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How do hormones travel from endocrine glands to target tissues?

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human endocrine system The principal glands of the female and male human endocrine systems.

Hormones travel from endocrine glands to target tissues primarily through the bloodstream. Most hormones are secreted into the general circulation to reach distant target tissues.12

In the blood, hormones exist in two states: as free, unbound molecules or bound to specific transport proteins produced by the liver. While bound hormones act as a reservoir to maintain stable concentrations, only the free, unbound hormone can exit the circulation to bind with receptors on or within target cells.12

Additionally, the body utilizes specialized portal circulations for more direct transport:
* Hypothalamic-hypophyseal portal circulation: Directs neurohormones from the hypothalamus to the anterior pituitary gland.2
* Hepatic portal circulation: Transports hormones from the pancreas, such as insulin and glucagon, directly to the liver before they enter general circulation.2