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Hormones
are chemicals that are released into the blood by
endocrine glands
i.e. Glands with no ducts. Hormones act on specific
target organs
that recognize them.
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The main endocrine glands in the body are the
hypothalamus, pituitary, pineal, thyroid, parathyroid
and
adrenal glands,
the
pancreas, ovaries
and
testes
.
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The
hypothalamus
is situated under the
cerebrum
of the brain. It produces or controls many of the hormones released by the pituitary gland lying adjacent to it.
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The
pituitary gland
is divided into two parts: the
anterior pituitary
and the
posterior pituitary
.
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The
anterior pituitary
produces:
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Growth hormone
that stimulates body growth
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Prolactin
that initiates milk production
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Follicle stimulating hormone
(
FSH
) that stimulates the development of
ova
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Luteinising hormone (LH
) that stimulates the development of the
corpus luteum
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Plus several other hormones
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The
posterior pituitary
releases:
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Antidiuretic hormone
(ADH) that regulates
water loss
and raises
blood pressure
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Oxytocin
that stimulates milk “let down”.
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The
pineal gland
in the brain produces
melatonin
that influences
sexual development
and
breeding cycles
.
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The
thyroid gland
located in the neck, produces thyroxine, which influences the
rate of growth
and
development
of young animals. Thyroxine consists of 60%
iodine
. Lack of iodine leads to
goitre
.
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The
parathyroid glands
situated adjacent to the thyroid glands in the neck produce
parathormone
that regulates blood
calcium
levels and the excretion of
phosphates
.
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The
adrenal gland
located adjacent to the kidneys is divided into the outer
cortex
and the inner
medulla
.
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The
adrenal cortex
produces:
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Aldosterone
that regulates the blood concentration of
sodium and potassium
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Cortisone
and
hydrocortisone
that affect
glucose, protein
and
fat
metabolism
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Male and female
sex hormones
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The
adrenal medulla
produces
adrenalin
responsible for the
flight, fright,
fight
response that prepares animals for emergencies.
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The
pancreas
that lies in the first bend of the small intestine produces
insulin
that regulates blood
glucose
levels.
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The
ovaries
are located in the lower abdomen produce 2 important sex hormones:
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The
follicle cells
of the developing ova produce
oestrogen
, which controls the development of the
mammary glands
and prepares the uterus for pregnancy.
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The
corpus luteum
that develops in the empty
follicle
after ovulation produces
progesterone
. This hormone further prepares the
uterus
for pregnancy and maintains the pregnancy.
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The
testes
produce
testosterone
that stimulates the development of the
male reproductive system
and
sexual characteristics
.