Gastrointestinal Physiology
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Questions and Answers

During which kind of potentials do significant quantities of calcium ions enter the fibers and cause most of the contraction?

  • Synaptic potentials
  • Action potentials
  • Slow wave potentials
  • Spike potentials (correct)
  • What is the term for the nervous system that lies entirely in the wall of the gut?

  • Central nervous system
  • Enteric nervous system (correct)
  • Sympathetic nervous system
  • Parasympathetic nervous system
  • How many plexuses make up the enteric nervous system?

  • One
  • Three
  • Two (correct)
  • Four
  • What is the primary function of the myenteric plexus?

    <p>Controlling GI movements</p> Signup and view all the answers

    What is the function of some neurons in the myenteric plexus?

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

    What is the function of the submucosal plexus?

    <p>Controlling GI secretion</p> Signup and view all the answers

    What is the origin of many sensory signals in the GI tract?

    <p>The GI epithelium</p> Signup and view all the answers

    How is the parasympathetic supply to the gut divided?

    <p>Into cranial and sacral divisions</p> Signup and view all the answers

    What is the primary function of the alimentary tract?

    <p>To provide a continual supply of water, electrolytes, vitamins, and nutrients</p> Signup and view all the answers

    What is the correct order of the layers of the GIT wall from outside towards the lumen?

    <p>Serosa, longitudinal muscle layer, circular muscle layer, submucosa, mucosa</p> Signup and view all the answers

    What is the typical range of voltage of slow waves in the GI smooth muscle?

    <p>5-15 millivolts</p> Signup and view all the answers

    What is the normal resting membrane potential in the smooth muscle fibers of the gut?

    <p>Between -50 and -60 millivolts</p> Signup and view all the answers

    What happens when the resting membrane potential of the GI smooth muscle becomes more positive than about -40 millivolts?

    <p>The muscle fiber becomes more excitable</p> Signup and view all the answers

    What is the effect of NE or EP on the smooth muscle fiber membrane?

    <p>It hyperpolarizes the membrane</p> Signup and view all the answers

    What is the effect of acetylcholine on the smooth muscle fiber membrane?

    <p>It depolarizes the membrane</p> Signup and view all the answers

    What ions enter the smooth muscle fiber during slow waves?

    <p>Only sodium ions</p> Signup and view all the answers

    What triggers the relaxation of the internal anal sphincter?

    <p>Signals from the myenteric plexus</p> Signup and view all the answers

    What is the primary function of secretory glands in the GIT?

    <p>To secrete digestive enzymes and provide mucus</p> Signup and view all the answers

    What stimulates the secretion of digestive enzymes in the GIT?

    <p>Contact of food with the epithelium</p> Signup and view all the answers

    What is the effect of sympathetic stimulation on GIT glandular secretion?

    <p>It has a dual effect</p> Signup and view all the answers

    What is the composition of esophageal secretions?

    <p>Entirely mucous</p> Signup and view all the answers

    What is the location of the glands that secrete mucus for lubrication in the esophagus?

    <p>In the main body of the esophagus</p> Signup and view all the answers

    What is the parasympathetic reflex involved in?

    <p>Facilitating defecation</p> Signup and view all the answers

    What is the role of the pelvic parasympathetic nerve fibers?

    <p>To transmit signals to the descending colon, sigmoid, and rectum</p> Signup and view all the answers

    How many phases of gastric secretion are there?

    <p>3</p> Signup and view all the answers

    What is the primary function of oxyntic glands?

    <p>Producing gastric acid</p> Signup and view all the answers

    What is the main function of pancreatic amylase?

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

    What is the role of bile in fat digestion?

    <p>It emulsifies fat particles</p> Signup and view all the answers

    What is the function of carboxypolypeptidase?

    <p>Splitting peptides into individual amino acids</p> Signup and view all the answers

    What is the function of pancreatic lipase?

    <p>Hydrolyzing neutral fat into fatty acids and monoglycerides</p> Signup and view all the answers

    What is the other important function of bile besides fat digestion?

    <p>Serving as a means for excretion of waste products</p> Signup and view all the answers

    What is the primary function of pancreatic juice?

    <p>Breaking down proteins, carbohydrates, and fats</p> Signup and view all the answers

    What initiates enterogastric inhibitory reflexes?

    <p>The degree of acidity of the chyme</p> Signup and view all the answers

    What is the primary site of digestion and absorption?

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

    What is the function of the enzymes secreted by the brush border of the villi?

    <p>Digestion of specific food substances</p> Signup and view all the answers

    What is the result of the intrinsic defecation reflex?

    <p>Forcing feces toward the anus</p> Signup and view all the answers

    What is the location of the myenteric plexus in the intrinsic defecation reflex?

    <p>Rectal wall</p> Signup and view all the answers

    What is the function of the peptidases in the small intestine?

    <p>Splitting small polypeptides into amino acids</p> Signup and view all the answers

    What is the result of the stimulation of the pyloric pump by food in the duodenum?

    <p>Increased tone of the pyloric sphincter</p> Signup and view all the answers

    What is the surface area of the small intestine comparable to?

    <p>A tennis court</p> Signup and view all the answers

    Study Notes

    Gastrointestinal Physiology

    • The alimentary tract provides the body with a continual supply of water, electrolytes, vitamins, and nutrients through:
      • Movement of food through the GIT
      • Secretion of digestive juices and digestion of food
      • Absorption of water, electrolytes, vitamins, and digestive products
      • Circulation of blood through the GI organs to carry away absorbed substances
      • Control of all these functions by local, nervous, and hormonal systems

    Physiologic Anatomy of the GI Wall

    • The GI wall consists of five layers from outside to lumen:
      • Serosa
      • Longitudinal muscle layer
      • Circular muscle layer
      • Submucosa
      • Mucosa

    Electrical Activity of Gastrointestinal Smooth Muscle

    • Slow waves:
      • Are slow, undulating changes in resting membrane potential
      • Intensity varies between 5 and 15 millivolts
    • Spike potentials:
      • Are true action potentials
      • Occur automatically when resting membrane potential becomes more positive than about −40 millivolts
      • Normal resting membrane potential in smooth muscle fibers is between −50 and −60 millivolts
    • Factors that depolarize the membrane:
      • Stretching of the muscle
      • Stimulation by acetylcholine
      • Stimulation by several GI hormones
    • Factors that hyperpolarize the membrane:
      • Effect of NE or EP on the fiber membrane
      • Stimulation of the sympathetic nerves that secrete mainly NE at their endings

    Neural Control of Gastrointestinal Function—Enteric Nervous System

    • The GI has its own nervous system called the enteric nervous system (ENS)
    • The ENS lies entirely in the wall of the gut, beginning in the esophagus and extending to the anus
    • The ENS is composed of two plexuses:
      • Myenteric plexus (outer plexus) lying between the longitudinal and circular muscle layers
      • Submucosal plexus (inner plexus) lying in the submucosa
    • The myenteric plexus controls mainly GI movements
    • The submucosal plexus controls mainly GI secretion and local blood flow
    • The ENS can function independently, but stimulation by the parasympathetic and sympathetic systems can greatly enhance or inhibit GI functions

    Autonomic Control of the Gastrointestinal Tract

    • The parasympathetic supply to the gut is divided into cranial and sacral divisions
    • Powerful factors that inhibit stomach emptying (duodenal factors):
      • Degree of distention of the duodenum
      • Presence of any degree of irritation of the duodenal mucosa
      • Degree of acidity of the chyme
      • Degree of osmolality of the chyme
      • Presence of certain breakdown products in the chyme

    Small Intestine Function

    • Digestion: enzymes are intracellular (disaccharidases and aminopeptidases)
    • Absorption: completed in the small intestine, large surface area (as large as a tennis court area)
    • Secretion: secretion of digestive enzymes by the brush border of the villi
    • Motility: movement of food through the small intestine

    Secretion of Digestive Enzymes

    • The enterocytes of the mucosa, especially those that cover the villi, contain digestive enzymes that digest specific food substances while they are being absorbed through the epithelium
    • These enzymes include:
      • Peptidases for the splitting of small polypeptides into amino acids
      • Disaccharidases that break down disaccharides into monosaccharides
      • Small amounts of lipases for the digestion of fat

    Defecation Reflexes

    • There are two types of defecation reflexes:
      • Intrinsic reflex mediated by the local enteric nervous system in the rectal wall
      • Parasympathetic reflex that involves the sacral segments of the spinal cord

    Secretory Functions of the GIT

    • Secretory glands have two primary functions:
      • Secrete digestive enzymes in most areas of the GIT
      • Provide mucus for lubrication and protection of all parts of the GIT

    Basic Mechanisms of Stimulation of the GIT Glands

    • Contact of food with the epithelium stimulates secretion (direct contact stimulation of the surface glandular cells by the food)
    • Parasympathetic stimulation increases the GIT glandular secretion rate
    • Sympathetic stimulation has a dual effect (sympathetic stimulation alone decreases secretion, but parasympathetic stimulation increases the secretion)

    Esophageal Secretions

    • Esophageal secretions are entirely mucous and provide lubrication for swallowing
    • The main body of the esophagus is lined with many simple mucous glands

    Pancreatic Secretion

    • The pancreatic digestive enzymes are secreted by pancreatic acini and large volumes of sodium bicarbonate solution are secreted by the small ductules and larger ducts leading from the acini
    • The combined product (enzymes + sodium bicarbonate) flows through a long pancreatic duct that joins the common bile duct
    • Pancreatic enzymes for digesting proteins:
      • Trypsin
      • Chymotrypsin
      • Carboxypolypeptidase
    • Pancreatic enzymes for digesting carbohydrates:
      • Pancreatic amylase
    • Pancreatic enzymes for digesting fat:
      • Pancreatic lipase
      • Cholesterol esterase
      • Phospholipase

    Secretion of Bile by the Liver

    • Bile serves two important functions:
      • Aids in fat digestion and absorption by emulsifying fat particles and aiding in absorption of digested fat end products
      • Serves as a means for excretion of several important waste products from the blood

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