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MHT-CET : Biology Entrance Exam

MHT - CET : Biology - Hormonal Coordination Know More

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  • Endocrine system is formed of endocrine glands which are also called ductless glands.
  • The branch of biology which deals with the study of endocrine glands and functions of their hormones is called endocrinology. Thomas Addison is called the father of endocrinology.
  • The collective study of nervous system and endocrine system of body is called neuro-endocrine system.
  • Heterocrine glands are partly endocrine and partly exocrine. Exocrine part releases the secretions through duct while endocrine part releases hormones directly in the blood due to lack of duct.
  • The hormones are carried from the glands to the organs through blood. These organs on which the hormones act are called target organs.
  • The word hormone was coined by Starling in 1905.
  • Two English physiologists William M. Bayliss and Earnst H. Starling discovered the first hormone secreted by the mucosa layer of duodenum. This was called secretin and its action is to stimulate the secretion of pancreatic juices. But the first isolated hormone was insulin which was isolated from pancreas of dogs by Banting and McLeod.
  • Hormones may be amines, steroids or proteins.
  • Examples of amine hormones are thyroxine from thyroid gland, epinephrine and nor-epinephrine from adrenal gland.
  • Examples of steroid hormones are cortisol, corticosterone, etc. from adrenal gland, testosterone from testes, progesterone from ovaries.
  • Examples of proteinous hormones are TSH, FSH, LH, ACTH, etc. from pituitary gland; insulin and glucagon from pancreas; parathormone from parathyroid gland.
  • Characteristic Features of Hormones:

1.      They are released in blood and transported through blood.

2.      They are produced in very low concentration.

3.      They have low molecular weight, thus can easily pass through capillaries.

4.      They are inactivated or destroyed when their function is over.


  • The term 'hormone' was coined from the Greek word 'Hormaein' which means to excite. Starling in 1905 coined this word.
  • Thyroid gland is the largest endocrine gland (5 3 cm) in size and 25 gm in weight. Thyroid hormones regulate BMR, i.e., basal metabolic rate of body. They control rate of cell respiration as well as energy production in mitochondria. Thus, these hormones control mental, physical as well as sexual growth of body by Calorigenic effect. Thyroidless tadpole larva of frog does not undergo metamorphosis.
  • Exophthalmic goitre produced due to hyperthyroidism is also called Grave's disease.
  • Hashimoto's Disease: When thyroxine secretion becomes very less due to age factor or injury to thyroid gland, the antibodies are formed which destroy thyroid gland. This is called Hashimoto's disease.
  • Parathyroid glands are four in number. Two glands are present in each lobe of thyroid gland. These glands secrete parathormone (PTH) which increases calcium level in blood. Parathormone is also called Collip's hormone because it was reported by Phillip Collip in 1925.
  • Thyrocalcitonin and Parathormone are antagonistic to each other.
  • Adrenal gland shows two distinct regions, namely, adrenal cortex and adrenal medulla. Adrenal cortex secretes 40 different steroid hormones called corticoids.
  • Adrenal glands are also called '4-S glands' because they control sugar metabolism, salt retention, source of energy and sex hormone secretion.
  • Deficiency of mineralocorticoids causes Addison's disease during which sugar level in blood decreases, nervous depression, low blood pressure and bronze like skin colour appears.
  • Oversecretion of cortisol (glucocorticoids) causes Cushing's syndrome during which sugar level in blood rises, loss of weight, rise in blood pressure and swollen face, hands, etc. appears.
  • Sex corticoids stimulate secondary sexual characters of male type. Over secretion of these in female causes, virilism, in which male type secondary sexual characters such as hoarse voice, facial hair appear in the female.
  • Adrenalin (epinephrine) is secreted by adrenal medulla. This hormone has same biological effect as of sympathetic nervous system. Adrenalin is called emergency hormone because it prepares the body to face certain emergency conditions like fall in blood pressure, cold, pain, anger, injury, fear, etc. The adrenal glands are thus 'glands of emergency'.
  • Hypothalamus is the base of diencephalon. It shows neurosecretory cells which secrete oxytocin and vasopressin. These hormones are stored in the axons of neurosecretory cells which extend in the posterior lobe of pituitary gland.
  • Pituitary gland is very small (15 3 mm). It is called 'Master gland' or 'Master of endocrine orchestra' or 'Executive officer of hypothalamus'.
  • Melanocyte stimulating hormone secreted by pars intermedia controls synthesis and dispersal of melanin in the skin of fish, amphibians and causes darkening of skin.
  • Adenohypophysis of pituitary is a pharyngeal outgrowth, and is thus called Rathke's pouch.
  • Pineal body is a very small knob-like structure present in the mid brain. It secretes melatonin hormone, which controls development and concentration of melanin of skin of frog-making the skin lighter in colour.
  • Pancreas is a heterocrine gland because it is partly endocrine and partly exocrine in function. Islets of Langerhans form the endocrine part while the acini form the exocrine part of gland. Islet of Langerhans show three types of cells, namely, alpha cells secreting glucagon, beta cells secreting insulin and gamma cells which are precursors of alpha and beta cells.
  • Glucagon and insulin are antagonistic hormones.
  • Ovaries secrete three female hormones, namely, estrogens, progesterone and relaxin.
  • Progesterone is secreted by corpus luteum while relaxin is secreted by corpus albicans. Estrogen is secreted by graafian follicles.
  • Leydig's cells of testes produce testosterone which controls secondary sexual characters and growth of secondary sex organs.
  • Contraceptive pills contain progesterone and estrogens which check ovulation and pregnancy in female.

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