The Heart and Circulation

• The heart:

  • Pump that pushes blood around the body
  • Enclosed by a membrane - the pericardium
  • Composed of a cardiac muscle.
• Chambers

  • Heart has 4 chambers, separated by the septum.
  • The upper chambers (the atria) receive blood.
  • The lower chambers (the ventricles) are the pumping chambers
• Blood Vessels

  • Superior Vena Cava - major vein bringing blood to the heart from the head and upper body.
  • Inferior Vena Cava - major vein bringing blood to the heart from the lower body and legs.
  • Aorta - main artery that takes blood to all parts of the body (except the lungs).
  • Pulmonary Arteries - carry deoxygenated blood to each lung.
  • Pulmonary Veins - bring oxygenated blood to the heart from the lungs.
• Semilunar Valves

  • Prevent backflow from arteries to the ventricles.
  • Pulmonic semilunar valve - lies between the right ventricle and pulmonary artery.
  • Aortic semilunar valve - lies between the left ventricle and the aorta.
• AV Valves

  • Prevent backflow from the atria to the ventricles.
  • Tricuspid atrioventricular valve - lies between the right atrium and right ventricle.
  • Bicuspid atrioventricular valve - lies between the left atrium and the left ventricle.
• Chordae Tendinae

  • The strong tendons that hold the Atrioventricular valves in position.
• Blood Vessel Types:

  • Arteries - muscular blood vessels that carry blood away from the heart.
  • Arterioles - small arteries that direct blood flow to various tissues of the body.
  • Capillaries - microscopic blood vessels that connect arterioles and venules, allowing the exchange of substance.
  • Venules - small veins that direct blood flow towards the heart from tissues.
  • Veins - blood vessels that carry blood towards the heart.
• Blood Vessel Structure:

  • Arteries - have thick walls that can withstand high pressures with small lumens.
  • Veins - have thin walls with large irregular lumens.
  • Capillaries - consist only of a single layer of cells, allowing for efficient exchange.
• Pathway of blood

  1. Deoxygenated blood from the body fills the right atrium from both the superior and inferior vena cava

  2. The tricuspid AV valve opens, letting blood flow into the right Ventricle. It then closes - allowing no blood flow the wrong way

  3. The right ventricle then pumps, pushing blood through the right semilunar valve into the 2 pulmonary arteries (one to each lung) which goes to the lungs where it is oxygenated

  4. The oxygenated blood comes back from the lungs via four pulmonary veins (2 from each lung) into the left atrium

  5. The bicuspid AV valve opens, allowing blood to flow into the left Ventricle

  6. The left ventricle pumps, pushing blood via the left semilunar valve through the aorta to the body and to the hearts own blood vessels
• Cardiac cycle:

  • The sequence of events that occur in one complete beat of the heart.
  • Systole - the pumping phase of the cycle, when the heart muscle contracts.
  • Diastole - the filling phase of the cycle, when the heart muscle relaxes.
• Cardiac Output:

  • The volume of blood pumped by the heart per minute.
  • The heart rate is the number of heart beats per minute
  • The stroke volume is the volume of blood in milliliters, pumped out of the heart with each beat.
  • Cardiac output = heart rate x stroke volume
  • An average person has a resting heart rate of 70 beats/min and stroke volume of 70 mL/beat.