Circulatory

• Anatomy of the heart

  • Conduction
  • Blood vessels
• 3 main layers of the heart

  • Endocardium
  • Myocardium
  • Epicardium
• Endocardium


  Glistening layer covering the inner surface of the atria and ventricles<|>Lined by endothelium, consists of polygonal squamous cells<|>Subendocardium - thin layer of loose connective tissue consisting of collagen fibers, elastic fibers, blood vessels, nerves, branches of impulse conducting portion of the heart
• Myocardium


  Forms the main mass of the heart<|>Consists of cardiac muscle cells<|>Strands of connective tissue contains a rich vascular network<|>Ordinary cardiac muscle fibers are designed for contraction
• Epicardium


  Visceral layer of the pericardium<|>Lined by single layer of mesothelial cells<|>Thin layer of connective tissue containing elastic fibers, blood vessels, nerves<|>Parietal layer of the pericardium contains elastic fibers, collagenous fibers, fibroblasts, fixed macrophages, covering layer of mesothelial cells
• Purkinje fibers


  Modified cardiac muscle fibers<|>1-2 nuclei, centrally located<|>Cytoplasm rich in mitochondria & glycogen<|>Impulse generating & conducting fibers of the heart<|>Myofibrils are reduced in number, limited to the periphery<|>More sarcoplasm with abundant glycogen<|>Nuclei are more rounded and often in groups of 1-2<|>Larger diameter<|>Lack the Transverse-tubules of cardiac muscle
• Impulse conducting system


  • SA node
  • AV node
  • Bundle of His
• SA node


  Pacemaker of the heart<|>Found in the region of sulcus terminalis
• AV node


  Located in the posterior lower part of the inter atrial septum below the posterior leaf of the aortic valve
• Bundle of His


  Located in the dense connective tissue of the trigonum fibrosum dextrum<|>Continuous into the septum membranoceum where it divides into 2 branches
• Both the parasympathetic & sympathetic divisions of the autonomic nervous system innervate the heart
• Sympathetic


  Increases the heart rate
• Parasympathetic


  Decreases the heart rate
• Cardiac skeleton


  Dense connective tissue<|>Main parts: septum membranaceum, fibrous portion of the interventricular septum, attachment for the free ends of some fibers of the heart muscle, trigona fibrosa, annuli fibrosa
• Blood vessels


  • Arteries
  • Capillaries
  • Veins
• 3 basic structural components of blood vessels

  • Endothelium
  • Smooth muscle fibers
  • Connective tissue
  • Ground substance
• Endothelium


  Simple squamous epithelium<|>Acts as a semipermeable barrier between blood plasma and interstitial tissue fluid<|>Produce vasoactive factors: nitric oxide, endothelins, vasoactive agents, conversion of circulating Angiotensin I to Angiotensin II
• Vascular endothelial growth factor (VEGF)


  Regulates the formation of the vascular system from embryonic mesenchyme (Vasculogenesis)<|>Promotes capillary outgrowth from existing vessels (Angiogenesis)
• Smooth muscle fibers


  Occur in the walls of all vessels larger than capillaries<|>Arranged helically<|>In arterioles and small arteries, it is frequently connected by gap junction
• Connective tissue


  Collagen fibers found throughout the wall: subendothelial layer, between muscle layer, outer layer
• Ground substance


  Contributes to the wall's physical properties<|>Affects permeability and diffusion of substances through the wall<|>Glycosaminoglycans concentration is higher in arterial than venous tissues
• Tunica intima


  • Innermost layer
  • Single layer of endothelial cells
  • Subendothelium - delicate loose connective tissue
  • Internal elastic membrane (lamina) - fenestrated elastic sheet that forms the boundary between the tunica intima and tunica media
• Tunica media


  Middle layer<|>Consist of circumferentially arranged smooth muscle cells and connective tissue: elastic fibers, collagen fibers, reticular fibers, proteoglycans, glycoproteins<|>External elastic lamina - found in larger vessels, separates the tunica media and tunica adventitia
• Tunica adventitia


  Outermost layer<|>Consist of loose connective tissue: type I collagen, elastic fibers, blood vessels, nerves<|>Vasa vasorum - blood vessels that provide metabolites to these layers<|>Nervi vasorum - nerves, larger in veins than arteries
• Types of arteries


  • Large arteries
  • Medium-sized arteries
  • Arterioles
• Large arteries


  Conducting arteries<|>Elastic arteries<|>Tunica intima - formed by polygonal endothelial cells, subendothelial layer with plenty of collagenous and elastic fibers, internal elastic membrane not prominent<|>Tunica media - formed by fenestrated elastic membranes arranged in concentric manner, smooth muscle, reticular fibers, proteoglycans & glycoproteins<|>Tunica adventitia - made up of loose connective tissue, collagenous and elastic fibers, blood vessels, nerves, presence of vasa vasorum
• Medium-sized arteries


  Also called muscular arteries<|>Distributing arteries<|>Tunica intima - formed of squamous endothelial cells, internal elastic membrane very prominent<|>Tunica media - composed of smooth muscle, elastic fibers, reticular fibers, proteoglycans
• Arterioles


  Average diameter is 0.5um<|>3 layers present: internal elastic membrane not prominent, tunica media composed of 1-2 layers of smooth muscle, tunica adventitia formed of loose connective tissue with few collagenous & elastic fibers
• Capillaries


  Walls composed of a single layer of endothelial cells resting on a basement membrane & thin adventitia of connective tissue fibers<|>Continuous (tight) capillaries - most common, characterized by distinct continuity of endothelial cells with tight junctions<|>Fenestrated capillaries - characterized by fenestrae through the squamous endothelial cells which are closed by diaphragms, basal lamina is continuous
• Veins


  Thin walled vessels<|>Carry blood from the capillary networks towards the heart<|>Characterized by a thickest coat of tunica adventitia<|>Wider lumen<|>Valves may be present in some veins<|>Internal elastic membrane absent except in large veins<|>Vasa vasorum present
• Large veins


  • SVC & IVC
  • Internal jugular vein
  • Innominate vein
  • Portal vein
  • Splenic vein
  • Superior mesenteric vein
  • External iliac vein
  • Renal vein
  • Azygos vein