The Stomach Anatomy and Functions

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Questions and Answers

What is the primary function of gastric lipase in the stomach?

To digest proteins from meat

To neutralize stomach acid

To emulsify dietary fats

To split butterfat molecules found in milk (correct)

What is one key factor that stimulates gastric emptying?

Low pH levels in the stomach

Presence of large amounts of fat in the diet

Nerve impulses due to stomach distension (correct)

High levels of secretin in the blood

Which type of food spends the least amount of time in the stomach?

Foods rich in fat

Foods abundant in carbohydrates (correct)

Protein-rich foods

Foods high in fiber

Which hormone is NOT involved in inhibiting gastric emptying?

Gastrin Signup and view all the answers

What is the role of rennin in the digestive process?

To coagulate casein in milk Signup and view all the answers

What is a primary function of gastric juice?

It kills many ingested bacteria. Signup and view all the answers

Which phase of gastric secretion is triggered by the sight, smell, or taste of food?

Cephalic Phase Signup and view all the answers

What initiates the gastric phase of secretion?

Presence of food in the stomach Signup and view all the answers

Which hormone is released in response to partially digested proteins in the duodenum?

Enterogastrin Signup and view all the answers

What effect does stomach gastrin have on the gastric glands?

It stimulates them to secrete large amounts of gastric juice. Signup and view all the answers

Which factor can slow down digestion in the stomach?

Emotional stress Signup and view all the answers

What does the enterogastric reflex do?

Inhibits gastric secretion. Signup and view all the answers

Which nerve transmits impulses that stimulate gastric secretion?

Vagus nerve Signup and view all the answers

Which part of the stomach is located directly below the cardia?

Fundus Signup and view all the answers

What type of cells in the gastric glands secrete pepsinogen?

Zymogenic (peptic) cells Signup and view all the answers

What is the main function of hydrochloric acid in gastric juice?

Converting pepsinogen to pepsin Signup and view all the answers

Which layer of the stomach is primarily responsible for its ability to contract and churn food?

Muscularis Signup and view all the answers

What is the approximate daily production volume of gastric juice?

2500 ml Signup and view all the answers

Which of the following is NOT a component of gastric juice?

Insulin Signup and view all the answers

Which type of cells secrete intrinsic factor in the stomach?

Parietal (oxyntic) cells Signup and view all the answers

What is the role of the pyloric sphincter?

To regulate the passage of content into the duodenum Signup and view all the answers

What stimulates the secretion of secretin, cholecystokinin (CCK), and gastric inhibiting peptide (GIP)?

Presence of acid or partially digested proteins Signup and view all the answers

What is the main purpose of the mixing waves in the stomach?

To macerate food and mix it with gastric secretions Signup and view all the answers

How is pepsin activated in the stomach?

By conversion from pepsinogen due to hydrochloric acid Signup and view all the answers

Which of the following best describes the role of mucus in the stomach?

To protect the stomach lining from pepsin Signup and view all the answers

What type of digestion occurs in the stomach in addition to mechanical digestion?

Chemical digestion Signup and view all the answers

Which of the following factors would NOT initiate the reflex inhibiting gastric secretion?

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

What pH range is pepsin most effective at during the stomach's digestive process?

pH 2 Signup and view all the answers

What characterizes mechanical digestion in the stomach?

The peristaltic mixing waves reducing food to chyme Signup and view all the answers

Study Notes

The Stomach

The stomach is a muscular organ in the gastrointestinal tract.
It has four main sections: cardia, fundus, body, and pylorus.
The cardia surrounds the lower esophageal sphincter.
The fundus is the rounded part above and to the left of the cardia.
The body is the large central portion of the stomach.
The pylorus is the narrow inferior region connecting to the duodenum and has a pyloric sphincter.

Stomach Linings

The stomach wall has the same four layers as other parts of the GI tract.
These layers are mucosa, submucosa, muscularis, and serosa.
Mucosa: simple columnar epithelium with rugae (folds), gastric glands (pits).
Submucosa: loose areolar connective tissue.
Muscularis: three layers of smooth muscle (outer longitudinal, middle circular, inner oblique). This allows for churning, breaking food into small pieces, mixing with gastric juices, and moving it into the duodenum.

Gastric Glands

The gastric glands have several types of secreting cells.
Zymogenic (peptic) cells: secrete pepsinogen (an enzyme precursor).
Parietal (oxyntic) cells: secrete hydrochloric acid and intrinsic factor.
Mucous cells: secrete mucus.
Enteroendocrine cells: secrete stomach gastrin.

Gastric Juice

Gastric juice is a mixture of secretions from different cells.
It contains hydrochloric acid, mucus, and enzymes (pepsinogen → pepsin).
Approximately 2500 ml of gastric juice are produced daily.
It has a pH of 2.

Composition of Gastric Juice

Cations: Na+, K+, Mg2+, H+
Anions: Cl-, HPO42-, SO42-
Pepsin I-III
Gelatinase
Mucus
Intrinsic factor (important for vitamin B12 absorption)
Water
Hydrochloric acid

Hydrochloric Acid

Hydrochloric acid converts pepsinogen to pepsin.
It plays several roles, including killing bacteria, aiding in protein digestion, and stimulating bile and pancreatic juice release.
It is formed by the combination of H+ and Cl– ions.

Regulation of Gastric Secretion

Gastric secretion is regulated by both nervous and hormonal mechanisms.
Parasympathetic impulses (via the vagus nerve) stimulate gastric gland secretions of pepsinogen, HCl, and mucus.
Stomach gastrin is secreted by the gastric glands in response to food entering the stomach.
Emotions like anger or fear slow down digestion.

Stimulation of Gastric Secretion

Divided into three phases: cephalic (reflex), gastric, and intestinal.
Cephalic phase: triggered by sight, smell, and taste of food.
Gastric phase: triggered by food distension in the stomach.
Intestinal phase: triggered by partially digested proteins & fats entering the duodenum.

Inhibition of Gastric Secretion

Occurs in the presence of food in the small intestine.
The small intestine sends impulses to the medulla to inhibit gastric secretion.
Various stimuli (distension, acid, partially digested proteins), initiate the enterogastric reflex and hormone production.

Hormonal Inhibition of Gastric Secretion

The intestinal mucosa secretes hormones (secretin, CCK, GIP) to inhibit gastric secretion and decrease motility.
These hormones are stimulated by acid, partially digested proteins, fats, and irritants.

Digestion in the Stomach

Digestion occurs mechanically and chemically.
Mechanical digestion involves mixing waves (peristaltic contractions) churning food, mixing with secretions, and creating chyme.
Chemical digestion involves pepsin (protein digestion), and gastric lipase (limited role in fat digestion)

How Pepsin Works

Pepsin is most active in the acidic stomach environment (pH 2).
Pepsinogen is converted to pepsin by HCl (hydrochloric acid) in the stomach.
Mucus protects the stomach lining from being digested by pepsin.

Further Chemical Digestion

Gastric lipase: present in the stomach (best at pH 5-6), aids in milk fat digestion.
Rennin: produced by infant stomachs, helps digest milk protein (casein).

Regulation of Gastric Emptying

Gastric emptying is stimulated by nerve impulses (due to distension), and stomach gastrin.
The stomach empties its contents into the duodenum within ~2-6 hours.
The rate of stomach emptying is determined by the duodenum’s ability to process chyme.

Inhibition of Gastric Emptying

The enterogastric reflex and hormones (secretin, CCK, GIP) inhibit gastric emptying.
Various factors (distension, acid, partially digested proteins/fats) in the duodenum trigger these mechanisms.

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Description

This quiz covers the anatomy of the stomach, including its main sections and layers. It also explores the role of gastric glands and their importance in digestion. Assess your knowledge about the structure and functioning of this vital organ.