Adrenal cortex regulation

A mineralocorticoid hormone— synthesized in the adrenal cortex regulates blood pressure and volume by stimulating the kidneys to absorb Na, Cl, and HCOj-... 

Two AT-II receptors, AT and AT2 are known and show wide distribution (27). The AT receptor has been cloned and predominates ia regions iavolved ia the regulation of blood pressure and water and sodium retention, eg, the aorta, Hver, adrenal cortex, and ia the CNS ia the paraventricular nucleus, area postrema, and nucleus of the soHtary tract. AT2 receptors are found primarily ia the adrenal medulla, utems, and ia the brain ia the locus coeruleus and the medial geniculate nucleus. AT receptors are GCPRs inhibiting adenylate cyclase activity and stimulating phosphoHpases C, A2, and D. AT2 receptors use phosphotyrosiae phosphatase as a transduction system. 

CRH (Corticotropin releasing hormone) is expressed in the nucleus paraventricularis of the hypothalamus and drives the stress hormone system by activating synthesis and release of corticotropin at the pituitary and in turn corticosteroid from the adrenal cortex. CRH is also expressed at many other brain locations not involved in neuroendocrine regulation, e.g. the prefrontal cortex and the amygdala. Preclinical studies have shown that CRH also coordinates the behavioral adaptation to stress (e.g. anxiety, loss of appetite, decreased sleepiness, autonomic changes, loss of libido). 

Glucocorticoids are secreted by the cells of the zona fasciculata in the adrenal cortex. Hydrocortisone is the most important, and regulates intermediary metabo-... 

The adrenal gland is located on the upper segment of the kidney (Fig. 42-1). It consists of an outer cortex and an inner medulla. The adrenal medulla secretes the catecholamines epinephrine (also called adrenaline) and norepineprhine (also called noradrenaline), which are involved in regulation of the sympathetic nervous system. The adrenal cortex consists of three histologically distinct zones zona glomerulosa, zona fasciculata, and an innermost layer called the zona reticularis. Each zone is responsible for production of different hormones (Fig. 42-2). 

Aldosterone A hormone produced in and secreted by the zona glomerulosa of the adrenal cortex. Aldosterone acts on the kidneys to reabsorb sodium and excrete potassium. It is also a part of the renin-angiotensin-aldosterone system, which regulates blood pressure and blood volume. 

Steroid hormones are produced by the adrenal cortex, testes, ovaries, and placenta. Synthesized from cholesterol, these hormones are lipid soluble therefore, they cross cell membranes readily and bind to receptors found intracellularly. However, because their lipid solubility renders them insoluble in blood, these hormones are transported in the blood bound to proteins. Furthermore, steroid hormones are not typically preformed and stored for future use within the endocrine gland. Because they are lipid soluble, they could diffuse out of the cells and physiological regulation of their release would not be possible. Finally, steroid hormones are absorbed easily by the gastrointestinal tract and therefore may be administered orally. 

A trophic hormone acts on another endocrine gland to stimulate secretion of its hormone. For example, thyrotropin, or thyroid-stimulating hormone (TSH), stimulates the secretion of thyroid hormones. Adrenocorticotropin, or adrenocorticotropic hormone (ACTH), stimulates the adrenal cortex to secrete the hormone cortisol. Both trophic hormones are produced by the pituitary gland in fact, many trophic hormones are secreted by the pituitary. The pituitary gland is sometimes referred to as the "master gland" because its hormones regulate the activity of other endocrine glands. 

The release of aldosterone from the adrenal cortex is regulated by two important factors ... 

The mechanism by which potassium regulates aldosterone secretion is unclear however, this ion appears to have a direct effect on the adrenal cortex. An increase in the level of potassium in the blood stimulates the release of aldosterone. The effect of aldosterone on the kidney then decreases the level of potassium back to normal. 

Many steroid hormones are regulated by this type of axis—e.g., thyroxin, cortisol, estradiol, progesterone, and testosterone. In the case of the glucocorticoids, the hypothalamus releases corticotropin-releasing hormone (CRH or corticoliberin, a peptide consisting of 41 amino acids), which in turn releases corticotropin (ACTFl, 39 AAs) in the pituitary gland. Corticotropin stimulates synthesis and release of the glandular steroid hormone cortisol in the adrenal cortex. 

Cortisol, the most important g/ucocorticoid, is synthesized by the adrenal cortex, it is involved in regulating protein and carbohydrate metabolism by promoting protein degradation and the conversion of amino acids into glucose. As a result, the blood glucose level rises (see p. 152). Synthetic glucocorticoids (e.g., dexamethasone) are used in drugs due to their anti-inflammatory and immunosuppressant effects. 

The tenn corticosteroids refers to steroid hormones secreted by the adrenal cortex. Corticosteroids are involved in a wide range of physiologic systems such as stress response, immune response, and regulation of inflammation, carbohydrate metabolism, protein catabolism, blood electrolyte levels, and behavior. 

The male and female gonads, as well as the placenta of pregnant females and, to a lesser extent, the adrenal cortex, produce a range of steroid hormones which regulate the development and maintenance of reproductive and related functions. As such, these steroid sex hormones have found medical application in the treatment of various reproductive dysfunctions. 

Glucocorticoids and mineralocorticoids are uniquely produced by the adrenal cortex, and are collectively termed corticosteroids. Apart from aldosterone, glucocorticoid secretion is regulated by the pituitary hormone, corticotrophin. The principal corticosteroids synthesized in the body are illustrated in Figure 1.6. Glucocorticoids generally exhibit weak mineralocorticoid actions and vice versa. 

While the rate limiting step of the cascade is the renin release, the biological active component is the octapeptide angiotensin n. It is an essential regulator of fluid and electrolyte balance as well as blood pressure. It exerts its actions on various structures like blood vessels, adrenal cortex, kidney and central nervous system. Although at least two different receptor subtypes for angiotensin II have been identified (ATi and AT2) the ATi-subtype is responsible for most of the cardiovascular effects of the agonist. 

The steroidal nature of adrenocortical hormones was established in 1937, when Reichstein synthesized desoxycorticosterone. Eventually it was clearly established that the adrenal cortex elaborated a number of hormones and that these compounds differed in their amount of inherent metabolic (glucocorticoid) and electrolyte regulating (mineralocorticoid) activity. The actions of these hormones extend to almost every cell in the body. In humans, hydrocortisone (cortisol) is the main carbohydrate-regulating steroid, and aldosterone is the main electrolyte-regulating steroid. 

Another major function of the adrenal cortex is the regulation of water and electrolyte metabolism. The principal mineralocorticoid, aldosterone, can increase the rate of sodium reabsorption and potassium excretion severalfold. This will occur physiologically in response to sodium or volume depletion or both. The primary site of... 

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