Stomach Anatomy and Functions

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Questions and Answers

What is the most important factor in the propulsion of contents during vomiting?

Contractions of the diaphragm and abdominal muscles (correct)

Relaxation of the fundus of the stomach

Increased intragastric pressure in the esophagus

Contraction of the lower esophageal sphincter

Which of the following autonomic changes is NOT typically associated with vomiting?

Decreased heart rate (correct)

Sweating

Increased breathing rate

Pupil dilatation

How do emetics produce vomiting in the body?

By reducing gastric motility

By blocking the vomiting center directly

By irritating the gastrointestinal tract mucosa or stimulating central areas (correct)

By promoting saliva production in the glands

What role do sensory impulses from the gastrointestinal tract play in vomiting?

They reach the vomiting center through sympathetic and parasympathetic nerves Signup and view all the answers

Which stimulant can cause vomiting due to its effect on the chemosensitive trigger zone?

Morphine Signup and view all the answers

What primarily stimulates gastric acid secretion during the cephalic phase?

Psychic stimuli such as seeing or thinking of food Signup and view all the answers

Which factor is NOT a damaging factor contributing to the development of peptic ulcers?

Prostaglandins Signup and view all the answers

In the gastric phase of gastric acid secretion, which mechanism is primarily involved?

Both nervous and hormonal mechanisms Signup and view all the answers

What is the primary cause of a gastric ulcer?

Infection with H. pylori Signup and view all the answers

How does chronic stress affect gastric acid secretion?

It stimulates secretion Signup and view all the answers

Which condition is characterized by ulceration of the duodenal mucosa?

Duodenal ulcer Signup and view all the answers

Which treatment option for peptic ulcers primarily works by suppressing acid production?

Omeprazole Signup and view all the answers

What role does the vagus nerve play in the regulation of gastric acid secretion?

It stimulates secretion directly and indirectly Signup and view all the answers

What is the primary role of pepsinogens in the digestive system?

To hydrolyze proteins into short chain peptides Signup and view all the answers

Which enzyme is primarily responsible for the hydrolysis of triacylglycerols in the stomach?

Gastric lipase Signup and view all the answers

What function does intrinsic factor serve in the digestive system?

It combines with vitamin B12 to facilitate its absorption Signup and view all the answers

Which component is secreted by the mucus neck cells and surface epithelial cells for protection?

Mucus and bicarbonate Signup and view all the answers

What stimulates the secretion of gastrin?

Distension of the stomach and digestion products Signup and view all the answers

Which physiological function is NOT directly associated with gastrin?

Inhibiting gastric motility Signup and view all the answers

What is the optimum pH range for pepsin activity?

1.8 - 3.5 Signup and view all the answers

In cases of deficiency of intrinsic factor, what condition can arise?

Megaloblastic anemia Signup and view all the answers

What are the main components secreted in gastric juice?

Pepsinogen and Hydrochloric Acid Signup and view all the answers

Which regions of the stomach are associated with specific secretory functions?

Body and Antrum with different gland types Signup and view all the answers

Which cell type is responsible for secreting hydrochloric acid in the stomach?

Oxyntic cells Signup and view all the answers

What role does gastric acid play in digestion?

Activates pepsinogen to pepsin Signup and view all the answers

During which phase is approximately 30% of gastric acid secretion stimulated?

Cephalic phase Signup and view all the answers

Which function of the stomach is mainly responsible for the storage and control of emptying into the duodenum?

Storage function Signup and view all the answers

Which cell type is responsible for secreting gastrin in the stomach?

G cells Signup and view all the answers

What is the primary pH range of gastric juice?

1-4 Signup and view all the answers

What characterizes the proximal part of the stomach during receptive relaxation?

It accommodates food and is involved in esophageal motility. Signup and view all the answers

Which reflex mediates the process of receptive relaxation in the stomach?

Vagovagal reflex Signup and view all the answers

What is the primary function of peristaltic contractions in the stomach?

To propel and retropulse food within the digestive tract. Signup and view all the answers

What role does the pylorus play in gastric emptying?

It regulates the outflow of chyme into the duodenum. Signup and view all the answers

Which factor is known to slow gastric emptying?

Presence of fat in the duodenum Signup and view all the answers

What is the gastric emptying time for a healthy intact stomach?

6 hours Signup and view all the answers

How does the pylorus function during gastric emptying?

It closes when pressure from the peristaltic contraction approaches. Signup and view all the answers

What physiological process occurs during fasting in the stomach?

Migrating Myoelectric Complexes (MMC). Signup and view all the answers

What initiates peristaltic contractions in the stomach?

Distension of the stomach. Signup and view all the answers

Which of the following sequences correctly describes the mechanism of vomiting?

Nausea, deep breath, glottis closed, breath held. Signup and view all the answers

Which of the following components is essential for the coordinated motility activities during gastric emptying?

Duodenal bulb Signup and view all the answers

Which hormone is primarily involved in regulating Migrating Myoelectric Complexes (MMC)?

Motilin Signup and view all the answers

What is the role of slow wave activity in gastric motility?

It establishes the foundation for the electrical rhythm of gastric contractions. Signup and view all the answers

What triggers the vomiting reflex apart from irritants in the stomach?

Over distension of the stomach or duodenum. Signup and view all the answers

What is the primary function of the gastroduodenal pump in gastric emptying?

To regulate the rate of gastric emptying. Signup and view all the answers

Which of the following best describes the condition known as emesis?

Forceful expulsion of stomach and intestinal contents. Signup and view all the answers

Study Notes

Stomach Activities

Two main activities in the stomach are gastric secretion and gastric motility.

Stomach Anatomy

The stomach is sac-like and divided into three regions: fundus, body, and antrum.
The stomach wall has distinct layers.
The mucosa has folds (rugae) and pits opening into gastric glands.
Different cell types in the mucosa secrete various gastric juice components, including hydrochloric acid (HCl), intrinsic factor, pepsinogen, gastrin, mucus, and bicarbonate.

Stomach Regions

The esophagus connects to the stomach at the lower esophageal sphincter.
The fundus is the top portion of the stomach.
The body is the main part of the stomach.
The antrum is the lower portion of the stomach, which connects to the duodenum via the pyloric sphincter.
The duodenum is the first part of the small intestine.

Stomach Functions

Storage: The stomach stores food and controls its emptying into the duodenum (most important functions)
Digestion: The stomach digests food using enzymes, HCl, and motility, three main food types are digested
Secretion: The stomach secretes HCl, pepsinogen, intrinsic factor, gastric lipase, mucus, and bicarbonate.
Absorption: The stomach absorbs water, alcohol, and some drugs.
Protection: The stomach protects its lining using bicarbonate mucus barrier, and secretion of inactive pepsinogen.

Gastric Secretion

Composition: Gastric juice contains hydrochloric acid, pepsinogen & gastric lipase, mucus, bicarbonate, and intrinsic factor.
Rate: The rate of secretion is 2-3 liters per day.
pH: Gastric juice is highly acidic (pH 1-4).
Protection: Mucosa needs protection from its own secretions.

Glands and Cell Types in Gastric Mucosa

Body: Parietal glands contain oxyntic cells, chief cells, and mucus neck cells.
Antrum: Pyloric glands contain mucus neck cells and G cells.

Gastric Hydrochloric Acid Secretion

Origin: Secreted by parietal cells in oxyntic glands.
Functions: Essential for activating pepsinogen to pepsin, for acidifying stomach contents, and to sterilize foods, for absorbing iron & calcium
pH: Stomach acidity is maintained between 1-4

Mechanisms for HCl Secretion

The process involves complex cellular mechanisms and transporters to move hydrogen ions (H+) into the lumen of the stomach.

Cellular Mechanisms of HCl Secretion

Secretion stimulated by acetylcholine, gastrin, histamine.

Regulation of Gastric Acid Secretion

Cephalic Phase: Responsible for about 30% of gastric acid secretion that occurs through reflex, involving several stimuli like smell, taste, and thinking of food.
Gastric Phase: Responsible for about 60% of gastric acid secretion, stimulated by the presence of food in the stomach.
Intestinal Phase: Responsible for about 10% of gastric acid secretion, triggered by the presence of food in the small intestine.

Peptic Ulcer

Cause: A lesion in the stomach or duodenum caused by the erosive action of HCl and pepsin.
Types: Gastric ulcer (stomach) and duodenal ulcer (duodenum).
Causes of ulcers: Loss of protective mucus barrier, damage factors (HCl, pepsin, H pylori, NSAIDs, smoking, stress, and alcohol).
Treatment: antacids, omeprazole, cimetidine, ranitidine, and surgery.

Secretion of Pepsinogens, Gastric Lipase, Intrinsic Factor, Mucus & Bicarbonate, Gastrin

Pepsinogens: Inactive precursors of pepsin, activated by HCl and pepsin.
Gastric Lipase: Enzyme to digest fat.
Intrinsic Factor: Glycoprotein to absorb vitamin B12.
Mucus and Bicarbonate: Provide a protective barrier for the stomach lining.
Gastrin: Hormone stimulating gastric acid secretion.

Gastric Lipase

Hydrolyzes triacylglycerols (particularly those with short-chain fatty acids).
Acts at a pH of 4-7.
Less important than pancreatic lipase.

Intrinsic Factor

Secreted by parietal cells.
Combines with vitamin B12 to protect it during passage in the small intestine.
Absorbs vitamin B12 in the distal ileum.

Mucus & Bicarbonate

Secreted by mucus neck cells and surface epithelial cells.
Creates a protective barrier against mechanical and chemical damage.

Gastrin

Secreted by G cells in the antrum and upper small intestine.
Stimulates gastric acid secretion and other functions. (physiological & pharmacological functions)
Regulated by many factors including emotions and high stomach acidity.

Gastric Motility

Orad Region: Fundus and proximal body, thin walled, and responsible for receptive relaxation.
Caudal Region: distal body and antrum, thick walled, responsible for peristaltic contractions, responsible for mixing and grinding food.
Slow Wave Activities: The electrical basis of gastric motility, originating in the greater curvature at a rate of 3/minute.

Components of Gastric Motility During Fed State

Receptive relaxation, peristaltic contractions, and gastric emptying.

Receptive Relaxation

Relaxation of the proximal part of the stomach, including the fundus and proximal body to accommodate food.
Continuation of esophageal motility.
Mediated through the vagovagal reflex.

Peristaltic Contractions

Main motility function in the distal part of the stomach.
Propulsion and retropulsion of food.
Grinding and mixing of food.
Initiated by distension and mediated by vagovagal reflexes.

Gastric Emptying

The process releases partially digested food into the duodenum.
It is regulated by coordinated motility activities in the antrum, pylorus, and duodenal bulb (gastroduodenal pump).
Emptying time varies from 1.5-6 hours for healthy stomachs.

Regulation of Gastric Emptying

The rate of emptying is dependent on conditions like the state of the stomach, pyloric sphincter, and duodenum.
Factors that control gastric emptying: characteristics of food in stomach (chemical & physical), factors that influence rate such as: gastrin & presence of H+ & fats in duodenum.,

Factors enhance gastric emptying: gastrin & large volumns of food.
Factors slow gastric emptying: presence of H+ & fats in the duodenum

Migrating Myoelectric Complexes (MMCs)

Peristaltic contractions that replace the fed state gastric motility functions.
Occur in fasting state.
Clean the stomach.

Vomiting (Emesis)

Mechanism: Forceful expulsion of stomach and intestinal contents through the mouth involving a number of steps: (salivation, retching, increased pressure in the stomach)
Regulation: Centrally regulated by a vomiting center in the medulla, and also receives inputs from different areas of the brain, and the gastrointestinal tract.
Stimulation: Stimulated by irritant substances, over distension, and over stimuli from internal and external environments.
Components: Autonomic changes including increased heart rate, increased breathing rate, sweating, and dilated pupils, accompanied by peripheral or central stimulation of various receptors (irritation of mucosa, etc.)

Control of Vomiting

Medulla centers: Two centers in the medulla are involved in the regulation.
- Vomiting center
- Chemosensitive trigger zone
Sensory Input: Sensory signals from the gastrointestinal tract (distension or irritation), vestibular system, and other areas reach the vomiting center.
Drug effects: Drugs like morphine affect the chemosensitive trigger zone which influences the vomiting center

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Description

Explore the anatomy and functions of the stomach through this informative quiz. Learn about gastric secretion, motility, and the specific regions of the stomach. Test your knowledge on the roles and structures that contribute to digestion and food storage.