blood vessels and functions

• Blood


  Transports substances around the human body and defends it against diseases
• Main components of blood

  • Plasma
  • Red blood cells
  • White blood cells
  • Platelets
• Plasma


  • Transports blood cells, ions, soluble food materials, hormones, carbon dioxide, urea, vitamins
• Red blood cells


  • Contain haemoglobin for oxygen transport
• White blood cells


  • Perform phagocytosis, antibody formation and tissue rejection
• Platelets


  • Contain fibrinogen to form fibrin, causing clotting
• Mankind has always considered blood to be a symbol of life
• When an injured person has lost a lot of blood, a blood transfusion is necessary
• In a unicellular organism, no part of the cell is far from the external environment, so oxygen and nutrients can diffuse through the cell membrane and waste products can be rapidly removed
• In complex multicellular organisms, numerous cells are found deep in the body, far from the external environment, so simple diffusion alone cannot bring enough oxygen and food materials to these cells in time, nor can it remove waste products with sufficient speed
• Transport system in humans

  Consists of a series of blood vessels that run through the entire body, blood which flows through the vessels carrying materials around the body, and a heart (muscular pump) which ensures the fluid keeps flowing through the vessels