Week 27 - The Cardiovascular System

• The cardiovascular system consists of:

  • A muscular pump (the heart)
  • A series of tubes (the blood vessels)
  • A liquid (the blood)
• Functions of the cardiovascular system include:

  • Transport of materials around the body (to and from all parts of the body)
  • Circulation of oxygen, nutrients (glucose, fatty acids) & water
  • Removal of waste products (CO2, metabolic waste, heat)
  • Cell-cell communication (hormones)
  • Immune defence (White blood cells, antibodies)
• Divisions of circulation:

  • Pulmonary circulation:
  • Right side receives blood from tissues and sends it to lungs for oxygenation
  • Systemic circulation:
  • Left side receives newly oxygenated blood from lungs and pumps it to tissues
• Blood flows because liquids move from high to low pressure regions

  • Contraction of the heart creates pressure without changing the volume of blood
  • Pressure in ventricles is called driving pressure
  • Hydrostatic Pressure: exerted by a fluid which is not moving and force is exerted equally in all directions
  • Pressure = Force / Area
• Flow usually means flow rate, the volume of blood that passes a given point in the system per unit of time

  • Velocity of flow (or simply velocity), the distance a fixed volume of blood travels in a given period of time
  • The tendency of the cardiovascular system to oppose blood flow is called Resistance
  • Velocity depends on the flow rate and the cross-sectional area
• Factors affecting resistance to fluid flow:

  • Resistance increases as the length of the tube increases
  • Resistance increases as the viscosity (thickness) of the fluid increases
  • Resistance decreases as the tube's radius increases
  • A decrease in blood vessel diameter is known as vasoconstriction
  • An increase in blood vessel diameter is called vasodilation
• The heart is divided by a central wall or septum

  • Each half functions as an independent pump that consists of an atrium and a ventricle
  • The two sides contract in a coordinated fashion
  • Atria receive blood returning to the heart, right from tissues, left from lungs
  • Ventricles pump blood away from the heart
• Heart valves:

  • Atrioventricular valves control blood flow between atria and ventricles
  • Semilunar valves control blood flow between the ventricles and the arteries
  • During ventricular contraction, the semilunar valves are open but the atrioventricular valves remain closed
  • During ventricular relaxation, the semilunar valves prevent blood from flowing back into the ventricles
• Cardiac muscle:

  • Contractile fibers are organized into sarcomeres
  • Attached to each other by intercalated discs containing desmosomes and gap junctions
  • Autorhythmic cells signal for contraction and have no organized sarcomeres
  • Action potential in cardiac myocytes is similar to neurons and skeletal muscle but longer
• Electrical conducting system of the heart:

  • Sinoatrial (SA) Node acts as the main heart pacemaker
  • Depolarization wave spreads rapidly via Internodal pathways to Atrioventricular (AV) node
  • Purkinje fibers conduct electrical signals rapidly down the Atrioventricular bundle/Bundle of His in the ventricular septum
• Electrocardiogram (ECG):

  • Records electrical activity of the heart
  • Consists of waves, segments, and intervals
  • 3 major waves on a normal ECG are P wave, QRS complex, and T wave
• Cardiac cycle:

  • Two main phases are diastole (relaxation) and systole (contraction)
  • Atria and ventricles do not contract and relax at the same time
  • Cardiac cycle begins with the atria and ventricles at rest
• Blood pressure:

  • Measured in mm Hg
  • Blood flow through the heart is governed by pressure
  • Fluid flows from high to low pressure
• Cardiac cycle & the Pressure-Volume Graph:

  • Represents changes in left ventricular pressure/volume during one cardiac cycle
  • Follows left heart & aortic pressures, left ventricular volume, & the ECG through 1 cardiac cycle
• Gallops, Clicks, and Murmurs:

  • Gallops are additional sounds recorded with very sensitive electronic stethoscopes or in certain abnormal conditions
  • Clicking sounds are made by abnormal movement of valves
  • Murmurs are "whoosh" sounds from blood leaking through incompletely closed or stenotic valves