Cardiac cycle, cardiac output, ECG; double circulation; regulation of cardiac activity

CARDIAC CYCLE (1 Heat beat 1 systole & diastole)

• Cardiac cycle comprises of following steps :-
  a) Atrial systole
  (i) SA Node stimulation; triculpid and bicuspid valve open
  (b)Beginning of ventricular systole
• 
• AV node stimulation ; tricuspid and bicuspid valves closes to produce the first heart sound called "LUBB". (·15 sec) - Low pitch.
  (c) completion of ventricular systole
  (i) semi lunar valves open ;
  (d) Beginning of ventricular diastole
  (i) semi lunar valve closes to produce the second heart sound called "TUBB" (·1sec) - High pitch.
  (e) Completion of ventricular diastole
  (i) Again tricuspid and bicuspid valves open as the pressure in ventricles fall.

CARDIAC OUTPUT (Heart Output)

• Cardiac output is the amount of blood pumped by heart in one minute.
  [C.O] = heart beat rate × stroke volume
  = 72 beats/minute × 70 ml/beat
  = 5040 ml / minute = 5.5 L/min.

ECG

• It is measured in the form of graph that is been produced by the excitation of cardiac muscles which was firstly recorded by Waller
• Father of ECG is EINTHOVEN.
• 
• P → Atrial depolarization / contraction due to SA node activator.
  QRS complex → ventricular depolarization due to AV node activation.
  T → Ventricular repolarisation end of T wave → end of systole.

Double Circulation :-

• Both systemic circulation (greater circulation/peripheral circulation) and pulmonary circulation comprise double circulation.
• In systemic circulation oxygenated blood flows from left ventricle to all parts of body and deoxygenated blood flows from various parts to right atrium.
• Flow of blood from heart to lungs and vice versa constitute pulmonary circulation.

REGULATION OF CARDIAC ACTIVITY

• Neural regulation
  Cardiac centre (medulla oblengata)
• 
• Heart Rate decreases when the impulses receivers from aorta or carotid sinus.
• Heart rate increases when the impulses received from vena cava
• Hormonal regulation (influences SA Node)
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