Hormone, adrenal cortex anterior pituitary

Hypothalamo-pituitary function Anterior pituitary hormones Posterior pituitary hormones Adrenal cortex Adrenal medulla Thyroid Pancreas INTRODUCTION... 

ACTH adrenocorticoh ophic hormone is a peptide hormone released by anterior pituitary cells in response to shessful stimuli that causes the synthesis and release of cortisol (corticosteroid) from the adrenal cortex. It is an important component of the hypothalamic-pituitary-adrenal (HPA) axis. ACTH is released from pro-opiomelanocortin and secreted from corticotropes in response to corticotropin-releasing hormone (CRH) released by the hypothalamus. 

Adrenocorticotropic Hormone (ACTH) (Corticotropin) Anterior Pituitary (Corticotroph) 39 aa 2p25 Stimulates steroidogenesis in all three zones of the adrenal cortex, thereby increasing secretion of cortisol, DHEAS, and aldosterone. Stimulated by CRH and inhibited by cortisol. 

Control of secretion of anterior pituitary hormones also includes inhibition by hormones produced by target organs. For example, CRH stimulates the anterior pituitary to secrete ACTH, which in turn stimulates the adrenal cortex to secrete corticosteroids. Corticosteroids then feed back to inhibit the secretion of ACTH. Feedback mechanisms are important for the control of most hormones. For example, insulin (qv) secretion from the pancreas increases in response to increased blood glucose resulting from ingestion of a meal. Insulin increases tissue uptake and metaboHsm of glucose, which lowers blood glucose and in turn reduces insulin secretion. 

Pregnenolone is transported from the mitochondria to the ER, where a hydroxyl oxidation and migration of the double bond yield progesterone. Pregnenolone synthesis in the adrenal cortex is activated by adrenocorticotropic hormone (ACTH), a peptide of 39 amino acid residues secreted by the anterior pituitary gland. 

This section of the chapter discusses FSH, LH, GH, and ACTH. FSH and LH are called gonadotropins because they influence the gonads (the organs of reproduction). GH, also called somatotropin, contributes to the growth of the body during childhood, especially the growth of muscles and bones. ACTH is produced by the anterior pituitary and stimulates the adrenal cortex to secrete the corticosteroids. The anterior pituitary hormone, TSH, is discussed in Chapter 51. Prolactin, which is also secreted by the anterior pituitary, stimulates the production of breast milk in the postpartum patient Additional functions of prolactin are not well understood. Prolactin is the only anterior pituitary hormone that is not used medically. 

Corticotropin (ACTH) is an anterior pituitary hormone that stimulates the adrenal cortex to produce and secrete adrenocortical hormones, primarily the glucocorticoids. 

The adrenal gland lies on the superior surface of each kidney. It is a double organ composed of an outer cortex and an inner medulla In response to ACTH secreted by the anterior pituitary, the adrenal cortex secretes several hormones (the glucocorticoids, the mineralocorticoids, and small amounts of sex hormones). 

Adrenal hormone production is controlled by the hypothalamus and pituitary gland. Corticotropin-releasing hormone (CRH) is secreted by the hypothalamus and stimulates secretion of adrenocorticotropic hormone (ACTH), also known as corticotropin from the anterior pituitary. ACTH, in turn, stimulates the adrenal cortex to produce cortisol. When sufficient or excessive cortisol levels are reached, a negative feedback is exerted on the secretion of CRH and ACTH, thereby decreasing overall cortisol production. The control of adrenal androgen synthesis also follows a similar negative-feedback mechanism. 

The primary glucocorticoid released in humans is cortisol (also known as hydrocortisone). Cortisol synthesis and secretion are under the control of specific hypothalamic and pituitary hormones.7,24 31 Corticotropinreleasing hormone (CRH) from the hypothalamus stimulates the release of adrenocorticotropic hormone (ACTH) from the anterior pituitary. ACTH travels in the systemic circulation to reach the adrenal cortex, where it stimulates cortisol synthesis. Cortisol then travels in the bloodstream to various target tissues to exert a number of physiologic effects (see Physiologic Effects of Glucocorticoids, later). 

Adrenocorticotropin is a peptide hormone produced in the anterior pituitary. Its primary endocrine function is to stimulate synthesis and release of cortisol by the adrenal cortex. Corticotropin can be used therapeutically, but a synthetic derivative is more commonly—and almost exclusively—used to assess adrenocortical responsiveness. A substandard adrenocortical response to exogenous corticotropin administration indicates adrenocortical insufficiency. 

As mentioned in Chapter 1, perhaps the purest form of drug therapy is the replacement of inadequate amounts of an endogenous substance such as a hormone. Any gland that normally secretes a hormone is a potential target for hypofunctioning. Classical examples include Addison s disease (adrenal cortex), dwarfism (anterior pituitary), juvenile-onset insulin-dependent diabetes (pancreas), and hypothyroidism (thyroid). 

ACTH (adrenocorticotropic hormone, corticotropin) is a 39-amino-acid peptide synthesized and secreted by the corticotrope cells of the anterior lobe of the pituitary gland. ACTH acts on several target tissues, including the adrenal cortex, adipose tissue and brain. It is synthesized as part of proopiomelanocortin (POMC) as amino acids 132-170 of this molecule, which is proteolytically cleaved to produce ACTH [1],... 

The glucocorticoid cortisol is secreted from the adrenal cortex as a stress response under the control of adrenocorticotropic hormone (ACTH, corticotropin) produced by the anterior pituitary. Cortisol promotes catabolism by inducing synthesis of specific proteins. Cortisol binds to a cytosolic cortisol receptor which then translocates to the nucleus and switches on the expression of specific genes, notably that for PEP carboxykinase (PEPCK). Cortisol-induced expression of the key gluconeogenesis enzyme PEPCK increases levels of the enzyme and hence increases gluconeogenesis and available blood glucose. The cAMP-and cortisol-mediated pathways for induction of PEPCK expression are further linked by CREB-dependent expression of a coactivator protein PGC-1 that promotes cortisol-dependent expression of PEPCK. 

Adrenocorticotropic hormone derives from the anterior pituitary in response to the leptin-or stress-induced anorexigenic, hypothalamic CRH. Corticotropin (like enkephalins and MSHs) derives from a precursor polypeptide pro-opiomelanocortin. Corticotropin induces the catabolic adrenal cortex corticosteroid cortisol and the mineralocorticoid aldosterone (Chapter 11) and is an important regulator of immune responses including chemotaxis and phagocytosis. Corticotropin acts via GPCRs to activate Gas and increase cAMP in anterior pituitary cells. 

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