The word ‘Hormone’ is derived from Greek word ‘hormao’ which means “I impel” or “I arouse to activity”. William M. Bayliss and Ernest H. Starling (1904) termed that important chemical substance as hormone though it was first proposed by W. B. Hardy.
In animal physiology, it denotes a specific substance which is effective in a very low concentration and it is transported to other part of the organism from their site of synthesis, where they cause specific physiological effects. But the site of synthesis of plant hormone synthesis and their place of action is not differentiable although there are certain evidences indicating their effects are far away from the site of synthesis.
Hormones are active in minute amounts and act as chemical messengers. A hormone can cause a variety of response depending upon the nature of tissue or organ in which that hormone is acting. Plant hormones have been referred to as growth regulators or growth substances.
Definition of Hormone
Hormone is an organic substance which is produced naturally within the organism, controlling growth or other physiological functions at a site remote from its place of origin and active in minute amounts.
According to William M. Bayliss and Ernest H. Starling (1904), Hormone is a chemical agent released from one group of cells which travels through the body fluid to distant places to affect different group of cells.
Actually, hormone is the organic chemical substance synthesized by a specific organ or local group of cells and secreted into the body fluid such as tissue fluid or blood which carries it to other sites of the body where it exerts an effect on the activities of the cells is known as hormone.
Properties of Hormone
Chemical Nature of Hormones
Based on chemical nature, hormones may be proteins, steroids, peptides, or amino acid derives.
1. Steroid hormones
Testes, adrenal cortex, placenta and ovaries etc release steroid hormones such as testosterone, aldosterone, corticosterone, oestrogen and progesterone, etc.
2. Proteinaceous hormones
Pancreas and anterior lobe of pituitary glands secretes proteinaceous hormones. Such as growth hormone, Follicle-stimulating hormone (FSH), etc
3. Peptide hormones
Hormones which are composed of amino acids, known as peptide hormones. Such as Melanocyte stimulating Hormone (MSH), vasopressin, Anti-diuretic Hormone(ADH) and, Adrenocorticotropic Hormone (ACTH), etc.
Site of Formation of Hormone
In plants hormones are mainly formed in the meristematic tip of the coleoptiles, growing tips of the leaves, roots and in the buds.
In animals hormones are formed and secreted from the endocrine glands and local group of cells.
Site of Action of Hormone
Except few local hormones most of the hormones can not function at the place of origin of living bodies. They function on some distant tissues organs from its place of production. The function of different types of hormones takes place individually in minute amounts.
Due to over secretion or less secretion or non secretion of hormones, different types of diseases occur. In short it can be stated that hormones are different chemical substances which after producing in minute amounts in certain places of the living body, functions at a site remote from their site of synthesis.
Hormone as Chemical Messenger
As messenger sends messages from one place to another place, similarly chemical substances like hormones after production in one part of an organism are transported to another part of the organisms, where they excite the organs or tissues of that part.
As hormone functions at a site far away from its place of origin, hence hormones are called chemical messenger. Hormones also play an important role in the chemical co-ordination of the living body.
Difference Between Hormones and Enzymes
Hormones are chemically of different types such as protein, steroid etc.
Enzymes are always protein in nature.
Hormones generally never act at their place of origin, they act at a site remote from their place of origin, exception-local hormones.
Enzymes after secreting within the living cells, influence the different types of chemical reactions within that cell.
Generally hormones are secreted from the endocrine glands such as pituitary, testes, ovaries, Thyroid glands, etc.
Enzymes are secreted from the exocrine glands such as salivary glands, sweat glands, etc.
Action of hormone is slow.
Action of enzyme is comparatively faster.
Hormones act as messenger because it triggers different functions in the body.
Enzyme act as catalyst which make acceleration the rate of a chemical reaction.
Hormone secretions are affected by the age.
Secretion of enzymes are not affected the age.
It controls the metabolic activities of the body.
It plays a part in metabolism in the body.
The value of pH or temperature does not affect on hormone to perform functions but some cases, it is effected by various external factors.
The value of pH or temperature effect on the functions of enzymes.
Hormones have low molecular weight.
Enzymes show higher molecular weight.
The functions of hormones do not depend on enzyme activities.
The functions of enzymes depend on hormone signaling.
Morphogenesis, especially secondary sex characters are regulated by the hormones.
Enzyme cannot regulate morphogenesis.
Hormones are diffusible by means of cell membrane.
Enzymes are non-diffusible by means of cell membrane.
Hormones are destroyed after their specific functions are over. They are excreted as soon as their functions are over.
Enzymes are never destroyed or become inactive after their specific functions are over. They remain unchanged at the end of the reaction.
Examples: Thyroxin, Auxin, FSH, ACTH, etc.
Examples: Amylase, pepsin, lipase, trypsin, etc.
Hormones are secreted from the endocrine gland playing a very important role in the body by influencing and regulating lots of functions. It is also called chemical messengers and help to trigger many important functions in the body.
You might also read: Hypophysis or Pituitary Glands