AQA AS Biology - C5

AQA AS Biology (NEW), Chapter 5, The heart & heart disease

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  • Created by: Alanna
  • Created on: 10-12-10 15:28

5.1 The structure of the heart (BASIC)

Structure - BASIC

  • Two seperate pumps - side by side
    • The left deals with OXYGENATED blood
    • The right deals with DEOXYGENATED blood
  • Each pump has 2 chambers
    • ATRIUM: ~ thin walled, stretches as it collects blood, thin muscular wall as the blood only has to be pumped a small distance.
    • VENTRICLE: ~ thicker muscular walls as the blood has to be pumped a longer distance (lungs or rest of body)
  • Ventricles: pump blood AWAY from the heart, into the ARTERIES
  • Atria: recieve blood from the VEINS
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5.1 Structure of the heart - Structure

    • Left Atroventricular (BICUSPID) valves: two cup-shaped flaps on the LEFT side
    • Right Atroventricular (TRICUSPID) valves: three cup-shaped flaps on the RIGHT side
    • Connecting heart to lungs: PULMONARY VESSELS
    • Vessels conncted:
      • Aorta connected: LEFT ventricle, carries oxygenated blood to all parts of body except lungs
      • Vena Cava connected: RIGHT atrium, brings deoxygenated blood back from tissues of body
      • Pulmonary Artery connected: RIGHT ventricle, carries deoxygenated blood to lungs (Unusual for artery to carry deoxygenated blood)
      • Pulmonary Vein connected: LEFT atrium, brings oxygenated blood back from lungs (Unusual for vein carry oxygenated blood)



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5.1 Structure of the heart, cont

Supplying the heart muscles with oxygen

  • Oxygenated blood in the LEFT side of the heart is not used for the hearts own respartitory needs
    • Heart muscle supplied by OWN blood vessels
      • Coronary Arteries: branch off aorta shortly after it leaves heart
      • Blockage of these arteries leads to myocardial infraction (heart attack)
        • As area of heart muscle is deprived of oxyge it dies = heart attack.
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5.1 Structure of the heart, cont


  • Although left ventricl has thicker walls than right, their internal volumes are the same.
  • The left and right side of the heart contract together


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5.2 The cardiac cycle

Cardiac Cycle (BASIC)

  • TWO phases of the beating of the heart:
    • Contraction (SYSTOLE)
    • Relaxation (DIASTOLE)
  • Contraction:
    • Atria: Atrial Systole
    • Ventricle: Ventricular Systole
  • Valves:
    • Atrioventricular Valves
    • Semi-lunar Valves
    • Pocket Valves

 Cardiac Output = Heart Rate * Stroke Volume



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5.2 The cardiac cycle

Realxation of the heart (DIASTOLE)

  • Blood returnes to atria of heart through pulmonary vein (from lungs) & vena cava (from body).
  • As atria fills the pressure in them rises
    • Pushing open the atrioventricular valves & allowing blood to pass into ventricles
  • Muscular walls of BOTH atria & ventricles relaxed at this stage
  • The relaxation of the ventricle wall reduces the pressure within the ventricle
    • Causes pressure to be lower than that of the aorta anf pulmonary artery so the semi-lunar valves in aorta & pulmonary artery colses
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5.2 The cardiac cycle

Contraction of atria (ATRIAL SYSTOLE)

  • Muscles of atrial walls contracts, forcing remaining blood into the ventricles
  • Blood only has to be pushed a short distance
    • Therefore muscular walls of atria thin
  • During this stage the ventricle walls remain RELAXED

Contraction of the ventricles (VENTRICULAR SYSTOLE)

  • After short delay to allow ventricles to fill with blood, their walls contract simultaniously, increasing blood pressure within them
    • Forces atrioventricular valves shut preventing backflow of blood
  • With atrioventricular valves closed the pressure rises further, forcing semi-lunar valves open, forcing blood into the pulmonary artery & aorta
    • Walls of ventricles are much thicker as they have to pump blood much further
  • Left ventricle walls are thicker as they have to pump blood to the extremerties of the body compared to the right (only has to pump blood to lungs)
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5.2 The cardiac cycle

Valves & control of blood flow

  • IMPORTANT to keep blood flowing in the right direction around the heart & body
  • Are instances in circulartitory system when pressure difference would result in blood flowing in the wrong direction
    • Valves are used to prevent this
  • Valves are designed so that they open whenever the difference in blood pressure either side of them favours the movement of blood in the requiered direction
    • When pressure difference is reversed the valves are designed to close
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5.2 The cardiac cycle

Examples of Valves

  • Atrioventricular Valves: between the atriums & ventricles, these prevent backflow of blood when contraction of ventricles means that ventricular pressure is greater than the atrial pressure.
    • Closure of valves ensures that when the ventricles contract blood moves into the aorta & pulmonary arteries rather than back to the atria
  • Semi-lunar Valves: In the aorta & pulmonary artery.
    • Prevents backflow of blood into ventricles when recoil of elastic walls of vessels create greater pressure in vessels than ventricles
  • Pocket Valves: In veins that occur throughout system
    • Ensure when veins are squeezed (e.g. muscles contract) blood flows back to the heart rather than away from it

Designs of valves = basically the same, made up of number of flaps of tissue that is cusp-shaped (when blood collects within the 'bowls' they are pushed together to form a tight fit & prevent to flow of blood

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5.2 The cardiac cycle

Cardiac Output

  • Volume of blood pumped by one ventricle of the heart in one minute
  • It depends on two factors:
    • The heart rate
    • The Stroke volume (volume of blood pumped out at each beat)

Cardiac Output = Heart Rate * Stroke Volume


Pressure & Volume changes of heart

  • Mammals have closed circulatitory system (bloos confined to vessels)
    • This allows pressure witin them to be mantained & regulated
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5.2 The cardiac cycle

How the Cardiac Cycel is controlled

  • Cardiac muscles myogenic (contraction initiated from muscle)
  • Within wall of right atrium = group of cells Sinostrial Node (SAN) often referd to as peacemaker
  • Sequence of events=
    • Wave of electrical activity spreads from SAN across both atria causing them to CONTRACT
    • Layer of non-conductive tissue (atrioventricular septum) prevents waves crossing to ventricles
    • Wave of electrical activity allowed to pass through 2nd group of cells atrioventricular node (AVN) which lies between the atria
    • AVN after short delay conveys wave of electrical activity between ventricles along series of specialist muscle fibre = bundle of His
    • Bundle of His conducts wave through atrioventricular septum to base of ventricles where bundle branches into smaller fibres
    • Wave of electrical activity released from fibres causing ventricles to contact quickly at the same time, from apex upwards
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5.3 Heart Disease

Examples of Heart Disease

  • Coronary Heart Disease (CHD)
  • Atheroma
  • Thrombosis
  • Aneurysm
  • Myicardial Infraction

Risk factors associated with CHD

  • Smoking
  • High Blood Pressure
  • Blood Cholesteral
  • Diet
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5.3 Heart Disease


  • Affects pair of blood vessels, the coronary arteries, which supply the heart with the products it needs for respiration
  • Blood flow through these vessels may be impared by the build up of fatty deposits known as atheroma
  • If blood flow to heart muscles interupted, it can lead to myocardial infraction (heart attack)


  • Fatty deposit that forms within the walls of an artery, begins as fatty streaks that are accumulations of white blood cells that have taken up LDL's
  • Streaks enlarge to form irregular patch (atheromatous plaque), are deposits of cholesterol, fibers & dead muscle cells
  • Buldge into lumen, causing artery to narrow so blood flow reduced
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5.3 Heart Disease


  • If atheroma breaks through lining of blood vessel it forms a rough surface that interupts otherwise smooth flow of blood
  • May result in formation of blood clot ot thrombus, in condition known as thrombosis
  • Thrombosis may block blood vessel, reducing or preventing flow of blood to tissues beyond
  • The region of tissue deprived of blood often dies due to lack of oxygen & other products that the blood normally supplies
  • Sometime thrombus is carried from origin and loges (&blocks) another artery.
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5.3 Heart Disease


  • Atheromas that lead to thrombus also weaken artery walls
  • Weakened points swell to form balloon like, blood filled structure, known as aneurysm
  • Aneurysms frequently burst leading to haemorrhage & loss of blood to the region of the body surved by that artery
  • A brain aneurysm is known as a cerebrovascular accident (CVA) or stroke.

Myocardial Infraction

  • Refers to reduced supply of oxygen to the heart (myocardium) muscles
  • Results from blockage of coronary arteries
  • If occurs close to junction of coronary artery & aorta the heart will stop beating as the blood supply will be completely blocked
  • If blockage further along coronary artery then symptoms = less severe
    • Smaller area suffering from lack of oxygen
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5.3 Heart Disease

Risk Factors associated with CHD


  • Two main products in tabacco that increase likelyhood of developing CHD:
    • Carbon Monoxide: conbines easily (& irreversably) with haemoglobin to form carboxyhaemoglobin. Reducing oxygen-carrying capacity of blood. This leads to heart needing to wokr harder to supply the same amount of oxygen. This can lead to
      • Raised blood pressure, which increases risk of CHD & strokes
      • Insufficiant supply of Oxygen to heart during exercise, this can lead to chest pains (anguna) or in sever cases myocardial infraction
    • Nicotine: stimulated production of adrenaline, increasing the heart rate & blood pressure
      • Greater risk of suffering CHD or a stroke
      • Nicotine leads to red blood cells becomming more 'sticky', leading to a higher risk of thrombosis & hence strokes & myocardial infraction.
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5.3 Heart Disease

High Blood Pressure

  • DNA can cause high blood pressure
  • BUT lifestyle choices e.g excessice prolonged stress, certain diets, lack of exercise, can alos incereas risk of high blood pressure
  • Increases risk of CHD due to following factors:
    • Higher pressure in the arteries, heart muscles must therefore work harder to pump blood around the them
    • Higher blood pressure within arteries means that they are more likely to develope an aneurysm (& burst causing) haemorrhage
    • To resist higher pressure within them, walls of blood vessels may thicken & harden restricting flow of blood
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5.3 Heart Disease

Blood Cholesteral

  • Cholesteral essentail component of membranes, an esentail biochemical that must be transported in the blood
  • Carried in plasma as tiny spheres of lipoproteins, there are two main types:
    • High-Density (HDL's): remove cholesteral from tissues & transport to liver for excretin, help protect arteries against heart disease
    • Low-Density (LDL's): transport cholesteral from liver to tissues, including artery walls, which they infultrate, leading to the development of atheroma & hence heart disease.


  • High levels of salt: raise blood pressure
  • High levels of saturated fat: increase LDL's & hence blood level concentration
  • Food that act as antioxidants reduce chance of heart disease, so does non-starch polysaccharide (dietary fibre)
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