Podcast
Questions and Answers
What is the primary function of the stomach in the digestive process?
What is the primary function of the stomach in the digestive process?
Which of the following is NOT a function of the pancreas?
Which of the following is NOT a function of the pancreas?
What type of carbohydrates can be directly absorbed by the small intestine?
What type of carbohydrates can be directly absorbed by the small intestine?
What is the primary role of bile acids in the digestive process?
What is the primary role of bile acids in the digestive process?
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What is the primary function of the large intestine?
What is the primary function of the large intestine?
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What is the primary function of the salivary glands?
What is the primary function of the salivary glands?
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What type of transport process is involved in glucose moving against its concentration gradient?
What type of transport process is involved in glucose moving against its concentration gradient?
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What is the primary function of SGLT1 in carbohydrate absorption?
What is the primary function of SGLT1 in carbohydrate absorption?
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Which of the following is NOT a pathway for protein digestion and absorption?
Which of the following is NOT a pathway for protein digestion and absorption?
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What type of transport is involved in the exit of glucose, galactose, and fructose across the basolateral membrane?
What type of transport is involved in the exit of glucose, galactose, and fructose across the basolateral membrane?
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How many major pathways are involved in protein digestion and absorption?
How many major pathways are involved in protein digestion and absorption?
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Which of the following sugars is NOT transported by SGLT1?
Which of the following sugars is NOT transported by SGLT1?
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Which of the following enzymes is responsible for the completion of starch digestion in the lumen of the small intestine?
Which of the following enzymes is responsible for the completion of starch digestion in the lumen of the small intestine?
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What is the primary function of the sodium/glucose transporter 1 (SGLT1) in the small intestine?
What is the primary function of the sodium/glucose transporter 1 (SGLT1) in the small intestine?
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Which of the following types of carbohydrates is not digestible by the human body?
Which of the following types of carbohydrates is not digestible by the human body?
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What is the primary site of carbohydrate digestion in the human body?
What is the primary site of carbohydrate digestion in the human body?
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Which of the following enzymes is inactivated by gastric acid?
Which of the following enzymes is inactivated by gastric acid?
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What is the product of starch hydrolysis by salivary and pancreatic amylases?
What is the product of starch hydrolysis by salivary and pancreatic amylases?
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What is the primary function of gastric and pancreatic proteases in protein digestion?
What is the primary function of gastric and pancreatic proteases in protein digestion?
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What is the fate of oligopeptides in the enterocytes?
What is the fate of oligopeptides in the enterocytes?
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What is the primary source of protein that is digested and absorbed in the small intestine?
What is the primary source of protein that is digested and absorbed in the small intestine?
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What is the characteristic of essential amino acids?
What is the characteristic of essential amino acids?
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What is the fate of proteins in the small intestine of adults?
What is the fate of proteins in the small intestine of adults?
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What is the difference between protein absorption in adults and neonates?
What is the difference between protein absorption in adults and neonates?
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What is the uncertainty regarding protein absorption in adults?
What is the uncertainty regarding protein absorption in adults?
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Study Notes
Carbohydrate Digestion
- Carbohydrates require hydrolysis to monosaccharides before absorption
- Some polymers are digestible, while others are not; non-digestible polymers are classified as fiber
- Dietary fiber is a non-digestible polymer found in fruits, vegetables, and cereals and can be either soluble or non-soluble
- Glycogen is the storage form of carbohydrates in animals, equivalent to starch in plants
Intraluminal Hydrolysis
- Digestion of carbohydrates involves two steps: intraluminal hydrolysis and membrane digestion
- Intraluminal hydrolysis involves the breakdown of starch to oligosaccharides by salivary and pancreatic enzymes
- Salivary amylase initiates starch digestion in the mouth, but is inactivated by gastric acid
- Pancreatic alpha-amylase completes starch digestion in the small intestine, producing disaccharides
- Disaccharides cannot be absorbed by the small intestine and require further digestion to produce absorbable monosaccharides
Membrane Digestion
- Membrane digestion involves the hydrolysis of oligosaccharides to monosaccharides by brush border disaccharidases
- The small intestine has three brush border oligosaccharidases: lactase, maltase, and sucrase-isomaltase
- Each enzyme has a specific hydrolytic function
Carbohydrate Absorption
- The three monosaccharide products of carbohydrate digestion (glucose, galactose, and fructose) are absorbed by the small intestine in a two-step process
- The first step involves uptake across the apical membrane into the epithelial cell
- The second step involves coordinated exit across the basolateral membrane
- The sodium/glucose transporter 1 (SGLT1) is responsible for glucose and galactose uptake at the apical membrane
- Fructose is absorbed by facilitated diffusion through GLUT5
Organisation of the Gastrointestinal System
- The gastrointestinal tract is a tube specialized for sequential processing of food
- The tract consists of hollow organs (mouth to anus) and accessory glands and organs that add secretions to the hollow organs
- Each hollow organ serves a specialized function, separated by sphincters at key locations
- The mouth and oropharynx initiate mechanical breakdown and lubrication of food, and propel food into the esophagus
- The esophagus serves as a conduit to the stomach
- The stomach provides temporary food storage, churns, and secretes proteases and acid to facilitate digestion
- The small intestine continues digestion and is the primary site for nutrient absorption
- The large intestine reabsorbs fluids and electrolytes, but does not absorb nutrients, and stores faecal matter before expulsion
- Accessory glands include salivary glands, pancreas, and liver
Nutrient Digestion and Absorption
- Digestion is the enzymatic conversion of complex dietary substances to a form that can be absorbed
- Most, but not all, digestive processes occur in the small intestine
- Absorption is the process of taking up nutrients into cells or across tissues and organs through diffusion or osmosis
Protein Digestion
- Proteins must be digested into their constituent oligopeptides and amino acids before being taken up by enterocytes
- Digestion-absorption of proteins occurs through four major pathways
- Proteins are digested into peptides and amino acids by luminal enzymes (proteases) from the stomach and pancreas
- Brush border peptidases fully digest some oligopeptides to amino acids, while cytosolic peptidases digest oligopeptides that directly enter the enterocyte
- Both gastric and pancreatic proteases are secreted as proenzymes that require conversion to their active form for protein hydrolysis
- The protein that is digested and absorbed in the small intestine comes from both dietary and endogenous sources
- Nine of the 20 amino acids are essential, meaning they are not synthesized in adequate amounts by the body and must be derived from animal or plant sources
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Description
This quiz covers the digestion of carbohydrates, including the role of hydrolysis, types of polymers, and the importance of dietary fibre and glycogen.
