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?

It provides optimum pH for pancreatic enzyme function Signup and view all the answers

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

Production from carbon dioxide and water Signup and view all the answers

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

Stimulate appetite Signup and view all the answers

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

Beta cells Signup and view all the answers

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

Irritation and distension Signup and view all the answers

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

Alkaline HCO3- rich fluid Signup and view all the answers

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

Digestive enzymes Signup and view all the answers

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

Overactive secretion of aqueous salts Signup and view all the answers

Which of the following influences gastric emptying regulation most significantly?

Gastric distension and endocrine signals Signup and view all the answers

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

Secretion of digestive enzymes Signup and view all the answers

What role does pepsin play in the stomach?

Activates pepsinogen autocatalytically Signup and view all the answers

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

Intrinsic factor Signup and view all the answers

How does histamine influence gastric function?

Stimulates HCl secretion Signup and view all the answers

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

Inhibits HCl secretion Signup and view all the answers

What is the role of gastrin in the gastric system?

Stimulates HCl secretion and motility Signup and view all the answers

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

H+/K+ ATPase Signup and view all the answers

What protective role does mucus play in the gastrointestinal tract?

Protects mucosa from acid damage Signup and view all the answers

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

Gastroferrin Signup and view all the answers

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

It helps produce HCl from CO2 and H2O Signup and view all the answers

What mechanism aids in bicarbonate secretion from gastric cells?

Cl-/HCO3- exchanger Signup and view all the answers

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

Inhibits gastric emptying Signup and view all the answers

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

Gastrin Signup and view all the answers

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

It inhibits gastric emptying Signup and view all the answers

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

Promotes secretion of pancreatic and biliary bicarbonate Signup and view all the answers

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

Enterogastrones release Signup and view all the answers

What effect does motilin have in the digestive system?

Initiates the migrating motor complex Signup and view all the answers

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

Increasing appetite Signup and view all the answers

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

Glucagon-like peptide-1 (GLP-1) 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?

Secretin Signup and view all the answers

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

Reduces HCl secretion Signup and view all the answers

What role do pancreatic secretions play in digestion?

They neutralize stomach acid and digest macromolecules. Signup and view all the answers

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

Intestinal phase Signup and view all the answers

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

Cholecystokinin (CCK) Signup and view all the answers

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

Autocatalysis initiated by enterokinase Signup and view all the answers

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

To export H+ ions during bicarbonate secretion. Signup and view all the answers

Which enzyme is activated by trypsin in the pancreatic secretions?

Chymotrypsinogen to chymotrypsin Signup and view all the answers

What initiates the cephalic phase of pancreatic secretion?

Vagal stimulation due to thoughts of food Signup and view all the answers

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

Na+ Signup and view all the answers

What does secretin stimulate in pancreatic ducts?

Secretion of aqueous NaHCO3 solution Signup and view all the answers

How does CCK affect pancreatic acinar cells?

Stimulates secretion of digestive enzymes Signup and view all the answers

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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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.