Hormonal Regulation of the GI Tract
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Questions and Answers

What role does HCO3- play in the small intestine?

  • Increases the acidity of chyme
  • Inhibits pancreatic enzyme function
  • Neutralises acidic chyme entering the duodenum (correct)
  • Promotes erosion of the mucosa

Which transporter is primarily responsible for HCO3- secretion across the apical membrane of pancreatic duct cells?

  • K+/H+ ATPase
  • Na+/Cl- cotransporter
  • Na+/H+ exchanger
  • Cl-/HCO3- exchanger (correct)

What effect does the lack of functional CFTR have on pancreatic secretion?

  • Reduces fluid secretion (correct)
  • Enhances bicarbonate transport
  • Decreases enzyme secretion
  • Increases fluid secretion

How does HCO3- secretion influence pancreatic enzyme function?

<p>It provides optimum pH for pancreatic enzyme function (A)</p> Signup and view all the answers

What is the source of HCO3- necessary for secretion in pancreatic duct cells?

<p>Production from carbon dioxide and water (D)</p> Signup and view all the answers

What roles do peptide hormones primarily play in the body's physiology?

<p>Stimulate appetite (D)</p> Signup and view all the answers

Incretins primarily affect which type of pancreatic cells to promote insulin release?

<p>Beta cells (D)</p> Signup and view all the answers

Which factors are known to enhance secretion in the small intestine?

<p>Irritation and distension (C)</p> Signup and view all the answers

What type of secretions do duct cells in the pancreas produce?

<p>Alkaline HCO3- rich fluid (C)</p> Signup and view all the answers

What composition of secretions is primarily absent in succus entericus of the small intestine?

<p>Digestive enzymes (C)</p> Signup and view all the answers

What is the mechanism behind secretory diarrhea in conditions like cholera?

<p>Overactive secretion of aqueous salts (C)</p> Signup and view all the answers

Which of the following influences gastric emptying regulation most significantly?

<p>Gastric distension and endocrine signals (C)</p> Signup and view all the answers

Which of the following describes a primary role of the pancreas' exocrine function?

<p>Secretion of digestive enzymes (C)</p> Signup and view all the answers

What role does pepsin play in the stomach?

<p>Activates pepsinogen autocatalytically (C)</p> Signup and view all the answers

Which substance facilitates the absorption of vitamin B12 in the gastrointestinal tract?

<p>Intrinsic factor (C)</p> Signup and view all the answers

How does histamine influence gastric function?

<p>Stimulates HCl secretion (C)</p> Signup and view all the answers

What is the primary function of somatostatin in the gastric environment?

<p>Inhibits HCl secretion (D)</p> Signup and view all the answers

What is the role of gastrin in the gastric system?

<p>Stimulates HCl secretion and motility (D)</p> Signup and view all the answers

Which cellular mechanism helps regulate the secretion of HCl in parietal cells?

<p>H+/K+ ATPase (D)</p> Signup and view all the answers

What protective role does mucus play in the gastrointestinal tract?

<p>Protects mucosa from acid damage (B)</p> Signup and view all the answers

Which component directly binds Fe2+ for absorption in the intestine?

<p>Gastroferrin (D)</p> Signup and view all the answers

How does the presence of carbonic anhydrase benefit the parietal cells?

<p>It helps produce HCl from CO2 and H2O (C)</p> Signup and view all the answers

What mechanism aids in bicarbonate secretion from gastric cells?

<p>Cl-/HCO3- exchanger (D)</p> Signup and view all the answers

What role does cholecystokinin (CCK) play in the digestive process?

<p>Inhibits gastric emptying (B)</p> Signup and view all the answers

Which hormone is primarily responsible for stimulating H+ secretion by gastric parietal cells?

<p>Gastrin (A)</p> Signup and view all the answers

How does glucose-dependent insulinotropic peptide (GIP) affect gastric emptying?

<p>It inhibits gastric emptying (A)</p> Signup and view all the answers

What is the primary function of secretin in the small intestine?

<p>Promotes secretion of pancreatic and biliary bicarbonate (D)</p> Signup and view all the answers

Which factor contributes to the reducing gastric secretion during the intestinal phase?

<p>Enterogastrones release (C)</p> Signup and view all the answers

What effect does motilin have in the digestive system?

<p>Initiates the migrating motor complex (B)</p> Signup and view all the answers

Ghrelin is known for its effects on which aspect of digestion?

<p>Increasing appetite (D)</p> Signup and view all the answers

Which of the following hormones is associated with the incretin effect?

<p>Glucagon-like peptide-1 (GLP-1) (B)</p> Signup and view all the answers

The release of which hormone is triggered by H+ ions and fatty acids in the lumen of the duodenum?

<p>Secretin (B)</p> Signup and view all the answers

What is the role of prostaglandin E2 (PGE2) in gastric acid secretion?

<p>Reduces HCl secretion (D)</p> Signup and view all the answers

What role do pancreatic secretions play in digestion?

<p>They neutralize stomach acid and digest macromolecules. (C)</p> Signup and view all the answers

Which phase of pancreatic secretion is triggered primarily by the presence of acid in the duodenum?

<p>Intestinal phase (A)</p> Signup and view all the answers

Which hormone is released in response to fat and protein in the duodenal lumen?

<p>Cholecystokinin (CCK) (C)</p> Signup and view all the answers

What mechanism is primarily responsible for the activation of trypsinogen into trypsin?

<p>Autocatalysis initiated by enterokinase (A)</p> Signup and view all the answers

What is the function of the Na+/H+ exchanger in the pancreatic secretion process?

<p>To export H+ ions during bicarbonate secretion. (B)</p> Signup and view all the answers

Which enzyme is activated by trypsin in the pancreatic secretions?

<p>Chymotrypsinogen to chymotrypsin (B)</p> Signup and view all the answers

What initiates the cephalic phase of pancreatic secretion?

<p>Vagal stimulation due to thoughts of food (C)</p> Signup and view all the answers

Which electrolyte is crucial for the function of the Na+/H+ exchanger in pancreatic cells?

<p>Na+ (C)</p> Signup and view all the answers

What does secretin stimulate in pancreatic ducts?

<p>Secretion of aqueous NaHCO3 solution (D)</p> Signup and view all the answers

How does CCK affect pancreatic acinar cells?

<p>Stimulates secretion of digestive enzymes (D)</p> Signup and view all the answers

Flashcards

Pancreatic secretions

The pancreas has both endocrine and exocrine functions. Endocrine secretions include hormones like insulin and glucagon, while exocrine secretions include digestive enzymes and bicarbonate-rich fluid.

Incretins

Hormones that stimulate insulin release from the pancreas, and act in a feed-forward manner.

Succus entericus

Intestinal juice, approximately 2 liters secreted daily, with varying composition.

Secretion Control

Intestinal juice secretion is influenced by factors such as distension, irritation, gastrin, CCK, secretin, parasympathetic activity (increasing), and sympathetic activity (decreasing).

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Pancreatic Duct Cells

Cells that secrete an alkaline (rich in bicarbonate) fluid into the duodenum.

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Secretions of the Small Intestine

Small intestine secretions include mucus (protection), aqueous salts (digestion help), and lack digestive enzymes.

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Control Mechanisms

These are factors that regulate the production & amount of digestive juice from the small Intestine.

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Secretory Diarrhea

Excessive intestinal secretion leading to diarrhea, often related to abnormal ion transport.

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Pancreatic Secretion Phases

Pancreatic secretion has three phases: Cephalic, Gastric, and Intestinal. Each phase involves different stimuli and contributes varying percentages to the total secretion.

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Pancreatic Enzymes

Pancreatic enzymes (proteases, amylase, lipase) are crucial for digesting food. They are secreted in inactive forms and activated in the duodenum as they complete the digestive process.

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Secretin

A hormone released by S cells in response to acidic chyme in the duodenum. It stimulates the release of bicarbonate-rich pancreatic juice.

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CCK

A hormone released by I cells in response to fat and protein in the duodenum. It stimulates the release of digestive enzymes from the pancreas.

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Pancreatic Bicarbonate

Released by the pancreas into the duodenum, neutralizing stomach acid (HCl).

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Trypsinogen

An inactive precursor of the protease trypsin.

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Enterokinase

An enzyme that activates trypsinogen, initiating the activation cascade of pancreatic proteases.

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Zymogen Granules

Storage vesicles in acinar cells that hold inactive enzymes (e.g., proteases).

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Pancreatic Lipase

An enzyme secreted by the pancreas which helps in the digestion of lipids (fats).

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Cephalic Phase

First phase of pancreatic secretion, stimulated vagal activity leading to acinar cell stimulation.

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Pepsin activation

Pepsinogen is activated by pepsin, a process called autocatalysis.

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Intrinsic Factor

A protein that binds vitamin B12, aiding its absorption in the gut.

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Gastroferrin

Binds Iron (Fe2+) facilitating absorption.

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Histamine's role

Stimulates HCl production in the stomach.

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Mucus function

Protects the stomach lining from acid.

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Gastrin's effect

Stimulates stomach acid secretion and motility.

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Somatostatin's action

Inhibits stomach acid production.

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Parietal cell role

Creates Hydrogen ions (H+) for acid production.

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Proton pump (H+/K+ ATPase)

Actively transports H+ ions out of the parietal cell & K+ in.

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Chloride Bicarbonate Exchanger

Exchanges Cl- for HCO3- across the cell membrane.

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Gastric Acid Inhibition

The process by which the production of stomach acid is reduced, involving the cephalic, gastric, and intestinal phases.

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Cephalic Phase Acid Inhibition

The decrease in vagal nerve activity after a meal ends, and the stomach empties.

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Somatostatin

A hormone released from D cells in the stomach to inhibit gastrin secretion during the gastric phase.

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Intestinal Phase Acid Inhibition

Factors that reduce gastric motility also reduce gastric secretion, like reflexes and enterogastrones.

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Secretin

A hormone released by S cells in the duodenum in response to acidity and fat in the small intestine, stimulating pancreatic bicarbonate secretion.

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Cholecystokinin (CCK)

A hormone released in response to fats and proteins in the small intestine, inhibiting gastric emptying and stimulating pancreatic enzyme release, gallbladder contraction and bile ejection.

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GIP (Glucose-dependent Insulinotropic peptide)

A hormone released by K cells to stimulate insulin release from the pancreas, and inhibit gastric emptying.

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GLP-1 (Glucagon-like peptide-1)

A hormone released by L cells that stimulates insulin secretion, inhibits glucagon, and decreases gastric emptying and appetite.

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Motilin

A hormone released during fasting states that initiates the migrating motor complex in the digestive system.

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Ghrelin

A hormone released from the stomach and intestines, stimulating appetite and increasing gastric acid secretion

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HCO3- Secretion

Pancreatic duct cells secrete bicarbonate (HCO3-) into the duodenum to neutralize acidic chyme, optimizing pH for enzyme function and protecting the mucosa.

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Na+/H+ exchanger

A membrane transporter that exchanges sodium (Na+) for hydrogen (H+) ions, helping maintain pH balance during bicarbonate secretion.

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Basolateral membrane HCO3-

Bicarbonate (HCO3-) is transported out of the cells using transporters like a Na+/HCO3- cotransporter at the basolateral membrane, increasing the concentration required for secretion.

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Apical membrane HCO3-

HCO3- is secreted into the pancreatic duct lumen (apical). This is where enzymes and other chemicals are introduced into the digestive track.

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CFTR and Bicarbonate Secretion

Cystic fibrosis transmembrane conductance regulator (CFTR) plays a role in bicarbonate secretion. Patients with cystic fibrosis often exhibit reduced fluid secretion due to CFTR dysfunction.

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Study Notes

Hormonal Regulation of the Gastrointestinal Tract

  • The gastrointestinal tract is regulated by hormones.
  • Images show microscopic structures of cells and tissues within the stomach.
  • Images are electron micrographs from a 1989 handbook on cell biology.

Learning Objectives

  • Students should be able to outline the gross anatomy and mechanical functions of the stomach.
  • Students should be able to describe the process of gastric emptying and its controls.
  • Students should be able to list the gastric gland secretions and their functions.
  • Students should be able to draw a diagram showing how HCI is produced and regulated.
  • Students should be able to describe the 3 phases of gastric secretion and their controls.
  • Students should be able to understand the overall mechanism of how acetylcholine, histamine, and gastrin enhance HCI secretion (via H+/K+ATPase).
  • Students should be able to understand hormonal control of the small intestine.
  • Students should understand how the pancreas exerts control on the GI tract via endocrine and exocrine mechanisms.

The Stomach

  • J-shaped, 50-1000ml capacity.
  • Upper region relaxes receptively to accommodate food from the esophagus.
  • Starting point for protein digestion (pepsin and HCI).
  • Continues carbohydrate digestion (salivary amylase).
  • Mixes food with gastric secretions to form liquid chyme.
  • Stores food prior to passing into the small intestine.
  • Secretes 2 litres of gastric juice per day.

Mechanical Activity of the Stomach

  • Occurs in two types: orad (tonic), and caudad (phasic).

Control of Stomach Emptying

  • Strength of antral waves (or pump) and pyloric sphincter opening control chyme delivery to the duodenum.
  • Governed by gastric and duodenal factors.
  • Rate of emptying is proportional to volume of chyme in the stomach.
  • Distension increases motility from smooth muscle stretch and intrinsic nerve plexus stimulation.

Duodenal Factors

  • The duodenum must be ready to receive chyme.
  • Neuronal response (enterogastric reflex) decreases antral activity.
  • Hormonal release of cholecystokinin (CCK) inhibits stomach contraction.
  • Stimuli within the duodenum that drive neuronal and hormonal responses include fat, acid, hypertonicity, and distension.

Secretory Activity of the Stomach

  • Stomach mucosa is classed as oxyntic gland area (proximal stomach) and pyloric gland area (distal stomach).
  • Gastric mucosa comprises surface lining, pits, and glands.
  • Glands responsible for several secretions located at the base of the pits.

Secretions of the Gastric Glands

  • Parietal cells secrete hydrochloric acid (HCl) and intrinsic factor.
  • Chief cells secrete pepsinogen.
  • G cells secrete gastrin.
  • Enterochromaffin-like cells secrete histamine.
  • D cells secrete somatostatin.

Functions of the Gastric Secretions

  • HCL, activates pepsinogen to pepsin; denatures protein; kills most micro-organisms.
  • Pepsinogen, inactive precursor of peptidase pepsin; autocatalytic.
  • Intrinsic factor and gastroferrin, bind vitamin B12 and Fe2+ respectively.
  • Histamine, stimulates HCl secretion.
  • Mucus, protective.
  • Gastrin, stimulates HCl secretion and motility.
  • Somatostatin, inhibits HCl secretion.
  • Mucus, protective.

The Three Phases of Gastric Acid Secretion

  • Cephalic phase: before food reaches the stomach.
  • Gastric phase: when food is in the stomach.
  • Intestinal phase: after food leaves the stomach.

The Cephalic Phase

  • Vagus stimulates enteric neurons.
  • ACh released directly activating parietal cells.
  • GRP released causing gastrin to be released to systemic circulation.
  • Histamine released from ECL cells locally activates parietal cells.

The Gastric Phase

  • Distension of the stomach activates reflexes.
  • Food buffers pH.
  • D cell inhibition via somatostatin.
  • Amino acids (e.g. tryptophan, phenylalanine) stimulate G cells.

Inhibition of Gastric Acid Secretion

  • Cephalic phase: vagal nerve activity decreases following cessation of eating and stomach emptying.
  • Gastric phase: antral pH falls, release of somatostatin, decrease in gastrin secretion, prostaglandin E2 (PGE2).
  • Intestinal phase: factors that reduce gastric motility also reduce gastric secretion.

Secretions of the Small Intestine - hormones (1)

  • G cells secrete gastrin (into blood).
  • S cells secrete secretin (in response to H+ and fatty acids in lumen).
  • I cells secrete cholecystokinin (CCK).

Secretions of the Small Intestine - hormones (2)

  • K cells secrete glucose-dependent insulinotropic peptide (GIP).
  • L cells secrete glucagon-like peptide-1 (GLP-1).
  • M cells secrete motilin.
  • Gr cells secrete ghrelin.

Secretions of the Small Intestine (Juice)

  • Succus entericus is approximately 2 litres daily.
  • Composed of various digestive enzymes, mucus (for protection), and aqueous salts.

Pancreatic Secretions

  • Endocrine (insulin, glucagon) secreted to the blood.
  • Exocrine (digestive enzyme, aqueous NaHCO3 solution) secreted to the duodenum.

Secretion of the Pancreatic Duct Cells

  • Duct cells secrete approximately 1-2 litres of alkaline fluid containing high bicarbonate (HCO3) content per day for optimal pH.
  • Neutralizes acidic chyme entering the duodenum.
  • Protects the mucosa from erosion by acid.
  • Involves multiple channels to secrete appropriate fluids including Na+/K+ ATPase, Na+/H+ exchangers, K+/H+ ATPase.

Control of Pancreatic Secretion

  • Cephalic (vagal stimulation).
  • Gastric (gastric distension, vagovagal reflex).
  • Intestinal (see below, 70-80% total secretion

Pancreatic Enzymes

  • Acinar cells secrete enzymes that digest food.
  • Specific digestive proteases, amylases, and lipases are found and are crucial components of the pancreatic enzymes cascade.

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Hormonal Regulation of the GI Tract PDF

Description

This quiz covers the hormonal regulation of the gastrointestinal tract, focusing on the stomach and small intestine. Students will explore the gross anatomy, functions, and the hormonal controls involved in gastric secretion and emptying. Understanding the roles of acetylcholine, histamine, and gastrin in HCl production is also emphasized.

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