blood and blood vessels

• Arteries

  Carry blood away from the heart
• Arteries

  Divide to form capillaries
• Capillaries

  Give nutrients, oxygen and other materials to cells, and take away waste materials
• Capillaries

  Gradually join up again to form veins
• Veins


  Carry blood back to the heart
• Arteries

  • Have strong and thick walls to withstand high blood pressure
  • Contain elastic tissue that stretches and recoils with the force of the blood
• Veins

  • Have valves to prevent backward flow of blood
  • Have a wider lumen to allow for smooth continuous flow of blood at lower pressure
• All arteries, with the exception of the pulmonary artery, branch from the aorta
• All veins, with the exception of the pulmonary and hepatic portal veins, join up to one of the two venae cavae
• The liver has two blood vessels which supply it with blood: the hepatic artery supplies it with oxygen, and the hepatic portal vein brings blood from the digestive system
• All blood leaves the liver in the hepatic vein
• Components of blood

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


  The liquid part of blood that allows for many substances to be dissolved in it
• Red blood cells


  • Made in the bone marrow
  • Lack a nucleus to allow for packing of haemoglobin
  • Biconcave shape and small size give a large surface area to volume ratio
• Haemoglobin

  A protein that contains iron and readily combines with and releases oxygen
• White blood cells

  • Have a nucleus and can move around and squeeze through capillary walls
  • Fight pathogens and clear up dead blood cells
• Phagocytosis


  The process by which some white blood cells fight pathogens by taking in and digesting bacteria
• Platelets

  Small fragments of cells involved in blood clotting
• Blood clotting stops pathogens from entering the body through breaks in the skin and prevents excessive blood loss
• Phagocytes

  Cells which can move around the body, engulfing and destroying pathogens. They can also destroy any of your own cells that are damaged or worn out.
• If you get a cut or a graze on your skin, phagocytes will collect at the site of the damage, to engulf and digest any microorganism that might possibly get in.
• Blood platelets

  Small fragments of cells which contain no nucleus. They are produced in the red bone marrow and are involved in the clotting of blood.
• Blood clotting not only protects the body against the entry of bacteria and viruses, but it also prevents too much blood loss.
• Blood clotting

  1. Platelets bump into the rough edges of a cut and react by releasing chemicals

  2. Damaged tissues around the blood vessels also release chemicals

  3. Fibrinogen changes into fibrin

  4. Fibrin forms fibres which mesh across the wound

  5. Red blood cells and platelets get trapped in the tangle of fibrin fibres, forming a blood clot
• Prothrombin


  A coagulation factor that is produced by the liver. Vitamin K is needed for the production of this.
• Prothrombin activation


  1. Prothrombin is broken down to form thrombin

  2. Thrombin acts as a protease enzyme which breaks down the insoluble fibrinogen into fibrin so that the clotting of red blood cells can occur
• Oxygen

  • Oxygen diffuses into the blood from the alveoli in the lungs
  • The biconcave shape of the red blood cells enables the rapid diffusion of oxygen in and out of cells
  • When oxygen diffuses into the red blood cells, it readily combines with haemoglobin (Hb) to form oxyhaemoglobin (oxyHb)
  • The blood is taken to the heart in the pulmonary veins and pumped out of the heart in the aorta
  • Arteries branch from the aorta to supply all parts of the body with oxygenated blood
  • When it reaches a tissue in need of oxygen, the oxyHb gives up its oxygen to become Hb again
• Due to the fact that the capillaries are so narrow, the oxyHb in the red blood cells is taken very close to the tissues which need oxygen. The oxygen, therefore, has only a short distance to diffuse.
• Colour of blood


  OxyHb is bright red, whereas Hb is purplish-red. The blood in the arteries therefore has a brighter red colour than the blood in the veins.
• Carbon dioxide

  • As the cells in our bodies respire, they produce Carbon Dioxide
  • This Carbon Dioxide diffuses through the walls of the capillaries into the blood
  • Most of the Carbon Dioxide is carried by the blood plasma in the form of hydrogencarbonate ions HCO³ˉ and a small amount is carried by the Hb in the red blood cells
  • Blood containing Carbon Dioxide is returned to the heart in the veins and then to the lungs in the pulmonary arteries
  • Carbon Dioxide diffuses out of the blood and is passed out of the body when we respire
• Transport of food materials

  • Digested food includes nutrients such as; amino acids, fatty acids, glycerol, monosaccharides (such as glucose), water, vitamins and minerals
  • All of these substances dissolve in the plasma in the blood capillaries located in the Villi
  • The capillaries in the villi then join together to form the Hepatic Portal Vein which takes these dissolved nutrients to the liver
  • The liver processes each nutrient and returns some of it to the blood
  • The nutrients are then carried, dissolved in the blood to all parts of the body
• Transport of urea

  • Urea is a waste substance that is made in the liver
  • It is dissolved in the blood plasma and carried to the kidneys where it will then be excreted in the urine
• Transport of hormones

  Hormones are made in the endocrine glands and are dissolved in the blood plasma to be carried around the body
• Transport of heat


  • Many parts of the body, especially the muscles give off heat
  • This heat is transported to all parts of the body to help keep the rest of the body warm
• Plasma proteins

  • Consist of many different proteins dissolved in the plasma
  • Fibrinogen is an example of a plasma protein