Heart and Heart Disease

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  • Created by: claire
  • Created on: 16-12-13 21:55

Heart Structure

Left side deals with oxygenated blood from lungs. Right side deals with deoxygenated blood from body

  • Atrium - thin walled, elastic, stretches, only has to pump blood short distance to ventricle
  • Ventricle - thicker walled, creates enough pressure to pump blood to lungs/body

2 separate pumps because blood has to pass through capillaries in lungs to present large s.a for exchange of gases, large drop in pressure, blood flow to rest of body would be slow without 2 pumps.

  • Aorta - connected to left ventricle, carries oxygenated blood to body
  • Vena cava - connected to right atrium, brings deoxygenated blood back from body tissues
  • Pulmonary artery - connected to right ventricle, carries deoxygenated blood to lungs
  • Pulmonary vein - connected to left atrium, brings oxygenated blood from lungs

Blockage of coronary arteries leads to myocardial infarction, area of heart muscle deprived of oxygen

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Cardiac cycle

  • Diastole - blood returns from atria through pulmonary vein and vena cava. As atria fills, pressure rises, atrioventricular valves open, blood passes into ventricles. Relaxation of ventricle wall reduces pressure within ventricle, causes pressure to be lower in aorta and pumonary artery, semi lunar valves close
  • Atrial Systole - muscle of atrial walls contract, forcing blood into ventricles. Thin walls as blood is pushed a short distance. Ventricle muscle walls relaxed. Atrioventricular valves open, semilunar valves closed
  • Ventricular systole - Ventricle walls contract, increasing blood pressure within, shutting strioventricular valves to prevent backflow of blood into atria. Pressure rises further, semi lunar valves open, pushing blood into pulmonary artery and aorta. Ventricle walls thicker, blood pumped further

Valves open whenever difference in blood pressure either side of them favours the movement of blood in required direction

  • Atrioventricular valves - prevent backflow of blood when contraction of ventricles leads to ventricular pressure exceeding atrial pressure
  • Semilunar valves - prevent backflow of blood into ventricles when recoil action of elastic walls of vessels create greater pressure in vessels than ventricles
  • Pocket valves - veins, when skeletal muscles contract, blood flows to heart
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Cardiac Cycle

cardiac output = heart rate x stroke vol

Myogenic - contraction initiated from within muscle itself

  • Wave of electrical activity spreads out from sinoatrial node across both atria, causing them to contract
  • Atrioventricular septum is non conductive, prevents wave crossing to ventricles
  • Wave of electrical activity passes through atrioventricular node
  • Atrioventricular node conveys wave of electrical activity between ventricles along bundle of His
  • Bundle of His conducts wave through atrioventricular septum to base of ventricles
  • Wave of electrical activity released from smaller fibres, causing ventricles to contract from apex of heart upwards
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Pressure and Volume Changes of Heart

Aorta Pressure

  • Rises when ventricles contract, blood forced into aorta
  • Gradually falls but not low, elasticity of wall creates recoil action which produces temporary rise in pressure at start of diastole

Atria Pressure

  • Relatively low, thin walls can't create much pressure. Highest when contracting
  • Drops when left atrioventricular calve closes and walls relax
  • Gradual rise, atria fills with blood
  • Drop when left atrioventricular valve opens and blood moves into ventricle

Ventricle Pressure

  • Low, gradual increase as fill with blood as atria contract
  • Left atrioventricular valves close, rise as thick ventricle walls contract
  • As pressure rises above aorta's, blood forced into aorta, pressure falls

Ventricle Volume

  • Rises as atria contract, ventricles fill with blood
  • Drops as blood forced into aorta and semilunar valve open
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Heart Disease

Atheroma

Accumalations of w.b.c that have taken up low density lipoproteins enlarge to form atheromatous plaque. Made up of deposits of cholesterol, fibres, dead muscle cells. Atheromatous plaque bulge into lumen of artery, narrower, blood flow reduced. 

Thrombosis

Atheroma breaks through endothelium of blood vessel, forms rough surface, results in blood clot/thrombus. Blocks vessel, reduces supply of blood to tissues, region of tissue dies because of lack of O2, glucose.

Aneurysm

Atheromas that lead to thrombosis weaken artery walls which form anearysm. Aneurysms burst, lead to haemorrhage.

Myocardial Infarction

Results from blockage in coronary arteries. If occurs in junction of coronary artery and aorta, heart stops beating, blood supply cut off. If occurs further along coronary artery, milder symptoms, smaller area of muscle suffers of O2 deprivation

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Risk Factors Associated with Coronary Heart Diseas

Smoking

  • Carbon monoxide combines with haemoglobin to form carbohaemoglobin, reduces O2 carrying capacity. To supply equivalent quantity of oxygen to tissues, heart works harder, leads to higher blood pressure. Insufficient supply of O2 to heart muscle in exercise, angina.
  • Nicotine stimulates adrenaline production, increases heart rate and blood pressure. Makes platelets more sticky 

High Blood Pressure

  • Heart works harder to pump blood into arteries, more prone to failure
  • Arteries more likely to develop aneurysm, burst, haemorrhage
  • Walls of arteries thicken and harden to resist high pressure, restricts flow of blood

Blood Cholesterol

  • Carried in plasma as lipoproteins
  • High density lipoproteins remove cholesterol from tissues, transport to liver for excretion, protect arteries against heart disease
  • Low density lipoproteins transport cholesterol from liver to tissues, leads to atheroma

Diet

  • High levels of salt raise blood pressure
  • High levels of saturated fat increase LDL levels and blood cholesterol concentration
  • Antioxidants and non start polysaccharide reduce risk
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