Write notes on working of the heart of man.

Working of heart includes the following.
1. Generation and conduction of action potentials.
2. Cardiac cycle.
3. Double circulation.
1. Generation and conduction of action potentials :
* Sino-atrial node(SAN) generates action potential carried towards atrio-ventricular node(AVN).
AVN spreads it to ventricular muscles through Purkinje fibres.
2. Cardiac Cycle :
* It consists of 3 phases.
i) Atrial systole ii) Ventricular systole iii) Cardiac diastole
i. Atrial systole :
* The SAN generates an action potential which stimulates both the atria to contract.
* 30% of blood flows into ventricle during atrial systole.
ii. Ventricular Systole :
* Action potentials are conducted through AVN, bundle of his to Purkinje fibres and ventricular
muscles.
* Ventricular contraction increases the pressure causing the closure of AV valves.
* It results in the production of first heart sound known as ‘Lub’.
* Semilunar valves open and blood in ventricles flows into aortic arches.
iii. Cardiac Diastole :
* The ventricles now relax and the ventricular pressure falls causing the closure of the semi
lunar valves.
* This results in the production of second heart sound ‘Dub’.
* All the heart chambers are now in relaxed state. AV valves open and 70% of ventricular filling
occurs.
Stroke Volume :
* The volume of blood pumped out by each ventricle for each heart beat is 70ml.
Cardiac Output :
* The volume of blood pumped out by heart from each ventricle per minute.
* Cardiac output = Stroke volume × No. of beats per minute.
* 70ml × 72beats = 5040ml/min. or 5 litres.
3. Double circulation :
* Blood passes through the heart twice in two complete separate circulatory pathways called
pulmonary and systemic circulations.
* Pulmonary circulation : Deoxygenated blood from heart goes to lungs for oxygenation.
* Systemic circulation : It carries O₂ and nutrients from heart to body parts.