ANATOMY AND PHYSIOLOGY OF HEART

HEART LOCATION RESTS ON THE DIAPHRAGM NEAR THE MIDLINE OF THE THORACIC CAVITY

LAYER OF THE HEART PERICARDIUM - membrane that surrounds and protect the heart –PARIETAL & VISCERAL LAYER EPICARDIUM (external) – thin layer of connective tissue and fat, protection. MYOCARDIUM (middle) – muscle tissue, contract ENDOCARDIUM (inner) – endothelial cell, smooth, blood collection and pumping.

HEART LAYER

HEART CHAMBER

HEART VALVE

SYSTEMIC AND PULMONARY CIRCULATION

CONDUCTION SYSTEM Inherent and rhythmical beat is due to autorhythmic fibers of the cardiac muscle. These fibers have 2 important function - Act as pace maker - Form the conduction system

CARDIAC CYCLE

ATRIAL SYSTOLE Lasts for 0.1 sec Atrial depolarization causes atrial systole (contract) It contributes a final 25ml of blood to each ventricle End of atrial systole is also end of ventricular diastole end-diastolic volume is 130 ml

VENTRICULAR SYSTOLE Lasts for 0.3 sec It is caused by ventricular depolarization (contract) Isovolumetric contraction lasts for 0.05 seconds when both the semilunar and atrioventricular valves are closed.

RELAXATION PERIOD Both atria and ventricles are relaxed. Lasts for 0.4 sec. When heart beats faster the relaxation time shortens. Ventricular repolarization causes ventricular diastole.

CARDIAC OUTPUT CO = STROKE VOLUME (SV) X HEART RATE (HR) FOR A RESTING ADULT CO = 70mL/beat x75beats/min = 5250 mL/min = 5.25 L/min *Stroke volume = volume of blood pumped from the left ventricle per beat, ~ 70mls=70kg. *Normal range CO = 4-8 L/min

HEART CONTRACTILITY Contractility is the ability of muscle cells to contract after depolarization. This ability depends on how much the muscle fibers are stretched at the end of diastole. Overstretching or under stretching these fibers alters contractility and the amount of blood pumped out of the ventricles. Physiologic characteristics of the conduction cells depend on :  Automaticity – ability to spontaneously generate and discharge electrical impulse  Excitability – ability of the cell to respond to an electrical impulse  Conductivity – ability to transmit an electrical impulse from one cell to the next  Rhythmicity  Contractility – ability of the cell to shorten and lengthen its fiber  Tonicity – normal presence of tone or tension in a muscle

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