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Control and coordination in our body are brought about by two main systems ie Nervous system and the Endocrine system. Actions of the nervous system are mediated through nerves, whereas actions of the endocrine system are mediated through hormones. Because of the 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 the removal of hormones from the bloodstream 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 to control their functioning, metabolism, growth, differentiation, etc. Like other communication networks, the endocrine system contains transmitters, signals, and receivers that are called hormone-producing cells, hormones, and receptors.
Endocrine system in association with the nervous system functions in a coordinated way to maintain a homeostatic state within the body.
Endocrinology is the study of endocrine glands, hormones, and hormonal disorders. Thomas Addison is the father of endocrinology. The first endocrine disease reported was Addison’s disease (1855) caused by the destruction of the adrenal cortex. Berthold laid the foundation of endocrinology
The word endocrine is derived from a Greek word, which means “I separate within”. A person who specializes in endocrinology is an endocrinologist. The discovery of hormone production by the brain led to the emergence of a new discipline called Neuroendocrinology .
A gland is any cell or tissue which is secretory. (Liver is the largest gland of the body. The pancreas is the second largest gland). Based on the presence or absence of ducts glands are of the 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. sweat glands, tear glands, gastric glands, intestinal glands, liver, mammary glands.
Endocrine glands (ductless glands): Those glands which do not have ducts directly pour their secretion into blood. These are also called glands 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 or product by way of a duct and the endocrine tissue discharges its secretion into blood. Eg. ovaries, testes, pancreas.