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Endocrine system       Endocrine system is a group of glands that work together to control and coordinate the activities of animals. Glands are groups of cells which produce specific chemicals called hormones. The first hormone was discovered by English scientists William Bayliss and Ernest Straling in 1903. Hormones do a variety of jobs in our body.

Types of Glands

In animal body two types of glands are present:

    1. Exocrine glands and
    2. Endocrine glands

Exocrine Glands

       Those glands which secrete hormones via a duct directly into their target organ are called exocrine glands, e.g., live and salivary glands.

Endocrine Glands

       Those glands which do not have a duct and secrete hormones directly into the blood are called endocrine glands, e.g., pituitary glands, thyroid glands, adrenal glands, testes, ovaries etc. these glands are also known as ductless glands as they do not have ducts for secretion of hormones.

We will now discuss various endocrine glands present in human body.

1. Pituitary Gland (Master Gland)

       Pituitary gland is located just below the brain. Pituitary gland is also called master gland because the hormones secreted by pituitary gland regulate the working of all the other endocrine glands present in the body. In the body following hormones are secreted by pituitary gland.

    1. Growth Hormone (GH)
    2. Thyroid Stimulating Hormone (TSH)
    3. Follicle Stimulating Hormone (FSH)
    4. Anti-diuretic Hormone (ADH)
    5. Oxytocin

2. Thyroid Glands

       Thyroid gland is located in the neck in our body. The hormone produced by thyroid gland is called thyroxine. The function of thyroxine hormone is to increase metabolic rate and control growth of body. Deficiency of thyroxine hormone in the body may cause a disease called goiter.

3. Parathyroid gland

       These are four separate glands which are present on the backside of thyroid glands. These glands produce a hormone called parathormone which maintains the level of calcium and phosphate in blood.

4. Pancreas

       The pancreas lies below the stomach in our body. It secretes two hormones: insulin and glucagon. Insulin decreases the level of sugar in blood. In case of deficiency of insulin in the body, the level of sugar rises in the blood above the normal level. The rise of blood sugar level in the body causes a disease called diabetic mellitus.

The function of glucagon is opposite to that of insulin. It increases the level of sugar in blood.

5. Adrenal Gland

       The human body has two adrenal glands one above each kidney. The hormone secreted by adrenal glands is called adrenaline. It is also called emergency hormone, because it is produced under the conditions of fear, anger and stress. Adrenaline hormone prepares the body to face these situations by increasing body temperature, metabolic rate, heart beat and flow of blood to muscles and increase availability of glucose in blood to give us a lot of energy.

6. Testes

       These are two glands which are present only in males. These glands secrete male sex hormone called testosterone. Testosterone controls the development of male sex organs and male sex characters like beard, moustache, low pitch voice and more body hair.

7. Ovaries

       These are two glands which are present only in females. These glands secrete two female sex hormones called oestrogen and progesterone. The oestrogen controls the development of female sex organs and female sex characters such as high pitch voice, breasts and soft skin. The progesterone controls the formation of placenta and maintenance of pregnancy.

       It should be noted that the hormone testosterone produced from the testes of males and oestrogen and progesterone produced from the ovaries of females are also called sex hormones.

Test Your Understanding and Answer These Questions:

  1. What are sex hormones?

  2. What is endocrine system?

  3. What is diabetes? How is it caused?

  4. What are characteristics of hormones?

  5. Why pituitary gland is called master gland?

  6. Name the scientists who discovered hormones.

  7. List the functions of testosterone and oestrogen.

  8. Why adrenaline hormone is called emergency hormone?

  9. Give differences between endocrine and exocrine glands.

  10. Write the names of three hormones secreted from pituitary gland.

  11. What are endocrine glands? Why these are called ductless glands?

  12. Name the hormones secreted by thyroid, parathyroid and pancreas.

  13. How the hormones secreted by endocrine glands reach their target organs?

  14. Give the names of some endocrine glands present in human body. Also write the names of hormones produced by them and their functions.

  15. Write the name of a disease caused by deficiency of insulin and excess of thyroxine in the body.