MODULE 8: DIGESTIVE SYSTEM

• Parts of Digestive System

  1. Mouth
  2. Pharynx
  3. esophagus
  4. Stomach
  5. Small intestine
  6. Large intestine
  7. Rectum
  8. Anus
• Pharnyx

  1. Nasopharynx- It is not the part of digestive system
  2. Oropharynx- It is situated posterior to oral cavity.
  3. Laryngopharynx- It is situated below the oropharynx and connected to the oesophagus.
• Cells in Stomach:

  1. Mucus cells- It secrete the alkaline mucous for protecting the epithelium from hydrochloric acid.
  2. Parietal cells- It secrete hydrochloric acid; the acid activates release of pepsin for protein digestion. The acid also kills micro-organisms swallowed with the food.
  3. Chief cells- It secrete pepsin. These cells are locatedmin the fundic region.
  4. G-Cells- It secrete gastrin which stimulates the secretion of hydrochloric acid.
• Cells in Stomach:

  • Mucus cells
  • Parietal cells
  • Chief cells
  • G-Cells
• Mucus cells

  • It secrete the alkaline mucous for protecting the epithelium from hydrochloric acid.
• Parietal cells

  • It secrete hydrochloric acid;
  • the acid activates release of pepsin for protein digestion.
  • The acid also kills micro-organisms swallowed with the food.
• Chief cells

  • It secrete pepsin.
  • These cells are located in the fundic region.
• G-Cells

  • It secrete gastrin which stimulates the secretion of hydrochloric acid.
• Gastric Secretions

  • pepsinogen
  • pepsin
  • hydrochloric acid
  • mucus
  • intrinsic factor
• pepsinogen

  from chief cells

  • iinactive form of pepsin
• pepsin

  from pepsinogen in presence of HCI

  • protein splitting enzyme
• hydrochloric acid

  from parietal cells

  • needed to convert pepsinogen to pepsin
• mucus

  from goblet cells and mucous glands

  • protective to stomach wall
• intrinsic factor

  from parietal cells

  • required for vitamin B 12 absorption
• Phases of Gastric Secretion

  • Cephalic phase
  • Gastric phase
  • Intestinal phase
• Cephalic phase

  • triggered by smell, taste, sight, or thought of food
  • parasympathetic impulses trigger gastric juice secretion
• Gastric phase

  triggered by presence of food in stomach

  gastrin released

  • gastric juice secreted
• Intestinal phase

  triggered by movement of food into small intestine

  intestinal cells release intestinal gastrin

  • secretion of gastric juice
• Regulation of Gastric Secretions

  Release into bloodstream (1,4)

  Stimulation (2,3)

  1. Parasympathetic preganglionic nerve fiber (in vagus nerve)
  2. Parasympathetic-postganglionic impulses stimulate the release of gastric juice from gastric glands
  3. Impulses stimulate the release of gastrin

  Bloodstream

  4. Gastrin stimulates glands to release more gastric juice
• Pancreatic Juice

  • pancreatic amylase- splits glycogen into disaccharides
  • pancreatic lipase- breaks down triglycerides
  • trypsin, chymotrypsin, and carboxypeptidase digest proteins
  • nucleases- digest nucleic acids
  • bicarbonate ions- make pancreatic juice alkaline
• 5. Acidic chyme enters duodenum

  1. Intestinal mucosa releases secretin into bloodstream
  2. Secretin stimulates pancreas

  Bloodstream

  3. Pancreas secretes pancreatic juice rich in bicarbonate ions

  4. Bicarbonate ions neutralize acidic chyme

  (5-1) Hormonal signals released into bloodstream

  (4-4) Stimulation of effector organ
• peptidase - breaks down peptides into amino acids
• sucrase, maltase, lactase- break down disaccharides into monosaccharides
• Lipase- breaks down fats into fatty acids and glycerol
• enterokinase- converts trypsinogen to trypsin
• somatostatin- hormone that inhibits acid secretion by stomach
• cholecystokinin- hormone that inhibits gastric glands, stimulates pancreas to release enzymes in pancreatic juice, stimulates gallbladder to release

  bile
• secretin- stimulates pancreas to release bicarbonate ions in pancreatic juice
• Factors that increase your risk of acute gastritis

  include:

  • taking NSAIDs
  • taking corticosteroids
  • drinking a lot of alcohol
  • having a major surgery
  • kidney failure
  • liver failure
  • respiratory failure