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Questions and Answers
What is the role of salivary amylase in carbohydrate digestion?
What is the role of salivary amylase in carbohydrate digestion?
Which enzyme is responsible for the final stages of digesting carbohydrates in the small intestine?
Which enzyme is responsible for the final stages of digesting carbohydrates in the small intestine?
At what pH is salivary amylase inactivated?
At what pH is salivary amylase inactivated?
Which of the following sugars is absorbed more slowly during carbohydrate digestion?
Which of the following sugars is absorbed more slowly during carbohydrate digestion?
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What is the main cause of lactose intolerance?
What is the main cause of lactose intolerance?
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What product is primarily obtained from the digestion of carbohydrates?
What product is primarily obtained from the digestion of carbohydrates?
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Which of the following correctly describes the transport mechanism for glucose and galactose?
Which of the following correctly describes the transport mechanism for glucose and galactose?
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What is the final stage of carbohydrate metabolism called?
What is the final stage of carbohydrate metabolism called?
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What primarily powers the active absorption of glucose?
What primarily powers the active absorption of glucose?
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Which glucose transporter is responsible for basal glucose uptake across all cells?
Which glucose transporter is responsible for basal glucose uptake across all cells?
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In which tissues is GLUT4 primarily found?
In which tissues is GLUT4 primarily found?
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What is a key feature of GLUT2 in liver cells?
What is a key feature of GLUT2 in liver cells?
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Where is GLUT3 mainly expressed?
Where is GLUT3 mainly expressed?
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What happens if phlorhizin is introduced into the body?
What happens if phlorhizin is introduced into the body?
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Which glucose transporter is known to have constitutive transport activity?
Which glucose transporter is known to have constitutive transport activity?
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Which glucose transporter would you expect to find in skeletal muscle tissue?
Which glucose transporter would you expect to find in skeletal muscle tissue?
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Study Notes
Digestion of Carbohydrates (CHO)
- Digestion begins in the oral cavity with saliva containing α-amylase, which hydrolyzes starch into maltose and oligosaccharides.
- Salivary amylase is inactivated at pH 4.0; thus, carbohydrate digestion transitions to the small intestine.
- Pancreatic amylase continues the digestion, producing maltose, glucose, and isomaltose (two glucose molecules linked by 1-6 linkage).
- Intestinal disaccharidases, including maltase, sucrase, lactase, and isomaltase, further break down sugars.
- Lactose intolerance occurs due to lactase deficiency, leading to osmotic diarrhea, affecting over 70% of adults globally.
Final Products of Carbohydrate Digestion
- Main products include glucose, fructose, galactose, and pentoses.
- Carbohydrate absorption occurs primarily as monosaccharides.
Absorption of Monosaccharides
- Absorption methods include active transport (against concentration gradient) and facilitated transport (diffusion).
- Glucose and galactose are absorbed actively, requiring specific structural configurations (OH on carbon 2, pyranose ring, methyl group at C5).
- Fructose absorption is slower, also involving active transport.
- Active glucose absorption relies on the sodium pump, functional in the small intestine and renal tubules.
Glucose Transporters (GLUT)
- GLUT1: Ubiquitously distributed; mediates low-level basal glucose uptake essential for cellular respiration. High levels in erythrocytes and barrier tissues, such as the blood-brain barrier.
- GLUT2: Bidirectional transporter located in the gut, liver, and pancreatic islets. Allows glucose movement for glycolysis and gluconeogenesis, regulating serum glucose levels in pancreatic beta cells.
- GLUT3: Predominantly found in the central nervous system and neurons, it is considered the primary glucose transporter in these tissues.
- GLUT4: Located in insulin-responsive tissues including skeletal muscle, adipose tissue, and heart. Critical for glucose uptake in response to insulin.
Summary of Monosaccharide Transport
- All three monosaccharides—glucose, galactose, and fructose—are transported from intestinal mucosal cells into the portal circulation via GLUT2.
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Description
Test your knowledge on the digestion of carbohydrates, including the roles of salivary and pancreatic amylase. Explore the final products of carbohydrate digestion and the absorption methods of monosaccharides, along with the implications of lactase deficiency. Assess your understanding of how carbohydrates are broken down and absorbed in the human body.
