HORMONE AND ITS ACTION

ROMI GUPTA

Term hormone was introduced by Starling and Bayliss in 1905.

Hormones are the chemical messengers produced by endocrine gland and transported by blood to other tissue or organ where these stimulate a change in some metabolic activity.

They are produced from by one type of cell and have regulatory effect on the activities of other type of cell or on itself.

The tissue or organ stimulated by a specific hormone are called Target Tissue/ Target organ.

HORMONES

Regulation of metabolic activities.

Controlling morphogenic activities.

Mental activities. Expression of

secondary sexual characters.

Integration and coordination of other endocrine glands.

FUNCTIONS OF HORMONE

Changing cell membrane permeability.

Activation of genes. Secondary messenger

hypothesis

MECHANISM OF HORMONE ACTION

Certain hormones change permeability of cell membrane for ions or substrate like Glucose and amino acids.

This changes metabolism of cell, accelerating or blocking the entrance of certain substrate into cells.

Eg. Glucogon, Glucocorticosteroid, Testosterone, Oestrogen,Vasopressin, etc.

CHANGING CELL MEMBRANE PERMEABILITY

Steroids are small molecules being highly soluble in lipids, easily pass through the cell membrane of target cell into cytoplasm.

Steroid, vitamin D, retinoid, and thyroid hormones enter target cells and alter gene expression by interacting with specific nuclear receptors.

Activated genes leads to synthesis of mRNA which in turn initiates synthesis of specific proteins.

ACTIVATION OF GENES

This theory was proposed by Sutherland for which he got noble prize in 1971.

According to this concept many of the protein polypeptides and amides type of hormones do not enter the cell because the plasma membrane is not permeable to them.

They acts as a primary messenger and deliver the chemical message from the endocrine gland to the membrane receptors present on the surface of target cell.

Membrane receptor is a mobile protein molecule having a specific recognition site for the specific hormone.

SECONDARY MESSENGER HYPOTHESIS

Hormone on reaching the target cell combines with specific membrane receptors.

↓ This combination promotes the

association of receptor moiety with regulatory protein (N-GDP) and facilitates its conversion to (N-GTP).

↓ N-GTP dissociate from the receptor

and interact with the enzyme Adenylate Cyclase present on the inner surface of cell membrane and activates it.

Activated Adenylate Cyclase catalyses the conversion of ATP to Cyclic AMP in cell cytoplasm.