Digestive System Anatomy and Function
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Questions and Answers

What is the primary site for the digestion and absorption of proteins and carbohydrates?

  • Small intestine (correct)
  • Esophagus
  • Stomach
  • Large intestine

    • Which mechanism of absorption requires energy to function?

  • Facilitated diffusion
  • Osmosis
  • Active transport (correct)
  • Passive diffusion

    • What process involves the breakdown of polymeric nutrient molecules into smaller units?

  • Metabolism
  • Fermentation
  • Hydrolysis
  • Digestion (correct)

    • Which of the following statements is true regarding absorption in the body?

    <p>Nutrients are absorbed by enterocytes lining the lumen.</p> Signup and view all the answers

    What role do membrane proteins play in facilitated diffusion during nutrient absorption?

    <p>They assist in the transport of molecules across the cell membrane.</p> Signup and view all the answers

    What is the primary function of endoglycosidase?

    <p>It cleaves bonds within polysaccharide chains.</p> Signup and view all the answers

    What is produced from the action of isomaltase?

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

    Where does carbohydrate digestion initially begin in the human body?

    <p>In the mouth</p> Signup and view all the answers

    Which enzyme specifically acts on maltose to produce glucose?

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

    What effect does the low pH in the stomach have on carbohydrate digestion?

    <p>It halts the action of salivary amylase.</p> Signup and view all the answers

    What is the role of the Na+/glucose cotransporter (SGLT1) in the absorption of monosaccharides?

    <p>Mediates the active transport of glucose along with sodium</p> Signup and view all the answers

    Which enzyme is primarily responsible for the activation of trypsinogen?

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

    Which of the following statements about pepsin is true?

    <p>It primarily acts on peptide bonds of aromatic residues.</p> Signup and view all the answers

    What amount of dietary protein digestion is primarily credited to pepsin?

    <p>15%</p> Signup and view all the answers

    What type of enzymes are trypsin, chymotrypsin, and elastase classified as?

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

    Which type of amino acids do carboxypeptidase A and B preferentially act upon?

    <p>Basic C-terminal residues</p> Signup and view all the answers

    Where are brush border enzymes most abundantly found within the digestive system?

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

    What advantage does the location of enteropeptidase provide to the pancreatic digestive system?

    <p>It prevents the activation of zymogens in the pancreas.</p> Signup and view all the answers

    What mechanism is primarily used for the absorption of di- and tripeptides?

    <p>Co-transport mechanism</p> Signup and view all the answers

    Which type of amino acids are primarily utilized as energy substrates within enterocytes?

    <p>Amino acids with acidic sidechains</p> Signup and view all the answers

    What enhances the absorption rate of amino acids compared to free amino acids?

    <p>Co-transport mechanism</p> Signup and view all the answers

    How do hydrophobic amino acids primarily enter the enterocytes?

    <p>Passive diffusion</p> Signup and view all the answers

    What role do intracellular peptidases play in protein absorption?

    <p>Hydrolyze internalized peptides</p> Signup and view all the answers

    What type of amino acid transporter is found in the basolateral border?

    <p>Na+-independent carriers only</p> Signup and view all the answers

    What generates the H+ gradient required for the uptake of di- and tripeptides?

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

    Which of the following statements about amino acid absorption is correct?

    <p>Co-transport is necessary for the transport of di- and tripeptides.</p> Signup and view all the answers

    What is the main product of salivary amylase digestion?

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

    Which enzyme is produced by the pancreas to aid in protein digestion?

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

    What type of bond cannot be cleaved by human digestive enzymes in cellulose?

    <p>β-1,4 bonds</p> Signup and view all the answers

    Which carbohydrate polymer is known as a major energy source in plants?

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

    What is a key feature that differentiates glycogen from amylopectin?

    <p>Branch point distance</p> Signup and view all the answers

    Study Notes

    Digestion and Absorption

    • Digestion breaks down polymeric nutrient molecules into monomers or small oligomers before absorption into the body
    • Most digestion and absorption occur in the small intestine
    • Absorption mechanisms include passive diffusion, facilitated diffusion, and active transport
    • Passive diffusion occurs down a concentration gradient
    • Facilitated diffusion utilizes membrane proteins within the enterocyte
    • Active transport requires energy-dependent membrane proteins within the enterocyte

    Surface area for absorption

    • The surface area for absorption is increased by villi and microvilli on the surface of the small intestine

    Villus structure

    • Villi are finger-like projections from the intestinal wall, lined with enterocytes that increase surface area for absorption

    Digestive enzymes

    • Food types are broken down by specific enzymes
    • Carbohydrates are digested by salivary and pancreatic amylases, as well as intestinal maltase, resulting in maltose and glucose
    • Proteins are digested by pepsin in the stomach, trypsin and peptidases in the small intestine, resulting in peptides and amino acids
    • Fats are acted upon by lipase from the pancreas and bile salts from the liver, resulting in fatty acids and monoacylglycerol

    Carbohydrates

    • Major sources of energy in the diet
    • Starch is a major source of carbohydrates, being a plant polymer of glucose monomers
    • Amylose and amylopectin are linear and branched polymers of glucose, respectively
    • Amylose contains α-1,4 bonds along the length of the chain
    • Amylopectin contains α-1,4 bonds along the length of the chain and α-1,6 bonds at branch points
    • Glycogen is a branched polymer of glucose found in animal sources and has branch points closer together than amylopectin

    Carbohydrates: Digestion

    • α-amylases, secreted from salivary glands and pancreas, break α-1,4 linkages in carbohydrates
    • Products of digestion are branced oligosaccharides, dextrins, maltose, and glucose
    • Digestion starts in the mouth with salivary amylase, continues within the bolus in the stomach, and then continues in the duodenum by pancreatic amylase

    Brush Border Enzymes

    • Embedded in microvilli of the brush border of the small intestine
    • Further breakdown of starch and other sugars
    • Isomaltase breaks down isomaltose to glucose
    • Glucoamylase breaks down small oligosaccharides to glucose
    • Maltase breaks down maltose to glucose
    • Lactase breaks down lactose to glucose and galactose
    • Sucrase breaks down sucrose to glucose and fructose

    Absorption of Monosaccharides into the Enterocyte

    • Passive diffusion of monosaccharides is possible but slow
    • Hexose transporters, such as the Na+/glucose cotransporter (SGLT1) and Na+ independent hexose transporter (GLUT5), facilitate monosaccharide absorption

    Proteins

    • Polymers of amino acids joined together by peptide bonds
    • Diverse in sequence
    • Digested by endopeptidases and exopeptidases
    • Provide fixed nitrogency and essential amino acids

    Protein: Digestion in the Stomach

    • Low pH denatures proteins but is not sufficient for chemical hydrolysis
    • Pepsin, secreted as an inactive zymogen (pepsinogen) is activated by acidic conditions
    • Pepsin is an endopeptidase favoring aromatic peptide bonds
    • Responsible for digesting ~15% of dietary protein

    Proteins: Digestion in the Small Intestine

    • Pancreatic juice contains endopeptidases: trypsin, chymotrypsin, elastase
    • Pancreatic juice contains carboxypeptidases: carboxypeptidase B and carboxypeptidase A
    • All pancreatic proteases are produced as inactive zymogens
    • Products of digestion are oligo-, tetra-, tri-peptides

    Activation of Pancreatic Proteases

    • Trypsinogen is cleaved by enteropeptidase (enterokinase) to produce trypsin
    • Trypsin activates other zymogens, including trypsinogen
    • Enteropeptidase is only present in the gastrointestinal tract, preventing pancreatic damage by digestive enzymes

    Brush Border Enzymes

    • Most abundant in the jejunum
    • Attached to the membrane with their active sites facing the lumen to act on chyme
    • Also act within the lumen
    • Include oligopeptidases, dipeptidyl aminopeptidase, and leucine aminopeptidase which further degrade products of pancreatic enzymes to absorbable forms

    Protein Absorption - Peptides

    • Di- and tri-peptides are absorbed by a co-transport mechanism
    • Rate of absorption for peptides is faster than for free amino acids
    • H+ dependent co-transporter, generated by Na+/H+ exchange
    • Internalized peptides are hydrolyzed by intracellular peptidases
    • This is the main route for absorption of amino acids

    Protein Absorption - Amino Acids

    • Passive diffusion of relatively hydrophobic amino acids
    • Specific carrier systems exist in the brush border and basolateral border, including Na+ dependent co-transporters and Na+ independent transporters

    Protein Absorption Summary

    • Peptides and amino acids are absorbed from the intestinal lumen into the enterocyte
    • Peptides are hydrolyzed into amino acids by intracellular peptidases
    • Free amino acids are transported out of the enterocyte into the interstitial fluid
    • Amino acids are transported via the bloodstream to other tissues

    Reading

    • Medical Sciences by Jeannette Naish, Chapter 15
    • Smith & Morton - Systems of the Body "The Digestive System", especially Chapter 5 and 8
    • Lippincott's 4th edition - Chapter 15 and 7
    • Meisenberg and Simmons 2nd edition - Chapter 19

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    Digestion and Absorption of Protein and Carbohydrates PDF

    Description

    This quiz covers the processes of digestion and absorption, focusing on the role of the small intestine. It explores mechanisms such as passive diffusion, facilitated diffusion, and active transport, along with the structure and function of villi in enhancing nutrient absorption. Enhance your understanding of digestive enzymes and their specific functions as well.

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