Endocrine System

Endocrine System

Exocrine glands

Gland which have duct are called exocrine gland. Secretion of enzymes pass through it. Example - Digestive gland, Sweat gland, Mucous gland, Salivary gland etc.

Endocrine gland

These are ductless gland. Hormones are secreted by these gland. Hormones are sent to the different parts of the body through blood plasma. Example — Pituitary gland, Thyroid gland, Parathyroid gland etc.

1. Pituitary gland

It is situated in a depression of the sphenoid bone of the fore head. This is called sella - tunica.
» Its weight is approximately 0.6 grams.
» This is also known as master gland. Pitutary gland is controlled by hypothalmus.

The functions of the hormones secreted by Pituitary gland :
1. STH Hormone (Somatotropic hormone) : It controls the growth of the body especially the growth of bones. By the excessiveness of STH gigantism and acromegaly are caused, in which height of the human grows abnormally. Lack of STH causes dwarfism in human.
2. TSH Hormone (Thyroid Stimulating Hormone): It stimulates the thyroid gland to secrete hormone.
3. ACTH Hormone (Adrenocorticotropic Hormone) : It controls the secretion of adrenal cortex.
4. GTH Hormone (Growth Hormone) : It controls the functions of gonads.
5. LTH Hormone (Lactogenic Hormone) : Its main function is to stimulate secretion of milk in breasts for infants.
6. ADH Hormone (Antidiurelic Hormone) : It causes increase in blood pressure. It is helpful in maintaining the water balance in the body and reduce the volume of urine.

2. Thyroid gland

This is situated below the larynx on both side of respiratory trachea in throat of human.
» The hormones secreted by it are Thyroxine and Triiodothyronine.

Functions of Thyroxin
1. It increases the speed of cellular respiration.
2. It is necessary for the normal growth of the body particularly for the development of bones, hair etc.
3. The normal functions of reproductive organs depend on the activeness of thyroid gland.
4. It controls the water balance of the body in coordination with the hormones of pituitary gland.

Diseases Caused by the Deficiency of Thyroxin
1. Cretinism : This disease affects the children. The mental and physical retardness of the child.
2. Myxedema : In this disease which normally attack during youth the metabolism does not take place properly which causes reduction in heart beat and blood pressure.
3. Hypothyroidism : This disease is caused due to a chronic deficiency of thyroxin hormone. Due to this diseases the normal reproduction is not possible. Sometimes due to its deficiency, human becomes dumb and deaf.
4. Goitre : This disease is caused by the deficiency of iodine in food. In this disease the shape of the thyroid gland enlarges abnormally.

Diseases caused by the Excessiveness of Thyroxin
Exothalmic Goitre : In this disease eyes get bulging out of the eye socket with increased metabolic rate.

3. Parathyroid gland

This is situated in the right back of the thyroid gland of the throat. Two hormones are secreted by it.
(a) Parathyroid hormone : This hormone is secreted when there is a deficiency of calcium in the blood.
(b) Calcitonin : This hormone is released when there is excess of calcium in the blood is present.

Hence, hormone secreted by parathyroid gland controls the quantity of calcium in blood.

4. Adrenal gland

There are two parts of this gland –
(a) outer part is cortex
(b) inner part is medulla

Hormones secreted by cortex and their function:
(i) Glucocorticoids : This controls the metabolism of carbohydrate, protein and fat.
(ii) Mineralocorticoids : Its main function is reabsorption of ion by kidney ducts and to control the quantity of other on in the body.
(iii) Sex hormone : It controls the sexual behavior and secondary sexual characters.

Hormones secreted by Medulla and their function :
(a) Epinephrine - This is an amino add.
(b) Nor epinephrine-This is also an amino acid.
» The work of both the hormones is similar. These equally increase the relaxation and contraction of heart muscles. As a result, blood pressure increases and decreases.
» In case of sudden stop of heart beat, epinephrine is helpful in re-starting the heart beat.
» The hormone secreted by Adrenal gland is called fight flight, fright fight hormone.

5. Gonads

The following hormones are secreted by this :
(a) Estrogen : It completes the development of reproductive organs.
(b) Progesterone: It stimulates the thickening of uterus lining during ovarien cycle.
(c) Relaxin : During pregnancy it is found in uterus and placenta. This hormone smoothens the pubic symphysis and it widens the uterine cervix so that a child is delivered easily.

(2) Testes
The hormone secreted by it is called testosterone. It motivates the sexual behaviour and growth of secondary sexual characters.