MBBS Year 1 Gastrointestinal Physiology Lectures
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MBBS Year 1 Gastrointestinal Physiology Lectures

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Questions and Answers

What is the primary propulsion force that drives food through the GI tract?

  • Voluntary muscle movement
  • Gravity
  • Involuntary muscular contraction (correct)
  • Involuntary nervous stimulation

    • What is the primary function of the submucosa layer in the GI tract?

  • Absorption of nutrients
  • Support and structure for the mucosa (correct)
  • Secretion of digestive enzymes
  • Muscular contraction and relaxation

    • What is the primary site of nutrient absorption in the GI tract?

  • Liver
  • Stomach
  • Mouth
  • Intestine (correct)

    • What is the function of hormones released by endocrine cells in the GI epithelium?

    <p>Regulation of digestion and absorption</p> Signup and view all the answers

    What is the function of salivary and gastrointestinal fluid secretions in the GI tract?

    <p>To provide optimal pH and ionic composition for digestion</p> Signup and view all the answers

    What is the function of the enterohepatic circulation in the GI tract?

    <p>Regulation of bile secretion</p> Signup and view all the answers

    What is the primary site of initial digestion of food in the GI tract?

    <p>Mouth and stomach</p> Signup and view all the answers

    What is the fate of salivary and gastrointestinal fluid secretions in the GI tract?

    <p>They are largely reabsorbed</p> Signup and view all the answers

    What is the primary function of the smooth muscles in the muscularis mucosae?

    <p>To create folds and ridges in the mucosa</p> Signup and view all the answers

    Which of the following is NOT part of the four concentric layers of the gastrointestinal tract?

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

    What is the role of Messner's plexus in the digestive tract?

    <p>Sending nerve fibers to the mucosa and muscularis layers</p> Signup and view all the answers

    Which secretion from the liver assists with digestion in the small intestine?

    <p>Bile salts</p> Signup and view all the answers

    In which part of the digestive tract does the majority of carbohydrate and amino acid absorption take place?

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

    What distinguishes the upper esophagus and anal sphincter from other parts of the muscularis externa?

    <p>Striated muscle fibers</p> Signup and view all the answers

    What type of connective tissue is primarily found in the lamina propria of the mucosa?

    <p>Vascularized loose connective tissue</p> Signup and view all the answers

    What is the main purpose of the muscular valves or sphincters in the gastrointestinal tract?

    <p>To separate different digestive organs</p> Signup and view all the answers

    What is the primary role of parietal cells in the gastric gland?

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

    What stimulates the secretion of histamine from enterochromaffin-like cells?

    <p>Action of gastrin on CCK2 receptors</p> Signup and view all the answers

    Which hormone is released by G cells and plays a role in stimulating parietal cells?

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

    How does PGE2 affect gastric acid secretion?

    <p>It inhibits the action of histamine</p> Signup and view all the answers

    What is the primary function of chief cells in the gastric gland?

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

    What is a key structural feature of parietal cells that aids in their function?

    <p>Specialized intracellular canaliculi</p> Signup and view all the answers

    What mediates the potentiation of acid secretion by parietal cells?

    <p>Simultaneous binding of two of three specific agonists</p> Signup and view all the answers

    What is the diameter of parietal cells in the gastric gland?

    <p>25 µM</p> Signup and view all the answers

    Which mechanism primarily contributes to the secretion of gastric acid in Zollinger-Ellison Syndrome?

    <p>Stimulation of ECL cells by histamine</p> Signup and view all the answers

    What is the typical pH range observed in the jejunum of patients with Zollinger-Ellison Syndrome?

    <p>1.0 to 3.6</p> Signup and view all the answers

    Which cellular component predominates in the exocrine function of the pancreas?

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

    What role does pepsinogen play in the pathophysiology of Zollinger-Ellison Syndrome?

    <p>It converts to pepsin in low pH environments</p> Signup and view all the answers

    Which part of the pancreas is predominantly drained by the main pancreatic duct?

    <p>All parts equally</p> Signup and view all the answers

    What is the primary factor leading to diarrhea in patients with Zollinger-Ellison Syndrome?

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

    Which characteristic is true of the pancreas's endocrine tissue?

    <p>It accounts for approximately 2-4% of pancreatic mass</p> Signup and view all the answers

    What type of nervous system innervation primarily influences pancreatic secretion?

    <p>Both sympathetic and parasympathetic nervous systems</p> Signup and view all the answers

    What effect does atropine have on saliva and blood flow?

    <p>It blocks saliva secretion but does not block blood flow.</p> Signup and view all the answers

    What is the primary mechanism that leads to increased salivary secretion?

    <p>Reflex response controlled by parasympathetic and sympathetic nerves.</p> Signup and view all the answers

    Which electrolytes are involved in the modification of primary saliva in the striated duct system?

    <p>Na+ and Cl- are reabsorbed while K+ and HCO3- are secreted.</p> Signup and view all the answers

    What role does the Na+-K+-2Cl- co-transporter play in salivary secretion?

    <p>It facilitates the reuptake of Cl- into acinar cells.</p> Signup and view all the answers

    What happens to Cl- conductance when the stimulation of salivary secretion stops?

    <p>It increases to restore KCl concentrations.</p> Signup and view all the answers

    What initiates the release of neurotransmitters and hormones in the salivary secretion mechanism?

    <p>Elevated intracellular Ca2+ following stimulation.</p> Signup and view all the answers

    In the context of salivary secretion, what is the significance of K+ channels on the basolateral membrane?

    <p>They assist in the activation of Cl- channels in the luminal membrane.</p> Signup and view all the answers

    Which of the following stimuli does NOT contribute to salivary secretion?

    <p>Low blood pressure in the salivary glands.</p> Signup and view all the answers

    Study Notes

    Overview of the Digestive System

    • The gastrointestinal (GI) tract comprises four main layers: serosa, muscularis externa, submucosa, and mucosa.
    • Functions of GI tract layers include protection, absorption, and motility regulation.

    Functions of Salivary, Gastric, and Pancreatic Secretions

    • Salivary secretions start digestion with enzymes like amylase that break down carbohydrates.
    • Gastric secretions, including HCl from parietal cells, facilitate protein digestion and create an acidic environment for pepsin activation.
    • Pancreatic secretions, rich in digestive enzymes, enter the small intestine, where they further aid in nutrient breakdown.

    Regulation of Digestion and Absorption

    • Digestion begins in the mouth and continues in the stomach; primary absorption of nutrients occurs in the small intestine.
    • Endocrine cells in the GI epithelium, like G cells, release hormones (e.g., gastrin) to modulate digestive activity.

    Mechanisms of Bile Secretion and Enterohepatic Circulation

    • Bile secretion is regulated by hormonal signals from the intestine, primarily cholecystokinin (CCK).
    • Enterohepatic circulation involves the recycling of bile acids from the intestine back to the liver.

    Histological Organization of the GI Tract

    • The GI tract, from esophagus to large intestine, consists of four concentric layers: mucosa, submucosa, muscularis externa, and serosa/adventitia.
    • Mucosa includes epithelium, lamina propria (connective tissue), and muscularis mucosae, enabling absorption and secretion.
    • Submucosa contains blood vessels, lymphatics, and neural plexus (Meissner's plexus) for regulation of the GI tract's functions.

    Salivary Secretory Mechanisms

    • Saliva formation occurs in a two-step process starting with isotonic primary fluid produced by acinar cells, modified in the ducts.
    • Salivary secretion is stimulated by sensory input like taste or smell, regulated by both parasympathetic and sympathetic nerves.

    Gastric Acid Secretion Regulation

    • HCl secretion in the stomach is mediated by gastrin, histamine, and acetylcholine acting on parietal cells.
    • Histamine from enterochromaffin-like cells plays a central role in stimulating gastric acid secretion.
    • Prostaglandin E2 (PGE2) inhibits gastric acid secretion by blocking histamine's action.

    Zollinger-Ellison Syndrome (ZES)

    • ZES is characterized by gastrin-secreting tumors (gastrinomas) in the pancreas or duodenum, leading to excessive gastric acid production.
    • Symptoms include peptic ulcers and diarrhea due to increased gastric acidity and pepsinogen conversion to active pepsin.

    Regulation of Pancreatic Secretion

    • The pancreas, approximately 90-100 g in weight, serves as a mixed endocrine and exocrine gland, primarily composed of acinar cells.
    • The main pancreatic duct drains digestive secretions into the duodenum, where they participate in nutrient digestion.
    • Pancreatic acini contain zymogen granules filled with digestive enzymes, responsible for significant digestive activity in the small intestine.

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    MBBS Year 1 GI Lecture Notes - Prof GE Mann PDF

    Description

    Summary notes for Prof GE Mann's GI Lectures 1-5, covering key concepts and information from narrated powerpoint lectures.

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