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Questions and Answers
Which neurotransmitter is NOT listed as being present in the bowel?
Which neurotransmitter is NOT listed as being present in the bowel?
What role does the pyloric sphincter play in gastric digestion?
What role does the pyloric sphincter play in gastric digestion?
Which of the following classes of cells are responsible for secreting gastric hormones?
Which of the following classes of cells are responsible for secreting gastric hormones?
During which phase do receptive relaxations occur in the stomach?
During which phase do receptive relaxations occur in the stomach?
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What function does the antrum primarily serve in gastric motility?
What function does the antrum primarily serve in gastric motility?
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Which hormone is known for its role in stimulating appetite and promoting food intake?
Which hormone is known for its role in stimulating appetite and promoting food intake?
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What is the primary function of hydrochloric acid in the stomach?
What is the primary function of hydrochloric acid in the stomach?
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Which part of the stomach acts as the primary storage area?
Which part of the stomach acts as the primary storage area?
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What primarily drives gastric emptying?
What primarily drives gastric emptying?
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Which of the following components regulates gastric emptying?
Which of the following components regulates gastric emptying?
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What is the role of the pyloric sphincter during gastric emptying?
What is the role of the pyloric sphincter during gastric emptying?
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Which substances trigger hormonal responses that influence gastric emptying?
Which substances trigger hormonal responses that influence gastric emptying?
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What occurs in the fundic area of the stomach?
What occurs in the fundic area of the stomach?
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What effect does secretin have when produced in response to low pH levels in the duodenum?
What effect does secretin have when produced in response to low pH levels in the duodenum?
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What is the primary purpose of chyme formation in the stomach?
What is the primary purpose of chyme formation in the stomach?
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How do the receptors in the duodenal and jejunal mucosa affect gastric emptying?
How do the receptors in the duodenal and jejunal mucosa affect gastric emptying?
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Which phase of gastric secretion accounts for 60% of the acid response to a meal?
Which phase of gastric secretion accounts for 60% of the acid response to a meal?
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What type of cells secrete gastrin in response to food intake?
What type of cells secrete gastrin in response to food intake?
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Which neurotransmitter primarily stimulates the parietal cells directly during the cephalic phase?
Which neurotransmitter primarily stimulates the parietal cells directly during the cephalic phase?
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How does somatostatin affect gastrin release?
How does somatostatin affect gastrin release?
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Which of the following substances is considered the strongest agonist for H+ secretion?
Which of the following substances is considered the strongest agonist for H+ secretion?
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Which factor is least responsible for stimulating acid secretion during the intestinal phase?
Which factor is least responsible for stimulating acid secretion during the intestinal phase?
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What is the primary function of intrinsic factor in the gastrointestinal system?
What is the primary function of intrinsic factor in the gastrointestinal system?
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Which mechanism is primarily involved in the vagovagal reflex during gastric phase?
Which mechanism is primarily involved in the vagovagal reflex during gastric phase?
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What triggers the release of pepsinogen from chief cells in the stomach?
What triggers the release of pepsinogen from chief cells in the stomach?
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What effect do alcohol and caffeine have on gastric secretion?
What effect do alcohol and caffeine have on gastric secretion?
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What condition can result from an autoimmune attack against parietal cells?
What condition can result from an autoimmune attack against parietal cells?
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What is the primary purpose of HCl in gastric secretions?
What is the primary purpose of HCl in gastric secretions?
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How does the gastric mucosal barrier protect the stomach lining?
How does the gastric mucosal barrier protect the stomach lining?
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What is the effect of Atropine on gastric secretions?
What is the effect of Atropine on gastric secretions?
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What occurs when the gastric mucosal barrier is compromised?
What occurs when the gastric mucosal barrier is compromised?
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Which enzyme specifically breaks down dietary triglycerides?
Which enzyme specifically breaks down dietary triglycerides?
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What is the consequence of the rapid turnover of gastric mucosa?
What is the consequence of the rapid turnover of gastric mucosa?
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What role does autocatalysis play in the activation of pepsinogen?
What role does autocatalysis play in the activation of pepsinogen?
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What is the primary mechanism by which peptic ulcers are formed in the stomach?
What is the primary mechanism by which peptic ulcers are formed in the stomach?
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Which of the following substances is absorbed directly into the bloodstream in the stomach?
Which of the following substances is absorbed directly into the bloodstream in the stomach?
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What physiological event initiates vomiting?
What physiological event initiates vomiting?
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What effect does excessive vomiting have on the body's acid-base balance?
What effect does excessive vomiting have on the body's acid-base balance?
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Which of the following accurately describes a characteristic of Helicobacter pylori?
Which of the following accurately describes a characteristic of Helicobacter pylori?
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What triggers the urge to vomit from the chemoreceptor trigger zone?
What triggers the urge to vomit from the chemoreceptor trigger zone?
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Why is the stomach unable to absorb food or water?
Why is the stomach unable to absorb food or water?
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What role do H2 receptor antagonists play in the treatment of gastritis?
What role do H2 receptor antagonists play in the treatment of gastritis?
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What is the most common cause of psychogenic vomiting?
What is the most common cause of psychogenic vomiting?
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How does the body protect the airway during vomiting?
How does the body protect the airway during vomiting?
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What effect does secretin have on gastric emptying?
What effect does secretin have on gastric emptying?
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Which hormone is released in response to fat digestion products in the duodenum?
Which hormone is released in response to fat digestion products in the duodenum?
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Which of the following describes the role of G-cells?
Which of the following describes the role of G-cells?
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What is the primary responsibility of mucus cells in the gastric mucosa?
What is the primary responsibility of mucus cells in the gastric mucosa?
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How does distension of the duodenum affect gastric emptying?
How does distension of the duodenum affect gastric emptying?
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What triggers the release of an unidentified hormone that slows gastric emptying?
What triggers the release of an unidentified hormone that slows gastric emptying?
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Which statement accurately describes the function of chief cells?
Which statement accurately describes the function of chief cells?
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How do emotions affect gastric motility?
How do emotions affect gastric motility?
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What is the pH level of hydrochloric acid in the gastric lumen?
What is the pH level of hydrochloric acid in the gastric lumen?
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Which of the following statements is true regarding pyloric sphincter function?
Which of the following statements is true regarding pyloric sphincter function?
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Study Notes
Gastric Digestion
- Gastric digestion involves the breakdown of food in the stomach.
- The stomach's main function is to store, digest, and regulate the emptying of food.
- Phases of gastric function include filling, storage, mixing, and emptying.
Gastric Phase of the Response to a Meal
- The gastric phase is one of the three phases of gastric secretion.
- The gastric phase begins after swallowing and involves multiple factors.
- A critical figure in the study of gastric function is Dr. William Beaumont and his 1825 study of Alexis St. Martin.
Regions of the Stomach
- The stomach is divided into regions with specific functions.
- The "muscular pump" (antrum) is responsible for mixing food with gastric juice.
- The fundus acts as a storage pouch.
Enteroendocrine Cells
- Enteroendocrine cells produce and release hormones that regulate gastric function.
- G cells secrete gastrin, stimulating acid secretion and motility.
- D cells secrete somatostatin to inhibit gastrin and acid secretion.
Stomach as an Endocrine Organ
- The stomach releases numerous hormones that affect the rest of the digestive tract and have other functions beyond digestion.
- Examples of hormones include gastrin, histamine, serotonin, somatostatin, melatonin, ghrelin, obestatin, peptide YY, ANP, leptin, neuropeptide W, nesfatin-1 , and estrogen.
The Stomach
- The stomach stores food, aids digestion via enzymes (HCl, Lipase, pepsin), and protects its walls through mucus and bicarbonate.
Stomach Motility
- Key functions of stomach motility include filling, storage, mixing, and emptying.
Gastric Filling
- Receptive relaxation allows the stomach to expand without a dramatic change in pressure.
- The lower esophageal sphincter (LES) relaxes to allow food entry.
Gastric Storage
- The fundic area acts as a pocket for gas and food that is stored before mixing.
- The mixing process is largely absent during the storage phase.
Gastric Mixing
- The pyloric sphincter plays a role in rhythmic contractions (peristaltic waves) of the antrum, which mix the ingested material with gastric secretions to form chyme.
- Chyme is a mixture of ingested food and gastric secretions that is progressively propelled towards the duodenum.
Gastric Emptying
- Gastric emptying involves the controlled release of chyme into the duodenum and depends on forces such as peristaltic contractions.
Gastric Emptying Regulation
- Variables such as peptides and amino acids, fat, acid, and hypertonicity regulate gastric emptying.
- Mechanisms that control gastric emptying include enterogastric reflex, hormones (e.g., CCK), and osmotic pressure of duodenal contents.
Acid in the Duodenum
- Acid entering the duodenum triggers secretin release.
- Secretin inhibits gastric emptying.
- Secretin stimulates the pancreas to secrete bicarbonate that neutralizes the acid.
- Acid in the duodenum signals the slowing of gastric emptying.
Fat Digestion Products in the Duodenum and Jejunum
- Fat digestion products decrease the rate of gastric emptying through cholecystokinin (CCK) and gastric inhibitory peptide actions.
Osmotic Pressure of Duodenal Contents
- Hyperosmotic duodenal and jejunal content slows gastric emptying by increasing gastric inhibitory responses
- These responses can involve either nervous or hormonal systems for inhibitory actions.
Peptides and Amino Acids in the Duodenum
- Peptides and amino acids in the duodenum trigger gastrin release,
- Gastrin stimulates parietal and chief cells.
- This process leads to increased antral contractions and pyloric sphincter constriction, decreasing the rate of gastric emptying.
Distension
- Overfilling (distension) of the duodenum inhibits further gastric emptying.
Storage Function
- The stomach stores food and its contents must not exceed the absorptive capacity of the small intestine.
In Summary
- The central nervous system, sympathetic and parasympathetic systems, and hormones regulate the rate of gastric emptying.
- The major regulatory factors include acid, fats, and hypertonicity/distension.
Emotions
- Emotions influence gastric motility.
- Sadness and fear decrease motility.
- Anger and aggression increase motility, as does intense pain.
Gastric Secretions - Mucosal Gland Cells in Gastric Pits
- The stomach secretes gastric juices that play a crucial role in digestion.
- Gastric juice primarily includes HCl and pepsinogen.
Gastric Mucosa (Corpus & Antrum)
- Both the corpus and antrum contain various cells involved in gastric function.
- Parietal cells secrete HCl.
- Chief cells secrete pepsinogen.
- G cells secrete gastrin.
- D cells secrete somatostatin.
- ECL cells secrete histamine
Mucus
- Mucus protects the stomach wall from its own acid and enzymes, acting as a physical barrier.
- The mucus layer also lubricates and protects, preventing digestion.
Hydrochloric Acid
- Parietal cells actively transport H+ against a substantial concentration gradient into the gastric lumen.
- Cl- is also actively transported into the lumen.
- The creation of HCl is critical for the stomach's function.
Parietal Cell Ultrastructure
- Parietal cells contain abundant mitochondria to power the high-energy HCl transport.
Gastric Acid Secretion
- Steps in gastric acid secretion involve the exchange of bicarbonate for chloride, which results in the production of HCl.
Gastrin Secretion
- Gastrin is secreted into the blood from G cells.
- Gastrin stimulates the parietal and chief cells to secrete acid.
Histamine
- Histamine is a powerful stimulator of acid secretion.
Somatostatin-Paracrine Effect
- Somatostatin is a paracrine regulator that inhibits gastrin release from G cells when the antrum contains acid.
Control of Acid Secretion
- Factors influencing gastric secretion involve both neural and hormonal mechanisms.
Intrinsic Factor
- Parietal cells in the stomach secrete intrinsic factor (IF) that binds to Vitamin B12 in the small intestine to allow its absorption.
Pepsinogen Secretion
- Pepsinogen, secreted by chief cells, is converted to pepsin by HCl, performing protein breakdown in the acidic gastric environment.
Stimulation of Chief Cells in Response to a Meal
- Acetylcholine, gastrin, and histamine stimulate pepsinogen secretion.
Other Enzymes (Lipase)
- Lipase in the stomach is not essential for lipid breakdown but participates in breaking down fatty acids and monoglycerides to aid digestion.
The Mucus-Bicarbonate Barrier of the Gastric Mucosa
- A protective layer of mucus and bicarbonate protects the gastric mucosa from damage caused by acid and enzymes.
The Stomach Lining
- The stomach lining constantly regenerates, preventing damage from gastric secretions.
H. pylori
- H. pylori can live in the acidic stomach environment due to its motility, location in the antrum, urease production, and toxin secretion.
Helicobacter Pylori
- One of the major discoveries in bacterial gastritis is Helicobacter pylori.
- Their work in conjunction helped win a Nobel prize in physiology.
Acid Inhibitory Therapy
- Proton pump inhibitors (PPIs) target the parietal cells to reduce acid production, playing an essential role in treating many gastric disorders.
The Stomach and Absorption
- The stomach does not absorb food or water under normal conditions.
Ethyl Alcohol and Aspirin
- Unlike other drugs, ethyl alcohol and aspirin are directly absorbed by the stomach.
Vomiting (Emesis)
- Vomiting is a forceful expulsion of gastric contents.
- It generally relies on reverse peristalsis and is controlled by the nervous system.
- Various factors such as chemical agents, odors, smells, touch, pain and elevated intracranial pressure can trigger vomiting.
Causes of Vomiting
- Many triggers can induce vomiting, including chemical agents, noxious stimuli in the digestive tract, emotional factors, or physical stimulation.
- Elevated intracranial pressure, head trauma, and intense pain also induce vomiting.
Excessive Vomiting
- Excessive vomiting leads to a decrease in plasma volume, dehydration, and circulatory problems, often resulting in metabolic alkalosis.
Beneficial Effect of Vomiting
- Vomiting can be beneficial in cases of accidental ingestion (poison) where emetics can remove noxious materials.
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