BIOCHEMISTRY - Main Regulators and Biological Fluids of the Human Body - 2016

2. HORMONES

Hormones are biologically active organic substances of diverse chemical structures produced by specialized Organs, namely Endocrine glands, which act as regulators of metabolic processes and physiological Functions. Currently, more than 50 of them are known. The term "hormone" was introduced by W. Bayliss and E. Starling in 1905 to describe an active substance (secretin) secreted by the intestinal mucosa, which enters the bloodstream, reaches the Pancreas, and stimulates it to secrete pancreatic juice.

Hormones are produced by endocrine glands (ductless glands), which lack excretory ducts but are rich in a capillary network, allowing hormones to enter the bloodstream directly.

The endocrine glands include (Fig. 7):

1) cerebral appendages:

 a) superior — Pineal Gland,

 b) inferior — Pituitary Gland;

2) Hypothalamus;

3) Thyroid Gland;

4) Parathyroid glands;

5) Thymus gland;

6) Adrenal Glands;

7) islets of Langerhans in the pancreas;

8) Gonads.

Once formed in the endocrine glands, many non-protein hormones bind to Proteins, which enhances their resistance to degrading agents and somewhat alters their effects. Hormone-Structure/178.html">Protein Complexes can also serve as transport or reserve forms of hormones, exerting their effects only after dissociating from the carrier protein.

Class="center">Fig. 7. Endocrine glands

The Cells of the organs where hormones exert their action (target organs) contain specific proteins known as Hormone Receptors. These proteins possess The ability to specifically bind only to certain hormones; therefore, target organs selectively Histology/2.html">EXTRACT FROM THE circulating Blood only those hormones required by the given organ to regulate its METABOLISM. This mechanism enables hormones to act with high selectivity on specific organs. Receptor proteins are located either inside the cells or embedded in The Cell membrane.

2.1. General Properties of Hormones

1. Action at a distance from the site of synthesis.

2. Specificity of action.

3. Short duration of action, i.e., high rates of synthesis and inactivation.

4. High biological activity. For instance, hormones exert powerful effects on the body at concentrations of 10 - 6 -10 -11mol/L. They enhance the mobilization of Energy Sources from storage depots and maintain their levels in the blood, preserve a constant Electrolyte Composition of blood and Tissues, stimulate The activity of the respiratory and circulatory systems, and accelerate oxidative and biosynthetic processes. The difference between hormones and Enzymes is that hormones do not participate in metabolic reactions, whereas the difference between hormones and Vitamins is that hormones are not utilized for the synthesis of Enzymes and Coenzymes.

5. Hormones act as messengers in transmitting information from the Central Nervous system to the cell.