While coordination by the nervous system produces an immediate response, a different kind of coordination is brought about by the endocrine system. This system depends on chemicals called hormones, which are released from special glands called endocrine glands, into the bloodstream. The hormones circulate round the body in the blood and eventually reach certain organs called target organs. Hormones speed up or slow down or alter the activity of those organs in some way. After being secreted, hormones do not remain permanently in the blood but are changed by the liver into inactive compounds and excreted by the kidneys. Serious deficiencies or excesses of hormones production give rise to illnesses.
Most of the pancreas cells produce digestive enzymes but some of them produce hormones. The hormone producing cells are arranged in small groups call
Adrenaline is a hormone that is produced in the adrenal glands, more precisely in an inner zone called the adrenal medulla. The adrenal glands are attached to the back of the abdominal cavity, one above each kidney. In response to a stressful situation, nerve impulses are sent from the brain to the adrenal medulla, which releases adrenaline into the blood. As adrenaline circulates around the body in the blood, it affects a great many organs, as shown in the table below:
ed islets and secrete their hormones directly into the bloodstream. One of the hormones is called glucagons and the other is insulin.
Fat depots Conversion of fats to fatty acids Fatty acids available in blood, for muscle contraction No sensation
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