Endocrine glands secrete certain chemicals known as
hormones. Hormones are extremely important secretions for
the regulation of body activities.
Differences between Endocrine and Exocrine glands
NEED FOR THE REGULATION OF BODY ACTIVITIES
The activities in our body are highly complex and they need to be so regulated that
every activity takes place at a proper time and in a correct sequence. For ex: the
gastric juice, bile and pancreatic juice should be poured into the food canal only
when there is food in it.
It is brought about by chemical regulators called hormones (horma: to stir up // to
excite // to put into action).
Hormones are secretions from specific cells or glands in the body, and are carried
to all parts through blood, but their effect is produced in one or more specific parts
only.
Most hormones are secreted by special glands, the endocrine glands (endo:
inside, crine: secrete) meaning "secrete internally", also called ductless glands
because their secretions are poured directly into the blood and not through any
special duct.
Endocrine system: Endocrine system consists of several glands/glandular cells
which bring about the overall common function of chemical coordination in the
body. Almost all endocrine glands act in a coordinated manner. They activate each
other and work as a system of organs called endocrine system.
GENERAL PROPERTIES OF HORMONES
1. Hormones are secreted from their source (an endocrine gland) directly into the
blood.
2. They act on target organs or cells usually away from their source.
3. Hormones are not stored in the body and are excreted from the system.
4. Hormones produced in one species usually show similar influence in other
species.
5. They are produced in very small quantities and are biologically very active.
6. Chemically, some hormones are peptides which are water soluble, some are
amines again water-soluble and some are steroids which are lipid-soluble.
7. Their excess (hypersecretion / oversecretion) or deficiency (hyposecretion /
undersecretion), both may lead to serious consequences.
8. Hormones are not stored in the body and are excreted from the system.
ENDOCRINE GLANDS
The principle endocrine glands in the human body
are:
1. Adrenal
2. Pancreas
3. Thyroid
4. Pituitary
1. Adrenal Glands
The adrenal glands are like caps
on the top of each kidney (ad:
near, renal: kidney). Each adrenal
gland consists of two parts –(i) a
central medulla (ii) a peripheral
cortex
(i) Adrenal medulla secretes adrenaline .It is a hormone, which prepares the body
to meet any emergency situation, for "fight" or for "flight". Extra energy and
strength is provided to the body in that situation. Extra hormone is released into
the blood at the time of emotional stress. When excited or angry, our adrenals
produce a lot of adrenaline.
FUNCTIONS OF ADRENALINE- THE EMERGENCY HORMONE
• It increases heart beat accompanied by an increase in blood pressure.
• It increases blood supply to the muscles while decreasing it to skin and visceral
organs.
• More glucose is released into the blood by the liver (like putting more fuel into
the engine). [The final dash to win a race is under the influence of adrenaline].
(ii) Adrenal cortex secretes many hormones but the best-known hormone is
cortisone (which suppresses inflammation).
The cortical hormones are categorized as:
a. Mineralocorticoids: regulates mineral metabolism, especially Na and K+ ions.
b. Glucocorticoids: regulates carbohydrate, protein and fat metabolism.
In general, the cortical hormones:
• Increase blood glucose concentration.
• Influence fat and protein metabolism.
• Regulate salt and water balance in the body.
• Adapt the body to "stresses" such as extreme heat or cold, burns, infections, etc.
• Certain cortical hormones behave like sex hormones. They are both male as well
as female hormones in both sexes. An overgrowth of cortex in young children
leads to a premature sexual maturity.
Women with beard & Men with breasts!
If there is an overgrowth of adrenal cortex in a mature woman, she develops
certain male characteristics, such as, a beard, moustaches and deep male voice.
The condition is known as adrenal virilism (Latin Virilism: maleness).
If the overgrowth occurs in mature men, they may develop some feminine
characteristics, such as, enlargement of breasts.
Hyposecretion of cortisone from adrenal cortex causes Addison's disease.
Symptoms are loss of energy, skin pigmentation, loss of weight, nausea,
hypoglycemia, sensitivity to cold and pain, increased susceptibility to infections,
etc.
Hypersecretion of cortisone from
adrenal cortex causes Cushing's
syndrome. Symptoms are obesity,
hyperglycemia (higher blood
sugar), osteoporosis, weakness,
salt and water retention.
2. Pancreas:
Pancreas is both a duct gland as well as
a ductless gland.
As a duct gland, its secretion (pancreatic
juice) is poured into the duodenum for
digestion.
As a ductless gland, it has special groups of
hormone-secreting cells called Islets of
Langerhans, which are scattered in the entire
gland (islets: little islands). The islet cells
produce three hormones - insulin, glucagon and
somatostatin from three different kinds of cells
called beta, alpha and delta cells respectively.
(1) Insulin secreted by beta cells
checks rise of sugar level in blood.
This it does in two principal ways:
(i) It promotes glucose utilisation by
the body cells, thereby reducing the
blood sugar level.
(ii) It stimulates deposition of extra
glucose of the blood as glycogen in
liver and muscles.
Under-secretion of insulin
Insufficient secretion of insulin causes diabetes (more correctly diabetes mellitus
or hyperglycemia). The word "mellitus" means honey, referring to the passage of
sugar (glucose) in urine.
A diabetic person:
• has high concentration of sugar in blood
• excretes a great deal of urine loaded with sugar.
• feels thirsty because of the loss of water through too much urination.
• loses weight and becomes weaker and weaker.
Over-secretion of insulin
• Sugar level in the blood is lowered.
• Brain may enter a state of coma.
A similar thing may happen to a diabetic patient if an overdose of insulin is given -
the patient may become unconscious. This is called insulin shock or
hypoglycemia and a prompt bite of sweet biscuits or sugar candy is helpful.
(2) Glucagon is secreted from alpha cells. It stimulates the breakdown of glycogen
in the liver to glucose, thus it raises sugar level in the blood.
HORMONES OF ISLETS OF LANGERHANS
(in Pancreas)
a. Insulin (from beta cells)
- Promotes glucose uptake by body cells
- Stimulates deposition of extra glucose (as glycogen) in liver and muscles
Deficiency causes diabetes mellitus (sugar diabetes)
Excess causes nerve cell starvation & brain coma.
b. Glucagon (from alpha cells)
- Stimulates liver to convert
glycogen into glucose
3. Thyroid
The thyroid is a bilobed (butterfly-
shaped) structure situated in front
of the neck just below the larynx
The two lobes are joined by a
narrow isthmus (interconnection). It secretes two hormones thyroxine and
calcitonin. Thyroxine regulates the basal metabolism.
A. Undersecretion (Hypothyroidism): Insufficient secretion of thyroxine may lead
to three conditions simple goitre, cretinism and myxoedema.
(i) Simple goitre is the enlargement of the thyroid and is visible
as a swelling in the neck. This is due to insufficient quantity of
iodine in food. This condition is common in the people living in
hilly regions where iodine is deficient in soil and hence in the
food grown there.
(ii) Cretinism is a condition which affects the growth of children showing dwarfism
and mental retardation.
(iii) Myxoedema is a condition that affects an adult if his thyroid
does not function properly; in this condition, the person
becomes sluggish with swelling of the face and hands.
Thyroid deficiencies are common in many parts of India. Use of
iodised salt (containing iodine) in food is recommended
because iodine is the active
ingredient in the production of
thyroxine.
B. Oversecretion (Hyperthyroidism): Excess of thyroxine
secretion may also cause a kind of goitre called
exophthalmic goitre (exo: outward, ophthalmos: eye).
A person having the problem of oversecretion shows:
• a marked increase in metabolic rate,
• rapid heartbeat,
• shortness of breath;
• eyes are protruded, and
• forms a goitre in the neck.
4. Pituitary
The pituitary gland is a small projection
(about the size of a pea) which hangs from
the base of the mid-brain below
hypothalamus . It is popularly called the
master gland because it seems to control
practically all other endocrine glands.
Pituitary gland has two distinct lobes, the anterior pituitary and posterior pituitary.
The front part of the posterior pituitary is different from the rest of the lobe and is
called the intermediate lobe. The intermediate lobe is almost absent in humans but
much larger and more functional in some lower animals.
A. HORMONES FROM ANTERIOR PITUITARY
Some important hormones produced by the anterior lobe
are as follows:
1. Growth hormone (GH) is essential for normal growth. It is
also called somatotropin (somatic: body, tropic:
stimulating).
• The deficiency of GH in childhood results in dwarfism.
• The oversecretion in childhood results in gigantism.
• If oversecretion of the growth hormone suddenly occurs in an adult, there is an
excessive growth of bones in the face (particularly the jaws) and in the hands and
feet. The person develops a large nose and thick lips. This condition is called
acromegaly
2. Thyroid stimulating hormone (TSH) activates thyroid to secrete thyroxin.
3. Gonad stimulating (Gonadotropic) hormones regulate the activities of the testes
and ovaries.
4. Adrenocorticotropic hormone (ACTH) regulates the activity of adrenal cortex.
B. HORMONES FROM POSTERIOR PITUITARY
The posterior lobe produces two hormones named vasopressin and oxytocin.
1. Antidiuretic hormone (ADH), also called vasopressin, constricts blood
vessels with rise in blood pressure.
2. Deficiency of ADH causes diabetes insipidus (water diabetes) in which
urination is frequent and copious, resulting in loss of water from the body
and the person becomes thirsty.
2. Oxytocin: stimulates vigorous contractions of the uterus in a pregnant mother,
leading to the birth of the baby. It also stimulates milk ejection.
