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Adrenal Gland
On top of each kidney is the adrenal gland, which itself can be divided into two regions - the adrenal cortex and the adrenal medulla. The adrenal medulla is the innermost portion of the adrenal gland and it is involved in producing epinephrine and norepinephrine. These two hormones are both water-soluble and are tyrosine derivatives. Although they are also used as neurotransmitters by the sympathetic division of the nervous system, the effect of the nervous system is short-term and does not last nearly as long as the effect created by the endocrine system. The epinephrine (also called adrenaline) causes an increase in heart rate and contractile force, increases the respiratory rate and increases the blood flow to skeletal muscle and the brain. It also increases the breakdown of glycogen into glucose, so it increases the amount of glucose that is readily available in the blood. Norepinephrine causes certain blood vessels to constrict, thereby increasing the blood pressure. Both epinephrine and norepinephrine are catecholamines. The adrenal cortex is the outermost region of the adrenal gland and it produces and releases corticosteroids, which are hormones that are produced from the steroid cholesterol. There are three main groups of corticosteroids that are released by the adrenal cortex - mineralocorticoid (aldosterone), glucocorticoid (cortisol and cortisone) and androgens (male sex hormones). These corticosteroids are controlled by the anterior pituitary gland, which releases the adrenocorticotropic hormone (ACTH) that stimulates the adrenal gland. The anterior pituitary gland itself is controlled by the hormones releases by the hypothalamus. When the blood concentration of the corticosteroids is high, it can inhibit the release of ACTH via negative feedback loop.
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