The word hormone is derived from the Greek word
hormoein (which means ‘to excite’). Hormones are therefore, chemical substances
produced in one part of the body but have effect on cells in another part of
the body of the organism. The cells (or organs) they affect are called target
cells or organs. In other words ‘target cells/organs are ones that respond
specifically to a particular hormone. There are certain organs or structures in
the body that produce hormones. These hormone- producing organs are called
ductless or endocrine glands (endocrine means inward secretion unlike exocrine means
outward secretion). Therefore hormones are secreted directly into the blood
without passing through ducts (tubes).
hormoein (which means ‘to excite’). Hormones are therefore, chemical substances
produced in one part of the body but have effect on cells in another part of
the body of the organism. The cells (or organs) they affect are called target
cells or organs. In other words ‘target cells/organs are ones that respond
specifically to a particular hormone. There are certain organs or structures in
the body that produce hormones. These hormone- producing organs are called
ductless or endocrine glands (endocrine means inward secretion unlike exocrine means
outward secretion). Therefore hormones are secreted directly into the blood
without passing through ducts (tubes).
The Pituitary Gland
Is a pea-sized organ situated on the underside of the
brain, close to the hypothalamus. It is sometimes called the master gland
because of its effects on the other endocrine glands. It plays a central role
in the network of hormonal communication. It produces six major hormones and
the targets of these pituitary hormones are other endocrine glands. It secrete
hormone from both front part (anterior) and back part (posterior) of the gland.
brain, close to the hypothalamus. It is sometimes called the master gland
because of its effects on the other endocrine glands. It plays a central role
in the network of hormonal communication. It produces six major hormones and
the targets of these pituitary hormones are other endocrine glands. It secrete
hormone from both front part (anterior) and back part (posterior) of the gland.
Hormones
produced by the major Hormones-Producing (i.e endocrine) glands and their
primary functions
produced by the major Hormones-Producing (i.e endocrine) glands and their
primary functions
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Endocrine gland
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Hormones
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Pituitary hormones function
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1.
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Hypothalamus
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Corticotropin-releasing
hormones (CRH) |
Stimulates
the pituitary to release andrenocorticotropic hormones (ACTH) |
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Gonadotropins-releasing
hormones (GnRH) |
Stimulates
the pituitary to release lutenizing hormone (LH) and follicle-stimulating hormone (FSH) |
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Thyrotropin-releasing
hormones (TRH) |
Stimulates
the pituitary to release thyroidstimulating hormone (TSH) |
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Growth-releasing
hormones (GHRH) |
Stimulate
the release of growth hormone (GH) from pituitary |
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Somatotropin
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Inhibits
the release of GH from pituitary |
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Dopamine
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Inhibits
the release of prolactin from pituitary |
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2.
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Anterior
pituitary |
ACTH
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Stimulate
the release of hormones from the adrenal cortex |
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LH
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In
women, stimulate the production of sex hormones (i.e. estrogens) in the ovaries as well as during ovulation.
In men
stimulates testosterone production in the testes |
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FSH
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In
women, stimulates follicle development.
In men,
stimulates sperm production |
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GH
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Promotes
the bodies growth and development |
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TSH
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Stimulate
the releases of thyroid hormone |
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Prolactin
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Controls
milk production (i.e. lactation) |
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3.
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Posterior
pituitary
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Vasopressin
(ADH) |
Help
control the body’s water and electrolytes level |
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Oxytocin
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Promote
uterine contraction during labour and activates milk ejaculation in nursing women |
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4.
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Adrenal
cortex |
Cortisol
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Help
control carbohydrate, protein and lipid metabolism, protects against stress |
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Aldosterone
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Help
control the bodies water and electrolytes regulation |
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5.
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Testes
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Testosterone
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Stimulate
development of male reproductive organ; sperm production and protein anabolism |
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6.
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Ovaries
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Estrogen
(produced by the follicle) |
Stimulate
development of female reproductive organ |
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Progesterone
(produced by the corpus luteum) |
Prepare
uterus for pregnancy and mammary lactation |
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7.
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Thyroid
gland |
Thyroid
hormones (i.e thyroixine (T4) and triodothyronine |
Control
metabolic processes in all cells |
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(T3)
Calcitonin
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Helps
control calcium metabolism (i.e lower calcium levels in blood) |
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8.
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Parathyroid
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Parathyroid
hormones (PTH) |
Helps
control calcium metabolism (i.e increases calcium levels in blood) |
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9.
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Pancreas
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Insulin
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Helps
control carbonhydrates metabolism (i.e lower blood sugar levels) |
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Glucagon
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Helps
control carhydrates metabolism (i.e increases blood sugar levels) |
The Thyroid Gland
Is situated in the throat, lying in front of the
larynx (voice box). It secretes an iodine containing compound, thyroxine, which
regulates the rate of body metabolism. Under activity of the thyroid results in
a general slowing down of the rate of metabolism. In the young, this means that
growth, both physical and mental, is retarded. Serious thyroid deficiency in
children gives rise to a condition known as cretinism. Nowadays deficiency can
be detected at a very early stage and its ill effects avoided by administration
of thyroid extract. Adults who suffer from thyroid deficiency are generally
lethargic and dull. Sometimes fluid accumulates in the lymph spaces under the
skin, causing swelling. This condition is known as myxoedema.
larynx (voice box). It secretes an iodine containing compound, thyroxine, which
regulates the rate of body metabolism. Under activity of the thyroid results in
a general slowing down of the rate of metabolism. In the young, this means that
growth, both physical and mental, is retarded. Serious thyroid deficiency in
children gives rise to a condition known as cretinism. Nowadays deficiency can
be detected at a very early stage and its ill effects avoided by administration
of thyroid extract. Adults who suffer from thyroid deficiency are generally
lethargic and dull. Sometimes fluid accumulates in the lymph spaces under the
skin, causing swelling. This condition is known as myxoedema.
Thyroid deficiency may be due to a diet deficient in
iodine, and the thyroid gland enlarges to form goitre. The condition is known
as endopthalmic goitre. This condition rarely occurs nowadays than it used to
be, because, in regions where iodine does not normally occur in sufficient
amounts, iodine is added to food or tablets taken. Table salt, for example, may
be iodized.
iodine, and the thyroid gland enlarges to form goitre. The condition is known
as endopthalmic goitre. This condition rarely occurs nowadays than it used to
be, because, in regions where iodine does not normally occur in sufficient
amounts, iodine is added to food or tablets taken. Table salt, for example, may
be iodized.
Over-activity of the thyroid causes a general rise in
metabolic rate. Growth in the young is increased. Adults become nervous, tense
and irritable. Treatment usually involves removal of part of the gland, which
often enlarges to form a goiter. The goiter is often accompanied by the
appearance of bulging eyes and is referred to as exophthalmic goitre.
metabolic rate. Growth in the young is increased. Adults become nervous, tense
and irritable. Treatment usually involves removal of part of the gland, which
often enlarges to form a goiter. The goiter is often accompanied by the
appearance of bulging eyes and is referred to as exophthalmic goitre.
The Parathyroid Gland
Consist of small patches of tissue embedded in the
thyroid. It secretes the parathyroid hormone (PTH) that functions to control
calcium balance.
thyroid. It secretes the parathyroid hormone (PTH) that functions to control
calcium balance.
The Adrenal Gland
Lies immediately above the kidney in man. It consists
of two parts (glands); an outer cortex and an inner medulla.
of two parts (glands); an outer cortex and an inner medulla.
The cortex produces hormones that regulate the
metabolism of glucose and sodium in the body. The medulla products two hormones
(adrenaline and noradrenalin) that prepares the body or the individual for
emergency action, for fight or fight, similar to the activities of the
sympathetic nervous system. The effects of the medulla hormones are widespread
and cause the following:
metabolism of glucose and sodium in the body. The medulla products two hormones
(adrenaline and noradrenalin) that prepares the body or the individual for
emergency action, for fight or fight, similar to the activities of the
sympathetic nervous system. The effects of the medulla hormones are widespread
and cause the following:
a) Increased heart and
breathing rate.
breathing rate.
b) Raised blood sugar
c) Redistribution of blood
away from the skin and gut capillary networks to the heart and skeletal
muscles.
away from the skin and gut capillary networks to the heart and skeletal
muscles.
d) Inhibition of digestive
activity
activity
e) Erection of hairs on the
skin
skin
f) Dilation of the pupil of
the eye
the eye
The Stomach
Produces hormones (gastrin) that stimulates secretion
of gastric juice that help in food digestion.
of gastric juice that help in food digestion.
The Duodenum (Intestine)
Produces three hormones. Secretin was the first hormones
to be identified. It is produced when acidic food from the stomach enters the
duodenum. Its secretion stimulates the pancreas to produce pancreatic
(digestive) juice.
to be identified. It is produced when acidic food from the stomach enters the
duodenum. Its secretion stimulates the pancreas to produce pancreatic
(digestive) juice.
The Pancreas
The pancreas within the islet of langerhans are four
types of cells which involved in regulation of blood glucose levels. Each type
of cell secretes a different type of hormone: α(alpha cell) which secrete
glucagon, increases glucose in the blood. β (beta cell) secrete insulin,
decrease glucose in the blood. δ (delta cell) secrete somatostation,
regulate/stop alpha and beta cells and γ (gamma cell) secrete pancreatic polypetide.
types of cells which involved in regulation of blood glucose levels. Each type
of cell secretes a different type of hormone: α(alpha cell) which secrete
glucagon, increases glucose in the blood. β (beta cell) secrete insulin,
decrease glucose in the blood. δ (delta cell) secrete somatostation,
regulate/stop alpha and beta cells and γ (gamma cell) secrete pancreatic polypetide.
The Gonads (Ovary and Testis)
The ovary produces the following 3 female hormones:
a) Oestrogen: stimulates the
development of female (secondary) sexual characteristics development of the egg
cell and growth of the uterus;
development of female (secondary) sexual characteristics development of the egg
cell and growth of the uterus;
b) Progesterone: Is the
pregnancy hormone that cause ovulation, uterine growth, etc
pregnancy hormone that cause ovulation, uterine growth, etc
c) Relaxine: relaxes pubic bone
ligaments before parturition.
ligaments before parturition.
The testis produces testosterone, a male hormone
responsible for sperm development and production and the development
(appearance) of male (secondary) sexual characteristics.
responsible for sperm development and production and the development
(appearance) of male (secondary) sexual characteristics.
The Placenta: Produces various hormones
that are concerned with its maintenance during pregnancy, e.g. the Human
chorionic gonadotropin (hCG)
that are concerned with its maintenance during pregnancy, e.g. the Human
chorionic gonadotropin (hCG)
Common Condition that
affects Endocrine System
affects Endocrine System
Human body undergoes charges, some natural and some
are not, this can affect the way the endocrine system works. Some of the
factors that affect endocrine organs includes aging, illness, stress, the
environment, and genetic.
are not, this can affect the way the endocrine system works. Some of the
factors that affect endocrine organs includes aging, illness, stress, the
environment, and genetic.
Aging: Despite age-related
changes, the endocrine system functions well in older people. However, some
changes occur because of normal damage to cells during the aging process and
genetically programmed cellular changes. These changes may alter the following:
hormone production and secretion, hormone levels circulating in blood,
biological activities, rhythms in the body, such as the menstrual cycle. Aging
process affects nearly every gland. For example the hypothalamus is responsible
for releasing hormones that stimulate the pituitary gland. During aging, there
is impaired secretion of some hypothalamic hormones. It also makes the
pituitary gland smaller and more fibrous and may not work as well.
changes, the endocrine system functions well in older people. However, some
changes occur because of normal damage to cells during the aging process and
genetically programmed cellular changes. These changes may alter the following:
hormone production and secretion, hormone levels circulating in blood,
biological activities, rhythms in the body, such as the menstrual cycle. Aging
process affects nearly every gland. For example the hypothalamus is responsible
for releasing hormones that stimulate the pituitary gland. During aging, there
is impaired secretion of some hypothalamic hormones. It also makes the
pituitary gland smaller and more fibrous and may not work as well.
Illness: May affect endocrine system
function in several ways: Acute or chronic conditions may
change endocrine function. Hormones are cleared from blood during circulation
to the target tissues. The liver and kidneys are primarily responsible for
clearing hormones. Several clearance processes become altered or slowed in
individuals who have chronic heart, liver, or kidney disorder.
function in several ways: Acute or chronic conditions may
change endocrine function. Hormones are cleared from blood during circulation
to the target tissues. The liver and kidneys are primarily responsible for
clearing hormones. Several clearance processes become altered or slowed in
individuals who have chronic heart, liver, or kidney disorder.
Pathologies: Create hormones imbalances
typified by either hyper secretion or hypo secretion.
typified by either hyper secretion or hypo secretion.
Stress: These include trauma
(severe injury) of any type, severe illness or infection. Intense heat or cold.
(severe injury) of any type, severe illness or infection. Intense heat or cold.
