The major endocrine glands in the body of man are given below:
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(i) Hypothalamus and pituitary gland:
The hypothalamus is located at the base of the brain. Its secretion controls the functioning of the pituitary.
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Its secretions are called releasing hormones. The pituitary gland is suspended from the hypothalamus. It is a small gland but produces a number of hormones. These hormones control the activities of other endocrine glands. So it has been known as the Master Gland.
(ii) Thyroid gland:
It is a two lobed gland and lies in front of the trachea. It produces hormone, thyroxine which contains iodine and regulates general metabolism.
It maintains the calcium level in the blood and bones. Deficiency of iodine in hormone causes swelling in the neck known as goitre.
(iii) Parathyroid gland:
These are four small glands, two on each side of the thyroid in the neck region. They produce Parathormone (calitonin).
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The proper development of bones depends upon this hormone.
(iv) Thymus gland:
This is large blabbed gland near the heart or in the upper part of the thorax. It is fully developed in young ones but as the animal grows, it is vanished. It accelerates metabolism and speeds up growth i.e., hastens sexual maturity.
(v) Pineal body:
It is located in the roof of the brain. Its removal retards the growth.
(vi) Adrenal gland:
They are two in number situated on the anterior end of each kidney. Each adrenal has two parts. The outer part is cortex and the inner is medulla. Cortex secretes a number of hormones which are divided into three groups.
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Medulla of adrenal gland secretes two hormones-adrenalin or epinephrine and nor- adrenalin or nor epinephrine.
These two hormones help the body to face and prepare emergency situation such as extreme danger or threats, by increasing the blood pressure, heart beat and glucose level of the blood.
(vii) Pancreas islets of lagerphones:
Pancreas is a double gland i.e., it is both an exocrine and endocrine gland. The endocrine part of pancreas is called islets of lagerphones.
The cells of islets of lagerphones secrete two hormones insulin and glucagons. The two hormones maintain the proper blood sugar level.
(viii) Gonads:
Both male and female organs, testes and ovary constitute the gonads and secrete male and female hormones respectively.
Testes:
Testes secrete a hormone testosterone from the interstitial cells (leydig cells). Testosterone regulates the development of secondary male sexual characters like pubic hair, depend voice, beard etc.
Ovary:
Ovaries produce estrogen and progesterone. These hormones stimulate the growth of female sex organs like uterus and ovaries. They are responsible for the secondary female sexual characters like development of mammary glands, onset of menstrual cycle etc.