The Ventricles – “Power Pumpers”
In another article you’ll learn about the upper chambers of the heart called the Atria. This one will focus on the lower chambers of the heart – called the Ventricles.
The ventricles are the powerful pumping chambers of the heart. Located below the atria, there are two ventricles, right and left. Together, by their actions, these chambers maintain the circulation of blood to every single organ system of the body. They thus maintain LIFE itself !
The ventricles are hollow structures with a capacity of about 120 ml. in the adult. The left ventricle is ellipsoidal in shape while the right is a little more irregular, seeming to be wrapped around the left ventricle.
The ventricle walls are made up of a special kind of muscle called “Cardiac Muscle“. In many ways, this muscle is very much like the muscles in your arms that help you lift things, or in your legs that help you stand, walk and run …. with one major difference.
Heart muscle does not tire.
Day after day and week after week, month after month and year after year, for the entire life-time of a human being, the heart works without rest. In an average person’s life, the heart beats two and a half BILLION times with no respite.
And that is indeed fortunate, since without the circulation of blood, you would die within minutes!
If you haven’t read “The Heart – An Overview”, I suggest that you do it now, since what follows contains some terms that may otherwise seem strange to you.
The heart muscle in the wall of the ventricles works to pump blood out of the chamber. Earlier, we have seen how “impure” blood returns to the heart from the body through the great veins (called the vena cava) and enters the right atrium.
When the ventricle relaxes (stops contracting), the tricuspid valve opens and this impure blood now enters the right ventricle, until it is full. The heart muscle in the wall of the right ventricle then contracts (or shortens) and the blood inside the cavity is compressed. Under pressure, this blood flows into the lungs through the pulmonary arteries to get purified.
Similarly, “purified” blood returns from the lungs back to the heart. After collecting in the left atrium while the heart relaxes, this blood flows across the open mitral valve into the left ventricle. When the left ventricle fills up, it also contracts by shortening of the muscle in its wall. Once again, blood is pressurized and pushed into the great artery called the aorta from where it is distributed to the rest of the body.
Because the major function of the ventricles is to pump blood to the different parts of the body, the right and left ventricles have some special modifications that help them to better perform this work.
The lung is rather elastic and the branches of the blood vessels entering it (pulmonary arteries) are also thin walled. This makes them less resistant to fluid flowing within them – that is, they are more “compliant“. As a result, the right ventricle has a relatively easier job to do than the left. Since it needs less muscle and energy to carry out this work, the right ventricle is much thinner than the left.
The left ventricle, on the other hand, is the “work-horse” of the heart. In fact, it might be said with much truth that the left ventricle is the only chamber that is absolutely necessary for the heart to function. Each of the other three chambers are “dispensable”, and in fact in some disease states the heart works almost normally without them!
The left ventricle pumps blood into the arterial system, and is responsible for circulating blood to each part of the body, right from the top of the head to the tip of the toes. Also, the arteries are thicker and stiffer than the lung blood vessels and offer greater resistance to blood flow.
So the left ventricle has to work much harder than the right to carry out it’s duty. And the blood is pumped from the left ventricle with much greater force than on the right side …. almost like a blast of water from a hose connected to a fire hydrant!
The pressure of blood ejected from the left ventricle (as measured in the aorta) is almost 120 to 140 mm.of Hg (millimeters of mercury).
A larger bulk of heart muscle is needed to do this. That is why the left ventricle is thick walled. The wall measures around half an inch in thickness, almost three times as thick as the right. And in certain diseases which increase the load on the left ventricle (like high blood pressure, for instance), the left ventricle wall may become even an inch thick or more!
For every heart beat, each ventricle pumps out around 70 to 80 ml. of blood. Since the average normal heart rate is 70 to 80 beats per minute, the output of each ventricle per minute is around 5 liters. This is called the cardiac output and is the amount of blood that is made available to the body to meet it’s nutritional needs.
The internal architecture of the ventricles is slightly different, reflecting their development from different parts of the primitive “heart tube” in fetal life. The right ventricle has coarse muscle strands in its walls called “trabeculae“, while the interior of the left ventricle is smooth. This fact is important to the determination of ventricle-type by tests like the echocardiogram and EKG in certain types of heart defects.
To carry out it’s pumping action, the heart muscle itself needs nourishment. This is provided by a special group of arteries called the coronary arteries, which are described in detail in another article.
When there is disease of these coronary arteries, due to a condition called atherosclerosis, the heart is not able to function normally. This condition is called “heart failure“. If the ventricle wall muscle is totally deprived of blood supply (for any reason), it cannot receive nutrition and dies. This condition is called a myocardial infarction – or in common terms, a “heart attack“.
From this discussion, I hope you’ve understood the importance of the ventricles in the heart’s function. In the next article, we’ll learn about the walls (or “septa”) that separate the two sides of the heart.