LEC77

• What is digestion?

  The breakdown of large food molecules

  
• Why is digestion important?

  It allows food molecules to be absorbed
• What is absorption in the digestive system?

  Transport of small food particles to blood
• What role do sphincters play in the GI tract?

  They isolate regions and prevent backflow

  
• What are the main functions of the digestive system?

  1. Ingestion of food
  2. Digestion
  3. Motility
  4. Secretion of digestive juices
  5. Absorption of digested products
  6. Storage and elimination of waste
  7. Protective functions (mechanical, chemical, immunological)
• What is peristalsis?

  A pattern of smooth muscle contractions

  
• Who first described peristalsis?

  Bayliss and Starling
• How does peristalsis function?

  Contraction above and relaxation below a bolus

  
• What mediates peristalsis?

  The intestine's local, intrinsic nervous system

  
• What stimulates afferent enteric neurons during peristalsis?

  Mechanical distension and mucosal irritation
• What neurotransmitters do excitatory motor neurons use?

  Acetylcholine and substance P
• What do inhibitory motor neurons stimulate?

  Relaxation of smooth muscle below the bolus
• What is lamina propria?

  Loose connective tissue in mucosa
• What is the function of lamina propria?

  Supports mucosal epithelium and immune defense
• What are the parts of the stomach?

  • Body
  • Antrum

  
• What are the types of gastric glands and their secretions?

  1. Mucus-secreting glands: Secrete mucus and HCO3
  2. Oxyntic (parietal) glands: Secrete HCl, pepsinogen, IF
  3. Pyloric glands: Secrete gastrin, mucus, pepsinogen

  
• What are the phases of gastric secretions?

  1. Cephalic phase: Before food arrives (30%)
  2. Gastric phase: When food enters (60%)
  3. Intestinal phase: When chyme enters duodenum (10%)

  
• What is the mechanism of HCl secretion by parietal cells?

  H2O and CO2 produce carbonic acid

  
• What happens to carbonic acid in parietal cells?

  It dissociates into H+ and HCO3–

  
• How is H+ transported into the stomach lumen?

  Via the H+–K+ ATPase ion pump

  
• What is the role of bicarbonate in HCl secretion?

  It is transported into the blood

  
• What neurotransmitters do inhibitory neurons use?

  Nitric oxide, vasoactive intestinal peptide, ATP

  
• What are the functions of the liver?

  • Production of bile
  • Protein production for blood plasma
  • Cholesterol production
  • Conversion of glucose to glycogen
  • Regulation of amino acids
  • Processing hemoglobin
  • Conversion of ammonia to urea
  • Clearing blood of drugs
  • Regulating blood clotting
  • Resisting infections
  • Clearance of bilirubin

  
• What is enterohepatic circulation?

  Reabsorption of bile acids into circulation

  
• Where is the pancreas located?

  Retroperitoneal, posterior to the stomach
• What are the types of pancreatic cells?

  • Endocrine: Islets of Langerhans (hormones)
  • Exocrine: Acini (digestive juices)

  
• What are the major proteolytic enzymes produced by the pancreas?

  Trypsin, chymotrypsin, carboxypeptidase
• What is the role of pancreatic amylase?

  Continues polysaccharide digestion
• How are monosaccharides absorbed in the small intestine?

  Absorbed as they are, no changes
• What enzymes digest disaccharides?

  Lactase, sucrase, maltase
• What is the absorption mechanism for glucose and galactose?

  Transported by secondary active transport with Na+

  
• How is fructose absorbed in the small intestine?

  Transported by facilitated transport

  
• What is the absorption mechanism for amino acids?

  Transported by secondary active transport with Na+

  
• How are fatty acids absorbed in the intestine?

  Bind with bile salts to form micelles

  
• What happens to triglycerides inside intestinal cells?

  They bind with proteins to form chylomicrons

  
• How are fat-soluble vitamins absorbed?

  Carried on lipids during absorption

  
• What are the gastrointestinal hormones and their actions?

  1. Gastrin: Increases gastric acid secretion
  2. CCK: Contracts gall bladder, increases pancreatic enzymes
  3. Secretin: Increases pancreatic bicarbonate secretion
  4. GIP: Stimulates insulin secretion, inhibits gastric secretion
  5. VIP: Vasodilation of GIT blood vessels

  
• What is the thick mucosa of the large intestine characterized by?

  Deep crypts and no villi

  
• What is gastroesophageal reflux (GERD)?

  Backward regurgitation of gastric contents

  
• What are common symptoms of GERD?

  Heartburn, coughing, pain when bending