absorption and assimilation

• Define what is meant by the terms 'absorption' and 'assimilation' :

  • Absorption = how nutrients are extracted from food and absorbed into the bloodstream - this occurs in the small intestine

  • Assimilation = the movement of digested food molecules into the cells of the body where they are used so they become part of the cell.
• Villi


  • Finger-like projections from the walls of the small intestine
  • Greatly increase the surface area over which absorption can take place
• Villi walls


  • Very thin (typically one cell thick)
  • Allows movement of materials across them by diffusion
  • Good network of blood capillaries to transport materials from the small intestine to the liver via the hepatic portal vein
• Diffusion


  • Movement of a substance from an area of high concentration to an area of lower concentration
  • Occurs in liquids and gases when their particles collide randomly and spread out
  • Important process for living things - how substances move in and out of cells
• Lacteal


  Central vessel connected to the lymphatic system
• Substances that enter the blood


  • Sugars
  • Amino acids
  • Minerals
  • Water soluble vitamins (B + C)
• Substances that enter the lacteal


  • Fatty acids
  • Glycerol
  • Fat soluble vitamins (A,D,E + K)
• Assimilation in the liver :

  • Assimilation is the movement of digested food molecules into the cells of the body where they are used to become part of those cells.
  • Excess glucose entering the liver is stored as glycogen and may then be broken down to be used for respiration as required.
  • Toxins such as drugs and alcohol are broken down in the liver.
  • The liver produces many kinds of proteins such as hormones, plasma proteins and proteins used for blood clotting.The liver takes dying red blood cells from the blood and converts the haemoglobin into bilirubin which helps to form bile.
• Absorption and assimilation


  Adaptations of the intestine wall for absorption:

  • Absorption refers to how the nutrients extracted from food are absorbed into the bloodstream. This occurs in the small intestine.
  • Villi and microvilli, which are finger-like projections, increase the surface area of the small intestine wall to enable efficient absorption.
  • Villi contain blood vessels and lacteal
  • Products of fat digestion enter lacteal.
  • Nutrients enter by diffusion.
  • Everything else enters the blood.
• The role of the liver in assimilation

  • Assimilation is the movement of digested food molecules into the cells of the body where they are used, so that they become part of those cells.
  • Excess glucose in the blood reaching the liver is converted into glycogen to be stored or broken down through respiration, producing energy.
  • The liver is where toxins such as alcohol are broken down.