GIT Reflexes and Hormonal Control
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Questions and Answers

What is the primary role of Cholecystokinin (CCK) in the GI tract?

  • Stimulate gallbladder contraction (correct)
  • Increase stomach motility
  • Enhance gastric emptying
  • Inhibit gastric acid secretion

    • Secretin is secreted in response to fatty foods in the duodenum.

    False

    Name one reflex that arises from the gut and travels to the sympathetic ganglia.

    Gastro-colic reflex

    CCK is secreted by 'I' cells in the mucosa of the duodenum and jejunum in response to the presence of ______ food.

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

    Match the following GI hormones with their functions:

    <p>Cholecystokinin (CCK) = Inhibits stomach motility and stimulates bile release Secretin = Increases bicarbonate secretion and decreases gastric acid secretion Gastric inhibitory peptide (GIP) = Inhibits gastric motility in response to fats and amino acids</p> Signup and view all the answers

    What type of cells line the liver sinusoids?

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

    The hepatic sinusoids are less permeable than other capillaries.

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

    What are the cells called that have a phagocytic function in the liver sinusoids?

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

    The cycle of substances secreted into the bile, absorbed by the intestine, and then returned to the liver is known as ________ circulation.

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

    Match the following liver functions with their descriptions:

    <p>Ingestion = Taking food into the mouth Absorption = Passage of digested products into the blood Secretion = Release of enzymes and bile into the GI tract Digestion = Mechanical and chemical breakdown of food</p> Signup and view all the answers

    Study Notes

    GIT Reflexes

    • Reflexes that occur entirely within the Enteric Nervous System (ENS) control GI secretion, peristalsis, mixing contractions, and local inhibitory effects.
    • Reflexes that arise from the gut, travel to the sympathetic ganglia, and then return to the GI-tract include:
      • Gastro-colic reflex: signals from the stomach cause evacuation of the colon.
      • Entero-gastric reflexes: signals from the colon and small intestine inhibit stomach motility and secretion.
      • Colono-ileal reflex: reflexes from the colon inhibit emptying of ileal contents into the colon.
    • Reflexes that travel from the gut to the spinal cord or brain stem and then back to GIT, such as the Defecation Reflex, produce powerful colonic, rectal, and abdominal contractions required for defecation.

    Hormonal Control of GI Function

    • Cholecystokinin (CCK) secreted by "I" cells in the duodenum and jejunum's mucosa in response to fatty foods.

      • Potent effect on gallbladder contractility, expelling bile into the intestine.
      • Relaxes the Sphincter of Oddi.
      • Inhibits stomach motility, allowing adequate time for fat digestion.
      • Augments pyloric sphincter contraction, inhibiting gastric emptying.

    • Secretin secreted by "S" cells in the duodenum's mucosa in response to acidic gastric juice.

      • Increases bicarbonate secretion by pancreatic duct cells, neutralizing small intestine acid.
      • Decreases gastric acid secretion.

    • Gastric Inhibitory Peptide (GIP) produced by "K" cells in the duodenum and jejunum's mucosa, in response to intestinal fat and amino acids.

    Hepatic Sinusoids

    • Large capillary spaces separating liver plates.
    • Lined by endothelial cells with flattened processes and fenestrae.
    • More permeable than other capillaries, permitting the passage of plasma proteins with protein-bound nonpolar molecules like fat and cholesterol.
    • Contain phagocytic Kupffer cells.

    Hepatic Portal Circulation

    • Arterial supply and venous drainage of the liver.
    • Veins of the Hepatic Portal System and its tributaries drain the digestive tract, spleen, and pancreas.

    Enterohepatic Circulation

    • Bile and drugs are secreted by the liver into the bile ducts.
    • The liver can clear the blood of particular compounds by removing them and excreting them with bile into the intestine.
    • Many compounds secreted with bile are not eliminated in feces, but can be absorbed through the small intestine.
    • These compounds enter hepatic portal blood, are carried back to the liver, and re-secreted into bile ducts.

    General Functions of the GIT

    • Ingestion: taking food into the mouth
    • Motility: churning and propelling food through the GI tract
    • Secretion: releasing water, acid, buffers, mucus, and enzymes into the lumen of the GI tract.
    • Digestion: mechanical and chemical breakdown of food.
    • Absorption: passage of digested products from the GI tract into the blood and lymph.
    • Elimination: excretion of fecal matter through defecation.

    Ingestion of Food

    • Hunger: Intrinsic desire for food, determining the amount ingested.
    • Appetite: Preferred food types, influenced by the feeding center in the lateral nucleus of the hypothalamus.
    • Satiety Center: Located in the ventromedial nucleus (VMN) of the hypothalamus, causing sensations of fullness.
    • Leptin: Long-term appetite suppressor, a protein secreted by adipocytes.

    Mastication (Chewing)

    • Increases the surface area of food particles for digestive enzymes.
    • Mechanical digestion in the mouth, involving chewing and mixing with saliva.
    • Creates a soft, flexible, easily swallowed mass called a bolus.

    Pharynx

    • Funnel-shaped tube connecting the internal nares to the esophagus and larynx.
    • Allows passage of food, fluids to the esophagus, and air to the trachea.
    • Lined with stratified squamous epithelium and mucus glands.
    • Divided into the nasopharynx, oropharynx, and laryngopharynx.

    Deglutition (Swallowing)

    • Propulsion of food from the mouth to the stomach.
    • Three stages:
      • Oral Stage: Voluntary, moving bolus to the back of the mouth.
           - Pharyngeal Stage: Involuntary, passing bolus over the epiglottis into the esophagus.      - Esophageal Stage: Involuntary, peristaltic waves moving bolus through the esophagus to the stomach.

    Salivary Glands

    • Parotid, Submandibular, and Sublingual glands, along with smaller oral glands, produce saliva.
    • Daily secretion: 800-1500 ml, averaging 1000 ml.

    Saliva Composition

    • Serous secretion: Contains Ptyalin (alpha-amylase), digesting starches.
    • Mucus secretion: Contains mucin, for lubrication and surface protection.

    Basic Mechanisms of Stimulation of GIT Glands

    • Contact of Food with Epithelium: Direct contact stimulation of glandular cells, triggering enteric nervous stimulation.
    • Autonomic Stimulation:
      • Parasympathetic: Stimulates secretion.
      • Sympathetic: Inhibits secretion.
    • Hormonal Stimulation: Hormones released by the gastrointestinal mucosa in response to food in the gut.
      • Hormones absorbed into the blood and stimulate gland secretions.

    Mucus Secretion

    • Thick secretion composed of water, electrolytes, and glycoproteins.
    • Importance:
      • Lubricates the GIT wall.
      • Protects the GIT wall.
      • Adheres to food and spreads as a thin film over surfaces.
      • Allows particles to slide along the epithelium easily.
      • Resistant to digestion by GI enzymes.
      • Buffers the GIT.

    Gastric Secretion (Phases)

    • Cephalic Phase:
      • Begins before food enters the stomach.
      • Triggered by sight, smell, taste, or thought of food.
      • Stimulated by vagus nerve, leading to gastrin release.
    • Gastric Phase:    - Triggered by food entering the stomach.    - Distension of the stomach, protein, and alcohol increase gastrin release.    - Gastrin stimulates parietal cells for Hcl production.
    • Intestinal Phase:
      • Begins when food leaves the stomach.
      • Excitatory: Partially digested food enters the duodenum, leading to small gastrin release and limited gastric secretion.
      • Inhibitory: Distension of the duodenum and the presence of fatty products, hypertonic chyme, and irritants in the duodenum trigger reflexes and release of enterogastrones, inhibiting gastric secretion and closing the pyloric sphincter.

    Gastritis

    • Inflammation of the gastric mucosa.
    • Usually superficial, but severe cases can damage the gastric mucosa causing atrophy.
    • Causes:
      • Chronic bacterial infection.
      • Ingested irritant substances (alcohol, aspirin) damaging the mucosal barrier.

    Peptic Ulcer

    • Excoriated area of stomach or intestinal mucosa.
    • Occurs when the rate of gastric secretion exceeds the mucosal protection.
    • Protection afforded by:
      • Gastroduodenal mucosal barrier
      • Mucus secretion.
      • Bicarbonate secretion.
      • Prostaglandins.

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    Description

    Explore the essential reflexes within the Enteric Nervous System that regulate gastrointestinal functions such as secretion, peristalsis, and defecation. Additionally, learn about the hormonal control, specifically the role of Cholecystokinin (CCK) in digestive processes. Test your knowledge on these vital components of the GI tract.

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