Cardiology

• Cardiovascular system


  Consists of blood vascular (cardiovascular) system and lymphatic vascular system
• Components of blood vascular (cardiovascular) system


  • Heart
  • Arteries
  • Capillaries
  • Veins

  
• Components of lymphatic vascular system


  • Lymph vessels
  • Lymph organs (Lymph nodes, tonsils & Spleen)
• Macro-vasculature


  Vessels with more than 0.1 mm in diameter, seen grossly
• Micro-vasculature


  Arterioles, capillaries and post-capillary venules, seen by microscope
• Heart


  Muscular, highly specialized portion of the vascular system, consists of 4 chambers
• Chambers of the heart


  • Right atrium
  • Left atrium
  • Right ventricle
  • Left ventricle
• Histological layers of the heart wall


  • Endocardium (inner layer)
  • Myocardium (middle muscular layer)
  • Epicardium (outer layer)

  
• Fibrous skeleton of the heart


  Fibrous central region that serves as base of the valves and site of origin and insertion of cardiac muscle cells
• Fibrous skeleton of the heart


  • Histologically composed of dense irregular connective tissue, with separated nodules of fibrocartilage

  
• Endocardium


  Lining of all internal surfaces of the heart, thicker in atria than ventricles

  
• Layers of endocardium


  • Endothelium (inner most layer)
  • Subendothelial layer (loose connective tissue)
  • Subendocardial layer (connective tissue with blood vessels, nerves, Purkinje fibers)
• Myocardium


  Composed of cylindrical branching involuntary cardiac muscle fibers, forms the main mass of the heart wall

  
• Myocardium


  • Thickness varies, thinnest in atria, thickest in left ventricle
• Epicardium


  Visceral pericardium, covered externally by simple squamous epithelium (mesothelium) and thin layer of connective tissue containing coronary vessels, nerves and adipose tissue
• Cardiac valves


  Flaps of tissue called cusps or leaflets, types are atrio-ventricular valves and semilunar valves
• Layers of cardiac valves


  • Fibrosa (dense irregular connective tissue)
  • Spongiosa (loose connective tissue)
  • Ventricularis (dense connective tissue with elastic fibers)
• Impulse-conducting system of the heart


  Sino-atrial node, atrio-ventricular node, atrio-ventricular bundle (bundle of His, right and left bundle branches, Purkinje fibers)

  
• Cells of impulse-conducting system


  • Modified cardiac muscle cells, except Purkinje fibers which are larger
• Purkinje fibers


  Modified cardiac muscle fibers that conduct impulses faster than ordinary heart muscle fibers, penetrate the myocardium of ventricles
• Light microscopic features of Purkinje fibers


  • Central nuclei (can be binucleated), cross striations, present in groups of two or more, generally larger and paler, clear perinuclear area
• Electron microscopic features of Purkinje fibers


  • Large amount of glycogen and mitochondria, less myofibrils tending to lie peripherally, less developed sarcoplasmic reticulum
• Innervation of the heart


  Parasympathetic nerve (vagus) ends near SA node, reduces heart rate; Sympathetic nerve ends near SA and AV nodes, increases heart rate; Free nerve endings between cardiac muscle fibers related to pain sensation
• Coronary artery obstruction


  Leads to myocardial infarction (necrosis of myocardium), a potentially life-threatening condition
• Partial/temporary coronary artery obstruction


  Leads to reduction of oxygen supply to myocardium, causing temporary pain (angina pectoris)
• The heart wall is composed of three layers, with the myocardium being the thickest
• The impulse conducting system is composed of modified cardiac muscle fibers
• Purkinje fibers are larger and paler than cardiac muscle fibers
• The cardiovascular system (II) lecture is presented by Dr. Lina Ali on 10/3/2024
• Blood vessels


  • Have three basic types of tissues arranged as layers from inside to outside: Endothelium, Smooth muscle cells, Connective tissue
• Mechanical factor


  Represented by blood pressure
• Metabolic factor


  Reflects the local needs of tissue
• Vascular endothelium


  • Lines the interior of blood and lymphatic vessels
  • Regulates inflammatory responses
  • Converts angiotensin I to angiotensin II
  • Converts bradykinin, serotonin, prostaglandins and noradrenaline to biologically inert compounds
  • Enhances lipolysis leading to formation of triglycerides and cholesterol
  • Produces endothelin, a vasoconstrictive factor
  • Produces nitric oxide, a relaxing agent
  • Produces vascular endothelial growth factors
  • Has anti-thrombogenic action
• Vascular smooth muscle cells


  • Found in all vessels, except capillaries and venules
  • Muscle fibers arranged in helical layers in tunica media
  • Each muscle is enclosed by basal lamina and connective tissue
• Vascular connective tissue


  • Variable amount present in different blood vessels
  • Collagen fibers type I in tunica adventitia, type III in tunica media, type IV in the basement membrane
  • Elastic fibers responsible for shrinkage of the expanded vascular wall, predominant in large arteries
  • Ground substance (ECM) affects the diffusion and permeability across the vessel wall
• Aging is associated with functional, structural and mechanical changes in arteries, including endothelial dysfunction, vascular remodeling, increased vascular stiffness and inflammation
• Layers of blood vessel wall


  • Tunica Intima (TI): Endothelium, Basal lamina, Subendothelial layer
  • Tunica Media (TM): Circular smooth muscle fibers, Elastic fibers, Reticular fibers, Fibroblast, Extracellular matrix
  • Tunica Adventitia (TA): Fibroelastic connective tissue, Fibroblast, Vasa vasorum
• Types of arteries


  • Large-size artery (Elastic/Conducting artery)
  • Medium-size artery (Muscular/Distributing artery)
  • Arteriole
• Large-size artery


  • TI relatively well developed, forms 10% of wall
  • TM very thick, characterized by fenestrated elastic lamellae, forms 70% of wall
  • TA loose connective tissue, forms 20% of wall
• Medium-size artery


  • TI thin layer with prominent thick internal elastic lamina
  • TM forms 50% of wall, consists of about 40 layers of circularly arranged smooth muscle fibers
  • TA forms 50% of wall, loose connective tissue with few vasa vasorum