The cardiac events that occur from the beginning of one
heart beat to the beginning of the next are called cardiac cycle.
1.To begin with, all the four chambers of heart are in a
relaxed state, i.e., they are in joint diastole. As the tricuspid and bicuspid
valves are open, blood from the pulmonary veins and vena cava flows into the
left and the right ventricle respectively through the left and the right atria.
The semilunar valves are close at this stage.
2.The SAN now generates an action potential which stimulates
both the atria to undergo a simultaneous contraction – the atrial systole. This
increases the flow of the blood into the ventricles by about 30 percent.
3.The action potential is conducted to the ventricular side
by the AVN and AV bundle from where the bundle of HIS transmits it through the
entire ventricular musculature. This causes the ventricular muscles to
contract. (ventricular systole), the atria undergo relaxation (diastole),
coinciding with the ventricular systole. Ventricular systole increases the
ventricular pressure causing the closure of tricuspid and bicuspid valves due
to attempted backflow of the blood into the atria. As the ventricular pressure
increases further, the semilunar valves guarding the pulmonary artery (right
side) and the aorta (left side) are forced open, allowing the blood in the
ventricles to flow through these vessels into the circulatory pathways.
4.The ventricles now relax (ventricular diastole) and the
ventricular pressure falls causing the closure of semilunar valves which
prevents the backflow of blood into the ventricles. As the ventricular pressure
declines further, the tricuspid and bicuspid valves are pushed open by the
pressure in the atria exerted by the blood which was being emptied into them by
the veins. The blood now once again moves freely to the ventricles. The
ventricles and atria are now again in a relaxed (joint diastole) state, as
earlier. Soon the SAN generates a new action potential and the events described
above are repeated in the sequence and the process continues.
5.This sequential event in the heart which is cyclically
repeated is called the cardiac cycle and it consists of systole and diastole of
both the atria and ventricles. As mentioned earlier, the heart beats 72 times
per minute, i.e., that many cardiac cycles are performed per minute. From this
it could be deduced that the duration of a cardiac cycle is 0.8 seconds.
Heart sounds –
S1 – first heart sound (lubb) produced due to closing of AV
valves at the beginning of ventricular systole.
S2 – second heart sound (dub) produced due to closing of
semilunar valves at the beginning of joint diastole.
*Some important points –
- ECG (Electro Cardio Gram) is a graphical representation of
the electrical activity of the heart during a cardiac cycle. To obtain a
standard ECG a patient is connected to the machine with three electrical leads
(one to each wrist and to the left ankle).
- Cardiac output = stroke volume*Heart beat
=70*72
= 5 liters (approximate 5040 ml.)
Disorders of cardiac cycle –
Before we study about disorders of cardiac cycle we should
know some general terms about it, so here we are telling you some of these –
+Blood pressure – pressure on blood vessels by blood
flow, is called blood pressure. It is majored by Spagnomanometer.
A general adult’s blood pressure should be – 120 –S.B.P. and
80 –D.B.P.
S.B.P. = systolic blood pressure and
D.B.P. = diastolic blood pressure
1.Hypertension – when
S.B.P.s value is greater than 140 and D.B.P.s value is greater than 90, this
state of cardiac cycle is called hypertension.
2.Hypotension – when
S.B.P.s value is less than 110 and D.B.P.s value is less than 70, this state of
cardiac cycle is called hypotension.
3.Atherosclerosis –
when blood vessels are blocked (not fully blocked) by deposition of
cholesterol, lipid etc. then blood pressure increases and this state is called
atherosclerosis.
4.CAD – when
cholesterol and lipid deposition took place in coronary artery, it is called
Coronary Artery Disease.
5.Arteroslerosis –
when calcium and cholesterol deposition on blood vessel’s wall then the wall of
blood vessel is get hard, so its elasticity is ended. And in the state of
hypertension blood vessel got damaged.
6.Angina pectoris –
when heart muscle doesn’t get enough O2 it started to pain, which is
called Angina pectoris.
7.Cardiac arrest (Heart
attack) – when heart stops beating or heart muscle damaged by
insufficient blood supply this is called cardiac arrest.
8.Heart failure –
it is also called Congestive Heart Failure, because in this state congestion in
lungs get higher. In this state heart can’t supply enough blood to different
body parts.
Don't walk as you are king, walk as you don't care who the king is .....!!
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