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What is the Endocrine System?

Endocrine System is a network of ductless glands of internal secretion. The endocrine glands produce and/or store various hormones, which are secreted directly into the bloodstream.
The chief endocrine gland is the pituitary, situated beneath the brain and divided into two lobes.
The front (anterior) lobe produces a group of stimulating (tropic) hormones that are carried to other endocrine glands—the thyroid, adrenals and sex glands—to trigger hormone production.
Other anterior pituitary hormones exert their influence directly.
They include prolactin, which maintains milk production from the breasts, and growth hormone. The back (posterior) of the pituitary stores two hormones:
  • ADH (vasopressin) - is carried to the kidneys to help control body water content;  
  • Oxytocin - assists the contraction of the uterus during labor and encourages the flow of milk from the breasts after the birth of the baby.
 The pineal gland secretes melatonin. The function is uncertain in humans but may help regulate sexual development and menstruation.

Each of the adrenal glands, situated over the kidneys, is divided into an outer (cortex) and inner (medulla) region. The medulla makes the hormones adrenaline (epinephrine) and noradrenaline (norepinephrine), which help to prepare the body for "fight or flight" in response to danger. The hormones of the cortex include steroids involved in the metabolizing of sugars and proteins and in balancing body water content.

The thyroid gland lies below the voicebox or upper part of the windpipe. It secretes hormones that control the rate at which cells use nutrients. Attached to the back of the thyroid are the four small parathyroid glands whose hormones regulate the amounts of calcium and phosphate in the blood, an activity vital to bone building.

The amount of glucose in the blood is governed by cells in the pancreas, situated beside the duodenum.
The endocrine cells of the gland are clustered m small masses and make two hormones: glucagon, which raises blood glucose levels, and insulin, which decreases them.

The sex glands—ovaries in a female and testes in a male—produce hormones that control the production of mature sex cells and help to determine a person's total sexual development.

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