Cardiovascular

• Cardiovascular system


  A closed system of the heart and blood vessels

  
• Cardiovascular system


  • The heart pumps blood
  • Blood vessels allow blood to circulate to all parts of the body

  
• Functions of the cardiovascular system


  • Transport oxygen
  • Transport nutrients
  • Transport cell wastes
  • Transport hormones to and from cells
• Heart


  • Size of a human fist, weighing less than a pound
  • Located in the thoracic cavity, between the lungs in the inferior mediastinum
• Orientation of the heart


  • Apex is directed toward left hip and rests on the diaphragm
  • Base points toward right shoulder
• Coverings of the heart

  • Pericardium (a double-walled sac)
  • Fibrous pericardium
  • Serous pericardium (parietal and visceral layers)
  • Pericardial cavity
• Walls of the heart


  • Epicardium
  • Myocardium
  • Endocardium

  
• Chambers of the heart

  • Right atrium
  • Left atrium
  • Right ventricle
  • Left ventricle
• Atria


  • Receiving chambers that assist with filling the ventricles
  • Blood enters under low pressure
• Ventricles


  • Discharging chambers that are thick-walled pumps
  • During contraction, blood is propelled into circulation
• Interatrial septum


  Separates the two atria longitudinally
• Interventricular septum


  Separates the two ventricles longitudinally
• Heart functions as a double pump


  • Right side works as the pulmonary circuit pump
  • Left side works as the systemic circuit pump
• Pulmonary circulation


  1. Blood flows from the right side of the heart to the lungs and back to the left side of the heart

  2. Blood is pumped out of right side through the pulmonary trunk, which splits into pulmonary arteries and takes oxygen-poor blood to lungs

  3. Oxygen-rich blood returns to the heart from the lungs via pulmonary veins

  
• Systemic circulation


  1. Oxygen-rich blood returned to the left side of the heart is pumped out into the aorta

  2. Blood circulates to systemic arteries and to all body tissues

  3. Oxygen-poor blood returns to the right atrium via systemic veins, which empty blood into the superior or inferior vena cava

  
• Left ventricle


  Has thicker walls because it pumps blood to the body through the systemic circuit
• Heart valves


  Allow blood to flow in only one direction, to prevent backflow

  
• Atrioventricular (AV) valves


  • Left AV valve: bicuspid (mitral) valve
  • Right AV valve: tricuspid valve
• Semilunar valves


  • Pulmonary semilunar valve
  • Aortic semilunar valve
• Operation of AV valves

  1. Blood returning to the atria puts pressure against AV valves, forcing them open

  2. As the ventricles fill, AV valve cusps hang limply into ventricles

  3. Atria contract, forcing additional blood into ventricles, AV valves open

  4. Ventricles contract, forcing blood against AV valve cusps, AV valves close

  5. Chordae tendineae tighten, preventing valve cusps from everting into atria
• Operation of semilunar valves


  1. As ventricles contract and intraventricular pressure rises, blood is pushed up against semilunar valves, forcing them open

  2. As ventricles relax and intraventricular pressure falls, blood flows back from arteries, filling the cusps of semilunar valves and forcing them to close
• Cardiac circulation


  The heart has its own nourishing circulatory system consisting of coronary arteries, cardiac veins, and the coronary sinus

  
• Blood in the heart chambers does not nourish the myocardium
• Intrinsic conduction system of the heart

  • Cardiac muscle contracts spontaneously and independently of nerve impulses
  • Spontaneous contractions occur in a regular and continuous way
  • Atrial cells beat 60 times per minute
  • Ventricular cells beat 20-40 times per minute

  
• Intrinsic conduction system of the heart


  1. Cardiac muscle contracts spontaneously and independently of nerve impulses

  2. Spontaneous contractions occur in a regular and continuous way

  3. Atrial cells beat 60 times per minute

  4. Ventricular cells beat 20−40 times per minute

  5. Need a unifying control system—the intrinsic conduction system (nodal system)

  
• Intrinsic conduction system of the heart


  • Two systems regulate heart activity: Autonomic nervous system and Intrinsic conduction system, or the nodal system
  • Sets the heart rhythm
  • Composed of special nervous tissue
  • Ensures heart muscle depolarization in one direction only (atria to ventricles)
  • Enforces a heart rate of 75 beats per minute
• Components of the intrinsic conduction system


  1. Sinoatrial (SA) node

  2. Atrioventricular (AV) node

  3. Atrioventricular (AV) bundle (bundle of His) and bundle branches

  4. Purkinje fibers
• Sequence of the intrinsic conduction system

  1. The sinoatrial node (SA node) starts each heartbeat

  2. Impulse spreads through the atria to the AV node

  3. Atria contract

  4. At the AV node, the impulse is delayed briefly

  5. Impulse travels through the AV bundle, bundle branches, and Purkinje fibers

  6. Ventricles contract; blood is ejected from the heart
• Tachycardia


  Rapid heart rate, over 100 beats per minute
• Bradycardia


  Slow heart rate, less than 60 beats per minutes
• Cardiac cycle


  1. One complete heartbeat, in which both atria and ventricles contract and then relax

  2. Systole = contraction

  3. Diastole = relaxation

  4. Average heart rate is approximately 75 beats per minute

  5. Cardiac cycle length is normally 0.8 second
• Atrial diastole (ventricular filling)


  1. Heart is relaxed

  2. Pressure in heart is low

  3. Atrioventricular valves are open

  4. Blood flows passively into the atria and into ventricles

  5. Semilunar valves are closed
• Atrial systole


  1. Ventricles remain in diastole

  2. Atria contract

  3. Blood is forced into the ventricles to complete ventricular filling
• Isovolumetric contraction


  1. Atrial systole ends; ventricular systole begins

  2. Intraventricular pressure rises

  3. AV valves close

  4. For a moment, the ventricles are completely closed chambers
• Ventricular systole (ejection phase)


  1. Ventricles continue to contract

  2. Intraventricular pressure now surpasses the pressure in the major arteries leaving the heart

  3. Semilunar valves open

  4. Blood is ejected from the ventricles

  5. Atria are relaxed and filling with blood
• Isovolumetric relaxation


  1. Ventricular diastole begins

  2. Pressure falls below that in the major arteries

  3. Semilunar valves close

  4. For another moment, the ventricles are completely closed chambers

  5. When atrial pressure increases above intraventricular pressure, the AV valves open
• Lub


  Longer, louder heart sound caused by the closing of the AV valves
• Dup


  Short, sharp heart sound caused by the closing of the semilunar valves at the end of ventricular systole
• Cardiac output (CO)


  Amount of blood pumped by each side (ventricle) of the heart in 1 minute

  
• Stroke volume (SV)


  Volume of blood pumped by each ventricle in one contraction (each heartbeat)