15 December 2017
THE HEART; HOW IT WORKS
A pump for life
The heart is a muscular organ. The size of an adult heart can be compared to that of a clenched fist. The heart is located in the center of the chest, between the two lungs. It is an amazing and resilient organ that pumps blood throughout the whole body.
It is a pump for life that starts pumping on the 14th day of fetal life.
The heart has a fibrous skeleton, valves and an electrical network.
The interior is composed of four hollow cavities. The upper cavities are called the atria and the two lower cavities are the ventricles.
A division between those cavities (called septum) makes it possible to have a right heart and a left heart, each one having one atrium and one ventricle.
Large blood vessels, arteries and veins are connected to the heart, allowing the blood to circulate to and from all the organs in the body. The blood supply to the heart itself is composed of two coronary arteries, on the right and on the left side of the heart.
The right cavities (right heart) receive the venous blood that collected waste and carbon dioxide (CO2) from the body. Then, they send this blood towards the lungs where the CO2 is expelled and replaced with the oxygen that is required for the body functions.
The left cavities (left heart) receive blood from the lungs. This blood now contains oxygen. That oxygenated blood will be distributed to the body organs and muscles by the main artery called the aorta.
Generally speaking, the veins are the blood vessels that transport the blood of the body to the heart. The arteries are the blood vessels that transport the blood from the heart to the body organs.
The right atrium is located above the tricuspid valve. The right ventricle is below it.
The left atrium is located above the mitral valve. The left ventricle is below it.
The valves separate the cavities, atria and ventricles, and the cavities of the large vessels that go in and come out of the heart.
The right atrium is separated from the right ventricle by the tricuspid valve. The right ventricle is separated from the pulmonary artery by the pulmonary valve.
The left atrium is separated from the left ventricle by the mitral valve, whereas the left ventricle is separated from the aorta by the aortic valve. There four valves make it possible to always have the blood circulate in one direction.
Working as a pump
The blood containing CO2 enters the right atrium by way of large veins from the top and the bottom of the body, the superior and inferior vena cava.
Blood fills the atrium, the pressure of the liquid makes the tricuspid valve open and blood enters the right ventricle.
The right ventricle then contracts and expels blood through the pulmonary valve to the pulmonary artery.
The pulmonary artery brings the "used" blood to the lungs where it gets rid of CO2 and gets oxygen.
In the lungs, the blood releases CO2 and refills with oxygen. CO2 is expelled from the body by the breathing process.
Oxygenated blood returns to the left atrium by way of the pulmonary veins.
The mitral valve opens under the pressure, and blood fills the left ventricle.
When the left ventricle contracts, blood is expelled through the aortic valve to the aorta.
Then the oxygenated blood empties its way to feed all the body organs and muscles from the aorta.
And then, the cycle starts again… it’s the cardiac cycle.
A red blood cell will require about 60 cardiac cycles to complete the pulmonary circuit and the rest of the body.
‘’ Great' ‘and ‘’ small’ ‘circulation
It is said that the right heart deals with the small circulation (only to the lungs) and that the left heart with the great circulation (to the rest of the body).
This is reflected in the structure of the ventricles: the right ventricle muscle is thinner than the muscle of the left ventricle, as it must generate greater effort to circulate the blood around the body
Perfect architecture for its function
The heart is an ingeniously constructed pump. Its anatomy is integrated into its function. The electrical system works so that the contraction of the ventricles moves from the bottom to the top, where the valves to the lungs and the aorta are located.
A bear runs after you!
The heart is sensitive to the needs for the body.
Should you need more oxygen in your muscles in order to escape a wild animal?
Not a problem, your heart is able to quintuple (x5) the blood flow in a few seconds. It will react to this intense need by tripling its rate and doubling its contraction force.