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Endocrine glands make chemicals called hormones and pass them straight into the bloodstream. Hormones can be thought of as chemical messages. From the blood stream, the hormones communicate with the body by heading towards their target cell to bring about a particular change or effect to that cell. The hormone can also create changes in the cells of surrounding tissues (paracrine effect). The endocrine system works with the nervous system and the immune system to help the body cope with different events and stresses. This branch of medicine – relating to the study of the endocrine system – is called endocrinology and is practiced by endocrinologists. The field is rapidly expanding due to understanding of the cellular pathways that hormones stimulate and the discovery of new hormones and their actions. Exocrine glandsAn exocrine gland, unlike an endocrine gland, is a gland that secretes substances (electrolytes, proteins or enzymes) straight to a target site via ducts or tube. Some examples include:
The pancreas is both an endocrine and exocrine organ. It releases certain enzymes to aid in digestion delivered to the gut via the pancreatic duct. The endocrine pancreas also releases hormones such as insulin and glucagon, which are hormones predominantly related to glucose metabolism, into the blood stream. Functions of the endocrine systemSome of the roles of the endocrine system include:
How hormones workA hormone will only act on a part of the body if it ‘fits’. A hormone can be thought of as a key, and its target site (such as an organ) has specially shaped locks on the cell walls. If the hormone fits the cell wall, then it will work. The hormones can set off a cascade of other signaling pathways in the cell to cause an immediate effect (for instance, insulin signaling leads to a rapid uptake of glucose into muscle cells) or a more delayed effect (glucocorticoids bind to DNA elements in a cell to switch on the production of certain proteins, which takes a while to produce). The endocrine system is a tightly regulated system that keeps the hormones and their effects at just the right level. One way this is achieved is through ‘feedback loops’. The release of hormones is regulated by other hormones, proteins or neuronal signals. The released hormone then has its effect on other organs. This effect on the organ feeds back to the original signal to control any further hormone release. The pituitary gland is well known for its feedback loops. Endocrine glands and organsThe main glands and organs of the endocrine system include:
Other lesser known endocrine organs include:
Problems of the endocrine systemNumerous problems can occur in the endocrine system. These can be considered as excessive or deficient hormone production. Endocrine organs are also prone to tumours (adenomas) which can over produce hormones. Some problems of the endocrine system include:
Where to get help
Things to remember
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This page has been produced in consultation with and approved by:
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