Podcast
Questions and Answers
Which enzyme is NOT involved in protein digestion in the small intestine?
Which enzyme is NOT involved in protein digestion in the small intestine?
Where are bile salts primarily released for lipid digestion?
Where are bile salts primarily released for lipid digestion?
What type of transport is primarily used for the absorption of monosaccharides in the small intestine?
What type of transport is primarily used for the absorption of monosaccharides in the small intestine?
Which statement about the absorption of lipids is correct?
Which statement about the absorption of lipids is correct?
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What percentage of gastrointestinal reabsorption of water and electrolytes occurs in the jejunum and ileum?
What percentage of gastrointestinal reabsorption of water and electrolytes occurs in the jejunum and ileum?
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Which gland is responsible for secreting mainly mucous saliva?
Which gland is responsible for secreting mainly mucous saliva?
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What is the role of Brunner’s glands in the small intestine?
What is the role of Brunner’s glands in the small intestine?
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What type of muscle is found in the upper third of the oesophagus?
What type of muscle is found in the upper third of the oesophagus?
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Which substance is NOT secreted by gastric glands?
Which substance is NOT secreted by gastric glands?
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Which process describes the contraction and relaxation of muscles to propel food in the gastrointestinal tract?
Which process describes the contraction and relaxation of muscles to propel food in the gastrointestinal tract?
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What regulates the flow of food from the stomach to the small intestine?
What regulates the flow of food from the stomach to the small intestine?
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What initiates primary peristalsis in the gastrointestinal tract?
What initiates primary peristalsis in the gastrointestinal tract?
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What is the primary function of saliva in the digestive process?
What is the primary function of saliva in the digestive process?
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Study Notes
Salivation and Mouth
- The parotid gland produces serous saliva to hydrate food.
- The sublingual gland produces mucus saliva to lubricate food.
- The submandibular gland produces serous saliva to hydrate food.
- The mouth aids in food lubrication and hydration, and contains digestive enzymes like lingual (salivary) amylase, lingual lipase, and lysozyme.
Gastric Digestion
- Gastric glands secrete acid, pepsinogen, lipase, and mucus.
Small Intestine - Acid Neutralization
- The duodenum receives chyme from the stomach.
- Brunner’s glands, pancreatic secretions, and gallbladder secretions neutralize chyme.
Motility in the Mouth
- Swallowing (deglutition) involves the epiglottis closing, the bolus being pushed back, the oropharynx relaxing, and peristalsis.
The Esophagus
- Propels digesting food to the stomach.
- The upper third is skeletal muscle, the lower two thirds are smooth muscle.
- Contractions of circular and longitudinal muscles create peristaltic waves.
- Peristalsis can be bidirectional.
Secretions Summary
- The mouth secretes saliva, enzymes, and mucus.
- The stomach secretes acid, pepsinogen, lipase, and mucus.
- The small intestine (duodenum) receives secretions from Brunner's glands, the pancreas, and the gallbladder.
Peristalsis
- Primary peristalsis begins at the pharynx, is regulated by the vagus nerve, involves skeletal muscle contraction, and circular muscle relaxations followed by contractions.
- Secondary peristalsis is initiated by the stretching of muscles by digesta, results in muscle contractions, and can be reversed.
Motility in the Stomach
- The lower esophageal sphincter (LOS) should remain closed.
- The pylorus regulates the flow of chyme from the stomach.
- Churning involves stomach muscle contractions, peristalsis, and the pylorus remaining closed.
- Emptying involves peristalsis, and the pylorus opening.
Motility Summary
- Autonomic motility, called peristalsis, begins in the mouth, involves the contraction of circular and longitudinal muscles, and the relaxation of circular muscles.
Digestion Before the Small Intestine
- Carbohydrates, proteins, and lipids are digested before entering the small intestine.
- A slow, constant flow of digesta to the small intestine is achieved even after a large meal.
Small Intestine Digestion
- The duodenum is where the majority of digestion occurs.
- The following enzymes aid in protein digestion in the duodenum: trypsin, chymotrypsin, elastase, carboxypeptidases, and aminopeptidases.
- Brush border aminopeptidases are located on the enterocytes, while others are secreted from the pancreas.
- Carbohydrate digestion in the duodenum involves the following enzymes: amylase, dextrinase, glucolyase, lactase, maltase, isomaltase, and sucrase.
- These brush border enzymes break down carbohydrates into monosaccharides for absorption.
- Lipid digestion in the duodenum involves the following components: lipase, bile salts, and bile acids.
- These components aid in the formation of lipid droplets.
Digestion Summary
- Protein digestion involves trypsin, chymotrypsin, elastase, carboxypeptidases, and aminopeptidases, which are secreted from the pancreas or the brush border of enterocytes.
- Carbohydrate digestion involves amylase, dextrinase, glucolyase, lactase, maltase, isomaltase, and sucrase. These enzymes are all located on the brush border of the small intestine.
- Lipid digestion involves lipase, bile salts, and bile acids, which are secreted from the pancreas and gallbladder.
Small Intestine Absorption: Proteins
- Absorption occurs in the duodenum and jejunum.
- Di- and tri-peptides, and amino acids are absorbed.
- Active transporters mediate absorption on the apical side of the intestinal epithelium.
- Passive transporters mediate absorption on the basolateral side.
Small Intestine Absorption: Carbohydrates
- Absorption occurs in the duodenum and jejunum.
- Monosaccharides are the form absorbed.
- Active transport occurs on the apical side of the intestinal epithelium.
- Passive transport occurs on the basolateral side.
Small Intestine Absorption: Lipids
- Absorption occurs in the duodenum, jejunum, and ileum.
- Lipid droplets are absorbed by endocytosis.
- Further digestion occurs in the intestinal lumen.
- Lipids are packaged into chylomicrons.
- Lacteals within the small intestine transport chylomicrons.
Small Intestine Absorption: Water and Electrolytes
- Absorption occurs in the jejunum and ileum.
- 90% of GI water is reabsorbed.
- Absorption is primarily driven by passive transport along an ion gradient.
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Description
This quiz covers the roles of the salivary glands, gastric digestion, and the process of food motility from the mouth to the esophagus. Understand how saliva aids in food lubrication and hydration, and learn about the digestive enzymes involved. Test your knowledge on the structure and function of the gastrointestinal tract.
