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.

http://coolbluez.t15.org