The term hormone is got from the Greek word ‘horman’ and it means ‘to excite’ or ‘to activate’. Hormones act as chemical messenger involved in transmission of information to the target organs.
Classification of hormones
Based on chemical nature, hormones are classified into three groups.
- Protein or peptide hormones
Examples are insulin, glucagon, oxytocin, anti-diuretic hormone
- Steroid hormones
Examples are Glucocorticoids, mineralocorticoids, testosterone, estrogen, progesterone
- Amino acid derivatives
Examples are adrenaline, nor adrenaline, thyroxine, tri-iodothyronine
Based on receptor binding, they are classified into
- Group 1 Hormones
They are lipophilic hormones that bind intracellular receptors to form hormone-receptor complexes. Examples are estrogen, calcitrol, androgens, thyroxine.
- Group 2 Hormones
These are hydrophilic hormones unable to diffuse through plasma membrane. These act as primary messengers and transfers signals to secondary messengers. Examples are adenylate cyclase and phosphatidyl inositol.
Based on the site of production,
- Hormones of pituitary
Examples are growth hormone, thyroid stimulating hormone, oxytocin, vasopressin
- Hormones of thyroid gland
The hormones are thyroxine, tri-iodo thyronine, thyrocalcitonin
- Hormones of parathyroid
Parathormone and calcitonin are secreted in parathyroid gland
- Adrenal hormones
Corticosteroids and sex hormones are examples for this group
- Pancreatic hormones
Insulin and glucagon are secreted by islet of langarhans of endocrine pancreas
- Thymus gland hormone
Thymosin is secreted here which produces T lymphocytes
- Pineal gland hormones
Melatonin and an unknown substance which inhibits puberty
- Local hormones
Acetyl choline, serotonin, prostaglandins come under this group. They act as chemical mediators and act around the area of secretion. Hence they are known as local hormones.