Digestive system

• Humans have to eat loads of food which is mostly used for energy so that we can move about and keep our metabolism running
• Main groups of nutrients needed

  • Carbohydrates (like starch and glucose)
  • Proteins
  • Fats
• Role of digestion


  To break all this food down into tiny pieces so that we can absorb it into our body cells
• Digestion process


  1. Physical breakdown (chewing)

  2. Chemical breakdown by enzymes
• Mouth


  1. Food placed in mouth

  2. Broken down physically by chewing

  3. Saliva released from salivary glands

  4. Saliva contains salivary amylase to break down carbohydrates
• Swallowing


  Food passes down the gullet/esophagus
• Stomach


  1. Muscular sac that contracts to push and mix food

  2. Produces pepsin enzyme to break down proteins

  3. Produces hydrochloric acid to kill bacteria and provide right environment for pepsin
• Small intestine


  1. Where digested food is absorbed into bloodstream

  2. Produces digestive enzymes to aid digestion

  3. Pancreas produces most digestive enzymes and pushes them into small intestine as pancreatic juices

  4. Gallbladder releases bile to neutralize stomach acid and emulsify fats
• Lining of small intestine

  • Has finger-like projections called villi to increase surface area
  • Only has a single layer of surface cells so nutrients only have to diffuse a short distance
  • Has a good blood supply to maintain concentration gradient
• Large intestine


  Absorbs excess water from leftover material, leaving behind feces stored in the rectum
• Recap of digestive process order

  • Food placed in mouth, chewed, mixed with saliva
  • Swallowed down esophagus into stomach
  • Stomach mixes and breaks down food
  • Food passes into small intestine, mixes with pancreatic juices and bile
  • Digested food absorbed into bloodstream from small intestine
  • Leftover material passes to large intestine, water absorbed, feces stored in rectum
• Bile

  1. neutralises acid from stomach making the ph more ideal for the enzymes to function, it can do this because the bile is alkaline.
  2. emulsifyes fat-helps to break down big fats into tiny droplets which give the fat a larger surface area on digestive enzymes to work on
  3. made in the liver but stored in the gall bladder and released into the small intestine
• How is exchange surface adapted to its function?


  Within the lining of the small intestines, there’s finger like projection called villi; these increase the surface area of the small intestine, meaning digested food can be absorbed into the blood stream quicker
• Villi adaptations

  • Single layer of cell, meaning nutrients have to diffuse a short distance
  • good blood supply, which maintains concentration gradient
• If all nutrients have been absorbed into bloodstream, still material left in the small intestine as lots of food we eat isn’t digestible and because of the secretions(gall bladder, stomach and pancreas) it’s going to be very water so then it passes through large instestine which absorbed all the excess water.
• The digestive system has two main roles. Briefly describe each of them. 


  Digestion - process of breaking down large food molecules into smaller molecules 

  Absorption - process of absorbing these small food molecules into the body
• When we chew food, our teeth physically break the food down into smaller pieces. 


  It make the food easier to swallow and increases the surface area for enzymes to act on
• Roles of the Bile

  1. Bile is made by the liver, but it is stored in the gall bladder , 
  2. After we have meal, it is released into the small intestine where it helps in two ways:
  3. One is to emulsify lipids, which means separate large droplets of lipid into smaller droplets. 
  4. The other is to neutralise the acid from the stomach, which bile can do because it is alkaline