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CARDIAC CYCLE
REMEMBER: systole = contraction , diastole = relaxation

1- atrial and ventricular diastole


blood returning from the large veins flows into the atria and then into the
ventricles if it from the body the tricuspid valves but if it comes from the lungs
so the blood goes through the bicuspid valve

2-atrial systole and ventricular diastole


it forces all the remaining blood in the atria to flow to the ventricles

3-ventricular systole and the atria diastole


it pumps the blood into the large arteries through the semilunar valves

cardiac output:

the volume of blood each VENTRICLES pumps per min
there are 2 factors for the cardiac output :
1- Heart rate (heart beats per min)
2- The stroke volume : the amount of blood each VENTRICLE pumps in a single
contraction _ average 70 ml and there are 72 beats per minute so it pumps the 5 L
in 1 min
-- during exerciecise it can increase x5

cardiac output = Heart rate X The stroke volume
Heart beats : the rhythmic heart beat are SPONTANEOUS they originate from the
cardic tissue itselt _not nerve_
So how it beats rthymic itself ?
There is 2 specialized bundle of thin cardic musle fiber
1- Sino-atrial node (SA): Buried in the wall of the right atrium near to its
connection with Vena Cava = sends impulses which stimulate the 2 atria to
contract
2- Atrio- ventricular node (AV):location _ at the junction between atria and
ventricular_
when the electric impulse reach it from SA it will spread through (Purkinje tissue)
from the interventricular septum to the ventrical walls to let them contract
The SA node connect with 2 nerves

1-the vagues nerve = decrease
2-Sympathetic = increase

Blood flow velocit
- if way the blood (arteries and veins ) go throw is the same diamitere so the velocity
of the blood at any point is the SAME
- if the blood go from wide to narrow it slows WHY?
The reason is that the no of the cappillaries is enormous , it is about 7 billion
and each one artery conveys blood to so many capillaries as result of that a
dermatic DECREASE of veloicty from arteries to capillaries as cap is 500
(0
...
contraction of a
heart VENTRICLE generates blood PRESSURE which exerts force in all
direction
The part of the force acting lenghtwise on the artry to let the blood flows from the
heart (the site of the highest pressure ) to the body
Anther part of this force acting sideways streches the artery
After the ventricle systole thr recoil(‫ )الرتداد‬of the arterial walls has a critical role
in the maintaining blood pressure so the blood flow throughtout the cardic cycle
The narrow diameter of the vessels generates resistance to flow
When it enters the veins the resistance disapper

Changes of the blood pressure during the cardic cycle
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The highest pressure is the SYSTOLE PRESSURE and it happen when the
ventircular contraction stretches the arteries = 120 mm/Hg
THE PRESSURE SURGE is caused due to the narrow openings of the arterioles
distortion the exit of the blood from the arteries
In heart contraction the blood enters the arteries faster than it can leave and the
vessles stratches cause of the rise in pressure
The lowest pressure is the DIASTOLIC PRESSURE =80 mm/Hg
Because the arteries remain pressureized throughout the cardic cycle blood flows
into cappilleries



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