Heart Anatomy PDF

The Circulatory System Function: pumps and directs blood cells and substances to all tissues of the body Components: Blood and Lymphatic Vascular systems Total length of vessels – 100,000 and 150,000 kilometers. BLOOD VASCULAR SYSTEM COMPONENTS: Heart Arteries Capillaries...

The Circulatory System Function: pumps and directs blood cells and substances to all tissues of the body Components: Blood and Lymphatic Vascular systems Total length of vessels – 100,000 and 150,000 kilometers. BLOOD VASCULAR SYSTEM COMPONENTS: Heart Arteries Capillaries Veins  Pulmonary circulation Pulmonary circulation transports oxygen-poor blood from the right ventricle to the lungs, where blood picks up a new blood supply. Then it returns the oxygen-rich blood to the left atrium. Systemic circulation Systemic circulation carries oxygenated blood from the left ventricle, through the arteries, to the capillaries in the tissues of the body. From the tissue capillaries, the deoxygenated blood returns through a system of veins to the right atrium of the heart.  Lymphatic system Function: transport of interstitial fluid from the tissue to the draining lymph node (LN) and back to the venous system via the thoracic duct. Begins with the lymphatic capillaries , which are thin-walled, closed-ended tubules carrying lymph, that merge to form vessels of steadily increasing size. The largest lymph vessels connect with the blood vascular system and empty into the large veins near the heart  Anatomy of heart Located in mediastinum Shifted 2/3 left of midsternal line Weights 200-300gr  Endocardium Endothelial layer – the innermost layer composed of simple squamous epithelium Subendothelial Layer (Myoelastic layer)- connective tissue (collagen, elastic fibers) and smooth muscle cells Subendocardial layer – connective tissue layer of variable thickness lacking smooth muscle; contains conducting Purkinje fibers, small vessels, nerves  ENDOTHELIUM Functions: Semipermeable barrier, allowing certain substances to pass across the wall of blood vessels Produces antithrombotic factors: heparin, antithrombin, plasminogen activator, prostacyclin… Produces procoagulant factors: von Willebrand factor, thromboplastin… Produces growth factors: Vasculogenesis, angiogenesis Vascular tone: vasodilation (endothelin 1) and vasoconstriction (prostacyclin and nitric oxide) Inflammatory response, produces interleukins  Purkinje fibers ✓ Cardiac muscle cells joined by intercalated disks ✓ Purkinje fibres are more pale staining than contractile cardiac muscle fibers due to glycogen fiiling much of the cytoplasm and displacing myofibrils to the periphery ✓ Impulse conducting fibers ❖ Intercalated disks – junctional complexes connect the ends of cardiac muscle fibers; allow muscle action potentials to spread from one cardiac muscl efiber to another Ventricular endocardium is comprised of a single layer of endothelial cells (with flattened inconspicuous nuclei) and varying amounts of subendothelial connective tissue on the ventricular luminal surface.  Myocardium The thickest layer Cardiac muscle fibers are arranged spirally around each chamber The myocardium is much thicker in the walls of ventricles, particularly the left, than in the atrial walls  Unique and distinguishing characteristics of cardiac muscle Intercalated discs - dark staining transverse lines; Contain many junctional complexes for firm adhesion (desmosomes, fascia adherents); allow muscle action potentials to spread from one cardiac muscle fiber to another Single centrally located, pale nuclei Striations Cardiocytes are branched, allowing them to connect with several other cardiocytes, forming a network that facilitates coordinated contraction.  EPICARDIUM Visceral layer of the pericardium; membrane surrounding the heart Consists of: Loose connective tissue, adipose tissue Epicardium is lined by Mesothelial cells – simple squamous epithelium, that also lines the pericardial space.  Pericardial cavity Located between the visceral and parietal serous pericardium The mesothelial cells secrete a lubricant fluid that prevents friction  Skeleton of the heart Dense fibrous connective tissue Composed of 4 fibrous rings (each encircling a valve); 2 trigones (membranous portions of the interatrial, interventricular and atrioventricular septa) Providing structural support for cardiac muscle Provides electrical isolation between the atria and the ventricles  Mitral valve Tricuspid valve Papillary muscles Papillary muscles Mitral valve separates the left atrium from the left ventricle; has 2 leaflets (anterior and posterior) The atrioventricular valves (tricuspid and mitral ) are supported by 2 papillary muscles shown in this 4-chamber view of the heart. The valves Tricuspid valve separates the right atrium from the are suspended from annular rings and tethered to right ventricle; has 3 leaflets (anterior, posterior, and papillary muscles by tendinous cords septal) and 3 papillary muscles  Valve leaflet and cardiac skeleton The fibrous cardiac skeleton consists of dense irregular connective tissue, which anchors the valves and surrounds the two atrioventricular canals, maintaining their proper shape. (Masson Trichrome X20) Cusp of an atrioventricular valve (arrow) and attached chordae tendineae (CT). These structures are largely dense connective tissue (C) covered with a thin layer of endothelium. The collagen-rich connective tissue of the valves is stained pale blue here and is continuous with the fibrous ring of connective tissue at the base of the valves, which fills the endocardium between the atrium (A) and o Semilunar and atrioventricular valves share same trilaminar histoarchitecture Fibrosa - Dense collagenous layer in continuity with annular connective tissue Fibrosa Spongiosa - Central layer, composed of loose connective tissue, fibroblasts, and valvular interstitial cells Ventricularis - Most elastic fiber-rich layer with multiple layers of elastic tissue ; Lines ventricular surfaces of both semilunar and atrioventricular valves ; Spongiosa Also coats tendinous cords Ventricularis Chordae tendineae - cords that extend from the cusps of both atrio ventricular valves and attach to papillary muscles, preventing the valves from turning inside-out during ventricular contraction. Valves and cords are covered by the nonthrombogenic endothelium. The core is dense collagen that is continuous with the valve fibrosa layer. There is a coating of prominent elastic tissue covering the cords as well.  Conducting system of the heart Generates and propagates waves of depolarization that spread through the myocardium to stimulate rhythmic contractions. Both the sinoatrial (SA) node (pacemaker), in the right atrial wall, and the atrioventricular (AV) node, in the floor of the right atrium, consist of myocardial tissue that is difficult to distinguish histologically from surrounding cardiac muscle. The AV node is continuous with specialized bundles of cardiac muscle fibers, the AV bundles (of His) that run along the interventricular septum to the apex of the heart, where they branch further as conducting (Purkinje) fibers that extend into myocardium of the ventricles Pulmonary artery Aorta Superior vena cava Left pulmonary vein  Trichrome stain SA node ○ Compact and polyhedral myocytes surrounded by dense collagenous tissue ○ Sarcoplasm and cross striations less prominent than typical myocytes ○ Sinus nodal artery courses through sinus node Sinoatrial node Sinoatrial node Sinus node artery Atrial myocardium Sinoatrial node Sinoatrial node Trichrome stain  Nodal myocytes Trichrome stain Sinus node artery  Trichrome stain AV node Compact "bulb" of smaller polyhedral myocytes merging with larger stellate to spindled myocytes with vacuolar sarcoplasm toward bundle of His Arterioventricular nodal artery courses through AV node ○ Connective tissue surrounds node, "insulating" adjacent myocardium AV node Tricuspid valve leaflet  Dense collagenous connective tissue AV nodal artery Trichrome stain Conduction system myocytes (vacuolization of the sarcoplasm) Components of cardiac conducting system Sinoatrial (SA) node (pacemaker) – in the right atrial wall, near SVC; initiate impulses Atrioventricular (AV) node – in the floor of the right atrium, near AV valve; slightly smaller Atrioventricular bundle (bundle of His) Conducting (Purkinje) fibers  Purkinje fibers - subendocardial conducting network of myofibers Pale-staining fibers (due to glycogen), larger than the adjacent contractile muscle fibers  Autonomic innervation of heart Both parasympathetic and sympathetic neural components innervate the heart. Ganglionic nerve cells and nerve fibers are present in the regions close to the SA and AV nodes, where they affect heart rate and rhythm, such as during physical exercise and emotional stress. Stimulation of the parasympathetic division (vagus nerve) slows the heartbeat. Stimulation of the sympathetic nerve accelerates activity of the pacemaker.