Cardiovascular System

• The heart is about the size of your clenched fist and sits in the chest cavity between two lungs
• The main function of the heart is to be a pump but actually it acts as a double pump (left and right)
• Your heart beats about 100,000 times in one day and about 35 million times in a year. During an average lifetime, the human heart will beat more than 2.5 billion times
• Functional Anatomy of the Heart

  The human heart consists of four "chambers" - two atrial and two ventricular cavities which are separated by muscle walls and valves
• The heart is the pump station of the body and is responsible for circulating blood throughout the body
• The lungs are responsible for delivering oxygen to the blood, and the heart circulates the blood to the lungs and different parts of the body
• The histologic picture of the cardiac muscle shows that it is striated in the same manner as typical skeletal muscle. The cardiac muscle has typical myofibrils that contain actin and myosin filaments which interdigitate and slide along each other during the process of contraction
• Right heart

  Consists of right atrium and right ventricle and the tricuspid valve between them. Blood flow is coming from the superior and inferior vena cava, enters into the atrium and through the tricuspid valve enters into the right ventricle. After the right ventricle contraction through the pulmonary valve, the blood moves into the pulmonary trunk
• Action potentials can be conducted from the atrial syncytium into the ventricular syncytium by way of a specialized conductive system
• The cardiac muscle is a syncytium because of the specific contacts between the muscle cells called intercalated discs. The electrical resistance through the intercalated discs is only one four-hundredth the resistance through the outside membrane of the cardiac muscle fiber which allows relatively free diffusion of ions
• The heart is composed of three major types of cardiac muscle: atrial muscle, ventricular muscle, and specialized excitatory and conductive fibers
• Fresh, oxygen-rich air is brought to the lungs through the trachea every time that you take a breath
• The heart pumps about 1 million barrels of blood during an average lifetime - that's enough to fill more than 3 super tankers
• The blood in the left heart is oxygenized - this is arterial blood
• The specialized excitatory and conductive fibers are not involved in muscle contraction. They contain few contractile fibrils. These fibers provide an excitatory system for the heart and a transmission system for rapid conduction of the cardiac excitatory signal throughout the heart
• The heart is composed of two separate syncytiums, the atrium syncytium that constitutes the walls of the two atria and the ventricular syncytium that constitutes the walls of the two ventricles. These are separated from each other by fibrous tissue that surrounds the valvular openings between the atria and ventricles
• The heart's walls are made up of muscle that can squeeze or pump blood out every time that the organ "beats" or contracts
• Your body has about 5-6 liters of blood. This 5-6 liters of blood circulates through the body three times every minute. In one day, the blood travels a total of 19,000 km
• Left heart

  Consists of left atrium and left ventricle and the mitral valve between them. Blood flow is coming from the pulmonary veins into the left atrium and then, through the valve, enters the left ventricle, which pumps the blood into the aorta
• The atrial and ventricular muscles are very similar to skeletal muscle by its structure but the duration of contraction is much longer
• The action potentials travel from one cardiac muscle cell to another, pass the intercalated disks, with only a slight hindrance. Therefore, cardiac muscle cells are tightly bound that when one of these cells becomes excited, the action potential spreads to all of them
• Valves


  Close and open passively based on pressure gradients
• Heart muscle organization

  Atria contract ahead of ventricular contraction for effective heart pumping
• Resting membrane potential of cardiac muscle cells is -85 to -95
• SA node


  Generates action potential that spreads into the atria
• Papillary muscles


  Contract during ventricular contraction to prevent bulging of valves backward toward the atria
• AV node

  Located in the septal wall of the right atrium, connected to SA node by internodal pathway fibers
• Endocardium

  Covers the heart cavities
• Valves

  • AV valves prevent back-flow from ventricles to atria during systole
  • Semilunar valves prevent back-flow from aorta and pulmonary arteries into ventricles during diastole
• Components of the heart

  • Atrial syncytium
  • Ventricular syncytium
  • AV bundle
  • Endocardium
  • Pericardium
  • AV valves
  • Semilunar valves
  • Papillary muscles
  • Chordae tendineae
  • SA node
  • Internodal pathways
  • AV node
  • AV bundle of His
  • Bundle branches
  • Purkinje fibres
• Excitatory and Conductive System of the Heart

  Generates rhythmical impulses for heart muscle contraction
• Impulse of excitation

  Shifts through SA node, AV node, AV bundle, and Purkinje fibers to reach the working myocardium muscle cells
• SL valves

  Operate differently than AV valves due to high pressure causing rapid closure
• Pericardium

  Double-layered outer surface of the heart with pericardial liquor between the layers to facilitate muscle contraction and prevent rubbing
• AV bundle of His


  Located in the upper part of the interventricular wall, splits into branches reaching the heart apex and further into Purkinje fibres
• Cardiac muscle is refractory to restimulation during the action potential
• Resting membrane potential of cardiac muscle cells

  • -85 to -95 mV
• Impulse of excitation

  1. Generates in the SA node

  2. Through the AV node

  3. AV bundle

  4. Purkinje fibers shifts on the muscle cells of the working myocardium
• Pacemaker potential

  1. Gradual depolarization of the SA node bringing the membrane potential to threshold, leading to an action potential

  2. Provides the SA node with automaticity - the capacity for spontaneous rhythmical self-excitation

  3. Determines the rate of depolarization and the next action potential
• Duration of the plateau in cardiac muscle ensures a contraction lasting 20 to 50 times longer than in skeletal muscle