Cardiovascular System

• The cardiovascular system is a closed system of the heart and blood vessels
• The cardiovascular system


  • The heart pumps blood
  • Blood vessels allow blood to circulate to all parts of the body
• The functions of the cardiovascular system are to transport oxygen, nutrients, cell wastes, hormones to and from cells
• Heart


  Size of a human fist, weighing less than a pound
• Location of the heart

  Located in the thoracic cavity, between the lungs

  
• Orientation of the heart

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


  A double-walled sac
• Layers of the pericardium

  • Fibrous pericardium (loose and superficial)
  • Serous membrane (deep to the fibrous pericardium and composed of parietal pericardium and visceral pericardium/epicardium)
• Functions of the pericardium

  • Keeps the heart contained within the chest cavity
  • Prevents the heart from over expanding when blood volume increases
  • Limits heart motion
  • Reduces friction between the heart and surrounding tissues
  • Protects the heart against infection
• Layers of the heart wall

  • Epicardium (pericardium, outside layer)
  • Myocardium (middle layer, mostly cardiac muscle, the layer that contracts)
  • Endocardium (inner layer, known as endothelium, lines the inner heart chambers, covers heart valves and continuous with the endothelium of large blood vessels)
• Chambers of the heart

  • Atria (right and left, receiving chambers, assist with filling the ventricles, blood enters under low pressure)
  • Ventricles (right and left, discharging chambers, thick-walled pumps of the heart, during contraction blood is propelled into circulation)

  
• Interatrial septum


  Separates the two atria longitudinally
• Interventricular septum


  Separates the two ventricles longitudinally
• Pulmonary circulation


  Blood flows from the right side of the heart to the lungs and back to the left side of the heart
• 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 is pumped out of right side through the pulmonary trunk, which splits into pulmonary arteries and takes oxygen-poor blood to lungs

  2. 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
• Heart valves


  Allow blood to flow in only one direction, to prevent backflow
• Types of heart valves

  • Atrioventricular (AV) valves (between atria and ventricles, left AV valve: bicuspid/mitral valve, right AV valve: tricuspid valve)
  • Semilunar valves (between ventricle and artery, pulmonary semilunar valve, aortic semilunar valve)

  
• Functions of AV valves

  • Anchored the cusps in place by chordae tendineae to the walls of the ventricles
  • Open during heart relaxation, when blood passively fills the chambers
  • Closed during ventricular contraction

  
• Functions of semilunar valves


  • Closed during heart relaxation
  • Open during ventricular contraction

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

  Built into the heart tissue and sets its basic rhythm, composed of specialized tissue, causes heart muscle depolarization in one direction only (atria to ventricles)

  
• Components of the intrinsic conduction system

  • Sinoatrial (SA) node (located in the right atrium, serves as the heart's pacemaker)
  • Atrioventricular (AV) node (at the junction of the atria and ventricles)
  • Atrioventricular (AV) bundle (bundle of His) and bundle branches (in the interventricular septum)
  • Purkinje fibers (spread within the ventricle wall muscles)

  
• Pathway 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

  
• Homeostatic imbalances


  • Heart block (damage to AV node causes ventricles to beat at their own rate, which is much slower, some or all of the time)
  • Ischemia (lack of adequate blood supply to the heart muscles)
  • Fibrillation (rapid, uncoordinated quivering of the ventricles; makes the heart unable to pump blood, major cause of death from heart attack in adult)
  • Tachycardia (rapid heart rate, over 100 beats per minute)
  • Bradycardia (slow heart rate, less than 60 beats per minutes)

  
• Cardiac cycle


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

  
• Average heart rate is approximately 75 beats per minute
• Cardiac cycle length is normally 0.8 second
• 5 events of the cardiac cycle

  1. Atrial diastole (ventricular filling)

  2. Atrial systole

  3. Isovolumetric contraction

  4. Ventricular systole (ejection phase)

  5. Isovolumetric relaxation

  
• Heart sounds


  • 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

  
• Heart murmurs


  Sounds during heartbeat cycle (whooshing or swishing) made by turbulent blood in or near your heart, not a disease but may/can indicate an underlying heart problem
• 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), about 70 ml of blood is pumped out of the left ventricle with each heartbeat

  
• Heart rate (HR)


  Typically 75 beats per minute
• Cardiac output = Heart rate (75 beats/min) x Stroke volume (70 ml/beat) = 5250 ml/min = 5.25 L/min

  
• Regulation of stroke volume

  • 60% of blood in ventricles (about 70 ml/2 ounces) is pumped with each heartbeat
  • Starling's law of the heart - the critical factor controlling SV is how much cardiac muscle is stretched, the more the cardiac muscle is stretched, the stronger the contraction
  • Venous return is the important factor influencing the stretch of heart muscle
  • Muscular pump plays a major role in increasing the venous return

  
• Factors modifying basic heart rate

  • Neural (ANS) controls (sympathetic nervous system speeds heart rate, parasympathetic nervous system, primarily vagus nerve fibers, slow and steady the heart rate)
  • Hormones and ions (epinephrine and thyroxine speed heart rate, excess or lack of calcium, sodium, and potassium ions also modify heart activity)
  • Physical factors (age, gender, exercise, body temperature influence heart rate, resting heart rate in fetus 140-160 beats per minute, average adult females 72-80, males 64-72)

  
• Blood vessels form a closed vascular system that transports blood to the tissues and back to the heart
• Types of blood vessels

  • Arteries and arterioles (carry blood away from the heart)
  • Capillary beds (vessels that play a role in exchanges between tissues and blood)
  • Venules and veins (return blood toward the heart)