Hormones- Properties, functions and classification

Hormones:

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:

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

Functions of hormones

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

Classification of hormone

Hormones are classified

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

A. On the basis of chemical nature:

Protein hormones: insulin, glucagon
Steroid hormone: sex hormones, glucocorticoids
Aminoacids derivatives hormones: epinephrine, nor epinephrine etc

B.  On the basis of mechanism of hormone action

1. Group I hormone (lipophilic hormone):

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

2. Group II hormones (water soluble hormone):

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:

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

iii. Secondary messenger is cGMP:

Atrial natriuretic peptide (ANP)

Hormones- Properties, functions and classification