The Heart

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Function of Blood

There are 5 functions of blood:

  • Carrying glucose and oxygen to cells.
  • Carrying excretory products.
  • Carrying hormones.
  • Forming part of the immune system.
  • Distributing heat
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Parts of Blood

  • Plasma: contains many dissolved substances to be transported around the body. Also contains fibrinogen, which is a soluble substance vital for the clotting of blood. Its main adaption is that it consists of water
  • Red blood cell: They contain haemaglobin, which carries oxygen. They are in a biconcave shape with no nucleus to increase surface area. They are flexible to pass through walls
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Parts of Blood (cont)

  • White blood cell: key to immune system in fighting againt infection.  Contain a nucleus and are made in the white bone marrow. They can change shape to squeeze through blood vessels.
  • Platelets: are tiny fragments of larger cells. They are involved in blood clotting
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Blood Clotting

  • Blood clotting prevents too much blood being lost, and prevents pathogens entering the body.
  • At the site of the cut, platelets break open and release thromboplastin.
  • Thromboplastin catalyses prothrombin -> thrombin.
  • Thrombin catalyses fibrinogen -> fibrin.
  • Fibrin forms a mesh, trapping blood cells. 
  • This is the cascade sequence.
  • Platelets also release serotonin, which narrows blood vessels.
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Circulation Systems

  • A circulatory system transports oxygen and nutrients around the body, and removes waste from the body.
  • Some animals have an open circulatory system, which is blood circulating in large open spaces
  • This is good for animals with a large surface area:volume ratio, which enables them to rely on simple diffusion.  
  • Most large animals have a closed circulatory system, where blood is contained in blood vessels.
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Circulation Systems (cont)

  • Small, closed circulation animals may have a single circulatory system.
  • Deoxygenated blood is pumped from the heart to the lungs. Oxygenated blood is pumped from lungs to body cells. Deoxygenated blood is pumped from body cells back to heart
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Circulation Systems (cont)

  • A double circulatory system conists of systematic circulation and pulminary circulation.
  • Pulminary circulation: deoxygenated blood is pumped from the heart to the lungs. Oxygenated blood from lungs to the heart.
  • Systematic circulation: oxygenated blood is pumped from heart to body cells. Deoxygenated blood from body cells to heart
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Circulation Systems (cont)

There are 4 advantages of having a double circulatory system:

  • Ensures oxygenated and deoxygenated blood do not mix.
  • Maximises oxygen delivery at high pressure.
  • Ensures tiny blood vessels do not burst.
  • Pumps blood hard to travel around the whole body.
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Blood Vessels


  • Thick outer walls and thick inner layer to withstand blood at high pressure and thin lumen to maintain it.
  • Elastic fibres in inner layer allow artery to stretch and recoil which mainains blood pressure.
  • Smooth muscle in inner layer can squeeze blood along.
  • Final layer surrounding lumen is the endothelium
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Blood Vessels (cont)


  • Thin outer wall and thin inner layer because large lumen gives low blood pressure.
  • Large lumen means veins can hold large volumes of blood.
  • Veins contain semi-lunar valves, which return low pressure blood to the heart, preventing backflow.
  • Inner layer also contains muscles and elastic fibres, for same reasons as arteries.
  • Also an inner endothelium layer
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Blood Vessels (cont)


  • Walls are 1 cell thick to allow very easy diffusion in and out of capillaries. 
  • Blood travels relatively slowly, giving substances more opportunity to diffuse.
  • Endothelium cell wall contains no elastic fibres, smooth muscle or collagen
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Features of the Heart

  • The heart muscle is myogenic. It can initiate its own contraction without needing an external nervous impulse.
  • The heart has intrinsic rythmicity. It can keep beating outside of the body, provided it has the right nutrients and conditions. 
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Cardiac Impulse Muscle

  • The sinoatrial node (SAN) is located in the upper right atrium.
  • The SAN can spontaneously contract, generating nerve impulses that make atria contract
  • The atrioventricular node (AVN) is located in the septum between the two atria.
  • The AVN sends impulses to the ventricles along the bundle of His
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Cardiac Impulse Muscle

  • SAN contracts and sends impulse to atria which causes atria to contracts.
  • Impulse reached AVN.
  • Delay at AVN to ensure ventricles contract after atria.
  • Impulse travels to ventricles via bundles of His.
  • Ventricles now contract
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Cardiac Cycle

  • Atrial systole: atria contract, ventricles relax, atrio-ventricular valves open, semilunar valves closed, blood moving into ventricles.
  • Ventricular systole: atria relax, venticles contract, atrio-ventricular valves closed, semilunar valves open, blood moving into arteries.
  • Diastole: atria relax, ventricles relax, atrio-ventricular valves open, semilunar valves closed, blood moving into atria and ventricles. 
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Cardiovascular Disease


  • Damage to cells lining artery leads to inflammatory response.
  • Build up of white blood cells, cholestrol, calcium salts, fibrous tissue and platelets in damaged area.
  • Formation of atheroma (plaque).
  • Causes loss of elasticity of artery and narrowing of lumen.
  • Causes high blood pressure
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Cardiovascular Disease (cont)


  • Lumen of artery is narrowed by plaque (atherosclerosis) and blood builds up behind blockage.
  • This causes wall of artery to bulge and become weakened.
  • This weakened artery may burst causing internal bleeding.
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Cardiovascular Disease (cont)


  • Plaque builds up in coronary arteries.
  • Blood flow to heart muscle reduced.
  • Heart muscle needs to respire anaerobically, which builds up lactic acid and oxygen debt.
  • This causes pain in chest which can spread to arms and jaw
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Cardiovascular Disease (cont)

Heart attack:

  • Complete blockage in a branch of the coronary artery.
  • Part of heart muscle becomes starved of oxygen, preventing aerobic respiration.
  • This causes scar tissue, due to death of cells. 
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Cardiovascular Disease (cont)


  • Caused by an interuption of blood supply to the brain, either by bleeding from damaged blood vessels or from blockage in blood vessels leading to brain.
  • Causes dizziness, slurred speach, paralysis of one side of body. 
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Energy in Food

  • The amount of energy stored in food can be measured with a calorimeter.
  • It measures the amount of energy released when a known quantity of food is completely burnt in oxygen.
  • Energy released is transferred to water and the temperature rise is measured.
  • 1 Calourie raises 1g of water by 1 degree
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Energy in Food

  • Basal metabolic rate (BMR) is the energy required to keep organs/cells working correctly when you are at rest.
  • BMR is calculated by heat loss in humans over a period of time.
  • BMR is higher if you have more muscle rather than  fat.
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  • Whether someone is obese or not can be determined by their body mass index (BMI),                                    = mass/height squared.
  • This factors mass against height, so being above a certain value makes you obese.
  • Being obese means you are more likely to have high blood pressure, suffer from CVD, have high blood cholestrol, and have type 2 diabetes. 
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High density lipoproteins:

  • Are made of unsaturated fats, cholestrol and protein
  • Carry cholestrol from tissues to liver so that it can be broken down.
  • So HDLs lower cholestrol level.
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Low density lipoproteins:

  • Made from saturated fats, cholestrol and protein.
  • Carry more cholestrol than HDLs, but carry cholestrol to cell membrane instead of inside liver.
  • Too many LDLs can saturate cell membrane, so there are more left in blood.
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  • Diurretics, Beta blockers, Sypathetic nerve inhibitors and ACE inhibitors all reduce blood pressure.
  • However, they may cause blood pressure to drop too low.
  • They may also cause coughing, swelling, impotence and fatigue.
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Treatments (cont)

  • Statins lower cholestrol by blocking the enzyme that makes cholestrol.
  • They block LDL synthesis.
  • However, they can cause fatal muscle inflammation, or there is a risk the patient may not try to live a healthy lifestyle because drug is so effective.
  • Plant stanols and sterols have the same effects as statins. 
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Treatments (cont)

  • Anticoagulates prevent blood clotting.
  • Doses must be carefully monitored otherwise blood will not clot at all.
  • May irritate stomach lining
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