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Questions and Answers
Which monosaccharide is absorbed via facilitated diffusion?
Which monosaccharide is absorbed via facilitated diffusion?
What type of transport is used for the absorption of glucose and galactose?
What type of transport is used for the absorption of glucose and galactose?
Which enzyme is primarily responsible for protein digestion in the stomach?
Which enzyme is primarily responsible for protein digestion in the stomach?
In the small intestine, which type of enzyme is responsible for the breakdown of smaller peptides into amino acids?
In the small intestine, which type of enzyme is responsible for the breakdown of smaller peptides into amino acids?
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Where do monosaccharides enter the bloodstream after absorption?
Where do monosaccharides enter the bloodstream after absorption?
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What is the primary function of pancreatic amylase in carbohydrate digestion?
What is the primary function of pancreatic amylase in carbohydrate digestion?
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Which of the following represents the majority of end products from carbohydrate digestion?
Which of the following represents the majority of end products from carbohydrate digestion?
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Where does carbohydrate digestion primarily continue after the stomach?
Where does carbohydrate digestion primarily continue after the stomach?
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Which of the following carbohydrates is broken down into glucose and fructose?
Which of the following carbohydrates is broken down into glucose and fructose?
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Which enzyme is responsible for initially breaking down starch in the mouth?
Which enzyme is responsible for initially breaking down starch in the mouth?
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What happens to salivary amylase in the stomach?
What happens to salivary amylase in the stomach?
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What percentage of dietary carbohydrates is typically consumed by humans daily?
What percentage of dietary carbohydrates is typically consumed by humans daily?
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Which organ is NOT directly involved in the digestive process of carbohydrates?
Which organ is NOT directly involved in the digestive process of carbohydrates?
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What is the role of bile salts in the digestion of fats?
What is the role of bile salts in the digestion of fats?
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What is the product of triglyceride digestion by lipases?
What is the product of triglyceride digestion by lipases?
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Which enzymes activate trypsin and chymotrypsin in the small intestine?
Which enzymes activate trypsin and chymotrypsin in the small intestine?
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Which process involves the breaking down of fat globules into smaller droplets?
Which process involves the breaking down of fat globules into smaller droplets?
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What is the primary method of absorption of amino acids into epithelial cells?
What is the primary method of absorption of amino acids into epithelial cells?
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Which cofactor is necessary for lipase to effectively digest fats?
Which cofactor is necessary for lipase to effectively digest fats?
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What is absorbed intact without needing to be digested?
What is absorbed intact without needing to be digested?
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What is the main function of dipeptidase in protein digestion?
What is the main function of dipeptidase in protein digestion?
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How do small fatty acids enter the bloodstream?
How do small fatty acids enter the bloodstream?
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Which statement about the absorption of lipids is correct?
Which statement about the absorption of lipids is correct?
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What is the fate of chylomicrons after they leave intestinal cells?
What is the fate of chylomicrons after they leave intestinal cells?
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What is necessary for the absorption of calcium in the intestines?
What is necessary for the absorption of calcium in the intestines?
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What types of transport are primarily involved in the absorption of electrolytes?
What types of transport are primarily involved in the absorption of electrolytes?
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How are water-soluble vitamins primarily absorbed in the intestine?
How are water-soluble vitamins primarily absorbed in the intestine?
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What is the primary mechanism for the absorption of water in the intestines?
What is the primary mechanism for the absorption of water in the intestines?
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Which enzyme is responsible for digesting RNA in the digestive system?
Which enzyme is responsible for digesting RNA in the digestive system?
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Study Notes
Chemical Digestion and Absorption
- Digestion is the process of breaking down complex food substances (carbohydrates, proteins, and lipids) into absorbable products.
- Absorption is the uptake of these products, where they are transported into cells in the small intestine.
- Several organs contribute to digestion and absorption, including the mouth, stomach, small intestine, liver, pancreas, and gallbladder.
- Each organ plays a specific role in degrading and/or absorbing food, utilizing enzymes and other substances for the process.
Digestion of Carbohydrates
- Dietary carbohydrate intake is 250-850 grams per day, contributing 50-60% of the diet.
- Major carbohydrates are polysaccharides (starch and glycogen), oligosaccharides (di-, tri-, tetra-, and pentasaccharides), and monosaccharides (glucose and fructose).
- In the mouth, salivary amylase converts starch to maltose.
- Stomach acid denatures salivary amylase, temporarily stopping carbohydrate digestion.
- In the small intestine, pancreatic amylase digests starch to maltose, maltriose, and dextrins within 15-30 minutes of chyme entry.
- Pancreatic amylase functions best in an alkaline environment, aided by bile salts.
- Brush border enzymes (maltase, sucrase, lactase) further break down disaccharides into monosaccharides (glucose, fructose, and galactose).
- Carbohydrate digestion is complete in the small intestine, primarily the jejunum and proximal ileum.
- Glucose accounts for 80% of end products, while galactose and fructose combine for the remaining 20%.
- Pentoses are also formed from nucleic acids and partial digestion of pentosans.
Absorption of Monosaccharides
- Monosaccharides are absorbed by enterocytes (intestinal cells) via various transport mechanisms.
- Glucose and galactose are absorbed via active transport with sodium.
- Fructose is absorbed by facilitated diffusion through GLUT5.
- Absorbed monosaccharides enter the bloodstream via the portal vein and travel to the liver.
- Diagrams show the active transport process with illustrations of SGLT1 and GLUT2, highlighting the crucial role of Na⁺ transport.
Fate of Glucose in the Body
- About 5% of absorbed glucose is stored as glycogen in the liver and muscles.
- Approximately 50-60% of absorbed glucose is catabolised to produce energy, yielding 4 kcal/gram when completely oxidized.
- Some intermediary products of glucose breakdown can be converted to amino acids.
- About 30-40% of absorbed glucose is converted to fat and stored.
Chemical Digestion: Proteins
- Protein digestion involves enzymes like pepsin in the stomach and various pancreatic and brush border enzymes in the small intestine.
- Pancreatic enzymes (trypsin, chymotrypsin, carboxypeptidase) break down polypeptides into smaller peptides.
- Brush border enzymes (aminopeptidases, carboxypeptidases, and dipeptidases) further break down these peptides to amino acids.
Absorption of Amino Acids & Dipeptides
- Amino acids and dipeptides are absorbed into epithelial cells through active transport using sodium or hydrogen ions.
- They then move out of the epithelial cells into the blood via diffusion.
Digestion of Fats
- Dietary fats include simple fats (triglycerides and cholesterol), compound fats (phospholipids), and associated fats (steroids and fat-soluble vitamins).
- Emulsification is the process where fat globules are broken down into smaller droplets by bile salts, increasing their surface area for lipolytic enzyme action.
- Lipases, aided by colipase, break down triglycerides into monoglycerides and free fatty acids.
- Phospholipids are digested by pancreatic phospholipase. Free cholesterol is absorbed intact.
- Micelles are formed from fatty acids, bile salts, monoglycerides, diglycerides, phospholipids and cholesterol.
- Micelles aid the absorption of fats by transporting them to the brush border of the small intestine for absorption.
Absorption of Fats
- Small fatty acids enter cells via simple diffusion and then enter the bloodstream.
- Larger fats enter cells as micelles.
- Bile salts are reabsorbed into the blood, reforming bile.
- Fat-soluble vitamins are absorbed along with fats, as they are found within the micelles.
- Inside epithelial cells, fats are rebuilt and coated with proteins to form chylomicrons.
- Chylomicrons exit the cells via exocytosis and travel through the lymphatic system to the bloodstream before being used by liver and fat tissues.
Digestion of Nucleic Acids
- Pancreatic juice contains nucleases (ribonuclease and deoxyribonuclease) that digest RNA and DNA, respectively.
- Nucleotides are further digested by brush border enzymes (nucleosidease and phosphatase) into pentose, phosphate, and nitrogenous bases.
- Nucleotides are absorbed by active transport.
Absorption of Electrolytes
- Electrolytes are absorbed from GI secretions and ingested foods and liquids.
- Sodium and potassium are absorbed through active transport via Na⁺/K⁺ pumps.
- Chloride, iodide, and nitrate are passively absorbed.
- Iron, magnesium, and phosphate ions are absorbed through active transport.
- Intestinal calcium absorption requires vitamin D and parathyroid hormone.
Absorption of Vitamins
- Fat-soluble vitamins travel in micelles and are absorbed by simple diffusion.
- Water-soluble vitamins are absorbed by diffusion.
- Vitamin B12 combines with intrinsic factor before absorption.
- Receptor-mediated endocytosis is another method of Vitamin uptake.
Absorption of Water
- About 9 liters of fluid enter the GI tract daily.
- The small intestine absorbs 8 liters, and the large intestine absorbs 90% of the remaining liter.
- Water absorption occurs via osmosis through cell walls into vascular capillaries within the villi.
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Description
Test your knowledge on the processes of chemical digestion and nutrient absorption in the human body. This quiz covers the roles of various organs and the breakdown of carbohydrates. Dive into how enzymes facilitate these crucial functions for understanding nutrition better.
