Heart and Disease

Biology AQA as new spec. Heart.

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Heart Structure

There are 2 pumps in the heart: The left has oxygenated blood from the lungs. The right has deoxygenated blood from the body.

The atrium:

  • is thin walled, elastic and stretches.
  • pumps blood to the ventricles.

The ventricles:

  • have thicker muscular walls to pump further.
  • the right has a thinner wall.

Each cardiac muscle cell is myogenic - it has its own rhythm.

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Vessels Into the Heart

The ventricles lead to the arteries. The veins lead to the atria.

Aorta leads from the left ventricle and carries oxygenated blood to the body.

Vena Cava lead to the right atrium and carries deoxygenated blood from the body.

Pulmonary Artery leads from the right ventricle and carries deoxygenated blood to the lungs.

Pulmonary Vein leads to left atrium and carries oxygenated blood from the lungs.

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Blood Vessels

Arteries have a:

  • Thick outer covering of tough collagen fibres which it uses to contract (tunica externa).
    A smooth middle layer of muscle and elastic (tunica media).

Veins have:

  • A thin outer covering.
    A very thin middle layer of muscle and elastic.
    Semi-lunar valves which prevent backflow of blood.


  • Are very thin (1 cell thick).
  • Exchange substances easily.
  • Slow blood flood down as have high resistance which is good for diffusion.
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It is mainly pressure that controls blood flow as blood flows from high to low pressure. If this is not wanted then valves are used.

Atrioventricular Valves:

  • Bicuspid on left and tricuspid on right.
  • Between atrium and ventricle.
  • Stop backflow when ventricles contract so blood moves to arteries.

Semi-lunar valves:

  • In aorta and pulmonary artery.
  • Stop backflow into ventricles when recoil as pressure is greater in vessels.

Pocket valves:

  • In veins so when they are squeezed blood flows to the heart and not away.
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Systole and Diastole of the Heart


  • Blood returns to the atria.
  • The pressure rises, opening the AV valves so blood flows into the ventricles.
  • All muscles in heart are relaxed.
  • The pressure is is lower in the ventricle than the aorta and pulmonary artery so semi-lumar valves open.

Atrial Systole:

  • Atrial walls contract forcing blood into ventricles.
  • Ventricles are relaxed.

Ventricular Systole:

  • Walls contract simultaneously which increases the pressure and shutting the AV valves.
  • Pressure rises opening semi-lunar and pushing blood into artery and aorta.
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Cardiac Output

Cardiac Output - this is the volume of blood pumped by 1 ventricle in 1 minute.

Heart rate - rate at which the heart beats.

Stroke volume - volume of blood pumped out at each beat.

cardiac output = heart rate x stroke volume

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Controlling the cardiac Cycle

Muscle is myogenic i.e. contraction initiated from muscle not nerves.

Sinoatrial node is the initial stimulus for contraction (pacemaker). A wave of electrical activity spreads from SAN across atria so they contract.

Atrioventricular septum stops wave crossing to ventricles.

Waves therefore passes through atrioventricular node between atria.

AVN conveys wave between ventricles along Bundle of His.

This conducts wave through AV septum to apex of ventricles.

Wave released from fibres so ventricles contract quickly at once from apex upwards.

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Coronary Heart Disease

Coronary heart disease affects coronary arteries which supply the heart muscle with oxygen.
Blood flow impaired by build up of fatty deposits (atheroma) which can leads to a myocardial infarction.

  • Carbon monoxide from cigarettes combine easily with haemoglobin so reduces ability to carry oxygen. This increases blood pressure.
  • Nicotine stimulates adreneline which increases heart rate and blood pressure. It makes the blood cells more sticky.
  • High blood pressure caused by lifestyle or genetics. Heart has to work harder, more likely to develop aneurysm and the artery walls thicken to resist pressure so restrict blood.
  • Cholesterol trasnported in blood by lipoproteins - High density ones remove cholesterol, low density take them from liver to tissues.
  • High levels of salt raise blood pressure.
  • High levels of saturated fat increase LDLs.
  • Antioxidants and non-starch polysaccharides reduce the risk of heart disease.
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Atheroma, Thrombosis, Aneurysm & Myocardial Infarc

Atheroma - A fatty deposit that forms on artery walls. Begins as fatty streaks that take up LDLs which enlarge to form an atheromous plaque. They bulge into lumen so it narrows. Increase the risk of thrombosis and aneurysm.

Thrombosis - If the atheroma breaks through the vessel lining it forms a rough surface that interupts blood flow. This leads to a blood clot (thrombus) which blocks the vessel, stopping blood supply.

Aneurysm - Atheromas that lead to a thrombus also weaken artery walls which swell to form blood-filled structure (aneurysm). These burst leading to haemorrage. A brain aneurysm is a stroke.

Myocardial Infarction - A reduced supply of oxygen to the heart muscle. It can stop the heart beating. Almost all show signs of atheroma and thrombosis.

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