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Haploid
gametes (sperm and ova) are produced by meiosis in the
gonads
(testes and ovaries).
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Fertilisation involves the fusing of the gametes to form a diploid
zygote
.
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The male reproductive system consists of a pair of
testes
that produce sperm (or
spermatozoa
), ducts that transport the sperm to the penis and glands that add secretions to the sperm to make semen.
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Sperm are produced in the
seminiferous tubules
, are stored in the
epididymis
and travel via the
vas deferens
or
sperm duct
to the junction of the bladder and the
urethra
where various accessory glands add secretions. The fluid is now called
semen
and is ejaculated into the female system down the
urethra
that runs down the centre of the penis.
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Sperm consist of a head, a midpiece and a tail.
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Infertility
is the inability of sperm to fertilize an egg while
impotence
is the inability to copulate successfully.
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The female reproductive system consists of a pair of
ovaries
that produce
ova
and
fallopian tubes
where fertilisation occurs and which carry the fertilised ovum to the
uterus
. Growth of the foetus takes place here. The
cervix
separates the uterus from the
vagina
, the birth canal and where the sperm are deposited.
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The
ovarian cycle
refers to the series of changes in the ovary during which the follicle matures, the ovum is shed and the
corpus luteum
develops.
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The
oestrous cycle
is the sequence of hormonal changes that occurs through the ovarian cycle. It is initiated by the secretion of
follicle stimulating hormone (F.S.H.),
by the
anterior pituitary gland
which stimulates the
follicle
to develop. The follicle secretes
oestrogen
which stimulates
mammary gland
development.
luteinising hormone (L.H.)
from the anterior pituitary initiates
ovulation
and stimulates the
corpus luteum
to develop. The corpus luteum produces
progesterone
that prepares the lining of the uterus for the fertilised ovum.
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Signs of oestrous
or heat differ. A bitch has a blood stained discharge, female cats and rats are restless and show the lordosis response, while cows mount other cows, bellow and have a discharge from the vulva.
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After fertilisation in the fallopian tube the
zygote
divides over and over by mitosis to become a ball of cells called a
morula
. Division continues to form a hollow ball of cells called the
blastocyst
. This is the stage that
implants
in the uterus.
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The
placenta, umbilical cord
and
foetal membranes
(known as the
placenta
) protect and provide the developing foetus with nutrients and remove waste products.