Control and coordination in our body is brought about by two main systems ie Nervous system and Endocrine system. Actions of nervous system are mediated through nerves, where as actions of endocrine system are mediated through hormones. Because of large diffusion distances and circulation delays involved, hormonal responses are generally slower in onset than those mediated by nerves. They are also more persistent, since removal of hormone from blood stream may take some time after secretion has stopped.
Endocrine system is a system of isolated glands that pour their secretions directly into venous blood or lymph for transportation to different organs in order to control their functioning , metabolism, growth, differentiation etc. Like other communication networks, endocrine system contains transmitters, signals and receivers that are called hormone producing cells, hormones and receptors.
Endocrine system in association with nervous system functions in a coordinated way to maintain homeostatic state within the body.
Endocrinology is study of endocrine glands, hormones and hormonal disorders. Thomas Addison is father of endocrinology. The first endocrine disease reported was Addison’s disease (1855) caused by destruction of adrenal cortex. Berthold laid foundation of endocrinology
The word endocrine is derived from a Greek word , which means “ i separate within”. A person who specialises in endocrinology is an endocrinologist. The discovery of hormone production by brain led to the emergence of a new discipline called Neuroendocrinology .
A gland is any cell or tissue which is secretory in nature. (Liver is largest gland of body. Pancreas is second largest gland). On the basis of presence or absence of ducts glands are of following types.
Exocrine glands (have ducts) : Those glands which have a duct for pouring their secretion onto the body surface or into the body, eg. sweatglands, tear glands, gastric glands, intestinal glands, liver, mammary glands.
Endocrine glands (ductless glands) : Those glands which do not have ducts and directly pour their secretion into blood. These are also calledglands of internal secretion. e.g. Pituitary, Thyroid, Adrenal etc.Secretions of endocrine glands are called Hormones
Heterocrine glands (mixed glands) : These consist of both exocrine tissue and endocrine tissue. The exocrine tissue sends its secretion orproduct by way of a duct and the endocrine tissue discharges its secretion into blood. Eg. ovaries, testes, pancreas.