HORMONES CLASSIFICATION AND MECHANISM OF ACTION

HORMONES

1. HORMONES AND ITS CLASSIFICATIONS B.MURUGAVENI I MSC BIOCHEMISTRY ROLL NO: 23PSBCH11 REG NO:23701511

2. WHAT’S HORMONE? : C hemical messengers that are secreted directly into the blood, which carries them to organs and tissues of the body to exert their functions . organic substances, produced in small amounts by specific tissues (endocrine glands), secreted into the blood stream to control the metabolic and biological activities in the target cells.

3. PROPERTIES OF HORMONES : 1.Hormones are produced by a specialized glands and are secreted directly into the blood stream . 2.Hormones are transported by the blood stream from the endocrine cells to serve as ' chemi-cal messenger' which act on target cells or organs by regulating the rates of specific metabolic reactions . 3.Hormones exert their effects not where they are locally produced, but on other tissues of the body . 4.Hormones are required in very small amounts and their effect may be excitatory or inhibitory depending upon their concentration and the physiological state of the responding tissue. 5.Hormones belong to different types of chemical structure. They may be steroids, proteins, peptides or amino acid derivatives.

4. FUNCTIONS : There are many types of hormones that act on different aspects of bodily functions and processes. Some of these include : Development and growth Metabolism of food items Sexual function and reproductive growth and health Cognitive (mental) function and mood Maintenance of body temperature and thirst

5. CLASSIFICATION OF HORMONES: Hormones can be classified according to their • Chemical nature , • Mechanism of action , • Nature of action , • Stimulation of Endocrine glands and • Effects of hormones

6. CHEMICAL NATURE OF HORMONE : Based on the chemical nature the hormones can be categorized into three groups; Protein or peptide hormones e.g. insulin, glucagon, antidiuretic hormone,oxytocin . Steroid hormones e.g. glucocorticoids, mineralocorticoids, sex hormones. Amino acid derivatives e.g. epinephrine, norepinephrine, thyroxine (T4), triidothronine (T3). But more specifically it is divided into six classes , they are hormones,steroid,amines , peptide, glycoprotein and eicosanoid.

7. GROUP I HORMONES : Group I hormones includes group of lipophilic hormones that are usually derived from cholesterol (except T, and T₁ ). Steroid hormones are lipophilic (fat-loving) - meaning they can freely diffuse across the plasma membrane of a cell . bind to receptors in either the cytoplasm or nucleus of the target cell, to form an active receptor-hormone complex. This activated complex will move into the nucleus and bind directly to DNA, acting as a transcription factor for gene expression . DNA  mRNA  protein causes biochemical changes in the cell. Examples of steroid hormones include those produced by the gonads (i.e. estrogen, progesterone and testosterone)

8. GROUP II HORMONES : Group II hormones include peptide hormones. A re hydrophylic and lipophobic (fat-hating) - meaning they cannot freely cross the plasma membrane. They bind to receptors on the surface of the cell, which are typically coupled to internally anchored proteins (e.g. G proteins ). The receptor complex activates a series of intracellular molecules called second messengers, which initiate cell activity. This process is called signal transduction, because the external signal (hormone) is transduced via internal intermediaries. Examples of second messengers include cyclic AMP (CAMP), calcium ions (Ca2+), nitric oxide (NO) and protein kinases. The use of second messengers enables the amplification of the initial signal (as more molecules are activated ) Peptide hormones include insulin, glucagon, leptin, ADH and oxytocin

9. NATURE OF HORMONE ACTION : a.Local hormones- These hormones have a specific local effect through paracrine secretion, for example, hormone testosterone. b.General hormones- These are hormones transported through circulation to the distal target tissue/organ examples are thyroid hormones and insulin.

10. STIMULATION OF ENDOCRINE GLAND : a)Tropic hormones- hormones that stimulate other endocrine gland for secretion examples are TSH which stimulate secretion of thyroid gland for the production of thyroid hormones b) Nontropic hormone- hormones that usually exert their effect on non-endocrine target tissues examples of these hormone are Thyroid hormone which increases the rate of oxygen consumption and metabolic activity of different cells in the body.

11. TROPIC HORMONES : Tropic hormones: 1 . Their primary function is to act at different endocrine glands than those from which are secreted, maintaining their integrity and regulating the secretion of other hormones . 2 . In the absence of these hormones their endocrine target tissues lose their structural integrity and stop secreting their hormones . 3.Example: Thyroid-stimulating hormone (TSH ). Non-tropic hormones: 1. They do not regulate the secretion of other hormones. They directly stimulate target cells to induce effects.2.Example: Insulin, catecholamines .

12. EFFECT OF HORMONES : a.Kinetic hormones: These hormones may cause muscle contraction, pigment migration, glandular secretion and others, example of these hormones is epinephrine. b.Metabolic hormones: These are hormones that mainly caused changes in the rate of metabolism and balance the reaction examples include insulin, glucagon, parathyroid hormones . c.Morphogenetic hormones: These are hormones that mainly involved in growth and differentiation in the body, examples are Follicle stimulation hormones, luitenizing hormones and thyroid hormones.

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