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Questions and Answers
What substance neutralizes the acidic chyme in the duodenum?
What occurs when there is an increase in the osmolarity of the duodenal contents?
Which factor primarily inhibits gastric emptying in response to chyme presence?
Where is gastric juice secreted from in the stomach?
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What effect do unneutralized H+ ions in the duodenum have on pancreatic enzymes?
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What is the main secretion of chief cells in the gastric glands?
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What is the primary role of gastric emptying regulation related to protein and carbohydrate digestion?
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What stimulates HCl secretion in the stomach?
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Which area of the stomach secretes gastric juice primarily?
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Which type of cell secretes thin watery mucus in the gastric mucosa?
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What triggers a reflex inhibition of gastric emptying?
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What is the primary function of gastrin?
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Where are enterochromaffin-like (ECL) cells located?
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Which cells are primarily responsible for secreting hydrochloric acid (HCl)?
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What triggers G cells to release gastrin?
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Which of the following is NOT a function of gastric secretory cells?
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What is the function of receptive relaxation in the stomach?
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Which of the following correctly describes the role of rugae in the stomach?
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What is the primary function of gastrin in gastric secretion?
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What factor is NOT involved in enhancing gastric emptying?
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Which factor is NOT associated with decreasing gastric secretion?
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Which nerve mediates the reflex relaxation of the stomach during receptive relaxation?
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How does the fluidity of chyme affect gastric emptying?
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What is one of the protective functions of mucus in the stomach?
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Which of the following inhibits gastric emptying when present in the duodenum?
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What happens to gastric secretion as food empties from the stomach into the intestine?
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What is the relationship between the amount of chyme in the stomach and the gastric emptying rate?
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Which condition is most commonly associated with peptic ulcers?
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What hormone inhibits gastric emptying when fat is present in the duodenum?
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Which phase of gastric secretion is primarily triggered by sight, smell, or taste of food?
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What is the role of somatostatin in gastric secretion?
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What happens when there is a broken gastric mucosal barrier?
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What is the role of the gastric mucosal border?
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Which statement is true regarding gastric emptying?
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Which of the following accurately describes pepsinogen?
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What is the effect of the gastric phase on gastric secretions?
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What is retropulsion in the context of gastric contractions?
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What can lead to peptic ulcers related to the gastric mucosal border?
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Which statement about gastrin is correct?
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What does receptive relaxation in the stomach allow for?
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Study Notes
Stomach Functions
- Stomach volume can change significantly from 50 ml when empty to 1500 ml when full
- Gastric folds, known as rugae, flatten with food intake and stomach relaxation
- Receptive relaxation: reflex relaxation triggered by eating and mediated by the vagus nerve
- Stomach's ability to accommodate large volume changes is essential for digestion
Gastric Filling & Receptive Relaxation
- Receptive relaxation is a reflex response that allows the stomach to expand to accommodate food intake
- This relaxation is triggered by the presence of food in the mouth and esophagus
- It is mediated by the vagus nerve, which carries signals from the brain to the stomach muscles
- This reflex allows for a gradual and comfortable filling of the stomach, preventing sudden distension
Gastric Emptying
- Rate of gastric emptying is influenced by the factors in both the stomach and the duodenum.
- Factors in stomach:
- Amount of chyme: Rate of stomach emptying is proportional to the volume of chyme present
- Stomach distension: Leads to increased gastric motility, directly stimulating smooth muscle and involving intrinsic plexuses and the vagus nerve, and via gastrin release.
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Chyme fluidity:
- Higher fluidity results in faster emptying
- Lower fluidity results in slower emptying
- Emptying of gastric contents into the duodenum can take several hours
Factors Affecting Gastric Emptying: Duodenal Influences
- Fat in the duodenum: Inhibits gastric emptying through the release of cholecystokinin (CCK) by I cells
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Acid in the duodenum:
- Inhibits gastric emptying through reflexes in the enteric nervous system.
- Stomach secretes HCl, creating acidic chyme, neutralized by NaHCO3 from the pancreas
- Unneutralized H+ in the duodenum inhibits gastric emptying, lasting until neutralization is complete
- Unneutralized H+ also inactivates pancreatic enzymes
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Hypertonicity in the duodenum:
- Occurs if absorption rate of amino acids and glucose lags behind digestion
- Causes an increase in osmolarity in the duodenum, pulling water from the surrounding tissues
- Reflexly inhibits gastric emptying to allow time for the duodenum to catch up
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Distension of the duodenum:
- Inhibits gastric emptying
- Allows the duodenum time to process the chyme
Gastric Digestive Juice
- Gastric juice is secreted by cells in the gastric mucosa.
- Two main areas of secretion:
- Oxyntic mucosa: Found in the body and fundus of the stomach.
- Pyloric gland area: Located in the antrum.
- Gastric pits are lined with gastric glands.
- Gastric pits are openings in the surface of the gastric mucosa.
- Gastric glands are found at the base of gastric pits and contain various cell types.
Gastric Secretory Cells
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Oxyntic glands: Found in the body and fundus
- Surface epithelial cells: Cover the gastric mucosa.
- Mucous cells: Line the gastric pits and entrance of glands, secrete thin, watery mucus.
- Chief cells: Line the deeper parts of glands, secrete pepsinogen.
- Parietal cells: Line deeper parts of glands, secrete HCl.
- ECL cells: Located in gastric glands, secrete histamine.
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Pyloric gland area: Located in the antrum
- G cells: Secrete gastrin in response to eating
Functions of Gastric Secretory Cells:
-
Gastrin: A hormone produced by G cells in response to eating.
- Stimulates parietal cells to secrete H+, and promotes gastric growth
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HCl: Secreted by parietal cells, plays a crucial role in:
- Activating pepsinogen: Convert pepsinogen into active pepsin for protein digestion.
- Killing bacteria: Helps destroy harmful microorganisms present in consumed food.
- Breaking down food: Helps mechanically breakdown food and mixes it with gastric juices.
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Pepsinogen: Secreted by chief cells.
- Inactive form of pepsin, activated by HCl in the stomach.
- Starts the digestion of proteins.
Control of Gastric Secretion:
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Cephalic phase:
- Initiated by the sight, smell, taste, or thought of food.
- Signals are sent from the brain via the vagus nerve to stimulate gastric secretion.
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Gastric phase:
- Triggered by the presence of food in the stomach.
- Distention of the stomach walls and the presence of peptides, amino acids, and caffeine encourage gastrin release, promoting gastric secretion.
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Intestinal phase:
- Occurs when chyme enters the duodenum.
- The presence of fats, amino acids, and acid in the duodenum elicits the release of hormones and reflexes that inhibit gastric secretion.
Factors Decreasing Gastric Secretion:
- Food moving from the stomach to the duodenum: Removes the major stimulus for gastric secretion
- Accumulation of gastric juices: Decreases gastric pH, triggering somatostatin release from D cells in the antrum, inhibits gastric secretion
- Fats, acid, and duodenal distension: These influences also decrease gastric secretion.
Mucus: A Protective Layer
- Mucus secreted by surface epithelial cells and mucus cells forms a protective layer on the gastric mucosa.
- Functions of mucus:
- Protection against mechanical injury: Covers the surface of the gastric mucosa.
- Protection against self-digestion: Prevents pepsin from digesting the stomach wall.
- Protection against acid injury: Neutralizes HCl near the gastric lining, preventing damage.
Peptic Ulcers
- Breakdowns in the gastric mucosal barrier can lead to peptic ulcers.
-
Causes:
- Helicobacter pylori: A bacterium responsible for >80% of peptic ulcers.
- Reflux in the esophagus: Excessive acidic gastric contents back up into the esophagus.
- Dumping of excessive acidic gastric contents into the duodenum: Can damage the duodenal lining.
- Contributing Factors:
- Ethyl alcohol
- Nonsteroidal anti-inflammatory drugs (NSAIDs)
- Stress
- Smoking
True/False Statements:
- The stomach can accommodate an increased volume: True. Receptive relaxation allows for rugae to flatten, enabling this increase without pressure change.
- The presence of acid in the duodenum speeds up gastric emptying: False. Acid slows down gastric emptying to allow time for the duodenum to neutralize the acid.
- Gastrin is the only agonist to stimulate parietal cell H+ secretion: False. Histamine, gastrin, and acetylcholine all stimulate H+ secretion.
- Gastric contractions that propel chyme against a closed pyloric sphincter result in retropulsion: True. This action helps mix chyme and break down food into smaller particles.
- Pepsinogen is in its inactive form when secreted: True. Pepsinogen needs to be converted to active pepsin by HCl.
- Most gastric secretion occurs during the intestinal phase: False. The majority of gastric secretion happens during the gastric phase.
- PUs can be caused by a broken GMB due to excessive NSAID use: True.
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Description
Explore the complex functions of the stomach, including its capacity to change volume and the role of receptive relaxation in accommodating food. Understand how gastric emptying is influenced by various factors in both the stomach and duodenum, crucial for effective digestion.
