10.3 Biology F4

• Cardiac muscles


  Contract repeatedly without fail to produce heartbeat and pump blood
• Sino-arterial (SA) node


  Also known as the pacemaker, located in the wall of the right atrium
• Atrioventricular (AV) node


  Located at the bottom of the right atrium, connected to the bundle of His
• Mechanism of heartbeat


  1. SA node generates electrical impulses

  2. Impulses spread through atrial muscle cells

  3. Atria contract to push blood to ventricles

  4. Impulses delayed at AV node

  5. Impulses reach ventricles through bundle of His

  6. Ventricles contract to pump blood out
• The heart's primary pacemaker is the sino-arterial (SA) node
• The SA node keeps the heart regular and relays impulses to the atrioventricular (AV) node
• The AV node has similar cardiac tissue to the SA node and relays impulses to the ventricles
• Pacemaker


  Smallest artificial pacemaker is the Medtronic Micra, placed in the heart without surgery
• Artificial pacemaker


  Sends small electrical charges to stimulate the heartbeat
• Atrial contraction


  Pushes oxygenated blood from left atrium to left ventricle, and deoxygenated blood from right atrium to right ventricle
• Electrical impulses from SA node

  Cannot flow directly to ventricles due to insulated ring tissues
• AV node


  Delays impulses for 0.1 seconds to ensure complete flow of blood from atria to ventricles
• Ventricular systole


  1. Impulses reach apex of heart and spread to all parts of ventricular walls

  2. Causes contraction wave in both ventricles

  3. Pushes oxygenated blood from left ventricle into aorta, and deoxygenated blood from right ventricle into pulmonary artery
• Cardiac diastole


  Relaxation of cardiac muscles, allowing blood to enter and fill the heart
• Cardiac systole


  Contraction of cardiac muscles
• Heart sounds


  1. First heart sound (lub) is produced when tricuspid and bicuspid valves close

  2. Second heart sound (dub) is produced when semilunar valves close
• Pumping of heart


  Insufficient for blood flow to continue through veins and return to heart
• Venous valves


  Ensure blood flows in one direction back to the heart
• Skeletal muscle contraction around veins


  Helps push blood back to the heart against gravity
• The main heart pacemaker is the sino-arterial (SA) node
• The term 'myogenic' means the heart can contract without nervous stimulation
• A person who stands too long may faint due to pooling of blood in the lower body, reducing blood flow to the brain
• Fingers may turn pale in cold conditions or when experiencing fear, due to vasoconstriction reducing blood flow to the extremities