A wave in JVP is due to -

Ans. is 'a' i.e., Atrial systole JUGULAR VENOUS PULSE.a waveIt is the positive presystolic wave produced by right atrial contraction.x descenta wave is followed by the negative systolic wave the x' descent.The x descent is produced due to atrial relaxation.The atrial relaxation is produced as a result of ventricular contraction.c waveThe x descent is interrupted by second positive wave the 'c' wave.It is produced by bulging of the tricuspid valve into the right atriumQ during RVisolvolumetric contraction.v waveIt is the positive systolic wave.It result from increase in the blood volume in the venacava during systole, when the tricuspid valve is closed.y descentFollowing the "v wave" this is a negative descending limb referred to as the y descent or diastolic collapse.It is due to tricuspid valve opening and rapid inflow of blood into the right ventricle.So there areThree visible major positive waves (a,c and v) andTwo negative waves (x and y).