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Hormones- Properties, functions and classification

Hormones:

  1. Hormones are the chemical messenger produced in small amount by endocrine glands, secreted into blood stream to control metabolism and biological activities in target cell or organs.

Characteristics or properties of hormone:

  1. Low molecular weight
  2. Small soluble organic molecules
  3. Rate of diffusion is very high and are readily oxidized but the effect does not remains constant
  4. It is effective in low concentration
  5. Travels in blood
  6. It has its target site different from where it is produce and  is specific to a particular target
  7. Hormones are non-specific for organisms and may influences body process of other individuals





Functions of hormones

  1. Regulatory and homeostasis functions
  2. Maintain consistency of interior of cell
  3. Permissive functions; movement of substance in and out of cell
  4. Integrative function; usually balance two system
  5. Developmental function; helps in development of foetus

Classification of hormone

Hormones are classified

  1. On the basis of chemical nature
  2. On the basis of mechanism of hormone action
    1. Group I hormone
    1. Group II hormone





A. On the basis of chemical nature:

  1. Protein hormones: insulin, glucagon
  2. Steroid hormone: sex hormones, glucocorticoids
  3. Aminoacids derivatives hormones: epinephrine, nor epinephrine etc

B.  On the basis of mechanism of hormone action

1. Group I hormone (lipophilic hormone):

  1. These hormones are lipophilic in nature.
  2. They are mostly derivatives of cholesterol.
  3. These hormones binds to intracellular receptors
  4. Example: Steroid hormones, Estrogen, androgen, glucocorticoids, cholcalciferol, thyroxine etc





2. Group II hormones (water soluble hormone):

  1. These hormones binds to cell surface receptors and stimulates the release of certain molecules (secondary messengers) to perform biochemical functions

On the basis of secondary messengers group II hormones are of 3 types;

i. Secondary messenger is cAMP:

  1. eg. Adrenocorticotropic hormone, FSH, LH, PTH,ADH, calcitonin, glucagon,

ii. Secondary messenger is phosphotidylinocitol/calcium or both:

  1. eg. Acetylcholine, vasopressin, cholecystokinin, gastrin, gonadotropin releasing hormone, thyrotropin releasing hormone,
  2. Insulin, chorynoic somato mamotropin, epidermal growth factors, fibroblast growth factors, GH, prolactin

iii. Secondary messenger is cGMP:

  1. Atrial natriuretic peptide (ANP)