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Questions and Answers
Where does the digestion of carbohydrates initially commence?
Where does the digestion of carbohydrates initially commence?
Which specific enzyme in saliva is primarily involved in initiating carbohydrate digestion?
Which specific enzyme in saliva is primarily involved in initiating carbohydrate digestion?
What is another common name used for the enzyme alpha amylase?
What is another common name used for the enzyme alpha amylase?
What process immediately precedes the action of bush border enzymes?
What process immediately precedes the action of bush border enzymes?
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Besides alpha amylase, what other substances in saliva aid carbohydrate digestion?
Besides alpha amylase, what other substances in saliva aid carbohydrate digestion?
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What is the primary role of the bush border enzymes?
What is the primary role of the bush border enzymes?
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When are the bush border enzymes described as coming into play?
When are the bush border enzymes described as coming into play?
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Which of the following best describes the timing of carbohydrate digestion?
Which of the following best describes the timing of carbohydrate digestion?
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What term best describes the molecular action that bush border enzymes carry out?
What term best describes the molecular action that bush border enzymes carry out?
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In the context of the text, what is directly happening to molecules as a result of the bush border enzymes?
In the context of the text, what is directly happening to molecules as a result of the bush border enzymes?
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What is the result of the initial action of salivary amylase on starch?
What is the result of the initial action of salivary amylase on starch?
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What is the primary reason salivary amylase becomes inactive in the stomach?
What is the primary reason salivary amylase becomes inactive in the stomach?
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Which of the following molecules are absorbed via a co-transport mechanism?
Which of the following molecules are absorbed via a co-transport mechanism?
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What type of bonds are broken by both salivary and pancreatic amylase?
What type of bonds are broken by both salivary and pancreatic amylase?
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Where is the absorption of co-transported molecules most efficient?
Where is the absorption of co-transported molecules most efficient?
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What is the primary role of pancreatic amylase after starch leaves the oral cavity?
What is the primary role of pancreatic amylase after starch leaves the oral cavity?
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In what direction does the efficiency of absorption for co-transported molecules generally decrease?
In what direction does the efficiency of absorption for co-transported molecules generally decrease?
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What are the final products of starch digestion by both salivary and pancreatic amylase?
What are the final products of starch digestion by both salivary and pancreatic amylase?
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What type of molecules are co-transported together?
What type of molecules are co-transported together?
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What is the primary function of peptidases within the enterocyte cytosol after absorption?
What is the primary function of peptidases within the enterocyte cytosol after absorption?
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Where does the hydrolysis of di- and tri-peptides to amino acids primarily occur?
Where does the hydrolysis of di- and tri-peptides to amino acids primarily occur?
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What happens to the rate of co-transport absorption in the digestive tract, after the duodenum?
What happens to the rate of co-transport absorption in the digestive tract, after the duodenum?
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What are the end products of di- and tri-peptide hydrolysis by cytosolic peptidases?
What are the end products of di- and tri-peptide hydrolysis by cytosolic peptidases?
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Which of the following best describes the molecules acted upon by peptidases within the enterocyte cytosol?
Which of the following best describes the molecules acted upon by peptidases within the enterocyte cytosol?
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The function of peptidases within the enterocyte cytosol is most closely related to which process?
The function of peptidases within the enterocyte cytosol is most closely related to which process?
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What is the primary effect of the mucosal block mechanism?
What is the primary effect of the mucosal block mechanism?
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Which condition is the mucosal block designed to prevent by limiting iron absorption?
Which condition is the mucosal block designed to prevent by limiting iron absorption?
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What is the direct result of the mucosal block on iron?
What is the direct result of the mucosal block on iron?
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The purpose of mucosal block can best be described as:
The purpose of mucosal block can best be described as:
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What is the ultimate goal of the mucosal block mechanism with respect to iron?
What is the ultimate goal of the mucosal block mechanism with respect to iron?
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Study Notes
Digestion and Absorption
- Digestion involves enzymes catalyzing carbohydrates, proteins, and lipids. Absorption is performed by specialized epithelial cells.
- Most absorption occurs in the small intestine; some in the stomach, and none in the esophagus (its primary function is transporting food).
- Most nutrients are absorbed before reaching the ileum. The colon absorbs remaining water and electrolytes.
- The small intestine has a specialized structure to increase nutrient absorption, including mucosal folds (Kerckring folds), villi, and microvilli.
- Mucosal folds triple the surface area. Villi increase it tenfold. Microvilli increase it twentyfold. The total surface area increase is about 600 folds.
Digestion and Absorption of Carbohydrates
- Carbohydrates are ingested as starch, sucrose, lactose, and cellulose. Cellulose is not digestible.
- Digestion begins in the oral cavity with salivary amylase (ptyalin). This enzyme breaks down starch's 1-4 alpha glycosidic bonds, creating smaller glucose polymers.
- Pancreatic amylase further breaks down starch in the small intestine, into maltose (two glucose units) and maltotriose (three glucose units).
- Brush border enzymes (lactase, sucrase, maltase, and alpha-dextranase) in the small intestine complete carbohydrate digestion, breaking down disaccharides into monosaccharides (glucose, fructose, and galactose).
Digestion and Absorption of Proteins
- Protein digestion starts in the stomach with pepsin and HCL, breaking peptide bonds between amino acids.
- Pepsin works best at acidic pH, and is deactivated in basic pH levels.
- Large polypeptides then move to the small intestine for further digestion by pancreatic endopeptidases and exopeptidases.
- Brush border enzymes (peptidases) break down small peptides into oligopeptides and amino acids.
- Di- and tri-peptides are transported into the enterocytes using a carrier-mediated transport system.
Digestion and Absorption of Lipids
- Bile, secreted by the liver, is crucial for lipid digestion.
- Bile salts are amphipathic, forming micelles, which solubilize lipids.
- Pancreatic lipase hydrolyzes triglycerides into monoglycerides and fatty acids.
- These products, along with phospholipids, cholesterol, and bile salts, form micelles.
- These micelles bring these products to the epithelial cells, where lipids diffuse into the cells.
- Inside epithelial cells, monoglycerides and fatty acids reform into triglycerides and combine with cholesterol, phospholipids, and proteins to form chylomicrons. These are then transported into the lymphatic system through the lacteals.
- Some glycerol and short-chain fatty acids diffuse directly into the blood capillaries.
Absorption of Water and Electrolytes
- Water is absorbed by following sodium ions across the epithelium.
- Electrolytes such as sodium are actively absorbed in the small intestine and colon.
Absorption of Vitamins
- Water-soluble vitamins are typically absorbed passively, except for vitamin C, B1, and B12. Vitamin B12 requires intrinsic factor for absorption.
- Lipid-soluble vitamins (A, D, E, and K) follow the same pathway as lipids, being absorbed with micelles and chylomicrons.
Absorption of Iron
- Iron is absorbed primarily in the upper part of the small intestine.
- Ferrous iron (Fe++) is more readily absorbed than ferric iron (Fe+++).
- Acidic pH and vitamin C enhance iron absorption. Conversely, elements like phosphorus, oxalates, and phytic acid can inhibit iron absorption.
- Iron is taken to the blood when needed, whereas excess is stored as ferritin and prevents toxic effects in the blood
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Description
Explore the processes of digestion and absorption, focusing on carbohydrates, proteins, and lipids. Learn about the role of the small intestine and the specialized structures that enhance nutrient absorption. Understand the significance of mucosal folds, villi, and microvilli in maximizing surface area.
