Different hormones are produced in different zones of the cortex and medulla of the<unk> . Light microscopy at magnification × 204. The<unk>  secretes a number of different hormones which are metabolised by enzymes either within the<unk>  or in other parts of the body. These hormones are involved in a number of essential biological functions. Corticosteroids Corticosteroids are a group of steroid hormones produced from the cortex of the<unk> , from which they are named. * Mineralocorticoids such as aldosterone regulate salt ("mineral") balance and blood pressure * Glucocorticoids such as cortisol influence metabolism rates of proteins, fats and sugars ("glucose"). *Androgens such as dehydroepiandrosterone. ;Mineralocorticoids The<unk>  produces aldosterone, a mineralocorticoid, which is important in the regulation of salt ("mineral") balance and blood volume. In the kidneys, aldosterone acts on the distal convoluted tubules and the collecting ducts by increasing the reabsorption of sodium and the excretion of both potassium and hydrogen ions. Aldosterone is responsible for the reabsorption of about 2% of filtered glomerular filtrate. Sodium retention is also a response of the distal colon and sweat<unk> s to aldosterone receptor stimulation. Angiotensin II and extracellular potassium are the two main regulators of aldosterone production. The amount of sodium present in the body affects the extracellular volume, which in turn influences blood pressure. Therefore, the effects of aldosterone in sodium retention are important for the regulation of blood pressure. ;Glucocorticoids Cortisol is the main glucocorticoid in humans. In species that do not create cortisol, this role is played by corticosterone instead. Glucocorticoids have many effects on metabolism. As their name suggests, they increase the circulating level of glucose. This is the result of an increase in the mobilization of amino acids from protein and the stimulation of synthesis of glucose from these amino acids in the liver. In addition, they increase the levels of free fatty acids, which cells can use as an alternative to glucose to obtain energy. Glucocorticoids also have effects unrelated to the regulation of blood sugar levels, including the suppression of the immune system and a potent anti-inflammatory effect. Cortisol reduces the capacity of osteoblasts to produce new bone tissue and decreases the absorption of calcium in the gastrointestinal tract. The<unk>  secretes a basal level of cortisol but can also produce bursts of the hormone in response to adrenocorticotropic hormone (ACTH) from the anterior pituitary. Cortisol is not evenly released during the day – its concentrations in the blood are highest in the early morning and lowest in the evening as a result of the circadian rhythm of ACTH secretion. Cortisone is an inactive product of the action of the enzyme 11β-HSD on cortisol. The reaction catalyzed by 11β-HSD is reversible, which means that it can turn administered cortisone into cortisol, the biologically active hormone. ;Formation Steroidogenesis in the<unk> s – different steps occur in different layers of the<unk>  All corticosteroid hormones share cholesterol as a common precursor. Therefore, the first step in steroidogenesis is cholesterol uptake or synthesis. Cells that produce steroid hormones can acquire cholesterol through two paths. The main source is through dietary cholesterol transported via the blood as cholesterol esters within low density lipoproteins (LDL). LDL enters the cells through receptor-mediated endocytosis. The other source of cholesterol is synthesis in the cell's endoplasmic reticulum. Synthesis can compensate when LDL levels are abnormally low. In the lysosome, cholesterol esters are converted to free cholesterol, which is then used for steroidogenesis or stored in the cell. The initial part of conversion of cholesterol into steroid hormones involves a number of enzymes of the cytochrome P450 family that are located in the inner membrane of mitochondria. Transport of cholesterol from the outer to the inner membrane is facilitated by steroidogenic acute regulatory protein and is the rate-limiting step of steroid synthesis. The layers of the<unk>  differ by function, with each layer having distinct enzymes that produce different hormones from a common precursor. The first enzymatic step in the production of all steroid hormones is cleavage of the cholesterol side chain, a reaction that forms pregnenolone as a product and is catalyzed by the enzyme P450scc, also known as cholesterol desmolase. After the production of pregnenolone, specific enzymes of each cortical layer further modify it. Enzymes involved in this process include both mitochondrial and microsomal P450s and hydroxysteroid dehydrogenases. Usually a number of intermediate steps in which pregnenolone is modified several times are required to form the functional hormones. Enzymes that catalyze reactions in these metabolic pathways are involved in a number of endocrine diseases. For example, the most common form of congenital<unk>  hyperplasia develops as a result of deficiency of 21-hydroxylase, an enzyme involved in an intermediate step of cortisol production. ;Regulation Negative feedback in the HPA axis Glucocorticoids are under the regulatory influence of the hypothalamus-pituitary-adrenal (HPA) axis. Glucocorticoid synthesis is stimulated by adrenocorticotropic hormone (ACTH), a hormone released into the bloodstream by the anterior pituitary. In turn, production of ACTH is stimulated by the presence of corticotropin-releasing hormone (CRH), which is released by neurons of the hypothalamus. ACTH acts on the<unk>  cells first by increasing the levels of StAR within the cells, and then of all steroidogenic P450 enzymes. The HPA axis is an example of a negative feedback system, in which cortisol itself acts as a direct inhibitor of both CRH and ACTH synthesis. The HPA axis also interacts with the immune system through increased secretion of ACTH at the presence of certain molecules of the inflammatory response. Mineralocorticoid secretion is regulated mainly by the renin–angiotensin–aldosterone system (RAAS), the concentration of potassium, and to a lesser extent the concentration of ACTH. Sensors of blood pressure in the juxtaglomerular apparatus of the kidneys release the enzyme renin into the blood, which starts a cascade of reactions that lead to formation of angiotensin II. Angiotensin receptors in cells of the zona glomerulosa recognize the substance, and upon binding they stimulate the release of aldosterone. Androgens Cells in zona reticularis of the<unk> s produce male sex hormones, or androgens, the most important of which is DHEA. In general, these hormones do not have an overall effect in the male body, and are converted to more potent androgens such as testosterone and DHT or to estrogens (female sex hormones) in the gonads, acting in this way as a metabolic intermediate. Catecholamines Primarily referred to in the United States as epinephrine and norepinephrine,<unk> ine and noradrenaline are catecholamines, water-soluble compounds that have a structure made of a catechol group and an amine group. The<unk> s are responsible for most of the<unk> ine that circulates in the body, but only for a small amount of circulating noradrenaline. These hormones are released by the<unk>  medulla, which contains a dense network of blood vessels.<unk> ine and noradrenaline act by interacting with adrenoreceptors throughout the body, with effects that include an increase in blood pressure and heart rate. Actions of<unk> ine and noradrenaline are responsible for the fight or flight response, characterised by a quickening of breathing and heart rate, an increase in blood pressure, and constriction of blood vessels in many parts of the body. ;Formation Catecholamines are produced in chromaffin cells in the medulla of the<unk> , from tyrosine, a non-essential amino acid derived from food or produced from phenylalanine in the liver. The enzyme tyrosine hydroxylase converts tyrosine to L-DOPA in the first step of catecholamine synthesis. L-DOPA is then converted to dopamine before it can be turned into noradrenaline. In the cytosol, noradrenaline is converted to epinephrine by the enzyme phenylethanolamine N-methyltransferase (PNMT) and stored in granules. Glucocorticoids produced in the<unk>  cortex stimulate the synthesis of catecholamines by increasing the levels of tyrosine hydroxylase and PNMT. Catecholamine release is stimulated by the activation of the sympathetic nervous system. Splanchnic nerves of the sympathetic nervous system innervate the medulla of the<unk> . When activated, it evokes the release of catecholamines from the storage granules by stimulating the opening of calcium channels in the cell membrane.
Adrenal gland
Adrenal cortex
Pituitary gland
Kidney
Liver
Ovary
Breast
Callus