LEC: CIRCULATORY SYSTEM

• Cardiovascular system


  The major function is transportation
• Heart


  • Managing blood supply
  • Producing blood pressure
  • Securing one-way blood flow
  • Transmitting blood
• Divisions of the circulatory system

  • Pulmonary circulation
  • Systemic circulation
• Layers of the heart tissue

  • Pericardium
  • Epicardium
  • Myocardium
  • Endocardium
• Pericardium


  The heart is enclosed in a double-walled sac called the pericardium and is the outermost layer of the heart
• Fibrous pericardium


  The loosely fitting superficial part of this sac that helps protect the heart and anchors it to surrounding structures
• Serous pericardium


  The slippery, two-layer pericardium where its parietal layer lines the interior of the fibrous pericardium
• Epicardium


  The visceral and outermost layer of the heart wall
• Myocardium


  The thick bundles of cardiac muscle twisted and whirled into ringlike arrangements that contract
• Endocardium


  The innermost layer of the heart, a thin, glistening sheet of endothelium that lines the heart chambers

  
• Endocardium


  • Consists of a very thin inner layer of endothelium and supporting connective tissue, a middle myoelastic layer of smooth muscle fibers and connective tissue, and a deep subendocardial layer that merges with the myocardium
  • Branches of the heart's impulse-conducting system are located in the subendocardial layer
• Myocardium


  • The thickest layer which consists of cardiac muscle with its fibers arranged spirally around each heart chamber
  • Much thicker in the ventricles, particularly the left ventricle

  
• Epicardium


  • A simple squamous mesothelium supported by a layer of loose connective tissue containing blood vessels and nerves
  • Corresponds to the visceral layer of the pericardium
  • Reflected back as the parietal layer lining the pericardium when large vessels enter and leave the heart
  • Cushions underlying structures with adipose tissue deposits and prevents friction within the pericardium with lubricant fluid
• Cardiac skeleton


  • Dense fibrous tissue that forms part of the interventricular and interatrial septa, surrounds all valves of the heart, and extends into the valve cusps and the chordae tendineae
  • Anchors and supports the heart valves
  • Provides firm points of insertion for cardiac muscle
  • Helps coordinate the heartbeat by acting as electrical insulation between atria and ventricles
• Chambers of the heart

  • Receiving chambers (atria)
  • Discharging chambers (ventricles)
  • Septum (interventricular septum, interatrial septum)
• Receiving chambers


  The two superior atria play a lighter role in the pumping activity of the heart
• Discharging chambers


  The two inferior, thick-walled ventricles are the actual pumps of the heart that propel blood out of the heart into circulation when they contract
• Septum


  The wall that divides the heart longitudinally, either the interventricular septum or the interatrial septum
• Associated great vessels

  • Superior and inferior vena cava
  • Pulmonary arteries
  • Pulmonary veins
  • Aorta
• Superior and inferior vena cava


  The heart receives relatively oxygen-poor blood from the veins of the body through these large vessels and pumps it through the pulmonary trunk

  
• Pulmonary arteries


  Carry blood to the lungs, where oxygen is picked up and carbon dioxide is unloaded
• Pulmonary veins


  Carry oxygen-rich blood from the lungs back to the left side of the heart
• Aorta


  Blood returned to the left side of the heart is pumped out into the aorta, from which the systemic arteries branch to supply body tissues
• Heart valves

  • Atrioventricular (AV) valves
  • Semilunar valves
• Atrioventricular (AV) valves


  Located between the atrial and ventricular chambers, prevent backflow into the atria when the ventricles contract
• Bicuspid (mitral) valve


  The left AV valve, consisting of two flaps or cusps of endocardium
• Tricuspid valve


  The right AV valve, consisting of three flaps
• Semilunar valves


  Guard the bases of the two large arteries leaving the ventricular chambers, including the pulmonary and aortic semilunar valves
• Pulmonary semilunar valve


  Lies between the right ventricle and the pulmonary artery, has three cusps
• Aortic semilunar valve


  Lies between the left ventricle and the aorta, has three cusps
• Components of the intrinsic conduction system

  • Cardiac muscle cells
  • Sinoatrial (SA) node
  • Atrioventricular (AV) node
  • AV bundle
  • Bundle branches
  • Purkinje fibers
• Intrinsic conduction system


  • Cardiac muscle cells can contract spontaneously and independently
  • Muscle cells in different areas have different rhythms
  • Sets the basic rhythm of the heart
  • Causes heart muscle depolarization in only one direction - from the atria to the ventricles
• Sinoatrial (SA) node


  Has the highest rate of depolarization, can start the beat and set the pace for the whole heart
• Pathway of the conduction system

  1. Depolarization wave initiated by SA node

  2. Passes through atrial myocardium

  3. Spreads to AV node, atria contract

  4. Passes rapidly through AV bundle

  5. Continues through bundle branches and Purkinje fibers, resulting in ventricular contraction and ejection
• Conducting system of the heart


  • Located within the subendocardial layer and adjacent myocardium
  • Consists of SA node, AV node, AV bundle, and subendocardial conducting network
  • Innervated by parasympathetic and sympathetic nerves that affect heart rate and rhythm
  • Purkinje fibers are pale-staining, larger than adjacent muscle fibers, with sparse myofibrils and much glycogen

  
• Cardiac cycle


  One complete heartbeat, including contraction (systole) and relaxation (diastole) of both atria and ventricles
• Systole


  Heart contraction
• Diastole


  Heart relaxation
• Cardiac cycle length


  Approximately 0.8 seconds, with the heart beating about 75 times per minute
• Phases of the cardiac cycle

  1. Mid-to-late diastole: Heart in relaxation, blood flowing passively into atria and ventricles

  2. Ventricular systole: Ventricular contraction, AV valves close

  3. Early diastole: Ventricles relax, semilunar valves close