What are hormones?
A hormone may be defined as
“ A chemical released from endocrine gland that
travels some distance to target tissues to have a
biological effect”
 Secreted in very small amounts as slight excess /
deficiency leads to a diseased state.
Transported, usually, in the blood
Target cells have specific receptors
 Regulates cell reactions by affecting gene
expression (often gene transcription factors)
Hormones are body’s chemical messengers. They travel in
bloodstream to tissues or organs to help them do their
work and maintain homeostasis. They work slowly, over
time, and affect many different processes, including:
 Growth and development
 Metabolism – how your body gets energy from the
foods you eat
 Sexual function
 Reproduction
 Mood
Classification Of Hormones
Hormones can be classified according to their chemical
nature, mechanism of action, nature of action, their
effects, and stimulation of Endocrine glands.
a) Hormones may be classified Into six categories a/c to
their chemical nature:
1. Peptide
2. Protein
3. Glycoproteins
4. Steroid
5. Amine
6. Eicosanoid
Hormones
Source
Examples
Steroid hormones
Derived from cholesterol which belong to a •
chemical compounds known as steroids
•
Amine hormones
Hormones derived from the modification of
amino acids are referred to as amine hormones.
Typically, the original structure of the amino acid
is modified such that a COOH, or carboxyl, group
is removed, whereas the NH3 +, or amine group
remains. Amine hormones are synthesized from
the amino acids tryptophan or tyrosine.
An example of a hormone
derived from tryptophan is
melatonin, while tyrosine
derivatives include thyroid
hormones and
catecholamines.
Peptide hormones
These hormones are made up of only few
amino acid residues and they are usually
present themselves in form of a linear
chains
• Oxytocin
• Vasopressin
Protein hormones
These hormones are build up from large
number of amino acid residues
Insulin, glucagon and
somatotropins.
Glycoprotein hormones
These are conjugated protein bound to
carbohydrate which include galactose,
mannose, fructose
luteinizing hormones, follicle
stimulating hormones, thyroid
stimulating hormones
Eicosanoid hormones
Made up of small fatty acid derivatives
Prostaglandins
sex hormones
adrenal cortex hormones