Hormones in Animals
Hormones are chemicals formed in one part of the body which are translocated by circulatory system to another part for stimulating, coordinating or inhibiting one or more processes. They are also called chemical messengers or informational molecules. The cells on which, hormone acts are called target cells. Organ, tissue or a cell that produces a secretion for performing a particular function is called gland. Depending upon their nature, glands are four of types-exocrine, endocrine, heterocrine and mixed organs.
Exocrine Glands They are glands which pour their secretion through a duct, e.g., sweat glands, salivary glands.
Endocrine Glands They are ductless glands which pour their secretion into circulatory system for reaching a target site, e.g., thyroid, adrenals.
Heterocrine Glands They are also called mixed glands as they produce both endocrine (hormonal) and exocrine (metabolic) secretions, e.g., pancreas.
Mixed Organs They are organs which besides having a metabolic or cryptogenic function also produce hormones, e.g., testes, ovaries.
Characteristics of Hormones
- Hormones are produced by endocrine or ductless glands.
- Hormones are poured by endocrine glands into the circulatory system for transport to target cells.
- Hormones are non-nutrient chemical substances.
- They function as chemical messengers or informational molecules.
- Hormones are generally formed in response to specific stimuli.
- They inhibit or stimulate specific processes in target cells.
- Hormones are consumed in starting and stopping reactions in the target cells.
- They are effective in very low concentrations.
- Hormones are very specific in their action.
- Deficiency or excess of a hormone causes disorders.
- They are small molecules but belong to diverse groups like proteins, peptides, amino acid derivatives, steroids, etc.