Hormones
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
When the level of blood sugar falls, no insulin is secreted allowing the level to return to normal. Two forms of diabetes are recognized, juvenile-onset and adult-onset diabetes. It may rise to such a high level that it is excreted in the urine or fall so low that the brain cells cannot work properly and the person goes into a coma. All diabetics need a carefully regulated diet to reduce the intake of carbohydrates and keep the blood sugar within reasonable limitsAdrenalineAdrenaline is a hormone that is produced in the adrenal glands, more precisely in an inner zone called the adrenal medulla. If the concentration of blood sugar increases (e. If anything goes wrong with the production or function of insulin, the person will show the symptoms of diabetes. In response to a stressful situation, nerve impulses are sent from the brain to the adrenal medulla, which releases adrenaline into the blood. after a meal), insulin is released from the islet cells. In both forms of diabetes, the patient is unable to regulate the level of glucose in the blood. The adrenal glands are attached to the back of the abdominal cavity, one above each kidney. One of the hormones is called glucagons and the other is insulin. ed islets and secrete their hormones directly into the bloodstream. As adrenaline circulates around the body in the blood, it affects a great many organs, as shown in the table below:Organ Effects of adrenaline Biological advantage Effect or sensationHeart Beats faster Sends more glucose and oxygen to the muscles Thumping heartBreathing centre of the brain Faster and deeper breathing Increased oxygenation of the bloodRapid removal of carbon dioxide PantingArterioles of the skin Constricts them Less blood going to the skin means more is available to the muscles Person goes palerArterioles of the digestive system Constricts them Less blood for the digestive system allows more to reach the muscles Dry mouthMuscles of alimentary canal Relax Peristalsis and digestion slow downMore energy available for action 'Hollow' feeling in stomachMuscles of body Tenses them Ready for immediate action Tense feelingShiveringLiver Conversion of glycogen to glucose Glucose available in blood for energy production No sensationFat depots Conversion of fats to fatty acids Fatty acids available in blood, for muscle contraction No sensationAll these effects make us more able to react quickly and vigorously in dangerous situations that might require us to run away or put up a struggle.
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