L5-6 digestive system

• processes of the digestive system:

  • digestion (physical and chemical breakdown of food)
  • absorption (transport of digestive end-products to bloodstream)
  • motility (peristaltic activity of muscle, propelling food along GI tract)
  • secretion (transport of digestive fluids into GI tract)
• accesory glands of the digestive system:

  salivary glands, pancreas, liver, gall bladder
• what are the 4 layers of the GI tract:

  1. mucosa
  2. submucosa
  3. muscularis
  4. serosa
• what layers are there to the mucosa?

  epithelium, lamina propria and muscular mucosa
• what is found in the submucosa?

  connective tissue, blood and lymphatic vessels
• the muscularis is made up of:

  circular layer and longitudinal layer
• the serosa is made of:

  connective tissue
• general structure of the GI tract:

  labels:

  A) lumen

  B) mucosa

  C) submucosa

  D) muscularis

  E) serosa

  F) nerve plexus

  
• mucosa membrane is composed on epithelial cells AKA

  enterocytes
• enterocytes include:


  absorptive, exocrine, goblet and endocrine cells
• the mucus membrane is replaced every _

  5 days
• exocrine


  secretion of enzymes into a duct directed at target
• endocrine


  secretion of hormones into the bloodstream
• saliva function:

  • lubrication
  • buffer
  • antibiotic action
  • taste
  • clean teeth
  • fluoride and calcium uptake to teeth
• how much saliva is secreted per day:

  0.75-1.5 litres
• oesophagus upper 1/3 has _ muscle

  skeletal
• oesophagus lower 2/3 has _ muscle


  smooth
• how long is the oesophagus approximately?

  25 cm
• how many sphincters are there in the GI tract?

  5
• what are the sphincters in the GI tract?

  • upper esophageal
  • lower esophageal
  • pyloric
  • ileocecal
  • anal
• gastric glands contain:


  parietal and chief cells
• vagus nerve is part of the parasympathetic nervous system
• gastrin and the vagus nerve trigger the release of:

  pepsinogen and HCl
• HCL secretion into the stomach:

  • H+ ions from CO2 and H2O by carbonic anhydrase are actively transported into the lumen and exchanged for K+ ions
  • bicarbonate ions are exchanged for Cl- ions, which diffuse into the lumen
  • results in the accumulation of HCl in the lumen
• what is a zymogen?


  a pro-enzyme that requires a biochemical change to become active
• pepsin is synthesised from pepsinogen in the stomach
• chymotrypsin is synthesised from chymotrypsinogen in the pancreas
• trypsin is synthesised from trypsinogen in the pancreas
• carboxypeptidase is synthesised from procarboxypeptidase in the pancreas
• elastase is synthesised from proelastase in the pancreas
• layers of the GI tract:

  • lamina propria
  • serosa
  • mucosa
  • submucosa
  • muscularis
  • epithelium
• pepsinogen:

  • activated by HCl in the stomach
  • first 44 amino acids are removed from pepsinogen to generate pepsin
  • pepsin activates more pepsinogen
• pepsin is an endopeptidase meaning it

  breaks internal peptide bonds of proteins to generate smaller fragments
• exopeptidases remove one amino acid at a time from either end of a polypeptide
• amylase digests:


  starch and glycogen
• activation of chymotrypsinogen

  labels:

  A) chymotrypsinogen

  B) trypsin

  C) chymotrypsin

  
• small intestine is made of:


  duodenum, jejenum and ileum
• Crypts of Lieberkuhn function:

  release bicarbonate rich fluid t neutralise chyme from the stomach
• duodenum receives:


  chyme from the stomach, enzymes from the pancreas, bile from the liver and gallbladder
• small intestines function:


  digestion, absorption of nutrients, water, vitamins and minerals