Absorption of materials

• Oxygen and nutrients from food must e absorbed into the bloodstream to be delivered to cells for respiration. Waste materials such as carbon dioxide must be removed from cells into the bloodstream
• Features that increase the efficiency of absorption

  • a large surface area
  • thin walls
  • extensive blood supply
• The lungs are the gas exchange organs. They consist of a large number of alveoli providing a large surface area for gas exchange.

  Oxygen into the blood is exchanged for carbon dioxide out of the blood

  
• Oxygen and carbon dioxide are absorbed through the thin alveolar walls to or from the blood capillaries

  
• In the capillary, the carbon dioxide from the bloodstream is diffused into the alveoli

  In the capillary, the oxygen from the alveoli is diffused into the bloodstream

  
• The Digestive system

  Many of the foods we eat are too large and insoluble to be absorbed into the blood. These foods must be digested to break them down into small soluble molecules that can be absorbed. Food is digested into the blood through the lining of the small intestine

  Fats ----> Fatty acids + glycerol

  Carbohydrates ----> Glucose

  Proteins ----> Amino acids
• The structure of the small intestine is specialised for rapid food absorption of small soluble molecules.

  The small intestine contains a large number of thin walled villi to provide a large surface area which increases the speed to absorption.

  
• Each villus had the following specialisation to aid absorption:

  • lining is one cell thick which increases the speed of absorption
  • capillaries in each villus to provide a good blood supply to take up and transport glucose and amino acids
  • lacteal to take up and transport the products of fat digestion- fatty acids and glycerol
• Network of capillaries within the villi will absorb glucose and amino acids.

  Lacteal absorbs fatty acids and glycerol