digestive system 3

• Nachos are not for everyone, as lactose intolerant people can experience gastric distress from consuming them
• Lactose


  Milk-sugar that can only be digested with the help of the enzyme lactase, which many adults do not produce enough of
• Lactase persistence trait spread as Neolithic groups trekked north and west through Europe
• Lactose intolerant people cannot break down lactose, so it is left to the bacteria in their large intestine to try to digest it, resulting in gas, bloating, and diarrhea
• The stomach is good at obliterating matter but not at chemically digesting or absorbing much
• Small intestine


  • It has a massive surface area due to folds, villi, and microvilli, allowing for efficient nutrient absorption
  • It has three main subdivisions: duodenum, jejunum, and ileum
• Brush border enzymes


  Enzymes bound to cell membranes in the intestinal mucosal layer, which can process food as it passes by without needing to be replaced
• Bile


  An emulsifier produced by the liver that keeps fat molecules from clumping together, allowing lipid-digesting enzymes to break them down
• Pancreatic juice


  Contains enzymes that break down proteins, fats, carbohydrates, and nucleic acids
• The large intestine absorbs remaining water and hosts gut bacteria that digest remaining chyme, releasing vitamins and gases
• Defecation


  1. Haustral contractions mix and chop feces

  2. Mass peristalsis movements clear out the large intestine

  3. Stretch receptors in the rectum trigger the defecation reflex

  4. Internal and external anal sphincters relax to expel feces
• For lactose intolerant people, the bacteria in the large intestine try to digest the lactose, resulting in gas, bloating, and diarrhea