Stomach

• What is digested in the stomach?

  protein
• The pH of the stomach is 2
• Oxyntic cells:

  • secrete hydrochloric acid in the stomach which kills bacteria, keeps the pH 2 so it is optimum for enzymes, and activates pepsinogen to pepsin.
• Chief cells/Zymogen cells:

  • secret pepsinogen (the inactive form of pepsin)
  • this prevents autolysis of protein in cells
  • in the stomach
• Oblique muscles:

  • in the stomach
  • churn the food to increase surface area for enzyme action
• Gut wall structure transverse section:

  A) serosa

  B) longitudinal muscles

  C) circular muscles

  D) submucosa

  E) mucosa

  F) lumen

  
• Gut wall structure longitudinal section:

  A) serosa

  B) longitudinal muscles

  C) circular muscles

  D) submucosa

  E) mucosa

  
• Stomach:

  • the stomach is a sack with a capacity of 1.5 litres
  • It has ridges called rugae to help with mechanical breakdown of food
  • muscles are found at the upper and lower ends of the stomach
  • the cardiac sphincter relaxes at the upper end, allowing food to enter
  • the pyloric sphincter relaxes to allow food to exit the stomach into the duodenum
  • Food remains in the stomach for up to 4 hours
  • the stomach can stretch
  • mucus is secreted from goblet cells to protect the stomach wall from the gastric enzymes and acid
• Functions of the stomach:

  • the stomach contains gastric juice (which is secreted by glands in the mucosa of the stomach wall) which consists of:
  • What aids in digestion:
  • hydrochloric acid secreted by oxyntic cells which kills most bacteria in the food, makes the stomach have a pH of 2, provides optimum pH for enzymes and activates peptidases e.g. pepsin
  • rennin which curdles milk
  • Chemical digestion:
  • enzymes found in the gastric juice are endopeptidase (pepsin) which hydrolyses large polypeptides
• The stomach has 3 thick layers of muscle to allow it to contract and relax and grind the food.
• The stomach absorbs simple chemicals such as alcohol, aspirin, water and salts
• What causes the denaturation of salivary amylase?

  Stomach acid as it is pH 2 so denatures amylase
• What causes the denaturation of salivary amylase?

  Stomach acid as it is pH 2 so denatures amylase
• Goblet cells:

  • secrete mucus to lubricate and protect the gut
• Role of rugae:

  • allow for expansion of the stomach after the consumption of foods and liquids.
  • This expansion increases the volume of the stomach to hold larger amounts of food.