Physiology Lecture 17: GI System Overview
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Questions and Answers

What is the primary purpose of brush border enzymes in carbohydrate digestion?

  • To transport nutrients to the liver
  • To facilitate lipid absorption
  • To digest carbohydrates into monosaccharides (correct)
  • To activate zymogens

    • How is glucose absorbed in the small intestine?

  • Exclusively through endopeptidases
  • Via active transport alone
  • By co-transport with sodium and facilitated diffusion (correct)
  • Only through passive diffusion

    • Which enzyme is responsible for breaking down sucrose into its component sugars?

  • Maltase
  • Glucoamylase
  • Sucrase (correct)
  • Lactase

    • What must occur before proteins can be absorbed in the intestinal tract?

    <p>They need to be digested into tri-, dipeptides and amino acids.</p> Signup and view all the answers

    What role do zymogens play in protein digestion?

    <p>They serve as storage forms for inactive enzymes.</p> Signup and view all the answers

    What is the effect of pepsin in protein digestion?

    <p>Pepsin begins the digestion of proteins but cannot fully complete it.</p> Signup and view all the answers

    Which carbohydrates are primarily absorbed through facilitated diffusion?

    <p>Fructose alone</p> Signup and view all the answers

    What type of enzyme is responsible for cleaving amino acids from the ends of polypeptides?

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

    What is the primary role of the microvilli on the absorptive cells in the small intestine?

    <p>To enhance the absorption surface area for nutrients</p> Signup and view all the answers

    Which part of the colon is primarily responsible for the storage of waste?

    <p>Sigmoid colon</p> Signup and view all the answers

    What is the end product of starch digestion by amylases?

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

    Which of the following carbohydrates must be digested before they can be absorbed?

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

    What major function is associated with the presence of over 700 species of bacteria in the colon?

    <p>Digestion of fiber and synthesis of vitamins</p> Signup and view all the answers

    Which enzyme is primarily responsible for initiating carbohydrate digestion in the mouth?

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

    Why are amylases limited in their ability to digest polysaccharides?

    <p>They cannot break bonds at branch points or terminal glucose monomers</p> Signup and view all the answers

    When considering the absorptive function of the small intestine, which feature is most significant?

    <p>The presence of villi and microvilli</p> Signup and view all the answers

    What types of carbohydrates are most commonly consumed in a typical diet?

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

    Which of the following types of cells are responsible for absorbing nutrients in the small intestine?

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

    What must happen to consumed nutrients before they can enter the bloodstream?

    <p>They undergo digestion through mechanical and chemical processes.</p> Signup and view all the answers

    Which component is primarily responsible for the initial digestion of carbohydrates in the mouth?

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

    Which layer of the gastrointestinal tract wall is responsible for the motility of the digestive process?

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

    What is the primary function of the small intestine?

    <p>Digestion and absorption of nutrients</p> Signup and view all the answers

    Which of the following cells is NOT found in the gastric pits of the stomach?

    <p>Pancreatic cells</p> Signup and view all the answers

    Which accessory gland plays a crucial role in the chemical digestion of fats?

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

    What structure prevents food from entering the trachea during swallowing?

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

    What is chyme?

    <p>The semi-liquid mass of partly digested food in the stomach</p> Signup and view all the answers

    The region of the small intestine where most digestion occurs is known as?

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

    Which sphincter controls the movement of food from the esophagus into the stomach?

    <p>Lower esophageal sphincter</p> Signup and view all the answers

    What is the function of glucoamylase in carbohydrate digestion?

    <p>Breaks down polysaccharides into glucose</p> Signup and view all the answers

    Which transport mechanism is used to absorb glucose and galactose in the small intestine?

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

    What are the end products of protein digestion before absorption?

    <p>Tripeptides, dipeptides, and amino acids</p> Signup and view all the answers

    What type of enzyme is pepsin, and what is its role in protein digestion?

    <p>Endopeptidase; it begins digestion of proteins</p> Signup and view all the answers

    Which sugar is absorbed solely through facilitated diffusion in the small intestine?

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

    What is the activation mechanism for zymogens in protein digestion?

    <p>Proteolytic activation</p> Signup and view all the answers

    What happens to proteins in the stomach during digestion?

    <p>They are partially digested by pepsin</p> Signup and view all the answers

    What component is primarily responsible for secreting inactive forms of digestive enzymes in the small intestine?

    <p>Zymogen granules</p> Signup and view all the answers

    What is the primary function of absorptive cells with microvilli in the small intestine?

    <p>Facilitating nutrient absorption</p> Signup and view all the answers

    Which role do carrier proteins on microvilli perform in the small intestine?

    <p>Transport of monosaccharides</p> Signup and view all the answers

    What is stored in the sigmoid colon?

    <p>Waste material</p> Signup and view all the answers

    Which type of cells in the colon play a significant role in digestion and nutrient production?

    <p>Bacterial cells</p> Signup and view all the answers

    What enables the microvilli to increase the absorptive surface area in the small intestine?

    <p>Their structural height</p> Signup and view all the answers

    What is produced by the bacterial species residing in the colon?

    <p>Vitamin K</p> Signup and view all the answers

    How do brush border enzymes function in the small intestine?

    <p>Breaking down disaccharides</p> Signup and view all the answers

    What type of digestion is most affected by the limitations of amylases?

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

    Which characteristic is essential for the absorptive function of the small intestine?

    <p>Villi structure</p> Signup and view all the answers

    Which component is primarily responsible for the digestion of starch in the small intestine?

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

    Which type of cell in the stomach is primarily responsible for secreting hydrochloric acid?

    <p>Parietal cells</p> Signup and view all the answers

    What is the primary function of G-cells in the gastric structure?

    <p>Releasing gastrin hormone</p> Signup and view all the answers

    What role do chief cells serve in the stomach?

    <p>Secretion of pepsinogen</p> Signup and view all the answers

    Which cell type in the gastric pits is primarily involved in the production of mucus?

    <p>Neck cells</p> Signup and view all the answers

    In the small intestine, which cell type is primarily responsible for the absorption of nutrients?

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

    What is the main function of salivary amylase produced by the salivary glands?

    <p>Initiating carbohydrate digestion</p> Signup and view all the answers

    Which type of cell in the small intestine secretes antimicrobial substances?

    <p>Paneth cells</p> Signup and view all the answers

    What is one of the roles of the gastric mucosal barrier?

    <p>Protecting stomach lining from acid</p> Signup and view all the answers

    Which layer of the gastrointestinal tract wall is responsible for motility and peristalsis?

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

    What is the primary function of the duodenum in the small intestine?

    <p>Digestion and nutrient absorption</p> Signup and view all the answers

    Study Notes

    Lecture 17: Human Physiology - Gastrointestinal System

    • Objectives:
      • Overview of GI system processes
      • Functional anatomy - brief overview
      • Digestion and absorption of nutrients and water
    • Required Reading:
      • Section 18.6 Regulation of the Digestive System (pages 645-651) - this is testable material!
      • Sections 18.1, 18.2, and 18.7 (selected portions)

    Overview of Gastrointestinal System Processes

    • Consumed nutrients are too large to enter the bloodstream directly.
    • Nutrients undergo digestion (mechanical and chemical) before absorption.
    • Motility and secretion aid digestion and absorption.

    Functional Anatomy of the GI System

    • Diagrams of the organs of the GI tract and accessory glands are presented in the slides (figures 20.2, 20.3, 20.5, 20.6)

    The Gastrointestinal Tract

    • Mouth:
      • Mastication (chewing)
      • Saliva (contains salivary amylase)
      • Tongue
    • Pharynx: Common passageway for air and food, glottis and epiglottis
    • Esophagus:
      • Upper esophageal sphincter
      • Lower esophageal sphincter
    • Stomach:
      • Contains gastric pits with different secretory cells (neck cells, chief cells, parietal cells, G-cells)
      • Stomach lining protected by gastric mucosal barrier
      • Chyme
    • Small intestine:
      • Primary site of digestion and absorption
      • Three divisions: duodenum, jejunum, ileum
      • Structure of the small intestine (villus, microvilli, brush border) relates to absorptive function.
        • Absorbing cells in villi have microvilli (brush border)
        • Enzymes associated with the villi (brush border enzymes) for digestion
    • Colon:
      • Ascending, transverse, and descending colon
      • Absorption of water and ions from chyme
      • Storage
      • More than 700 bacterial species live in the colon, responsible for fiber digestion and vitamin K and B7 production.
    • Digestion and Absorption of Nutrients and Water:
      • Carbohydrates, proteins, lipids
      • Water absorption

    Carbohydrate Digestion

    • Typical diet contains 500 grams of carbohydrates per day, mostly as disaccharides (sucrose, lactose, maltose) or polysaccharides (starch, cellulose, glycogen).
    • Only monosaccharides are absorbed; disaccharides and polysaccharides must be digested to monosaccharides.
    • Enzymes (salivary amylase, pancreatic amylase) digest starch to maltose and limit dextrins.
    • Brush border enzymes (dextrinase, glucoamylase, sucrase, lactase, maltase) complete carbohydrate digestion to monosaccharides.

    Carbohydrate Absorption

    • Glucose and galactose are absorbed via sodium cotransport across the apical membrane and facilitated diffusion across the basolateral membrane.
    • Fructose is absorbed via facilitated diffusion across both membranes.

    Protein Digestion

    • Two types of enzymes digest proteins: endopeptidases that split polypeptides, and exopeptidases that cleave amino acids.
    • Endopeptidases (pepsin) start in the stomach and then continue in the small intestine
    • Exopeptidases continue in the small intestine
    • Zymogens (inactive protein enzymes form) activate after a protein enzyme is converted to its active form
    • Digestion begins in the stomach (pepsin).
    • In the small intestine, pancreatic proteases (trypsin, chymotrypsin, carboxypeptidase) continue protein digestion.
    • Brush border enzymes (enterokinase, dipeptidases, tripeptidases) complete protein digestion to amino acids.

    Protein Absorption

    • Amino acids and small peptides are absorbed via sodium-linked secondary active transport or facilitated diffusion across the apical membrane.
    • Facilitated diffusion is used to move across the basolateral membrane

    Lipid Digestion

    • Typical diet contains 50 grams of lipids per day, mostly as triglycerides, some phospholipids, and cholesterol.
    • Lipids face special problems with digestion and absorption due to their insolubility in water.
    • Lipases (lingual, gastric, pancreatic) digest lipid molecules and break them down into fragments (fatty acids and monoglycerides).
    • Bile salts emulsify lipids, increasing the surface area for lipase action.

    Lipid Absorption

    • Free fatty acids and monoglycerides are absorbed via simple diffusion into intestinal cells.
    • The free fatty acids and monoglycerides reform triglycerides and are encased in chylomicrons.
    • Chylomicrons are secreted by exocytosis, entering lymphatic vessels.
    • Chylomicrons enter circulation.

    Absorption of Water

    • Water intake is up to 2 liters/day and secretions can be up to 7 liters/day.
    • Water absorption is passive, following the absorption of solutes (especially sodium) by osmosis.
    • Approximately 95% of ingested water is absorbed by the time chyme reaches the colon.

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    • Instructions are in the Canvas module.

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    Human Physiology GI System Lecture Notes PDF

    Description

    This quiz covers the key concepts of the gastrointestinal (GI) system, including its functional anatomy and processes involved in digestion and absorption. It draws on required reading sections that focus on the regulation of the digestive system and essential physiological functions. Test your understanding of the various components of the GI tract and their roles in nutrient processing.

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