Hormones are chemical messengers secreted in certain areas of the body by endocrine glands.

Characteristics of Hormones

 1)They are called chemical messengers as they act on target cells or organs of the body.

 2) They are produced in small quantities and their small amounts produce tremendous effect.

 3)They are transported to the target organs by blood.

 4)They are made of polypeptides or amino acids or steroids

 5)They cannot be stored as they are oxidized or destroyed easily.

 6)They are of low-molecular-weight so they can be easily absorbed by blood capillaries.

7)They are generally known antigenic,i.e. the body does not produce antibodies against them.

 8)They are soluble in water and blood and can diffuse through cell membranes.

 9)Excess or deficiency of hormones may result in physiological disorders.

 Functions of hormones

 1)growth, maturation and regeneration

2)reproductive activities

 3)metabolism and homeostasis

 4)Adaptation

Chemical nature of hormones

1)proteins or polypeptide hormones

 -Examples: insulin, glucagon, parathormone, oxytocin

 2)steroid(lipids) hormones

 -Examples:androgens, oestrogen, adrenocortical hormones

 3)Amino acid hormones

-Examples: adrenaline, epinephrine