THE ENDOCRINE SYSTEM
The endocrine is a body control system. It affects bodily activities by releasing chemical messages, hormones,
into the blood stream. It contains 2 types of glands, the endocrine and exocrine glands.
Exocrine glands secrete their products into ducts. The ducts then carry the secretions into body cavities or to
the body's surface. They include sweat, sebaceous, mucous and digestive glands.
Endocrine glands are ductless glands and secret their products directly into the blood. They include the
pituitary, thyroid, parathyroids, adrenal, and pineal glands as well as the pancreas, ovaries, and testes.
Hormones are chemical substances that function to maintain the homeostasis (balance) of the body by
stimulating changes in the cells in body organs.
Pituitary gland regulates many body activities and nicknamed the 'master gland'. It is located at the base of
the brain, in an area called the hypothalamus. It produces many hormones the main one being the Human
Growth Hormone (HGH), which causes growth of cells and the body.
Thyroid gland is situated just below the larynx and has two lobes on either side of the trachea. The principal
hormone it produces is called thyroxine. Thyroxine controls metabolism by increasing the rate at which
carbohydrates are burned and proteins and fats are broken down. It also helps regulate growth.
Parathyroid glands are attached to the outer surface of the thyroid gland. They release the parathyroid
hormones (PTH). PTH control the homeostasis of the blood, especially calcium and phosphate.
The adrenal glands are located just above each kidney. They are divided into the outer adrenal cortex and the
inner adrenal medulla. The adrenal cortex secretes hormones called corticosteroids, which have many
functions including anti-inflammatory functions. The adrenal medulla secretes i) adrenalin and ii) noradrenaline
both of which affect the central nervous system.
The pineal gland is located in the brain. It secretes at least one hormone, melatonin, which appears to affect
the secretion of hormones by the ovaries. Its other functions are somewhat obscure
The pancreas is both an exocrine and endocrine gland. The endocrine portion consists of clusters of cells
called the Islets of Langerhan. It secrets insulin a hormone which controls the blood sugar level.
The gonads are the ovaries and the testes. The ovaries secrete oestrogens and progesterone, and the testes
secrete testosterone.
HYPO AND HYPER SECRETION - Hypersecretion is oversecretion while hyposecretion is undersecretion of
hormones. Each condition can cause many disorders.
Gland
pituitary
thyroid
parathyroid
Hormone
human growth
hormone
thyroxine
parathyroid
hormones
Problem
Hypersecretion
Disease
 Gigantism
 Acromegaly (where the bones of the face, hands and feet are
enlarged)
Hyposecretion
 dwarfism
causes swelling of the face, limbs, and hands, slow metabolism
and mental dullness. Congenital myxoedema is called cretinism
enlargement of the thyroid gland which can lead to the need for a
thyroidectomy.
characterised by an increased basal metabolic rate and increased
pulse, also exophthalmos which is the distension of the eyeballs
causes softening of the bone
Myxoedema
Hypothyroidism or
Goitre
Hyperthyroidism or
Grave’s disease
Hyperthyroidism
Hypothyroidism
pancreas
insulin
adrenal
corticosteroids
Endocrine 2000
Low insulin levels diabetes mellitus
High insulin levels
- hypoglycaemia
Cushing’s
syndrome
leads to spasmodic twitching and contractions of muscles which is
called tetany.
results in excess sugar in the blood - hyperglycaemia. Causes
damage to blood vessels and organs - kidneys and eyes.
characterised by fainting and coma
characterised by protein loss, fatigue, osteoporosis, diabetes and
oedema
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Endocrine 2000
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