Gastrointestinal Tract Functions and Structure
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Questions and Answers

What is the primary action of GIP in response to an oral glucose load?

  • Promotes gastric H+ secretion
  • Inhibits H+ secretion from gastric parietal cells
  • Inhibits insulin release from the pancreas
  • Stimulates insulin release from the pancreas (correct)

    • Which substance is secreted in response to H+ in the lumen of the GI tract?

  • Gastrin releasing peptide
  • Vasoactive intestinal peptide
  • Histamine (correct)
  • GIP

    • What type of signaling do paracrines rely on for their action within the GI tract?

  • Neurological signaling through the nerves
  • Long-distance signaling through the bloodstream
  • Short-distance signaling to nearby target cells (correct)
  • Endocrine signaling in distant organs

    • Which action is associated with somatostatin in the GI tract?

    <p>Inhibits the release of all GI hormones</p> Signup and view all the answers

    Which neurocrine is known for being released in response to action potentials in GI tract neurons?

    <p>Vasoactive intestinal peptide (VIP)</p> Signup and view all the answers

    What is one primary function of the gastrointestinal tract?

    <p>To absorb water, electrolytes, vitamins, and nutrients</p> Signup and view all the answers

    Which plexus is responsible for controlling the motility of the gastrointestinal tract?

    <p>Myenteric plexus</p> Signup and view all the answers

    How does the parasympathetic nervous system affect the functions of the gastrointestinal tract?

    <p>It increases motility, secretion, and blood flow</p> Signup and view all the answers

    What type of reflexes are essential to gastrointestinal control?

    <p>Gastrointestinal reflexes</p> Signup and view all the answers

    What is the role of the submucosal plexus in the gastrointestinal tract?

    <p>Control of blood flow and secretion</p> Signup and view all the answers

    Which chemical transmitter is primarily associated with the sympathetic nervous system's control of GIT functions?

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

    Which part of the gastrointestinal tract is primarily innervated by the vagus nerve?

    <p>Upper large intestine</p> Signup and view all the answers

    Which aspect of the GIT functions is NOT controlled by the enteric nerve plexus?

    <p>Transportation of nutrients to cells</p> Signup and view all the answers

    What initiates the release of gastrin from the G cells of the gastric antrum?

    <p>Presence of protein in the stomach</p> Signup and view all the answers

    Which hormone primarily stimulates the pancreatic secretion of bicarbonate?

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

    What effect does cholecystokinin (CCK) have on gastric emptying?

    <p>Inhibits gastric emptying</p> Signup and view all the answers

    What is the primary role of somatostatin in relation to gastrin secretion?

    <p>Inhibits gastrin secretion</p> Signup and view all the answers

    Which reflex is characterized as a long reflex with the center in the spinal cord or brain stem?

    <p>Defecation reflexes</p> Signup and view all the answers

    What triggers the release of cholecystokinin (CCK) from I cells?

    <p>Presence of fats and proteins in the duodenum</p> Signup and view all the answers

    Which of the following actions is NOT associated with gastrin?

    <p>Inhibition of gastric H+ secretion</p> Signup and view all the answers

    What type of receptors respond to mechanical or chemical stimulation to increase gut motility?

    <p>Enteric nervous system receptors</p> Signup and view all the answers

    Study Notes

    Gastrointestinal Tract (GIT) Functions

    • The GIT's primary purpose is to provide the body with essential nutrients, electrolytes, vitamins, and water
    • This involves a complex series of steps:
      • Movement of food: Food is propelled through the digestive tract
      • Secretion of digestive juices: Digestive enzymes and fluids are released to break down food
      • Absorption of nutrients: The digested nutrients, water, and electrolytes are absorbed into the bloodstream
      • Blood circulation: Adequate blood flow to the GIT is essential for proper function
      • Control mechanisms: Local, nervous, and hormonal systems regulate all aspects of GIT function

    Structure of the GIT Wall

    • The GIT wall has four layers:
      • Mucosa: Innermost layer responsible for absorption and secretion
      • Submucosa: Contains blood vessels, lymphatics, and nerves
      • Muscularis propria: Muscle layers responsible for motility
      • Serosa/Adventitia: Outermost layer that protects the GIT

    Nervous Control of GIT Functions

    • Enteric Nerve Plexus (ENP):
      • The "gut brain" responsible for controlling motility and secretion in the GIT
      • Consists of two main plexuses:
        • Myenteric plexus: Located between the muscle layers, controls GIT motility
        • Submucosal plexus: Located in the submucosa, controls secretion and blood flow
      • The ENP receives sensory information from the GIT and uses local reflexes to regulate function
    • Parasympathetic System:
      • Promotes increased motility, secretion, and blood flow in the GIT
      • Opens sphincters
      • Carried via the vagus nerve and pelvic nerve:
        • Vagus nerve: Supplies the esophagus, stomach, pancreas, small intestine, and upper large intestine
        • Pelvic nerve: Supplies the lower large intestine, rectum, and anal canal
    • Sympathetic System:
      • Inhibits most GIT functions, decreasing motility, secretion, and blood flow
      • Closes the sphincters
      • Chemical transmitter is adrenaline
      • Arises from the thoracic and lumbar segments of the spinal cord

    Gastrointestinal Reflexes

    • Local reflexes:
      • Integrated within the enteric nervous system
      • Mechanical or chemical stimulation of gut receptors increases motility and secretion
    • Long reflexes:
      • Center of the reflex is in the spinal cord or brainstem
      • Examples:
        • Entero-gastric reflex: Regulates the flow of food from stomach to the small intestine
        • Gastro-colic reflex: Stimulates colon motility after food enters the stomach
        • Defecation reflex: Promotes the expulsion of feces

    Hormonal Control of GIT Functions

    • Gastrointestinal Hormones:
      • Chemical substances released from endocrine cells in the GIT mucosa
      • Enter the bloodstream and act on target cells in the GIT
      • Regulate secretions and motility
    • Gastrin:
      • Secreted by G cells in the gastric antrum
      • Stimulated by:
        • Protein in the stomach
        • Distention of the stomach
        • Vagal stimulation (via gastrin-releasing peptide)
      • Actions:
        • Increases H+ secretion by the parietal cells
        • Increases contraction of the stomach body
    • Cholecystokinin (CCK):
      • Secreted by I cells in the duodenal and jejunal mucosa
      • Stimulated by proteins and fats in the duodenum and jejunum
      • Actions:
        • Stimulates gallbladder contraction and relaxation of the sphincter of Oddi
        • Promotes pancreatic enzyme secretion
        • Slower gastric emptying (especially in response to fatty meals)
    • Secretin:
      • Secreted by S cells in the duodenum
      • Stimulated by H+ (acid) in the duodenal lumen
      • Actions:
        • Stimulates pancreatic HCO3- secretion to neutralize intestinal acid
        • Stimulates liver HCO3- and H2O secretion
        • Inhibits gastric H+ secretion by parietal cells
    • Glucose-Dependent Insulinotropic Peptide (GIP):
      • Secreted by the duodenum and jejunum
      • Stimulated by fat, protein, and carbohydrate
      • Actions:
        • Stimulates insulin release (especially after oral glucose intake)
        • Inhibits gastric H+ secretion

    Paracrines

    • Somatostatin:
      • Secreted throughout the GIT
      • Stimulated by H+
      • Actions:
        • Inhibits the release of all GI hormones
        • Inhibits gastric H+ secretion
    • Histamine:
      • Secreted by enterochromaffin-like cells in the gastric mucosa
      • Actions:
        • Increases gastric H+ secretion directly and through potentiating the effects of gastrin and vagal stimulation

    Neurocrines

    • Synthesized in GIT neurons
    • Released in response to action potentials
    • Examples
      • Vasoactive intestinal peptide (VIP):
        • Promotes relaxation of smooth muscle
        • Stimulates secretion
      • Gastrin releasing peptide (GRP):
        • Stimulates gastrin release
      • Enkephalins:
        • Inhibit GIT motility
        • Stimulate sphincter contraction

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    L1 Neuro-endocrine Control of Gastro-intestinal Tract PDF

    Description

    Explore the complex functions and structural layers of the gastrointestinal tract (GIT). This quiz covers everything from the movement of food and secretion of digestive juices to nutrient absorption and the anatomy of the GIT wall. Test your knowledge on these vital aspects of human digestion.

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