10

• Digestion


  The breakdown of foodstuff into the simplest forms to be easily absorbed
• Simplest forms of macromolecules

  • Monosaccharides (carbohydrates)
  • Amino acids (proteins)
  • Fatty acids and glycerol (lipids)
• Digestive system


  Includes: Salivary glands, esophagus, stomach, duodenum, small intestine (Jejunum, ileum), colon, rectum, liver, gall bladder and pancreas
• Salivary glands


  • Parotid
  • Submaxillary (submandibular)
  • Sublingual
• Saliva


  • Volume: 1000 - 1500 ml/ day
  • pH: 6.7 (slightly acidic)
  • Color: Colorless
• Composition of saliva


  • 99% water
  • 1% Solids (2/3 organic matters, 1/3 inorganic matters)
• Organic matters in saliva

  • Salivary amylase
  • Mucin
  • Lysozyme enzyme
• Inorganic matters in saliva

  • Ca, K, Na, Mg, SO4, PO4, HCO3, Cl
• Functions of saliva


  • Moistens the mouth and helps speech
  • Moistens the food and helps swallowing
  • Keeps the mouth clean
  • Digestion: salivary amylase acts on cooked starch converting it into maltose
  • Antibacterial action: Lysozyme kills bacteria
  • Excretory action: Mercury, lead and Iodide may be excreted
  • Buffering action: Saliva contains phosphate buffers
• Gastric juice


  • Volume: 1000 ml
  • pH: 1-2 (highly acidic due to the presence of HCI)
• Composition of gastric juice

  • 99% water
  • 1% Solids (2/3 organic matters, 1/3 inorganic matters)
• Organic matters in gastric juice

  • Enzymes: pepsin, rennin, lipase
  • Intrinsic factor
  • Mucin
• Inorganic matters in gastric juice

  • Na, K, Cl, H
• Functions of gastric secretion

  • Digestion: Pepsin, Rennin, Lipase enzymes
  • Intrinsic factor for vitamin B12 absorption
  • Mucin protects gastric mucosa
  • HCl activates pepsinogen, kills bacteria, helps iron and calcium absorption, stimulates secretin hormone
• Pepsin


  Secreted in an inactive form called pepsinogen, which is first activated by gastric HCl into pepsin. Then pepsin itself activates pepsinogen (autoactivation). Pepsin is an endopeptidase that hydrolyzes the bonds formed by aromatic amino acids.
• Rennin


  Causes the coagulation of milk (milk clot), important for infants as it prevents the rapid passage of milk from the stomach.
• Gastric lipase


  May be of value in infants, acting on milk fat. Initiates hydrolysis of triacylglycerols.
• Intrinsic factor


  A glycoprotein essential for vitamin B12 absorption.
• Mucin


  Covers the inner surface of gastric mucosa, protecting it from proteolytic effect of gastric enzymes.
• Functions of HCl


  • Activates pepsinogen into pepsin, gives optimum pH for pepsin action
  • Antibacterial action, kills bacteria and parasites
  • Helps iron and calcium absorption
  • Stimulates the secretion of secretin hormone from the duodenum
• Peptic ulcer


  A sore in the lining of the stomach (gastric ulcer) or duodenum (duodenal ulcer), commonly caused by infection with Helicobacter pylori or use of NSAIDs. Treated with antibiotics and acid reducers.
• Hartnup disease


  An autosomal recessive metabolic disorder affecting the absorption of neutral amino acids, particularly tryptophan.
• Intestinal juice (succus entericus)

  • Volume: 0.5 -1 liter / day
  • pH: 7.8
• Composition of intestinal juice

  • 98% water
  • 2% Solids (organic matters: mucin, enzymes; inorganic matters: Na, K, Cl, PO4, Ca, HCO3)
• Enzymes in intestinal juice

  • Disaccharidase (maltase, sucrase and lactase)
  • Aminopeptidase
  • Intestinal lipase
  • Nucleosidases and nucleases
• Osmotic diarrhea


  Indigestion of carbohydrates causes them to pass into the large intestine, leading to osmotic diarrhea.
• Lactose intolerance


  Due to lactase deficiency, leading to diarrhea and intestinal discomfort.
• Celiac disease


  An autoimmune disorder of the small intestine caused by a reaction to gluten (gliadin protein), leading to flattening of the intestinal lining and malabsorption of nutrients. Treated with gluten-free diet.
• Pancreatic juice


  • Volume: 1 liter /day
  • pH: 8 (most alkaline juice in the body)
• Composition of pancreatic juice

  • Inorganic substances: Ca, Na, K, HCO3, PO4
  • Organic substances: Mucin, Enzymes (Trypsin, chymotrypsin, elastase, carboxypeptidase, ribonuclease, deoxyribonuclease, amylase, lipase, cholesteryl ester hydrolases)
• Cystic Fibrosis


  A hereditary disease affecting the exocrine glands, causing thick mucus production and failure of exocrine pancreatic secretion, leading to undernutrition. Caused by a mutation in the CFTR gene.
• Bile


  The secretion of liver cells, stored in the gallbladder and released into the duodenum when food enters.
• Physical properties of bile

  • Volume: 0.5 liter / day
  • pH: 7.2
• Composition of bile


  • 97% water
  • 3% Solids (Organic matters: bile acids, bile pigments, mucin, cholesterol, fatty acids; Inorganic matters: mainly bicarbonate)
• Functions of bile


  • Digestion of lipids: emulsification and micelle formation
  • Absorption of lipids
  • Antibacterial action
  • Choleretic action: stimulates bile production
  • Neutralization of HCl
  • Excretory function
  • Keeps cholesterol soluble
• Gallstones


  Crystallization of cholesterol in bile due to changes in bile composition.
• Inflammatory bowel disease


  A collection of inflammatory conditions primarily affecting the intestines, with immune system attacking the GI tract. Includes Crohn's disease and ulcerative colitis.

  
• Crohn's disease


  Inflammation can affect any part of the GI tract, treated with glucocorticoids.
• Ulcerative colitis


  Inflammation affects the colon and/or rectum, with tissue destruction interfering with fluid and electrolyte absorption.

  
• Diverticulosis


  Pouches (diverticula) in the lining of the large intestine, which can become infected and inflamed (diverticulitis).