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Heart & It’s Rhythmical Contractions
Dr. Wasif Haq
General Anatomy of Heart• Myogenic organ, involved in blood
circulation.• Pericardial sac encloses the heart.• Three layers; Epicardium, Myocardium &
Endocardium.• 4 chambers; 2 receiving & 2 discharging
chambers.• Right side- Pulmonary blood flow.• Left side- Systemic blood flow.
Chamber & Valvular Anatomy• Right atrium collects deoxygenated blood
from Vena Cavas.• Tricuspid valve= Right atrium & right
ventricle, pushes blood towards ventricle.• Pulmonary valves= Right ventricle &
pulmonary arteries.• Left atrium receives oxygenated blood
from lungs.• Bicuspid valves/ Mitral= Left atrium &
ventricle.• Aortic valve= Left ventricle & aorta.
Aspects of Cardiac Muscles• Involuntary, striated muscle fibers.
• 1. Sarcomere: Contractile unit, thick (Myosin) & thin (Actin, Troponin & Tropomyosin) filaments.
• 2. Intercalated disk: Junctions occurring at end of cardiac cells, contraction as single unit.
• 3. Gap junctions: Present at intercalated disk, rapid electrical impulse transmission.
• 4. Mitochondria: Abundant quantity.• 5. T-tubules: Carry action potential to inside
of cell, well developed in ventricles.• 6. Sarcoplasmic reticulum: Storage of Ca++
ions.
Syncytium• Syncytium= Multi-nucleate cells resulting
from multiple cell fusion into an aggregate mass.
• Cardiac cells are interconnected, rapid excitation.
• Two types: a. Atrial syncytium, b. Ventricular syncytium.
• No transmission between two syncytiums because of separation by fibrous tissue except at A.V. bundle.
Rhythmical Contraction• S.A. Node
• Internodal Pathways
• A.V. Node
• A.V. bundle (Bundle of His)
• Bundle branches (2 left & 1 right)
• Purkinjee fibers.
Sinoatrial Node• Pacemaker.• Normal, rhythmical impulse generation.• Location: Superior, posterolateral wall of
right atrium, lateral to superior vena cava opening.
• Directly connected to atrial muscle fibers.
Internodal pathway• Anterior, middle & posterior internodal
pathways.• Impulse reaches A.V. node through
internodal pathway.
A.V. Node• Delay of impulse conduction from atria to
ventricles.• Allowing for ventricular filling before
ventricular contraction.• Delay occurs due to lesser gap junctions
causing greater resistance to conduction.
A.V. Bundle/ Bundle of His• Fibrous insulation all over atria &
ventricles except at A.V. bundle.• Very rapid conduction.• Impulse unidirectional only.
Bundle Branches• The bundle of His branches into the three
bundle branches: the right, left anterior and left posterior bundle branches .
• The bundles give rise to thin filaments known as Purkinje fibers.
Purkinjee Fibers• Rapid transmission of action potential by
Purkinjee fibers.• Few myofibrils, little tendency to contract.• Impulse from Purkinjee fibers travels to
ventricular muscle mass by ventricular muscle fibers themselves.
Take Home MessageIf having wisdom makes human proud, arrogant and ignorant towards his Creator then such wisdom is certainly and surely foolishness.
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