Human circulatory system

• Double circulation

  • Pulmonary circulation: Heart to lungs and back
  • Systemic circulation: Heart to body and back
• Human Circulatory System

  • Heart
  • Blood vessels
  • Blood
• Heart

  • When heart muscles contract, blood is forced out of the heart
  • When heart muscles relax, blood is pulled into the heart
• Blood Vessels

  • Arteries
  • Veins
  • Capillaries
• Arteries

  • Carry blood away from the heart
  • Most arteries carry oxygenated blood
• Veins

  • Carry blood towards the heart
  • Most veins carry deoxygenated blood
• Capillaries

  • Connect the arteries and veins
  • Have very narrow lumen and 1 cell thick walls to increase the rate of diffusion
  • Nutrients and waste products diffuse out of/into the blood
• Components of Blood

  • Red Blood Cells
  • White Blood Cells
  • Platelets
  • Plasma
• Red Blood Cells

  • Carry oxygen from lungs to all body cells
  • Do not have a nucleus to carry more haemoglobin which binds to oxygen
  • Are biconcave and flexible in shape to increase surface area for faster rate of diffusion of oxygen
• White Blood Cells


  Used to defend and respond to infections and diseases
• Platelets

  Help in clotting of blood to prevent excessive blood loss and bacteria from entering wound to prevent infections
• Plasma


  The fluid portion of blood, made of 90% water and a mixture of dissolved substances such as nutrients, hormones, waste products, and mineral salts
• Plasma dissolves and transports:

  • Glucose and amino acids from small intestines to cells
  • Hormones from glands to organs
  • Carbon dioxide from cells to lungs
  • Other waste products from cells to kidneys to excretory organs to be removed
• Blood is made up of 55% plasma, 45% red blood cells, less than 1% of white blood cells and platelets