The Endocrine System
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Introduction
to the Endocrine System
The
endocrine system refers to the hormone system of the body. H
ormones
are chemicals produced by living cells in very very small amounts. They are
transported around the body in the blood. Hormones regulate and co-ordinate
different organs in the body.
Click
on the picture for a large detailed image of the endocrine system.
Hormones
are classified into two groups
-
Peptides
-
Made of proteins
-
Fast acting
-
Short lived
-
E.g. Insulin and ADH
-
Steroids
-
Slow acting
-
Long lasting
-
Usually end in one
-
E.g. Testosterone and Progesterone.
Hormones
control themselves by a means of feedback control.
Feedback
control basically means that when the hormone is in large supply, the gland
stops making it.
When
the level of hormone is low, the gland secretes the hormone until the level
rises again.
The
Structure of the Endocrine system
The
endocrine system is made up with a series of glands located around the body. These
glands include:
-
Pituitary Gland
-
Thyroid Glands
-
Parathyroid Glands
-
Thymus
-
Pancreas
-
Adrenal Glands
-
Gonads
Each
of these glands produces hormones, which have a particular function in the body.
The
Pituitary gland is located in the hypothalamus (front of the brain) and is the
most important part of the endocrine system. The
Pituitary gland has two parts, the anterior and posterior.
The
Anterior part produces two hormones, ADH and Oxytocin.
ADH
is involved in water level control in the blood.
Oxytocin
controls lactation and is released from the pituitary when an animal is suckled.
The
Posterior part of the Pituitary produces a number of important hormones.
These include FSH (Follicle Stimulating Hormone), LH (Luteinizing Hormone),
Prolactin and Growth Hormones.
The
Pituitary also releases hormones which control the Adrenal and Thyroid glands.
The
thyroid glands are found on the trachea. The
main hormone produced is called thyroxine. This
hormone controls the growth and development of animals. Iodine is required for
its production.
Lack
of thyroxine causes deformation and retardation. The
glands swell if not enough hormone is produced this is called goitre in
humans. See the picture!!
These
are located on either side of the thyroid. They
produce two hormones: Parathormone and Calcitonin. These hormones control the
level of calcium, magnesium and phosphate in the body.
A
very small gland located on the neck. Has
some involvement in the production of lymphocytes, which are involved in immune
response.
The
Pancreas produces insulin.
It
is produced in the pancreas in the Islets of Langerhans.
Insulin
is required for the intake of glucose in cells and prevents the excess breakdown
of glycogen.
If
insulin is lacking, one outcome is the passing of glucose in the urine.
This
is called diabetes mellitus.
This
can cause coma because the brain needs glucose. Synthetic Insulin is now
available for diabetics.
It
must be injected because if it was eaten it would be digested.
The
adrenal glands are found near the kidney. They
produce over fifty different hormones which are vital for life.
Hydrocortisone is produced in the adrenal glands and is required to control
blood pressure and controls the loss of blood. Adrenalin is secreted from the
adrenal glands during stress. It redirects blood to the
head and increases the heartbeat. It makes the individual more acute
to their surroundings. It is usually secreted when frightened.
Another hormone called non-adrenalin, turns off the effects of adrenalin.
The gonads are the testes and ovaries. The hormones produced are involved in the reproductive systems of the animal. These include testosterone, oestrogen and progesterone. These hormones will be looked at in more detail in Animal Reproduction.
Quiz on this page coming soon
To find out more about the Reproductive System, click here!