Biology - Endocrine System



  • The endocrine system is study of the glands of an organism that secrete hormones directly into the circulatory system.

  • The organs through which the life running hormones are secreted are known as endocrine glands or simply ductless glands.

  • The hormone secreting glands are located in different parts of a human body (see the image given below).

Endocrine System
  • The scientific study of the endocrine system and its disorders is known as endocrinology.


  • The hormone is a complex but very important chemical substance released by the different glands in the body.

  • The hormone is mainly made up of amino acid, catecholemines, and steroids.

  • It is the hormone which is responsible for the overall growth and development; safety and security; behavior, sexual characteristics, and reproductive activities of a human body.

Types of Endocrine System

  • Following are the major types of endocrine system −

    • Hypothalamus

    • Pineal Gland

    • Pituitary Gland

    • Thyroid Gland

    • Parathyroid Gland

    • Adrenal Gland

    • Pancreas Gland

    • Reproductive Gland (Ovaries & Testes Glands)

  • Let’s discuss these glands in brief −


  • It is located at the base of the brain.

  • It releases Growth hormone-releasing hormone, Somatostatin hormone, etc., important for the growth.

Pineal Gland

  • It is located at the base of the brain.

  • It releases melatonin hormone helpful in lowering the core body temperature.

Pituitary Gland

  • With the size of a pea, the pituitary gland is found at the base of the human brain.

  • The average weight of pituitary gland is about 0.5 grams.

  • It is also known as hypophysis.

  • Following are the hormones secreted by the pituitary gland −

    • Growth hormone (somatotropin) − It is abbreviated as GH and it stimulates growth and cell reproduction.

    • Thyroid-stimulating hormone (thyrotropin) − It is abbreviated as THS and it stimulates iodine absorption by thyroid gland.

    • Adrenocorticotropic hormone (corticotropin) − It is abbreviated as ACTH and it stimulates corticosteroid and androgen.

    • Beta-endorphin − it inhibits perception of pain.

    • Prolactin − it stimulates milk synthesis and release from mammary glands.

Thyroid Gland

  • Thyroid gland is located just below the larynx in the throat (pharynx).

  • The hormone secreted by the thyroid gland is known as thyroxine.

  • Following are the important hormones secreted by the thyroid gland −

    • Triiodothyronine(T3) − It stimulated body oxygen and energy consumption. It also promotes protein synthesis.

    • Thyroxine − It increases the basal metabolic rate.

    • Calcitonin − It stimulates osteoblasts and bone construction.

Parathyroid Gland

  • It is located in the neck of a human body.

  • It releases parathyroid hormone that helps in regulating the amount of calcium in the blood as well as within the bones.

Adrenal Gland

  • Adrenal gland is found above the kidneys.

  • It releases the following major hormones −

    • Glucocorticoids − It stimulates gluconeogenesis and fat-breakdown in adipose tissue.

    • Mineralocorticoids − It stimulates active sodium reabsorption in kidneys.

    • Adrenaline − It increases the supply of oxygen and glucose to the brain and muscles.

    • Dopamine − It increases heart rate and blood pressure.

    • Enkephalin − It regulates pain.

Pancreas Gland

  • Pancreas gland is located in the abdominal cavity (behind the stomach).

  • Pancreas is a mixocrine gland, as it releases both enzymes and hormones.

  • It releases the following major hormones −

    • Insulin − It regulates the metabolism of carbohydrates, proteins, and fats.

    • Glucagon − It raises the concentration of glucose in the bloodstream.

    • Somatostatin − It inhibits release of insulin and glucagon.

Reproductive Gland

  • The reproductive gland is classified as Testes in Male and Ovary in Female.

  • Testes releases androgens (hormone) that help in strengthening muscle, increasing bone density, maturation of sex organs.

  • Ovary releases progesterone hormone that helps during pregnancy period.