absorption of materials

• Oxygen and nutrients from food must be 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.
• Tissues contain capillary networks that allow the exchange of materials to a cellular level.
• Surfaces involved in the absorption of materials have certain features in common:

  • Large surface area
  • Thin walls
  • Extensive blood supply

  These increase the efficiency at which materials are absorbed.
• 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 many blood capillaries.
• Nutrients from food are absorbed into the blood in the small intestine.
• The small intestine contains a large number of thin-walled villi to provide a large surface area for this absorption.
• The network of capillaries within the villi absorbs glucose and amino acids.
• The lacteal absorbs fatty acids and glycerol.