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==Overview==
==Overview==
Acromegaly is caused by prolonged overproduction of GH by the pituitary gland.  GH is part of a cascade of hormones that, as the name implies, regulates the physical growth of the body.  This cascade begins in a part of the brain called the hypothalamus.  The hypothalamus makes hormones that regulate the pituitary.  One of the hormones in the GH series, or "axis," is growth hormone-releasing hormone (GHRH), which stimulates the pituitary gland to produce GH.
Secretion of GH by the pituitary into the bloodstream stimulates the liver to produce another hormone called insulin-like growth factor I (IGF-I).  IGF-I is what actually causes tissue growth in the body.  High levels of IGF-I, in turn, signal the pituitary to reduce GH production.
The hypothalamus makes another hormone called [[somatostatin]], which inhibits GH production and release.  Normally, GHRH, somatostatin, GH, and IGF-I levels in the body are tightly regulated by each other and by sleep, exercise, stress, food intake, and blood sugar levels.  If the pituitary continues to make GH independent of the normal regulatory mechanisms, the level of IGF-I continues to rise, leading to bone overgrowth and organ enlargement.  High levels of IGF-I also cause changes in glucose (sugar) and lipid (fat) metabolism and can lead to diabetes, high blood pressure, and heart disease.
==Pathophysiology==
==Pathophysiology==
Growth hormone is synthesized and stored in somatotroph cells, which account for >50% of pituitary hormone secreting cells. Growth hormone production and secretion is regulated by hypothalamic GH-releasing hormone, ghrelin and somatostatin. IGF-1 inhibits growth hormone secretion by both direct effect on the somatrophs and indirectly through stimulation of somatostatin that inhibits growth hormone secretion. Growth hormone is secreted in sporadic pulses with minimal basal secretion determined by sex, age, neurotransmitters, exercise and stress.
<ref name="pmid26873451">{{cite journal| author=Dineen R, Stewart PM, Sherlock M| title=Acromegaly. | journal=QJM | year= 2016 | volume=  | issue=  | pages=  | pmid=26873451 | doi=10.1093/qjmed/hcw004 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=26873451  }} </ref>.
 
Growth hormone action is achieved via its interaction with a single-chain transmembrane glycoprotein receptor (GHR). The growth hormone molecule interacts with a preformed dimer of identical GHR pairs, causing internalization of the receptor to initiate signaling. As a consequence, two Janus tyrosine kinase 2 molecules undergo autophosphorylation and in turn phosphorylate the GHR cytoplasmic domain. This activates intracellular proteins involved in signal transduction and transcription (STAT).
 
The gene encoding the GHR is ubiquitously expressed, particularly in liver, fat and muscle. Growth hormone activation of the intracellular molecule STAT5b induces transcription of IGF-1. Systemic IGF-1 is synthesized primarily in the liver but also in extraheptatic tissues including bone, muscle and kidney and in the pituitary gland itself. IGF-1 circulates in serum bound to IGF-1 binding protein (IGFBP-3), or IGFBP-5, and acid-labile subunit in a 150-kD complex. Less than 1% of total serum IGF-1 circulates as a free hormone. The IGF-1 cellular effects are mediated by the IGF-1 receptor (IGF-1R), a heterotetrameric protein structurally similar to the insulin receptor. IGF-1 acts to mediate tissue growth or locally synthesized IGF-1 acts in a paracrine manner to regulate local GH target tissue growth<ref name="pmid26873451">{{cite journal| author=Dineen R, Stewart PM, Sherlock M| title=Acromegaly. | journal=QJM | year= 2016 | volume=  | issue=  | pages=  | pmid=26873451 | doi=10.1093/qjmed/hcw004 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=26873451  }} </ref>.


===Pathogenesis===
===Pathogenesis===

Revision as of 15:22, 3 August 2017

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief:


Overview

Pathophysiology

[1].

Pathogenesis

  • The exact pathogenesis of [disease name] is not fully understood.

OR

  • It is thought that [disease name] is the result of / is mediated by / is produced by / is caused by either [hypothesis 1], [hypothesis 2], or [hypothesis 3].
  • [Pathogen name] is usually transmitted via the [transmission route] route to the human host.
  • Following transmission/ingestion, the [pathogen] uses the [entry site] to invade the [cell name] cell.
  • [Disease or malignancy name] arises from [cell name]s, which are [cell type] cells that are normally involved in [function of cells].
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  • The pathophysiology of [disease/malignancy] depends on the histological subtype.

Genetics

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Gross Pathology

  • On gross pathology, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].

Microscopic Pathology

  • On microscopic histopathological analysis, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].

References

  1. ↑ Dineen R, Stewart PM, Sherlock M (2016). "Acromegaly". QJM. doi:10.1093/qjmed/hcw004. PMID 26873451.

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