Biochemistry: Digestion and Absorption
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Questions and Answers

What must happen to lipids before they are transported in the body?

  • They must be converted into glucose.
  • They must undergo enzymatic hydrolysis.
  • They must be packaged into lipoproteins. (correct)
  • They must be stored in adipose tissue.

    • Which statement is true regarding dietary proteins?

  • They are a source of essential amino acids for the body. (correct)
  • Animal sources provide less digestible proteins than plant sources.
  • They are completely absorbed in their native form.
  • They require no processing before absorption.

    • What role do proteases play in protein digestion?

  • They convert lipids into fatty acids.
  • They synthesize new proteins from amino acids.
  • They promote the absorption of carbohydrates.
  • They are responsible for degrading proteins into amino acids. (correct)

    • What forms must carbohydrates be in to be absorbed by the body?

    <p>Monosaccharides.</p> Signup and view all the answers

    What is a primary factor in the digestion of native proteins?

    <p>Denaturation by heat and gastric acid.</p> Signup and view all the answers

    Which transporter is primarily responsible for glucose and galactose absorption?

    <p>SGLT-1.</p> Signup and view all the answers

    What is a key characteristic of plant sources of protein compared to animal sources?

    <p>Lower essential amino acid content.</p> Signup and view all the answers

    In what organs are proteases primarily produced?

    <p>Stomach, pancreas, and small intestines.</p> Signup and view all the answers

    What is the primary function of saliva in digestion?

    <p>To provide lubrication for swallowing</p> Signup and view all the answers

    Which of the following describes the structure of the small intestine that enhances absorption?

    <p>Folds that increase the surface area</p> Signup and view all the answers

    What type of nutrients enter the vascular system through the portal vein?

    <p>Monosaccharides and amino acids</p> Signup and view all the answers

    Which enzyme type is primarily responsible for breaking down carbohydrates during digestion?

    <p>Disaccharidases</p> Signup and view all the answers

    Which is the correct sequence in nutrient absorption from the intestine to the bloodstream?

    <p>Villi → Microvilli → Blood</p> Signup and view all the answers

    What forms of carbohydrates are primarily absorbed in the small intestine?

    <p>Disaccharides and monosaccharides</p> Signup and view all the answers

    Where does the absorption of nutrients predominantly occur in the gastrointestinal tract?

    <p>Small intestine</p> Signup and view all the answers

    What is the primary fate of fat-soluble nutrients after absorption?

    <p>Transported via the lymphatic system</p> Signup and view all the answers

    What is the primary enzyme responsible for the initial hydrolysis of dietary carbohydrates in the mouth?

    <p>Salivary amylase</p> Signup and view all the answers

    Which of the following dietary carbohydrates is least likely to be digested in the stomach due to high acidity?

    <p>Starch</p> Signup and view all the answers

    What is the main product of starch digestion by pancreatic amylase?

    <p>Maltose</p> Signup and view all the answers

    Which of the following factors can influence the activity of pancreatic amylase?

    <p>pH level</p> Signup and view all the answers

    Which carbohydrate component requires specific enzymes for digestion in the brush border of the small intestine?

    <p>Disaccharides</p> Signup and view all the answers

    What is the primary function of hydrochloric acid (HCl) in digestion?

    <p>Denatures proteins for hydrolysis</p> Signup and view all the answers

    What percentage of carbohydrate digestion is completed by pancreatic amylase before reaching the small intestine?

    <p>60-80%</p> Signup and view all the answers

    Which enzyme is secreted by chief cells as an inactive form before activation?

    <p>Pepsin</p> Signup and view all the answers

    Which hormone is primarily responsible for stimulating the secretion of pancreatic amylase?

    <p>Cholecystokinin (CCK)</p> Signup and view all the answers

    What happens to di- and tripeptides once they enter the brush border of intestinal mucosa?

    <p>Hydrolyzed by intracellular dipeptidases and tripeptidases</p> Signup and view all the answers

    Which molecule represents an end product of carbohydrate digestion in the small intestine?

    <p>Glucose</p> Signup and view all the answers

    Which protease is NOT typically secreted by the pancreas?

    <p>Pepsin</p> Signup and view all the answers

    What is the primary role of amylase in the digestive process?

    <p>Hydrolysis of carbohydrates</p> Signup and view all the answers

    What is the significance of the pH level for salivary amylase function?

    <p>It inactivates the enzyme</p> Signup and view all the answers

    What mediates the absorption of oligopeptides in the intestine?

    <p>CCK and secretin</p> Signup and view all the answers

    How does the absorption of intact proteins occur in neonates?

    <p>Through endocytosis from colostrum</p> Signup and view all the answers

    What is the primary role of pancreatic proteases in digestion?

    <p>Break down large polypeptides into smaller peptides</p> Signup and view all the answers

    What role do large peptides play in the immune response?

    <p>They may stimulate antibody production</p> Signup and view all the answers

    Which ion is involved in the absorption of some dipeptides in the intestine?

    <p>H+</p> Signup and view all the answers

    At what age does the ability to absorb intact proteins significantly decline in neonates?

    <p>6 months</p> Signup and view all the answers

    Study Notes

    Objectives

    • Discuss digestion and absorption in the gastrointestinal tract (GIT): general principles, carbohydrates, proteins, lipids.
    • Describe absorption mechanisms for water, ions, vitamins, and minerals.

    Digestive System Processes

    • Digestion: Breakdown of food into smaller molecules.
    • Absorption: Uptake of nutrients into the body.
    • Motility: Movement of food through the GIT.
    • Secretion: Release of digestive enzymes and acids.
    • Excretion: Elimination of waste products.

    Carbohydrates

    • Types of Dietary Carbohydrates:
      • Monosaccharides: glucose, fructose, galactose.
      • Disaccharides: sucrose, lactose.
      • Polysaccharides: starch, glycogen, non-starch polysaccharides.

    Digestion of Carbohydrates

    • Salivary Amylase:
      • Hydrolyzes α(1→4) glycosidic bonds; 20-40% activity, inactivated in stomach due to acidity.
    • Pancreatic Amylase:
      • Identical to salivary amylase; 60-80% activity, optimal pH 7-8.
    • End products of carbohydrate digestion include maltose, maltotriose, and α-limit dextrins.
    • Brush Border Enzymes: Disaccharidases that act at the intestinal lining.

    Absorption of Carbohydrates

    • Occurs exclusively as monosaccharides (glucose, fructose, galactose) through specific transporters.
    • Transport Mechanisms:
      • SGLT-1 for glucose and galactose.
      • GLUT 5 for fructose.

    Proteins

    • Dietary Sources:
      • Essential amino acids derived from both animal and plant proteins.
    • Digestion of Proteins:
      • Native proteins are resistant; need denaturation (heat and gastric acid).
      • Proteases: Enzymes that degrade proteins, produced in stomach and pancreas.
    • Hydrochloric Acid (HCl): Denatures proteins, may kill bacteria.
    • Pepsin: Activated from pepsinogen in the stomach, releasing peptides.

    Absorption of Peptides

    • Di- and Tripeptides:
      • Enter through brush border, hydrolyzed to free amino acids by intracellular enzymes.
      • Some absorbed via H+ co-transport.
    • Free Amino Acids:
      • Transported into portal circulation, metabolized by liver or released into circulation.

    Absorption of Oligopeptides

    • Large peptides may be absorbed transcellularly or paracellularly, potentially stimulating immune response (allergies).

    Lipids

    • Lipids are insoluble in water and require packaging as lipoproteins (triglycerides, phospholipids, proteins, cholesterol) for transport.
    • Fat-soluble Vitamins: Absorbed along with lipids, entering the lymphatic system before bloodstream.

    Additional Nutrient Absorption

    • Water and Ions: Absorbed through intestinal walls into blood.
    • Vitamins and Minerals: Various transport mechanisms specific to each nutrient.

    Summary of Absorption

    • Nutrients enter the vascular system (water-soluble) or lymphatic system (fat-soluble).
    • Vascular nutrients include monosaccharides, amino acids, water-soluble vitamins, and minerals.

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    Description

    Explore the intricate processes of digestion and absorption of macromolecules in the gastrointestinal tract. This quiz will cover the general principles, as well as the specific digestion and absorption of carbohydrates, proteins, and lipids. Perfect for students seeking a deeper understanding of biochemistry principles.

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