surface. Just DNA with a tail.
How did evolution select for this in sperm?
Flagellum: propulsion
Mitochondria: power
Nucleus:DNA
Acrosome: a way into
the egg…
(digestive enzymes)
In order to deliver the gametes into the females’ reproductive
tract and to the females’ gametes, the penis must become
erect.
Blood flows into the erectile tissue and the build up of blood
pressure causes the penis to become rigid. Further stimulation
of the nerves on the penis triggers a series of smooth muscle
contractions that propel the sperm out of the penis.
The sensation of orgasm occurs when the control of the body
rapidly switches from one nervous center (the
parasympathetic) to another (the sympathetic).
Of the millions of sperm cells ejaculated into a female, only
a few will survive to meet the egg a couple of days later.
This is because the environment into which the sperm will
enter is very harsh and the vast majority die:
no energy source
very acidic
The male body provides these things to the sperm cell to
aid it on its journey to find the female gamete (the egg):
sugar
a basic solution to neutralize the acid
Why is the environment so harsh? What does evolution say?
So once sperm are formed and then sped on their way out of the vas
deferens by muscular contractions, they are mixed with three solutions
on their way, and then ejaculated into the female reproductive tract.
Seminal Vesicles:
fructose-rich fluid: energy for mitochondria
protaglandins: initiate female muscle contractions
Prostrate Gland:
alkaline (basic) fluid: neutralize the acids in the vagina
Bulbourethral Gland:
lubrication for penis to enter vagina and for sperm to move
more easily through the urethra
The resulting mixture is called Semen.
an ejaculation releases about 3 mL of semen
At puberty the hypothalamus
releases gonadotropin-releasing
hormone (GnRH).
GnRH stimulates the pituitary to
produce luteinizing hormone
(LH) and follicle stimulating
hormone (FSH)
LH causes the interstitial cells
to produce testosterone.
LH and FSH stimulate spermatogonia in the testes.
To much testosterone or INHIBIN triggers a negative feedback loop
which stops production of GnRH
If FSH was suppressed, but LH continued a man would be infertile but
not impotent.
Sperm production starts in boys at puberty. The production of
testosterone also triggers other secondary characteristics.
•Voice deepens
•Start to grow body hair
•Muscles start to develop
•height increases
•Testes drop