THE NORMAL HEART AND BLOOD CIRCULATION
The
blood circulation is a system which carries oxygen from lungs to the
body cells and carbon dioxide from cells to lungs. The lungs take oxygen
from the air and eliminate carbon dioxide in the air. Oxygen is essential
for cells life when dioxide represents a waste of their metabolism.
-Fig. 1.1
diagrammatic representation of the heart. SVC = superior vena cava;
IVC = inferior vena cava; RA = right atrium; RV = right ventricle; PA
= pulmonary artery; PV = pulmonary veins; LA = left atrium; LV = left
ventricle; Ao = aorta-.
The heart is a muscle which works is to pump the blood in the arteries.
From the heart raises the aorta, an artery which carries the blood everywhere
in the body by branching out and forming a network of very little vessels
called capillaries vessels . The blood in the arteries is rich of oxygen
which is released to the cells in the capillaries and the carbon dioxide
carried to the lungs. Thee capillaries gather together in a network
of vessels of crescent size called veins which carried the blood to
the heart. All the veins converge in to major veins, the superior vena
cava and the inferior vena cava, which enter in the right atrium. The
blood which arrive from the cava veins to right atrium has a low content
of oxygen and a blue color and it is called venous blood.
From the right atrium the blood passes in through the tricuspid
valve in the right ventricle where it is pumped in the over the pulmonary
valve with a pressure of 25 mmHg in the pulmonary artery. The pulmonary
branches out in two arteries, one for each lung. In the pulmonary capillaries
the blood id loaded with oxygen releasing carbon dioxide in the air
present in the lung taking a red color an d the name of arteriosus blood.
Through the pulmonary veins this oxygenated blood reaches the left atrium
and, through the mitral valve, the left ventricle from where it is pumped
in the aorta through the aortic valve. The four cardiac valves allow
blood to flow only in one direction.
-Fig
1.2
diagrammatic representation of heart and normal blood circulation. The
right heart side is colored in blue because it receives blood poor in
oxygen which is dark red also called venous blood.
The left side is colored in red because receives from lungs blood full
of oxygen which is red light-.
The
left ventricle works at a higher pressure. In a child, the pressure
in left ventricle is around 100 mmHg when the pressure in the left ventricle
is 25 mmHg.
Normally the right and the left side of the heart are
completely separated by the atrial septum and ventricular septum.
Muscular activity like walking, carrying weights, running, increases the request of oxygen from the muscles. To supply the heart increases is rate and the volume of blood pumped out from the ventricles per minute. This allows to increase oxygen transport by 10 or 20 times if necessary.
The muscular part of the heart is called myocardium. It receives oxygen through the coronary circulation formed by the right and left coronary arteries which origin from the aorta, immediately above the aortic valve and run over myocardial surface branching out in the muscle. The coronary network is completed by the coronary veins which drive the blood first in the coronary sinus and then in the right atrium.
The heart lies in the chest, on the left side, under the sternum and is wrapped in a protective bag called pericardium. The superficial part of the heart is called epicardium, a thin membrane which lies over the myocardium, when the internal part of the heart and the valves are covered by a shining membrane called endocardium.
If
the other muscles of the body depend on the brain for their activity,
the heart has a autonomic pacemaker which generate the electrical impulse
which determine the heart contraction. This pacemaker is the sinoatrial
node which is located in the right atrium, near the superior vena cava.
It produces rhythmically an impulse which diffuses through the atrium
and reaches the atrio-ventricular node. The A-V node receives the impulse
drives it through the His bundle, the right and left bundle branches
to the myocardial cells which answer by contraction and pumping the
blood into the aorta and the pulmonary arteries. So as soon as the electrical
impulse reaches the ventricles the heart beats an d the blood runs everywhere
in the body.
-Fig. 1.3
The coronary arteries are colored in red. From the aorta, above the
aortic valve they proceed, branching out, over heart surface-.
-Fig.
1.4
Diagrammatic representation of the conduction system.
SA = sinoatrial node; AV = atrio-ventricular node; His = His or common bundle
which take the electrical impulse from atria to the ventricles branching
in right and left bundle branches-.
