AS Biology (SNAB)

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  • Created by: Stanwee
  • Created on: 22-12-11 12:08

Why do many animals have a heart and circulation?

  • To move substances around the body
  • In very small organisms diffusion is used
  • In complex multicellular organisms, they are too large to move substances quickly enough. They use blood to carry vital substances around their bodies and a heart to pump it.

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Circulatory Systems


  • Blood circulates in large open spaces in inscet and some animal groups
  • Pumps into cavities around organs with substances diffusing in and out.
  • When the heart relaxes, blood is draen from the cavity back to the hear though small vavled opening along its lengths


  • Enclosed within tubes
  • Blood leaves heart under pressure and flows along arties/arterioles into capillaries. It then returns via venules and veins. Valves make sure blood only goes in one direction


  • Right ventricles pimps deoxygenated blood to lungs to get oxygen
  • Returns to heart to be pumped out to body via left ventricle
  • Flows through heart twice, extra pump, flows faster, higher metabolic rate.
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Importance of water as a solvent in transport

  • Unevenly distributed charge - polar molecule - forms V shaped molecule.
  • Hydrogen end is positive and oxygen end negative.
  • Attracts negative end of surrounding molecules - hydrogen bonding


  • Many chemicals disolve easily in water - vital reactions can occur in cytoplasm.
  • Chemicals can react as free to move and water is sometimes involved in reaction (hydrolisis/condensation reactions)
  • Dissolved substances can be transported via blood and lymph or xylem and phloem.
  • Ionic(NaCl) and Polar(-OH) molecules also dissolve easily in water .
  • Non-Polar molecules like lipids don't dissolve and form lipoproteins to enable transport in blood.
  • High heat capacity - Animals can avoid rapid changes to internal temperature,
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How do the structures of blood vessels (capillarie

  • Arteries' elastic walls stretch to accommodate blood during systole. During diastole the elasticity cause recoil behind blood helping push it forward. There are no valves due to high pressure. Thick walls prevent arteries bursting under high pressure. More collagen makes them more strong and durable. 
  • There is a steady flow of blood by he time it reaches the capillaries allowing rapid exchange through one cell thick walls. The network of capillaries lie very close to every cell to ensure rapid diffusion.
  • Blood flow in veins is assisted by the contraction of skeletal muscles during movement and breathing. Under low pressure so there are thinner walls and less collagen. Wide lumen as the blood does not need to be kept under pressure. Valves stop the backflow of blood. 
  • The heart cannot use any of the blood inside it's chambers due to lack of diffusion. Coronary arteries supply the heart.
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Atrial systole, ventricular systole and diastole


  • Blood returns to heart due to skeletal movement and breathing.
  • Blood under low pressure flows into left and right artia from pulmonary veins and vena cava. As atria fill the pressure opens the AV valves and blood leaks into the ventricles. The atria walls contract forcing more blood into ventricles. (Ventricular systole follows immediately after this)
  • Ventricles contract from base upwards, increasing pressure.
  • Blood pushed up and out through arteries. Pressure closes AV valves stopping backflow into atria.


  • Elastic recoil of the relaxing heart walls lowers pressure in atria and ventricles. 
  • Blood under high pressure in arteries is drawn back closing semi lunar valves preventing backflow. Coronary arteries fill during diastole. Low pressure in atria helps draw blood into heart from veins.

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The course of events that leads to atherosclerosis

  • Damage to endothelium due to high blood pressure or toxins from cigarettes
  • Once inner lining is breached an inflammatory response occurs. White blood cells leave blood vessel and move into artery wall. They accumulate chemical from blood like cholesterol. A deposit builds up called an atheroma.
  • Calcium salts and fibrous tissue build up resulting in hard swelling called a plaque.
  • This fibrous tissue causes the artery wall to lose elasticity. 
  • Plaques narrow the artery making it more difficult to pump blood around the body.
  • This higher blood pressure means that further plaques are more likely to form.
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The blood clotting process

  • When platelets (a type of blood cell without a nucleus) come into contact with the damaged vessel wall they change from flattened discs to long projections
  • Their cell surfaces change causing them to stick to the exposed collagen and form a temporary platelet plug.
  • A cascade of changes results in the soluble plasma  protein prothrombin to convert into thrombin. 
  • Thrombin is an enzyme which then catalyses the conversion of fibrinogen into long insoluble strands if fibrin. 
  • These fibrin strands form a tangled mesh that traps blood cells to form a clot.
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The factors that increase the risk of CVD - geneti

  • Single gene disorders increasing the likelihood of early development of CHD. e.g. familial hypercholestrolaemia mutations in the LDLR gene cause the LDL receptors not to form or have a shape making the removal of LDL from blood less efficient.
  • Apolipoprotein A mutation = low HDL levels, less removal of cholesterol, increased risk of CHD
  • Apolipoprotein B mutation = higher levels of LDL, more risk of CVD 
  • Apolipoprotein C mutation has three common alleles, E2, E3, E4. APOE4 = slower removal of cholesterol increasing risk of CHD.
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The factors that increase the risk of CVD - diet

  • Radicals resulting from when an atom has an unpaired electron are highly reactive and can damage many cell components including enzymes and genetic material. Some vitamins like vitamin C or antioxidants provide hydrogen atoms that stabilize the radical by picking up the electron and protect against heart disease.
  • A high salt diet causes kidneys to retain water. Higher fluid levels in the blood = elevated blood pressure = higher risk of CVD.
  • Higher cholesterol diets especially in LDLs mean that the LDLs overload membrane receptors resulting in high blood cholesterol levels. Saturated fats may also reduce activity of LDL receptors so the LDLs are not removed from the blood. This cholesterol may be deposited in the artery walls forming atheromas. 
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The factors that increase the risk of CVD - age

  • Prevalence of CVD increases with age
  • This may be due to the effects of ageing on the arteries and they tend to become less elastic and may be more easily damaged.
  • With age over risks may increase such as inactivity causing a rise in the numbe rof cases of CVD.
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The factors that increase the risk of CVD - gender

  • Overall, men have a higher risk of heart attack than women. But the difference narrows after women reach menopause. After the age of 65, the risk of heart disease is about the same between the sexes when other risk factors are similar.
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The factors that increase the risk of CVD - high b

  • Higher blood pressure or hypertension increases likelihood of atherosclerosis occurring.
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The factors that increase the risk of CVD - smokin

  • Haemoglobin carry carbon monoxide. Reduced oxygen supply = increased heart rate to provide oxygen
  • Nicotine simulated production of hormone adrenaline. Hormone causes increase in heart rate + arteries constrict raising blood pressure
  • Chemicals in smoke can damage lining of arteries causing atherosclerosis.
  • Has been linked to reduction in HDL levels.
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The factors that increase the risk of CVD - Inacti

  • Most common risk factor
  • Moderate exercise prevents high blood pressure e.g. walking
  • Exercise mantain healthy weight and raises HDL without affecting LDLs
  • Much more likely to survive a heart attack.
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