Hormonal Regulation of the GI Tract

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Questions and Answers

What primarily governs the delivery of chyme to the duodenum?

Gastric motility and pyloric sphincter opening (correct)

Neuronal signals from the duodenum

Consistency of food before reaching the stomach

Hormonal regulation from the pancreas

What effect does distension of the stomach have on motility?

Decreases motility due to increased pressure

Increases motility by stimulating intrinsic nerve plexuses (correct)

Has no effect on gastric emptying

Increases motility only when the pyloric sphincter is closed

What role do enterogastrones play in gastric emptying?

Stimulate gastric contractions to enhance emptying

Increase the volume of chyme in the stomach

Inhibit stomach contractions to delay emptying (correct)

Facilitate digestion of fats in the stomach

Which factor is NOT considered a gastric factor affecting stomach emptying?

Release of enterogastrones Signup and view all the answers

Which of the following substances in the duodenum most effectively delays gastric emptying?

Fat Signup and view all the answers

What is the consequence of hypertonicity in the duodenum on gastric emptying?

Guards against reduced plasma volume and circulatory disturbances Signup and view all the answers

What triggers the enterogastric reflex that slows gastric emptying?

Signals from the intrinsic nerve plexuses and ANS Signup and view all the answers

What role does somatostatin play during the gastric phase of digestion?

It decreases gastrin secretion. Signup and view all the answers

Which hormone is primarily responsible for promoting the secretion of pancreatic and biliary HCO3-?

Secretin Signup and view all the answers

Which hormone inhibits gastric emptying and also stimulates the release of insulin from pancreatic β-cells?

Glucose-dependent insulinotropic peptide (GIP) Signup and view all the answers

What is the effect of the hormone glucose-dependent insulinotropic peptide (GIP) on gastric motility?

It inhibits gastric motility. Signup and view all the answers

Which hormone is released from M cells during the fasting state to initiate the migrating motor complex?

Motilin Signup and view all the answers

What effect does the binding of histamine to H2 receptors have on adenylyl cyclase?

It activates adenylyl cyclase, increasing cAMP. Signup and view all the answers

What is the role of somatostatin in gastric acid secretion?

It binds to SST2R receptors, inhibiting adenylyl cyclase. Signup and view all the answers

During the resting state of the parietal cell, where is the majority of the H+/K+ATPase located?

In the cytoplasmic tubulovesicles. Signup and view all the answers

Which factor primarily stimulates the trafficking of H+/K+ATPase to the apical membrane?

Binding of secretagogues such as ACh and gastrin. Signup and view all the answers

What ions are primarily involved in the processes described in the gastric lumen?

H+ and Cl-. Signup and view all the answers

Which pathway does NOT contribute to the trafficking of H+/K+ATPase to the apical membrane?

Inhibition triggered by increased levels of somatostatin. Signup and view all the answers

What happens to cAMP levels when somatostatin binds to its receptor?

cAMP levels decrease. Signup and view all the answers

Which receptor is associated with the action of acetylcholine (ACh) in the parietal cells?

M3. Signup and view all the answers

In the stimulated state, what structural change occurs in the parietal cell?

Trafficking of H+/K+ATPase to the apical membrane. Signup and view all the answers

What triggers the cephalic phase of gastric acid secretion?

Visual stimuli of food Signup and view all the answers

Which statement correctly describes the gastric phase of gastric acid secretion?

It includes both physical and chemical mechanisms. Signup and view all the answers

During which phase of gastric acid secretion does the body prepare to receive food?

Cephalic phase Signup and view all the answers

What are the main controls of gastric secretion during the intestinal phase?

Neuronal and hormonal mechanisms Signup and view all the answers

What role do prostaglandins play in gastric acid secretion?

Inhibiting gastric acid secretion Signup and view all the answers

Which cranial nerve is primarily involved in the cephalic phase of gastric acid secretion?

Vagus nerve (CN X) Signup and view all the answers

Which of the following best describes the intestinal phase?

It occurs after chyme has left the stomach. Signup and view all the answers

What does the presence of food in the stomach primarily stimulate?

Gastric phase Signup and view all the answers

What is NOT a function of the cephalic phase in gastric acid secretion?

Direct chemical breakdown of food Signup and view all the answers

What mechanism primarily inhibits gastric acid secretion?

Prostaglandins action on D-cells Signup and view all the answers

What triggers the activation of G cells in the stomach?

Amino acids like tryptophan and phenylalanine Signup and view all the answers

In the context of gastric acid secretion, what role does vagal activation play?

It enhances the secretion of gastrin Signup and view all the answers

How does the buffering of pH by food affect gastrin release?

It decreases the inhibition of gastrin release Signup and view all the answers

Which neurotransmitter is primarily responsible for stimulating acid secretion in the stomach?

ACh (Acetylcholine) Signup and view all the answers

Which of the following best describes the role of ECL cells in gastric physiology?

They secrete histamine to promote acid secretion Signup and view all the answers

What is the primary effect of gastric distension on gastric secretion?

Stimulates the release of gastrin Signup and view all the answers

What happens to gastrin levels when somatostatin is released from D cells?

Gastrin levels decrease Signup and view all the answers

What effect does increased pH have on gastrin secretion?

It promotes the release of somatostatin Signup and view all the answers

Which component is primarily activated by enteric neurons to stimulate parietal cells?

ACh (Acetylcholine) Signup and view all the answers

Which of the following statements about the roles of neurotransmitters in gastric physiology is accurate?

ACh increases gastric motility and acid secretion Signup and view all the answers

Study Notes

Hormonal Regulation of the Gastrointestinal Tract

The gastrointestinal system is hormonally regulated.
There are different types of cells involved (e.g., parietal cells).
The stomach contains glands that secrete gastric juice.
The stomach has different regions (e.g., fundus and antrum).
Stomach emptying is controlled by the strength of antral waves and the pyloric sphincter.
The rate is proportional to the volume of chyme in the stomach.
Factors affecting emptying (e.g., consistency of chyme, duodenal factors).

Learning Objectives

Students should be able to outline the gross anatomy and mechanical functions of the stomach.
Describe the process of gastric emptying and its controls.
List the gastric gland secretions and their functions.

The Stomach

J-shaped, with capacity ranging from 50 to 1000ml.
Accommodates food from the esophagus.
Starts protein digestion (pepsin and HCI).
Continues carbohydrates digestion (salivary amylase).
Mixes food with gastric secretions into chyme.
Stores food before passing to the small intestine.
Secretes approximately 2 liters of gastric juice daily from gastric glands.

Mechanical Activity of the Stomach

Occurs in two types:
- Orad stomach (fundus and proximal body) – tonic.
- Caudad stomach (distal body and antrum) – phasic.

Control of Stomach Emptying

Strength of antral waves and pyloric sphincter opening determine chyme delivery.
Governed by gastric and duodenal factors.
Rate of emptying proportional to chyme volume.
Distension increases motility due to: stretch of smooth muscle, stimulation of intrinsic nerve plexuses, and increased vagus nerve activity and gastrin release.
Empting facilitated by thin liquid chyme.

Duodenal Factors

Duodenum must be ready to receive chyme.
Delays emptying through enterogastric reflex.
Enterogastrones (e.g., cholecystokinin CCK) inhibit stomach contraction.
Stimuli in the duodenum (e.g., fat, acid, hypertonicity, distension) drive neural and hormonal responses.

Secretory Activity of the Stomach

Mucosa is categorized into oxyntic gland area (proximal stomach) and pyloric gland area (distal stomach).
Composed of a surface lining, pits, and glands at the base of the pits.
These glands are responsible for various secretions.

Secretions of the Gastric Glands

Secretion includes hormones (e.g., gastrin).
Includes different types of cells (e.g., chief cells, parietal cells, G cells, D cells and ECL cells).
Different secretions have specific roles, such as activating pepsinogen to pepsin, stimulating HCI secretion, and binding vitamin B12.

Functions of Gastric Secretions

HCI activates pepsinogen and denatures proteins and kills microbes.
Pepsinogen activates to pepsin and is involved in protein digestion.
Intrinsic factor is crucial for Vitamin B12 absorption.
Gastroferrin is critical.
Histamine and other substances activate HCI secretion.
Mucous protects the stomach lining.

HCI Secretion Mechanism

Proton pumps actively secrete H+.
Bicarbonate is exchanged for Cl-, which enters the stomach lumen.

Gastrin and other hormones (e.g. ACh, Histamine)

Stimulate or inhibit HCl secretion.
Hormone functions can cause HCl secretion or have other functions.
Affect the H+/K+ATPase to promote HCl secretion.

Secretagogues Cause Trafficking of the H+/K+ATPase

Resting state—H+/K+ATPase is within cytoplasmic tubulovesicles.
Stimulated state—H+/K+ATPase moves to apical membrane.

Inhibition of Gastric Acid Secretion

Cephalic, gastric, and intestinal phases involve different mechanisms to inhibit secretion.
Vagus nerve activity decreases, and other factors (e.g., reduced pH) affect these phases.
Prostaglandins and somatostatin play a role in decreasing acid secretion.

Secretions of the Small Intestine- Hormones (1 & 2)

Small intestine secretes various peptide hormones (e.g., gastrin, secretin, CCK, GIP, GLP-1, Motilin, Ghrelin).
These hormones play roles in regulating digestion, nutrient absorption, and gastric emptying.

Secretions of the Small Intestine (Juice)

The small intestine secretes succus entericus, a juice with varying compositions.
Its secretion regulated by mechanisms, including hormones (e.g., gastrin, CCK, secretin) nerve activity, and distension.

Pancreatic Secretions

Contains both endocrine (e.g., insulin and glucagon) and exocrine (e.g., enzymes and bicarbonate) components.
Exocrine is the aqueous NaHCO3- solution to the duodenum as pancreatic juice.

Secretion of the Pancreatic Duct Cells

Pancreatic ducts secrete alkaline fluid (HCO3-) into the duodenum.
This neutralizes stomach acid, optimizes pH for enzymes, and protects the mucosa.
Mechanisms involve various transporters.

Pancreatic Enzymes

Acinar cells release enzymes (e.g., proteases, amylases, lipases) to digest food.
These enzymes are initially inactive to prevent premature activation.
Enterokinase activates the enzymes in the duodenum.

Control of Pancreatic Secretion

Cephalic, gastric, and intestinal phases regulate secretion.
These phases involve various stimuli (e.g., presence of acid in the duodenum, fat) that activate different pathways.

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Description

This quiz focuses on the hormonal regulation of the gastrointestinal tract, particularly the function and anatomy of the stomach. Students will explore gastric emptying processes, gastric gland secretions, and factors affecting digestion. Enhance your understanding of how hormones interact with the GI system.