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?

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

What is the role of rennin in the digestive process?

<p>To coagulate casein in milk (C)</p> Signup and view all the answers

What is a primary function of gastric juice?

<p>It kills many ingested bacteria. (D)</p> Signup and view all the answers

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

<p>Cephalic Phase (C)</p> Signup and view all the answers

What initiates the gastric phase of secretion?

<p>Presence of food in the stomach (D)</p> Signup and view all the answers

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

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

What effect does stomach gastrin have on the gastric glands?

<p>It stimulates them to secrete large amounts of gastric juice. (C)</p> Signup and view all the answers

Which factor can slow down digestion in the stomach?

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

What does the enterogastric reflex do?

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

Which nerve transmits impulses that stimulate gastric secretion?

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

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

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

What type of cells in the gastric glands secrete pepsinogen?

<p>Zymogenic (peptic) cells (B)</p> Signup and view all the answers

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

<p>Converting pepsinogen to pepsin (B)</p> Signup and view all the answers

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

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

What is the approximate daily production volume of gastric juice?

<p>2500 ml (B)</p> Signup and view all the answers

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

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

Which type of cells secrete intrinsic factor in the stomach?

<p>Parietal (oxyntic) cells (A)</p> Signup and view all the answers

What is the role of the pyloric sphincter?

<p>To regulate the passage of content into the duodenum (A)</p> Signup and view all the answers

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

<p>Presence of acid or partially digested proteins (A)</p> Signup and view all the answers

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

<p>To macerate food and mix it with gastric secretions (A)</p> Signup and view all the answers

How is pepsin activated in the stomach?

<p>By conversion from pepsinogen due to hydrochloric acid (C)</p> Signup and view all the answers

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

<p>To protect the stomach lining from pepsin (A)</p> Signup and view all the answers

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

<p>Chemical digestion (C)</p> Signup and view all the answers

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

<p>Presence of carbohydrates in the duodenum (D)</p> Signup and view all the answers

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

<p>pH 2 (A)</p> Signup and view all the answers

What characterizes mechanical digestion in the stomach?

<p>The peristaltic mixing waves reducing food to chyme (D)</p> Signup and view all the answers

Flashcards

Stomach Layers

The stomach wall has four basic layers similar to other parts of the gastrointestinal tract, but with modifications.

Gastric Mucosa

The lining of the stomach, folded into rugae when empty. Contains gastric glands opening into the lamina propria.

Gastric Glands

Small openings in the stomach lining containing cells that produce stomach secretions.

Pepsinogen

Enzyme precursor produced by zymogenic cells in gastric glands, and converted to pepsin by HCl.

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Hydrochloric Acid (HCl)

Acid secreted by parietal cells, activates pepsin, helps digestion and kills bacteria.

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Intrinsic Factor

Substance secreted by parietal cells vital for vitamin B12 absorption for red blood cell production.

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Stomach Muscularis

Three layers of smooth muscle (longitudinal, circular, oblique) enabling churning and mixing of food.

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Gastric Juice Composition

Mixture of secretions from different cells containing enzymes, acids, and other substances.

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Gastric Secretion

The production of gastric juice by the stomach, regulated by both nerves and hormones.

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Cephalic Phase

The initial phase of gastric secretion, triggered by stimuli before food enters the stomach (e.g., sight, smell, taste).

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Gastric Phase

Phase of gastric secretion triggered by food in the stomach, involving both nervous and hormonal mechanisms.

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Intestinal Phase

Phase of gastric secretion triggered by partially digested proteins in the small intestine, involving hormones like enterogastrin.

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Stomach Gastrin

A hormone secreted by the stomach that stimulates further gastric juice production and other processes.

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Enterogastric Reflex

A reflex that inhibits gastric secretion when food enters the small intestine.

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Parasympathetic Impulses

Nerve signals that stimulate gastric gland activity, promoting digestion.

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Vagus Nerve

The nerve carrying parasympathetic impulses to the stomach, vital for gastric secretion.

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Gastric lipase function

Gastric lipase is an enzyme that breaks down butterfat molecules in milk. It works best at a pH between 5 and 6.

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Infant stomach enzyme

Rennin, secreted by infant stomachs, helps digest milk protein (casein).

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Gastric emptying factors

Gastric emptying is stimulated by nerve signals (distension) and the hormone gastrin released by certain food types.

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Factors inhibiting gastric emptying

The enterogastric reflex, secretin, CCK, and GIP all slow down gastric emptying.

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Stomach emptying rate

The stomach empties its contents into the small intestine in 2-6 hours, with carbohydrate-rich food taking the shortest time and fat-rich food taking the longest.

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Nerve impulse inhibition

Nerve impulses from the duodenum to the medulla inhibit gastric secretion by reducing parasympathetic stimulation and increasing sympathetic activity.

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Duodenal stimuli

Distension, acid, partially digested proteins, or irritation in the duodenum trigger inhibitory reflexes.

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Hormonal inhibition

Intestinal hormones (secretin, CCK, GIP) decrease gastric secretion and motility.

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Hormone triggers

Acid or partially digested proteins, fats, fluids imbalances, and irritants in the intestine trigger hormone release.

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Mechanical Digestion

Mixing and maceration of food by stomach contractions, turning it into chyme.

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Chyme formation

Thick liquid formed by mixing food with gastric secretions due to stomach contractions.

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Pepsin activation

Pepsinogen, secreted by chief cells, becomes active pepsin in the acidic stomach environment (hydrochloric acid from parietal cells).

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Protein Digestion

Stomach's main role in protein digestion is initiating the process using pepsin.

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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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