GCSE AQA Biology 3 Heart & Blood

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• Its main job is to get food and oxygen to every cell in the body as well as carrying waste products to where they can be removed from the body.

1. Humans have a double circulatory system - 2 circuits joined together
   1. 1st one pumps deoxygenated blood to the lungs to take in oxygen which then returns to the heart
      1. 2nd one pumps oxygenated blood around to all the other organs, blood gives up its oxygen at the body cells & the deoxygenated blood returns to the heart

1. Pumping organ that keeps blood flowing around body - walls mostly made of muscle tissue
2. Has valves to make sure blood goes in right direction - not backwards
3. How the blood flows through the heart:
   1. 1) Blood flows into 2 atria from vena cava (from body) & pulmonary vein (from lungs)
      1. 2) Atria contract - pushing blood into ventricles
         1. 3) Ventricles contract - forcing blood into pulmonary artery (to lungs) & aorta (to body) and out of heart
            1. 4) Blood flows to organs through arteries & return through veins
               1. 5) Atria fill again & cycle starts over

1. Arteries - carry blood away from heart
   1. Heart pumps blood out at high pressure so walls are strong & eleastic
      1. Walls are thick compared to size of lumen - contain thick layers of muscle & elastic fibres to allow them to stretch & spring back
2. Capillaries - involved in exchange of materials at tissues
   1. Arteries branch into capillaries
   2. Really tiny - carry blood close to every cell in body to exchange substances with them
      1. Have permeable walls - substances can diffuse in & out
         1. Supply food & oxygen & take away waste
            1. Walls are one cell thick - decreases diffusion distance
3. Veins - carry blood to the heart
   1. Capillaries join up to form veins
      1. Blood is at lower pressure so walls don't need to be as thick as artery walls
         1. Have a bigger lumen to help blood flow despite lower pressure
            1. Have valves to keep blood flowing in right direction

1. Red blood cells
   1. Carry oxygen from lungs to cells
   2. Have a concave shape to give large SA for absorbing oxygen
   3. Don't have a nucleus - more room for oxygen
   4. Contain haemoglobin - in lungs, haemoglobin combines with oxygen to become oxyhaemoglobin, in body tissues, oxyhaemoglobin splits into haemosglobin & oxygen to release oxygen to cells
2. White blood cells
   1. Can change shape to engulf microorganisms
   2. Produce antibodies to fight microorganisms as well as antitoxins to neutralise toxins produced by microorganisms
   3. Do have a nucleus
3. Platelets
   1. Small fragments of cells - have no nucleus
   2. Help blood to clot at wound - stop blood coming out/microorganisms getting in
   3. Lack of platelets = excessive bleeding & bruising
4. Plasma
   1. Pale straw-coloured liquid which carries everything in blood
      1. It carries:
         1. RBC, WBC & platelets
         2. Soluble products of digestion (from gut to cells) e.g. glucose & amino acids
         3. Carbon dioxide (from organs to lungs)
         4. Urea (from liver to kidneys)
         5. Hormones
         6. Antibodies/antitoxins

1. Artificial blood
   1. When someone loses a lot of blood - heart can still pump remaining RBC (as long as volume can be topped up)
   2. Blood substitute - a salt solution (saline) which can replace lost volume
      1. Advantages: It's safe (if no air bubbles get in) & can keep people alive - may give patient enough time to produce new RBC otherwise...blood transfusion
         1. Ideally, artificial blood product would replace function of RBC (no need for blood transfusion) - being developed, problems with side effects
2. Artificial hearts & valves
   1. Artificial hearts
      1. Mechanical devices put into person to pump blood if own heart fails - usually temporary fix (to keep person alive until donor heart is found), can be permanent fix (reduces need for donor heart)
      2. Advantage: not rejected because they are made from metals/plastics (body doesn't recognise them as foreign & attack)
      3. Disadvantages: surgery to fit artificial heart can lead to bleeding/infection, don't work as well as healthy natural one (parts could wear out/motor could fail), blood doesn't flow through as smoothly (can cause blood clots/strokes) - patient has to take drugs to thin blood (can cause problems with bleeding if hurt in accident)
   2. Artificial valves
      1. If heart valves are defective - can be replaced with mechanical valves
         1. Much less drastic procedure than heart transplant - but still major surgery & problems with blood clots
3. Stents
   1. Coronary heart disease - when arteries that supply blood to muscle of heart get blocked by fatty deposits, causes arteries to become narrow, restricting blood flow which can result in heart attack
   2. Stents are tubes that are inserted into arteries to keep them open - making sure blood can pass through to heart muscles, keeps person's heart beating
      1. Advantage: way of lowering risk of heart attack in people with coronary heart disease
         1. Disadvantages: over time, artery can narrow again - stents can irritate artery & make scar tissue grow, patient has to take drugs to stop blood clotting on stent