Classification of Hormones: 5 Categories

The following points will highlight the five categories of classification of hormones. The categories are: 1. According to Chemical Nature  2. On the basis of Mechanism of Action  3. According to Nature of Action 4. According to Effect 5. On the basis of Stimulation of Endocrine Glands.

Category # 1. According to Chemical Nature:

(a) Steroid Hormones:

These are made up of lipids, which basically derived from cholesterol, e.g. Testosterone, Estrogen, Proges­terone etc.

(b) Amine Hormones:

These hormones are made up of amines. Amine hor­mone is derivative of the amino acid tyrosine.

e.g. T₃, T₄, epinephrine, norepineph­rine.

(c) Peptide Hormones:

These hormones are made up of few amino acid resi­dues only and present as simple lin­ear chain.

e.g. Oxytocin and vasopressin both consist of only 9-amino acid residues only.

(d) Protein Hormones:

These hormones are also made amino acid residues which are much more in numbers. They represent primary, secondary and tertiary configuration.

e.g. Insulin, glucagon, STH etc.

(e) Glycoprotein Hormones:

These hor­mones are glycoprotein in nature. They are conjugated protein where carbohydrate groups are mannose, galactose, fucose etc.

e.g. LH, FSH, TSH etc.

(f) Eicosanoids Hormones:

The eicosanoids are small fatty acid derivatives with a variety of arachidonic acid.

e.g. Prostaglandins.

Category # 2. On the Basis of Mechanism of Action:

(a) Group I hormones:

These hormones bind to intracellular receptors to form hormone-receptor complexes (HRC), through which their biochemical functions are mediated. These hor­mones are lipophilic in nature and are derivatives of cholesterol (except T₃ and T₄). They are found in circula­tion in association with transport pro­teins and possess relatively longer half-lives (hours or day). e.g. Estrogen, Progesterone, Test­osterone, T₃, T₄ etc.

(b) Group II hormones:

These hormones bind to cell surface (plasma mem­brane) receptors and stimulate the release of certain molecules, namely the second messengers which in turn, perform the biochemical functions. Thus, hormones themselves are lipophobic in nature, usually trans­ported in the free form and possess short half-lives (in minutes).

Group II hormones are subdivided into three categories on the basis of chemical nature of second messen­gers:

(i) The second messenger is cAMP. e.g. ACTH, FSH, LH etc.

(ii) The second messenger is phospholipid/inositol/Ca⁺⁺.

e.g. TRH, GnRH, Gastrin etc.

(iii) The second messenger is un­known.

e.g. STH, LTH, Insulin, Oxytocin etc.

Category # 3. According to Nature of Action:

(a) Local Hormones:

These hormones have got specific local effects by paracrine secretion.

e.g. Testosterone.

(b) General Hormones:

These hormones are transported by circulation to the distal target organ/tissue.

e.g. Insulin, Thyroid hormone etc.

Category # 4. According to Effect:

(a) Kinetic Hormones:

These hormones may cause pigment migration, muscle contraction, glandular secre­tion etc.

e.g. Pinealin, MSH, Epinephrine etc.

(b) Metabolic Hormones:

These hor­mones mainly changes the rate of metabolism and balance the reac­tion.

e.g. Insulin, Glucagon, PTH etc.

(c) Morphogenetic Hormones:

These hormones are involved in growth and differentiation.

e.g. STH, LTH, FSH, Thyroid hor­mones etc.

Category # 5. On the Basis of Stimulation of Endocrine Glands:

(a) Tropic Hormones:

These hormones stimulate other endocrine glands for secretion.

e.g. TSH of pituitary stimulates se­cretion of thyroid gland.

(b) Non-tropic Hormones:

These hor­mones exert their effect on non-endocrine target tissues.

e.g. Thyroid hormone increases the O₂ consumption rate and metabolic activity of almost every cells.