The heart and disease

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  • The heart and disease
    • Structure of the heart
      • The heart consists of four chambers; the left atrium, the right atrium, the left ventricle and the right ventricle.
      • The right atrium is supplied with oxygenated blood by the vena cava.
      • The right ventricle is positioned below the atrium and pumps blood up into the pulmonary artery which leads to the lungs, where it is oxygenated.
      • The left atrium is supplied with oxygenated blood by the pulmonary vein.
      • The left ventricle lies below the atrium, it it lined with a thick muscle wall so it can create enough force to pump the blood up in to the aorta ans all the way around the body.
      • Between each chamber of the heart there are valves which stop the blood from flowing backwards
        • the valves between the atria and the ventricles are called the atrioventricular valves.
        • The valves between the ventricles and the aorta/ pulmonary artery are called semi-lunar valves
    • The cardiac cycle
      • Cardiac output = stroke volume x heart rate.
        • Heart rate is the number of beats per minute.
        • Stroke volume is the volume of blood pumped during each heart beat.
      • The cardiac cycle pumps blood around the body.
        • 1. ventricles relax, atria contract.
          • When the atria contract the volume is decreased, increasing the pressure. This pushes the blood into the ventricles.
          • Blood flows into the ventricles to even out the pressure of the atrium and the ventricles.
        • 2. ventricles contract, atria relax
          • When the ventricles contract the volume decreases, this increases the pressure.
          • The increase in pressure forces the AV valves shut to preven the blood flowing back into the atria.
          • The pressure in the ventricles is higher than the pressure in the aorta and pulmonary artery os the blood is forced up which opens the SL valves.
          • Blood us forced out of the ventricles in to the arteries.
      • Cardiac muscle controls the regular beating of the heart.
        • The heart muscle is myogenic which means it can contract and relax without signals fron the nerve
        • 1. The process starts in the sino-atrial node (SAN) which is inn the wall of the right atrium.
          • The SAN acts like a pacemaker. It sets the rhythm of the heart beat by sending out regular waves of electrical activity to the atria walls.
        • 2. The waves of electrical activity cause the left atria to contract at the same time.
        • 3. A band of non-conducting collagen tissue prevents the waves from being passed directly from the atria to the ventricles.
        • 4. The waves of electrical activity are transfered to the atrioventricular node (AVN)
        • 5. The AVN passes the waves of electrical activity on to the bundle of His. But, there is a slight delay before the AVN reacts, to make sure the ventricles contract after the atria have emptied.
        • 6. The bundle of His is a group if muscle fibres responsible for conducting the waves of electrical activity to the purkyne fibres in the left and right ventricle walls.
        • 7. The Purkyne fibers carry the electrical activities into the ventricle walls, causing them to contract simultaneously.
    • Heart disease
      • Atheroma
        • If damage occurs to the endothelium of the artery, white blood cell and lipids from the blood, clump together under the lining to for fatty streaks.
        • over time more white blood cells, lipids and connective tissue build up and harden to form a fibrous plaque, called an atheroma.
        • The plaque partially blocks the lumen of the artery and restricts blood flow,which causes blood pressure to increase.
      • Aneurysm
        • An aneurysm is a balloon like swelling of the artery.
        • Atheroma plaques damage weaken arteries.
        • When blood flows through a weakened artery at high pressure, it may push the inner layers of the artery through the elastic layer.
        • An aneurysm may burst and cause a haemorrhage.
      • Thrombosis
        • Thrombosis is the formation of a blood clot.
        • An atheroma can rupture the endothellium of an artery. This damages the artery wall and leaves a rough surface
        • Platelets and fibrin (proteins) accumulate at the sight of damage and form a blood clot.
        • A blood clot can cause a complete blockage of the artery or it can become dislodged and block a blood vessel elsewhere in the body.
        • Debris from the rupture can cause another blockage to form further down the artery.
      • Myocardial Infarction
        • A myocardial infarction is more  commonly known as a heart attack.
        • The heart muscle is supplied with blood from the coronary artery.
        • If the coronary artery become blocked then the oxygen in the blood will not be able to reach the heart muscle needed by the heart for respiration
        • A heart attack can cause damage or death of the heart muscle
        • Symtoms of  a heart attack can include chest pain, shortness of breath and sweating
        • If large areas of the heart are affected then complete heart failure can occur, which is often fatal
      • Risk factors
        • Poor diet and high blood cholesterol
          • Cholesterol is the main constituents of fatty deposits that form atheromas
          • A diet high in salt also increase of disease because it increase the risk of high blood pressure
        • Smoking
          • Both carbon monoxide and nicotine found in cigarette smoke increase the risk of CHD.
          • Carbon monoxide combines with hemoglobin and reduces the amount of oxygen transported in the blood.
          • If the heart muscle doesn't receive enough oxygen it could lead to a heart attack.
          • The amount of antioxidants in the blood decreases which protect cells.
            • Fewer antioxidants means cell damage in the artery walls is more likely, this could lead to the formation of an atheroma.
        • High blood pressure
          • High blood pressure increase the risk of damage to the artery wall which increases the risk of atheroma formation
          • Anything that increase blood pressure also increases the risk of CHD
            • Being overweight
            • Not exercising
            • Excessive alcohol consumption
          • Atheromas can cause blood clots which could result in a myocardial infarction.

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