Table 1 lists 11 different endocrine-related cell types and their partner hormones that are present in the gastrointestinal system. A variety of the endocrine cells are dispersed throughout the gastric mucosa, small intestine, and colon. Two basic kinds of cells are identifiable by classical histological procedures of staining with chrome and silver: They are enterochromaffin cells and agyrophil cells or “silver-loving cells.” The enterochromaffin cells are sparsely present in the gastric (stomach) mucosa, but are fairly prevalent in the small and large intestines. In humans there are approximately twice as many agyrophil cells as enterochromaffin cells in the intestine.

Table1. Endocrine-related Cell Types and Their Hormones That Are Present in the Gastrointestinal System

By using immunofluorescent techniques, it has been shown that in the gastroenteropancreatic complex there may be as many as 11 different types of hormone-secreting cells. These cells are capable of secreting gastrin, motilin, secretin, cholecystokinin (CCK), somatostatin, histamine, GLP-1 (glucagon-like peptide), GLP-2, PYY (peptide YY) GIP, GIP (gastric inhibitory peptide), and the pancreatic polypeptides. In many cases, these cells have microvillar borders facing the lumen of the stomach or the intestine so that they can respond to chemicals in the stomach or intestinal contents. Most of the cells appear to produce a single peptide hormone, but in some instances they also produce biogenic amines such as histamine or 5-hydroxytryptamine.

There are four general pathways by which peptide hormone-secreting cells, also known as enteroendocrine cells, of the gastrointestinal tract can make their chemical messengers available; see Figure 1. The enteroendocrine cells are located in the intestine, the stomach, and the pancreas. These pathways include the following models: (a) Paracrine delivery where the hormone (H) or the neu rotransmitter (NT) moves from the endocrine cell source to immediately adjacent cells; (b) “Neurocrine” delivery where there is a release of an NT by the nerve to the adjacent environment; (c) “Open” endocrine cell delivery, where there is a release of the H from an endocrine cell that is “open” to the intestinal lumen so that the H can diffuse out and enter adjacent cells where there should be a cognate receptor; (d) “Closed” endocrine cell delivery in which the hormone-producing cell does not face the brush border surface and also cannot engage in paracrine delivery. The release of the hormone H is directly to the blood compartment where it can be transmitted to cells that have a receptor for the hormone (see Figure 1D). Examples of GI hormones that function via these path ways are as follows: paracrine fashion (PP, VIP), neurocrine (NPY, CGRP), open endocrine delivery (gastrin), and closed endocrine delivery (secretin, motilin, CCK). Figure 2 in section III.L provides a description in which stomach G cells and the hormone gastrin collab orate as both neurotransmitters (NT) that interact with a nerve for delivery and which then send an NT hormone to a specified receptor in a target cell.

Fig1. Schematic models describing pathways by which gastrointestinal hormone-producing cells make their chemical messengers either available locally or deliverable through the circulatory system or via activation of a neuron. (A) Paracrine delivery, where the hormone (H) or neurotransmitter (NT) moves from an endocrine cell to immediately adjacent cells. (B) Neurocrine delivery, where there is release of an NT by the nerve to the local environment, which can include mucosa, other nearby endocrine cells, or smooth muscle cells. (C) Release of a hormone(s) from an endocrine cell that is “open” via secretion of the H to the intestinal lumen and adjacent cells. (D) Release or secretion of hormones to the blood from an endocrine cell that is “closed” to adjacent cells and does not have an opening to the intestinal lumen.

Fig2. Integrated signal transduction by D cells, G cells, enterochromaffin-like (ECL) cells, and parietal cells in the antrum and fundus of the stomach, which results in the secretion of hydrochloric acid in the stomach so as to facilitate food denaturation. The left side of both panels A and B illustrates the various regions of the stomach. At the bottom of the antrum (left of panel A) and the bottom of the fundus (top left of panel B) there is a small black box. Each box identifies the zone of cells that are enlarged in the center of both panels A and B. In the center panel of this figure a second pair of black boxes identifies the single cells illustrated in the center and right sides of panels A and B, respectively. In the center of both right panels a capillary bed is illustrated in red and blue. In the right side of panel A, the combined partnership of the D and G cells’ gastrin releasing peptide (GRP) regulates the production in the G cell of the hormone gastrin (blue balls) which is released to the capillary bed for transport to the parietal cells in the stomach’s fundus region (see bottom right of panel B). The antrum’s receptor for the G cell’s gastrin releasing protein (GRP; see upper right panel) is present in the plasma membrane of D cells (at the top) and G cells (at the bottom). The GRP receptor binds the GRP hormone (small orange balls) as a ligand in response to a GRP nerve signal (see upper right panel B). As shown in the bottom right panel, the fundus’ oxyntic (acid secreting) parietal cells and the ECL cells receive the hormone gastrin from the capillary bed (small blue balls) which binds to their CCK2R plasma membrane receptor. This ligand-receptor action results in the production and secretion of essential hydrochloric acid. Following is a key to the abbreviations employed in this figure: G cells are a source of the endocrine hormone, gastrin; D cells are a source of the hormone somatostatin; ECL are enterochromaffin-like cells that are a type of neuroendocrine cells found in the stomach’s antrum in the vicinity of parietal cells; parietal cells are a source of hydrochloric acid which is secreted into the stomach; CCK2R is a plasma membrane receptor for gastrin; SSTR2 is a plasma membrane receptor for somastostatin; Ach is messenger produced by a postganglion cholinergic muscarinic nerve; histamine is an endocrine messenger that is derived from the amino acid histidine.

اخر الاخبار

اخبار العتبة العباسية المقدسة

قسم الشؤون الدينية يطلق الدورة التطويرية والفقهية الخامسة لملاكات العتبة العباسية المقدسة

قسم الشؤون الفكرية ينظّم ختمة قرآنية رمضانية لطلبة العلوم الدينية الأفارقة في النجف

شعبة الخطابة تقيم مجلسا للوعظ والإرشاد في الصحن الشريف تزامناً مع حلول شهر رمضان المبارك

قسم التطوير يختتم دورة إعداد المدربين لملاكات مديرية تربية كربلاء

المزيد

الآخبار الصحية

مفاجأة.. تحسين القدرة على التحمل لا يعتمد العضلات فقط

المرتفعات والأكسجين.. دراسة "مبشرة" لمرضى السكري

علماء يبتكرون "آلية" تتوقع موعد ظهور أعراض الزهايمر

ماذا يحدث لجسمك عند التوقف عن تناول الخضراوات والفواكه؟

المزيد

الآخبار التكنلوجية

رصد "القرش النائم" في أحد أقسى الأماكن على وجه الأرض

أسماك أعماق البحر تكشف نظاما بصريا يتجاوز "المألوف"

زوكربيرغ أمام القضاء في قضية إدمان المراهقين

"علي بابا" تكشف عن نموذج جديد للذكاء الاصطناعي

المزيد

مواضيع ذات صلة

Pancreatic, Biliary, and Intestinal Secretions

Leptin Functions as a Satiety Factor

Glucagon and Glucagon-like Peptides— Biosynthesis and Secretion

Adult Growth Hormone Deficiency

Hypopituitary crisis

Thyroid Replacement in TSH Deficiency

Glucagon’s Structure

Insulin and Its Glucose Transporter

Insulin Receptor

Insulin Structure

Biological Actions of T3

Adrenal Replacement in ACTH Deficiency