Cardiac Muscles Medical Presentation

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Published on : Mar 10, 2018 | Views : 1666 | Downloads : 1

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Cardiac Muscles Assignment group 662-671 Alia Elneanaey 669
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The Nodal cardiomyocyte Certain myocytes within the myocardium are adapted for the generation and conduction of electrical impulses from atria to ventricles. Usually, they are morphologically distinct from the normal myocardial cell; however, both can pass the signal for contraction - the flow of ions through intercellular gap junctions - to neigbouring cells. Cells of the cardiac conduction system are found in the: sinuatrial node internodal tracts atrioventricular node atrioventricular bundles Purkinje fibres the fibres that pass between these groups
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Sinoatrial node Location The SAN is located in the wall (myocardium) of the right atrium, laterally to the entrance of the superior vena cava in a region called the sinus venarum (hence sino- + atrial).
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Sinoatrial node Structure The cells of the SAN are spread out within a mesh of connective tissue, containing nerves, blood vessels, collagen and fat. The SAN cells are smaller and paler than the surrounding atrial cells, with the average cell being around 8 micrometers in diameter, and 20-30 micrometers in length. Unlike the atrial cells, SAN cells contain fewer mitochondria , have fewer myofibers and a smaller sarcoplasmic reticulum. This means that the SAN cells are less equipped to contract, compared to the atrial and ventricular cells.
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Sinoatrial node Histological image of the sinoatrial nodes. A indicates the sinoatrial nodal artery and N indicates the sinoatrial nodal cells.
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Sinoatrial node Low magnification stained image of the SA node and its surrounding tissue. The SA node surrounds the sinoatrial nodal artery, seen as the open lumen. Cardiac muscle cells of the right atrium can be seen to the left of the node, and fat tissue to the right.
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Sinoatrial node Function The main role of a sinoatrial node cell is to initiate action potentials, so that it can pass throughout the heart and cause contraction. Clinical hint sinus node dysfunction refers to a number of conditions causing physiologically inappropriate atrial rates. Symptoms may be minimal or include weakness, effort intolerance, palpitations, and syncope. Diagnosis is by ECG. Symptomatic patients require a pacemaker. Etiology : The most common cause of sinus node dysfunction is idiopathic SA node fibrosis, which may be accompanied by degeneration of lower elements of the conducting system.
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Atrioventricular node Location The AV node lies at the lower back section of the interatrial septum near the opening of the coronary sinus, which conducts the normal electrical impulse from the atria to the ventricles.
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Atrioventricular node Structure Its shape is almost spherical. The nodal cells contain less myofibrils than normal myocardial fibers, so they are lighter than myocardial fibers. There are two kinds of cells in the AVN; the “P” (pacemaker) cells and other cells with darker cytoplasm. The “P” cells are small and round or ovoid. They also have a large central nucleus. The amount of carbohydrates in the AVN cells is more than myocardial fibers. There is a loose framework of collagen fibers and a few of vessels and nerve fibers between the AV nodal cells.
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Atrioventricular node Histology of the atrioventricular node. A, In a transverse section through the atrioventricular septum, the atrioventricular node (arrows) abuts the central fibrous body (*) between the right atrium (RA) and the crest of the ventricular septum (VS). B, High magnification of the specialized muscle discloses a multidirectional array of myofibers with interstitial collagen. Masson's trichrome. MV, Mitral valve hinge-point; TV, tricuspid valve hinge-point.
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Atrioventricular node Function A wave of excitation spreads out from the sinoatrial node through the atria along specialized conduction channels. This activates the AV node. The cardiac conduction system (and AV node part of it) coordinates myocyte mechanical activity.
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