Physiology of the Digestive System
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Questions and Answers

What is the primary function of Auerbach's plexus (Myenteric plexus) within the gastrointestinal tract?

  • Regulation of hormone secretion
  • Facilitation of taste sensation
  • Control of peristaltic activity (correct)
  • Stimulation of salivary secretion

    • Which component primarily comprises the organic part of saliva?

  • Sodium
  • Potassium
  • Chloride
  • Mucin (correct)

    • Which nervous system activity generally inhibits secretion and motility in the gastrointestinal tract?

  • Local enteric reflexes
  • Parasympathetic stimulation
  • Central reflexes
  • Sympathetic stimulation (correct)

    • What percentage of saliva is produced by the submandibular glands?

    <p>70% (D)</p> Signup and view all the answers

    Which hormone is part of the gastrin family involved in gastrointestinal control?

    <p>Cholecystokinin (CCK) (A)</p> Signup and view all the answers

    Which of the following is NOT a function of the gastrointestinal tract?

    <p>Secretion of hormones directly into the bloodstream (A), Regulation of blood oxygen levels (@)</p> Signup and view all the answers

    Which of the following is not a function of saliva?

    <p>Regulation of blood sugar level (D)</p> Signup and view all the answers

    Which of the following best describes the intrinsic innervation of the GIT?

    <p>Includes two major networks of nerve plexuses (C)</p> Signup and view all the answers

    How do digestive enzymes function in the gastrointestinal tract?

    <p>They break down food into smaller molecules (A)</p> Signup and view all the answers

    Which of the following correctly identifies the composition of the gastrointestinal tract?

    <p>Composed of the alimentary canal and accessory organs (C)</p> Signup and view all the answers

    What is the primary function of gastrin hormone in the human body?

    <p>Stimulating gastric motility and growth (B)</p> Signup and view all the answers

    Which of the following is NOT a cause of gastritis?

    <p>High fiber diet (C)</p> Signup and view all the answers

    What is the primary role of bile in digestion?

    <p>Emulsification of lipids (C)</p> Signup and view all the answers

    Which statement regarding bilirubin is correct?

    <p>It is responsible for jaundice if levels are elevated. (B)</p> Signup and view all the answers

    Which function is primarily associated with the liver?

    <p>Detoxification of drugs and toxic substances (A)</p> Signup and view all the answers

    What is a primary consequence of untreated GERD?

    <p>Heartburn and potential esophageal complications (A)</p> Signup and view all the answers

    Which function is NOT associated with gastric acid secretion?

    <p>Digestion of carbohydrates (D)</p> Signup and view all the answers

    Which of the following is correct about achalasia?

    <p>It leads to massive dilation of the esophagus due to failure of sphincter relaxation. (A)</p> Signup and view all the answers

    What role does intrinsic factor play in the stomach?

    <p>Is essential for the absorption of vitamin B12 in the terminal ileum. (D)</p> Signup and view all the answers

    Which of the following is not part of the gastric mucosal barrier that protects the gastric mucosa from autodigestion?

    <p>Presence of gastric acid (C)</p> Signup and view all the answers

    Flashcards

    Myenteric or Auerbach's Nerve Plexus

    A network of neurons in the wall of the digestive tract responsible for controlling the movement of food (peristalsis).

    What is the Gastrointestinal Tract (GIT)?

    A long, muscular tube within the body, responsible for breaking down food and absorbing nutrients. It starts at the mouth and ends at the anus. It includes both the alimentary canal and accessory organs.

    Submucosal or Meissner's Nerve Plexus

    A network of neurons in the wall of the digestive tract responsible for regulating the secretions of the digestive glands.

    What is Digestion?

    The breakdown of food into smaller molecules that the body can absorb. This process involves both mechanical and chemical actions.

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    Enteric Nervous System

    The involuntary nervous system that controls the digestive organs, including the muscles and glands.

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    What is Absorption (in relation to the GIT)?

    The movement of digested nutrients from the GIT into the bloodstream.

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    What is the Enteric Nervous System?

    A network of nerves within the walls of the GIT. It plays a crucial role in controlling and regulating digestion.

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    Parasympathetic Innervation of the Digestive System

    The part of the autonomic nervous system that generally promotes digestive activity, increasing secretion and motility.

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    Sympathetic Innervation of the Digestive System

    The part of the autonomic nervous system that generally inhibits digestive activity, slowing down secretion and motility.

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    What is Extrinsic Innervation of the GIT?

    The nerve supply to the GIT that originates from the central nervous system. It modulates the actions of the Enteric Nervous System.

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    What is achalasia?

    The lower esophageal sphincter (LES) fails to relax, preventing food from passing into the stomach. This leads to a buildup of food in the esophagus, causing dilation and difficulty swallowing.

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    What is GERD?

    A condition where stomach contents back up into the esophagus, often causing heartburn. It results from a weak lower esophageal sphincter (LES) or increased abdominal pressure.

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    What are parietal cells?

    These cells secrete hydrochloric acid (HCl) in the stomach, which helps with food digestion and sterilization.

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    What is pepsinogen?

    This enzyme, secreted by chief cells, works with HCl to break down proteins in the stomach.

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    What is the gastric mucosal barrier?

    This barrier is made up of tight junctions between gastric mucosal cells, protecting the stomach lining from its own acids and enzymes.

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    Gastric Mucosal Barrier

    A protective barrier in the stomach lining, consisting of thick mucus, bicarbonate ions, and prostaglandins, preventing damage from gastric acid.

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    Gastritis

    Inflammation of the stomach lining, often caused by irritants like NSAIDs (e.g., aspirin), alcohol, or bacterial infections (e.g., Helicobacter pylori).

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    Peptic Ulcer

    An open sore in the lining of the stomach or duodenum, caused by the breakdown of the protective gastric mucosal barrier by gastric juice. Common causes include stress, smoking, spicy food, alcohol, NSAIDs, and Helicobacter pylori.

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    Liver

    The largest metabolic organ in the body, vital for various functions including blood filtration and storage, carbohydrate, fat, and protein metabolism, bile secretion, and detoxification of harmful substances.

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    Bile

    A fluid produced by the liver, containing bile salts, pigments, cholesterol, and other components, essential for fat digestion and absorption, and removal of waste products from the body.

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    Study Notes

    Physiology of the Digestive System

    • The gastrointestinal tract (GIT) is a long muscular tube of complex organs and glands, beginning at the mouth and ending at the anus. It works together to digest food.
    • The GIT is composed of the alimentary canal and accessory organs. 
    • Main functions of the GIT include digestion (breaking down food mechanically and chemically), absorption of digestive products, secretion of digestive juices, and excretion of waste products.

    Objectives

    • Define the gastrointestinal tract (GIT) and list its main functions.
    • Identify the nerve supply of the GIT and describe the control mechanisms of GIT functions.
    • Describe each organ in the GIT tract and mention its function.
    • Interpret the causes of common GIT disorders.
    • Classify GIT hormones based on location and function.
    • Differentiate between different digestive enzymes.

    Nerve Supply of the GIT

    • Intrinsic innervation (Enteric Nervous System): Two major networks of nerves (plexuses) are present in the GIT wall.
      • Meissner's (submucosal) plexus regulates exocrine and endocrine secretions of submucosal glands.
      • Auerbach's (myenteric) plexus regulates peristaltic activity of the muscle layer (motor function).
    • Extrinsic innervation (Autonomic Nervous System):
      • Parasympathetic innervation (vagus and pelvic nerves) is largely excitatory to the GIT, stimulating secretion and motility.
      • Sympathetic innervation (T5 to L2) is mostly inhibitory to the GIT, inhibiting secretion and motility.

    Control of GIT Functions

    • Nervous control:
      • Local enteric reflexes within the enteric nervous system
      • Ganglion reflexes to prevertebral ganglia
      • Central reflexes to the central nervous system (CNS).
    • Hormonal control through GIT hormones:
      • Gastrin family (gastrin and cholecystokinin (CCK))
      • Secretin family (secretin, glucagon, vasoactive intestinal peptide (VIP), gastric inhibitory peptide (GIP))
      • Other hormones (motilin, somatostatin, neurotensin)

    Mouth (Oral Cavity)

    • Mastication (Chewing): Rhythmic opening and closing of the mouth, essential for food digestion by breaking down large particles into smaller ones. Also aids in deglutition (swallowing) and stimulates taste buds.
    • Salivary Glands: Three pairs; parotid (25%), sublingual (5%), and submandibular (70%) glands. Produce saliva.

    Saliva

    • Primarily water (99.5%). Contains organic components (mucin, ptyalin, lysosomes, IgA) and inorganic components (Na, K, Cl, HCO3).
    • Functions:
      • Articulation (speech)
      • Buffering (maintains mouth pH at 7)
      • Cleaning
      • Digestion (CHO through salivary amylase)
      • Excretion
      • Facilitation of deglutition (swallowing)
      • Water regulation (decreases with dehydration)

    Oral Cavity Diseases

    • Salivary gland diseases: Mumps (inflammation of salivary glands), tumors (salivary adenoma, carcinoma)
    • Pharyngeal diseases: Tonsillitis (inflammation of tonsils), pharyngitis (pharynx infection), diphtheria (bacterial infection).

    Pharynx

    • Food passes from the oral cavity to the pharynx.
    • The soft palate closes the nasal cavity, preventing food from entering the nasal passages.
      • The epiglottis covers the larynx, ensuring food goes to the esophagus, not the trachea.

    Swallowing (Deglutition)

    • The passage of food from the mouth to the stomach via the pharynx.
    • Occurs in three phases: buccal (voluntary), pharyngeal (involuntary), and esophageal (involuntary).

    Esophagus

    • Food takes 4-8 seconds to pass.
    • Walls contain smooth muscles which contract in wave-like motions (peristalsis).
    • Esophageal sphincters (UES and LES) allow passage downwards and prevent backflow (regurgitation)
    • Peristalsis is wavelike contractions behind and relaxation in front of the bolus.

    Esophageal Diseases

    • Gastroesophageal reflux disease (GERD): Backflow of stomach contents into the esophagus due to lower esophageal sphincter incompetence. Symptoms include heartburn. Often associated with increased intra-abdominal pressure (e.g., pregnancy, obesity) and low gastrin levels.
    • Achalasia: Failure of the lower esophageal sphincter (LES) to relax upon food arrival, leading to esophageal dilation and difficulties in swallowing.

    Stomach

    • Food storage (6-8 hrs)
    • Mechanical breakdown of food
    • Digestion of proteins by pepsin
    • Sterilization via HCl and lysozyme
    • Secretion of intrinsic factor (necessary for B12 absorption)
    • Absorption of iron (due to acidic environment)
    • Regulation of chyme passage into the duodenum via pyloric sphincter

    Stomach Secretion

    • Volume is approximately 2.5-3 liters and highly acidic (pH ~1).
    • Constituents:
      • Gastric HCL (secreted by oxyntic/parietal cells)
      • Enzymes (e.g., pepsinogen secreted by chief/peptic cells)
      • Mucous
      • Intrinsic factor (secreted by oxyntic/parietal cells)
    • Functions of gastric HCL:
      • Sterilization
      • Bile stimulation
      • Calcium ionization aid in absorption
      • Iron reduction aid in absorption
      • Protein digestion (pepsinogen activation)

    Gastric Mucosal Barrier

    • Precursor to ulcers.
    • Components:
      • Tight junctions between cells
      • Protective mucous layer
      • Bicarbonate (HCO3-) secretion
      • Prostaglandin synthesis

    Gastric Diseases

    • Gastritis: Inflammation of the stomach.
      • Causes: Irritant drugs (NSAIDs), alcohol, bacterial infection (Helicobacter pylori).
    • Peptic ulcer: Ulceration of the gastric mucosa due to disruption of the protective gastric mucosal barrier.
      • Causes: Stress, smoking, spicy food, alcohol, NSAIDs, Helicobacter pylori.

    Liver

    • Largest and most important metabolic organ.
    • Functions:
      • Vascular function (storage and filtration of blood)
      • Metabolic functions (carbohydrate, fat, protein metabolism)
      • Bile secretion
      • Storage (glycogen, fat-soluble vitamins, iron, water-soluble vitamins)
      • Detoxification (drugs, toxins)

    Bile

    • Composition: Mainly water (97.5%), bile salts, pigments, cholesterol, fatty acids, lecithin, and inorganic salts.
    • Bile pigments (e.g., bilirubin) are a byproduct of hemoglobin breakdown and are excreted in the stool.
    • Functions:
      • Neutralization of acidic chyme
      • Emulsification & digestion of lipids
      • Absorption of lipids
      • Excretion (toxins, dyes, inorganic substances).

    Jaundice (Icterus)

    • Yellowish discoloration of the skin and whites of eyes due to increased bilirubin levels.
    • Types: Prehepatic (increased bilirubin production), Hepatic (liver dysfunction), Posthepatic (obstruction in bile flow).

    Small Intestine

    • Functions: 
      • Onward movement of food (peristalsis)
      • Secretion of intestinal juice (succus entericus) containing enzymes, water, mucus, and mineral salts
      • Protection from bacteria (e.g., Peyer’s patches)
      • Completion of chemical digestion
      • Absorption of most nutrients

    Motor Function of the Small Intestine

    • Mixing movements (segmentation): Non-adjacent segments contract and relax, churning the food.
    • Propulsive movements (peristalsis): Adjacent segments contract and relax, moving food distally.

    Large Intestine

    • Functions:
      • Defecation.
      • Digestion of cellulose (in some animals).
      • Excretion of heavy metals (e.g., Mg, arsenic).
      • Absorption of water and electrolytes.
      • Synthesis of vitamins (e.g., K, B vitamins).
      • Secretion of mucus.
      • Storage of fecal matter.
    • Types of Bacteria in Large Intestine: Beneficial bacteria (produce vitamin K, histamine, biotin, folic acid) and non-beneficial bacteria (that consume vitamins, produce waste products like histamine, tyramine and ammonia).

    Defecation

    • The evacuation of rectal and colon contents via the anal canal.
    • A reflex action (autonomic) in infants, which becomes controlled in adults.
    • The process involves stimulation of receptors in the rectal walls, leading to contraction of rectal muscles and relaxation of the anal sphincter.
    • Voluntary control can also be exerted via the cerebral cortex to inhibit or allow defecation.

    Intestinal Diseases

    • Appendicitis: Inflammation of the appendix, often requiring surgical removal (appendectomy).
    • Inflammatory Bowel Disease (IBD): Chronic inflammatory conditions, including
      • Crohn's disease: affects the entire thickness of the intestinal wall.
      • Ulcerative colitis: affects the mucosa and submucosa of the colon and rectum.

    GIT Hormones

    • Gastrin: Released from stomach and duodenum in response to peptides and amino acids. Stimulates acid and intrinsic factor secretion.
    • Cholecystokinin (CCK): Released from duodenum and jejunum in response to fatty acids and amino acids. Stimulates gallbladder contractions, pancreatic enzyme release, and bile release.
    • Secretin: Released from duodenum and jejunum response to acidic pH. Stimulates pancreatic bicarbonate secretion.
    • Motilin: Released throughout the gut, especially during fasting. Increases gut motility.

    Digestive Enzymes

    • Site of Production | Site of Action | Enzyme | Substrate | Products
    • -------------------- | ----------------- | -------- | ---------- | ---------
    • Salivary glands | Mouth | Amylase | Starch | Maltose
    • Stomach cells | Stomach | Pepsin | Protein | Amino acids
    • Liver | Small intestine | Bile salts | Fats | Fat droplets
    • Pancreas | Small intestine | Amylase | Starch | Maltose
    • Pancreas | Small intestine | Proteases | Protein | Amino acids
    • Pancreas | Small intestine | Lipase | Lipids | Glycerol and fatty acids
    • Small intestine | Small intestine | Disaccharidases (e.g., maltase) | Disaccharides | Monosaccharides
    • Small intestine | Small intestine | Peptidases | Peptides | Amino acids

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    Physiology of the GIT PDF

    Description

    This quiz focuses on the physiology and functions of the gastrointestinal tract (GIT), including its anatomy, nerve supply, and common disorders. Participants will learn about the processes of digestion, absorption, and hormonal regulation within the digestive system.

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