The heart
  The
heart is like a pump that distributes blood around
throughout the body. It is composed of two parts
which have separate functions:
The right side of the heart receives venous blood (“dark” or blue blood),
which comes from all over the body, and propels it towards the lungs, where
it is enriched with oxygen and becomes the 'red blood'.
Each part has a receiving chamber, called the atrium, and an ejecting chamber,
called the ventricle. The ventricles have a thick muscular wall, the myocardium,
which contracts regularly (at rest, at a rate of 60 to 70 times a minute) to
pump the blood towards the various organs; as the blood flows in the arteries,
it produces a characteristic beat called the pulse.
The atria are separated from
the ventricles by valves (the tricuspid valve to the right and the mitral valve
to the left), which have a one-way action: when the ventricle contracts to
squeeze the blood out into the artery, they prevent the blood from flowing
backwards
into the atrium; there are also valves at the ventricle exits (the pulmonary
valve at the exit of the right ventricle and the aortic valve at the exit of
the left ventricle) which prevent the blood, during diastole, from “flowing
backwards” towards the ventricle after being squeezed out into the artery.
For the myocardium to function normally, it must, like all the other organs,
receive oxygen-rich blood; this blood is brought to it by the coronary arteries,
which are the first branches of the initial aorta, starting a few centimetres
from where it begins.
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When the heart
is functioning normally, the coronary arteries provide
a normal supply of blood to the myocardium and thus the
myocardium and valves function properly. |
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What happens when you have coronary artery disease?
To function, the heart needs energy and oxygen,
supplied by the blood in the coronary arteries. Coronary artery disease occurs
when one or more of these arteries is partially obstructed by atheromatous plaques. Angina pectoris may occur when the artery is more than 50% obstructed.
During exertion, the body needs more oxygen.
If the coronary arteries are occluded, the supply to the heart becomes insufficient
in the case of considerable exertion. The corresponding area of the myocardium
suffers from ischaemia and lack of oxygen, which causes pains: this is stable
angina pectoris (stable angina).
The artery may sometimes contract at the site of an atheromatous plaque or this plaque may rupture and the pain then occurs when the person is at rest, this is unstable angina.
Coronary artery disease does not always develop gradually. If an atheromatous plaque ruptures, it may suddenly cause an embolism or a thrombosis, the artery is then completely obstructed.
In both cases, the muscle cells are deprived of oxygen.
They rapidly exhaust their reserves and die; this is an infarction. Like a plant that dries up, just the “skeleton” of the necrosed cells remains, which lose their ability to contract.
The consequences of the infarction depend above all on its extent; the greater the “dead” area, the more heart function is reduced.
This is the most frequent cause of heart failure.
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