The heart

• The heart

  Made of cardiac muscle, which contracts and relaxes

  It does not get fatigued.

  Coronary arteries supply cardiac muscle with oxygenated blood.
• 1. Deoxygenated blood enters right atrium from vena cava.
  2. Atria have thin muscular walls, as blood flows in pressure builds up until tricuspid valve opens to let blood pass into right ventricle.
  3. When both right atria and ventricle are filled with blood, the atrium contracts forcing all blood into ventricle.
  4. As ventricle contracts, tricuspid valve closes preventing backflow.
  5. Tendinous cords make sure valves don't turn inside out.
  6. Right ventricle contracts and forces blood through semilunar valves into pulmonary artery to the lungs.
• 1. Oxygenated blood from lungs enters left atrium from pulmonary vein.
  2. As pressure in atrium builds the bicuspid valve opens and blood flows into left ventricle. When both atrium and ventricle are full the atrium contracts forcing all blood into left ventricle.
  3. Left ventricle contracts, bicuspid valve closed.
  4. Muscular wall on left side is thicker.
  5. Blood flows through semilunar valves and out of the aorta.
• Diastole= heart relaxes.

  • Artria and ventricles fill with blood.
  • Volume and pressure of the blood in the heart build as the heart fills, but pressure in arteries is at a minimum.
• Systole= atria contract, followed by ventricles.

  • Pressure inside the heart increases dramatically and blood is forced out of the right side of the heart to the lungs.
  • The volume and pressure in the arteries is at a maximum.
• Rhythm of heart:

  Pacemaker, sino-atrial node causes atria to contract. Electrical activity from SAN is picked up by the atrio-ventricular node. The AVN stimulates the bundle of His, a bundle of conducting tissue made up of purkyne fibres which penetrate through the septum between the ventricles. Bundle of His splits into two branches and conducts a wave of excitation to the apex of the heart. At apex the purkyne fibres spread out through walls of ventricle. Spread of excitation triggers the contraction of ventricle starting at apex to empty ventricles.
• A layer of non-conducting tissue prevents the excitation passing directly to ventricles.
• Electrocardiograms

  = Measures the spread of electrical excitation through the heart as a way of recording what happens as it contracts.

  • Measures tiny electrical differences in the skin.
• Tachycardia= when heartbeat is very rapid 100 BPM.

  • Normal when exercising or have a fever.
  • If abnormal it may be caused by problems in electrical control of the heart.
• Bradycardia= when heart rate slows down to below 60 BPM.

  • Many have it because they are fit, training make heart beat more slowly and efficiently.
• ectopic heartbeat= extra heartbeats outside the normal rhythm.
• Arrhythmia= abnormal heart rhythm.

  • Rapid electrical impulses are generated in the atria. They contract very fast, but don't contract properly and only some impulses are passed to ventricles, which contract less often. So heart pumps blood less efficiently.