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Questions and Answers
Which component of saliva is most responsible for the lubrication of food?
Which component of saliva is most responsible for the lubrication of food?
- Mucin (correct)
- Haptocorrin
- Lingual lipase
- Alpha-amylase
What is the primary role of alpha-amylase in saliva?
What is the primary role of alpha-amylase in saliva?
- Binding vitamin B12
- Breakdown of proteins
- Digestion of dietary triglycerides
- Catalyzing the breakdown of carbohydrate polymers (correct)
Which characteristic of saliva facilitates the neutralization of gastric acid?
Which characteristic of saliva facilitates the neutralization of gastric acid?
- HCO3- secretion (correct)
- Presence of lactoferrin
- High Na+ concentration
- Activation of lingual lipase
What physiological change occurs in saliva during vomiting?
What physiological change occurs in saliva during vomiting?
What is the bicarbonate's effect on saliva's pH during resting conditions?
What is the bicarbonate's effect on saliva's pH during resting conditions?
What enzyme in saliva begins the digestion of dietary triglycerides?
What enzyme in saliva begins the digestion of dietary triglycerides?
Which hormone is primarily responsible for stimulating chief cells to secrete pepsinogen?
Which hormone is primarily responsible for stimulating chief cells to secrete pepsinogen?
Which glands are primarily responsible for the secretion of saliva?
Which glands are primarily responsible for the secretion of saliva?
What triggers the secretion of gastrin in the stomach?
What triggers the secretion of gastrin in the stomach?
What property of saliva's electrolytes can be described as hypotonic?
What property of saliva's electrolytes can be described as hypotonic?
What role does intrinsic factor (IF) play in the digestion process?
What role does intrinsic factor (IF) play in the digestion process?
What is the primary function of the bicarbonate-rich mucus secreted by mucous cells?
What is the primary function of the bicarbonate-rich mucus secreted by mucous cells?
Which cells are primarily responsible for secreting hydrochloric acid (HCl) in the stomach?
Which cells are primarily responsible for secreting hydrochloric acid (HCl) in the stomach?
Which of the following statements about gastric motility is true?
Which of the following statements about gastric motility is true?
The activation of which type of nervous activity triggers the secretion of pepsinogen?
The activation of which type of nervous activity triggers the secretion of pepsinogen?
What protects vitamin B12 from the acidic environment in the stomach before it reaches the duodenum?
What protects vitamin B12 from the acidic environment in the stomach before it reaches the duodenum?
What is the primary function of secretin in the context of gastric acid secretion?
What is the primary function of secretin in the context of gastric acid secretion?
Which of the following compounds plays the most significant role in stimulating gastric acid secretion?
Which of the following compounds plays the most significant role in stimulating gastric acid secretion?
How does bicarbonate play a role in the process of gastric acid secretion?
How does bicarbonate play a role in the process of gastric acid secretion?
What is the effect of fatty acids in the duodenum on gastric emptying?
What is the effect of fatty acids in the duodenum on gastric emptying?
Which receptor signaling is primarily involved in increasing intracellular cAMP levels in gastric parietal cells?
Which receptor signaling is primarily involved in increasing intracellular cAMP levels in gastric parietal cells?
What initiates the cephalic phase of gastric secretion?
What initiates the cephalic phase of gastric secretion?
Which factor does NOT affect the rate of gastric emptying?
Which factor does NOT affect the rate of gastric emptying?
Low pH in the duodenum primarily triggers the release of which hormone?
Low pH in the duodenum primarily triggers the release of which hormone?
Which channel is responsible for the diffusion of chloride ions into the secretory canaliculi during gastric acid secretion?
Which channel is responsible for the diffusion of chloride ions into the secretory canaliculi during gastric acid secretion?
What role does the pyloric sphincter play in gastric emptying?
What role does the pyloric sphincter play in gastric emptying?
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Study Notes
Saliva
- Secreted by parotid, submandibular, and sublingual glands in response to taste, smell, thought, and food presence.
- Composed of 98% water, with 2% consisting of:
- Electrolytes: lower sodium (Na+) and higher potassium (K+) concentrations, making saliva hypotonic.
- Proteins: includes mucin, haptocorrin, alpha-amylase, and lingual lipase.
- Bactericidal substances: thiocyanate, lysozyme, lactoferrin, and immunoglobulin A (IgA).
- Functions include:
- Lubrication of food mainly due to mucin.
- Digestion initiation with alpha-amylase breaking down carbohydrates and lingual lipase targeting triglycerides.
- Protection of vitamin B12 by binding it to haptocorrin.
- Neutralization of gastric acid through bicarbonate (HCO3-) when refluxed into the esophagus or during vomiting.
- Antibacterial effects.
Gastric Secretions
- Chief cells in the stomach secrete proenzyme pepsinogen, which converts to pepsin in acidic conditions.
- Gastrin, secreted by G cells, stimulates:
- Chief cells to release pepsinogen.
- Parietal cells to secrete hydrochloric acid (HCl).
- Gastric motility.
- Intrinsic factor (IF), a glycopeptide from parietal cells, is crucial for vitamin B12 absorption.
Mucus Production
- Mucous cells produce a bicarbonate-rich mucus coating the gastric mucosa.
- Protects gastric mucosa from acidity and lubricates the stomach wall to prevent friction damage.
Gastric Acid Secretion
- Parietal cells have features including:
- Close proximity to ECL cells.
- H+/K+-ATPase pumps for acid secretion.
- Multiple receptors (histamine H2, acetylcholine (ACh), and gastrin) for stimulation.
- Histamine, the major stimulus for gastric acid secretion, is released in response to gastrin and parasympathetic activity.
Phases of Gastric Secretion
- Cephalic phase: Initiated by anticipation or sensory signals, accounting for 30% of gastric acid during a meal.
- Gastric phase: Triggered by stomach distension; releases gastrin, histamine, and pepsinogen, accounting for 60% of gastric acid secretion.
- Intestinal phase: In response to acidic chyme entering the duodenum, secretin reduces acidity and inhibits gastrin release.
Gastric Emptying Control
- Influenced by:
- Chyme consistency: solids delay emptying until liquified.
- Chyme volume: larger volumes promote faster gastric emptying.
- Chyme content: proteins exit quickly, followed by carbohydrates; fats slow down emptying.
- Duodenal distension and high acid content inhibit gastric emptying via enteric nervous system feedback.
- Cholecystokinin (CCK) triggers slower gastric emptying in response to lipids, increasing pyloric tone.
- Other factors affecting gastric emptying include hyperosmolarity, sympathetic nervous activity, pain, and certain drugs.
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