Editor’s note: Physicians have a special place among the thinkers who have elaborated the argument for intelligent design. Perhaps that’s because, more than evolutionary biologists, they are familiar with the challenges of maintaining a functioning complex system, the human body. With that in mind, Evolution News & Views is delighted to present this series, “The Designed Body.” For the complete series, see here. Dr. Glicksman practices palliative medicine for a hospice organization.

Unlike the brain, the liver, and the kidneys, the heart has only one job to do. But oh, what a job! It is responsible for pumping the blood, which contains everything the cells need to live, to organs like the brain, the liver, and the kidneys.

But as with any job, there are certain parameters that define how well it is being done. A car’s job is to overcome the laws of nature to transport its driver from point A to point B in a certain amount of time. If it can’t do its job properly, it is likely due to problems like inadequate gas flow into the engine or poor cylinder compression. So too, there are certain parameters that must be met for the heart to do its job — otherwise, due to the laws of nature, the body won’t be able to function properly or may even die.

My last article in this series showed that since the heart is a muscle, it needs its own blood supply, which is provided by the coronary arteries. However, the laws of nature demand that the coronary arteries be wide enough to accommodate enough blood flow. A person with coronary artery disease has narrowing of the blood vessels and reduced blood flow to one or more regions of the myocardium.

Clinical experience tells us that people with this condition are not able to be as active as our earliest ancestors would have to have been to survive. When evolutionary biologists expound on how human life came into being, they must not only talk about how the heart looks, but also how it must work within the laws of nature to do its job properly. For, as important as having adequate and properly controlled coronary blood flow is for survival, so too is having proper valve function.

The heart is a muscular pump that is divided into a right and left side by a wall called the septum. The right side pumps blood to the lungs and the left side pumps blood to the rest of the body. Each side of the heart consists of a thin-walled upper chamber, called the atrium, and a more muscular lower chamber, called the ventricle.

There are “V” shaped, one-way valves that point in the direction of blood flow between the atria and the ventricles, and the ventricles and their outflow tracts. When the valves open, they direct blood forward to where it is supposed to go and when they close, they prevent blood from going backward to where it is not supposed to go. The triscuspid valve is located between the right atrium and ventricle and the pulmonary valve is located between the right ventricle and the main pulmonary artery. The mitral valve is located between the left atrium and ventricle and the aortic valve is located between the left ventricle and the aorta.

But how do the valves know when to open and close? Just as blood, because it is matter and has mass, must follow the laws of nature by being pumped throughout the body by the heart, so too, whether the heart valves stay open or closed is also a function of those same laws.

Imagine you are trying to get into a saloon through its swinging door. A heavily muscled bouncer is blocking you from the other side. What must you do to get inside? Pressure is defined as “the force per unit area applied in a direction perpendicular to the surface of an object”. To get into the saloon, you must apply more pressure to your side of the swinging door than the bouncer can apply to his.

When it comes to the heart and how its valves work within the laws of nature, it is important to remember that those laws state that the pressure inside a chamber with a given amount of fluid is inversely related to the size of the chamber. This means that with a given amount of blood inside an atrium or a ventricle, if its volume decreases, the pressure within it increases, and if its volume increases, the pressure within it decreases. Also, just like in meteorology, where air always moves from an area of higher to lower pressure, so too, when a pathway is available, blood always moves from an area of higher to lower pressure.

In the left side of the heart, at the beginning of systole, when the ventricle begins to contract, the pressure within it quickly rises above that of the left atrium, causing the mitral valve to close. This prevents blood from flowing back into the atrium. As systole continues, and contraction of the left ventricle peaks, the pressure within it rises above that of the aorta and forces the aortic valve to open. This allows blood from the left ventricle to flow out of the heart into the systemic circulation.

Then, as blood leaves the left ventricle and it begins to relax, the pressure within it quickly drops below that of the aorta, making the aortic valve snap shut to prevent blood from going back into the heart. Early in diastole, as the left ventricle relaxes further and venous blood from the lungs returns to the left atrium, the mitral valve opens because the pressure within the left atrium rises above that of the left ventricle.

Throughout diastole, the blood returning to the left side of the heart through the pulmonary veins enters the left ventricle through the left atrium by way of the open mitral valve. The same process takes place in the right side of the heart for the tricuspid and pulmonary valves as well. With diastole ending and systole beginning, the cardiac cycle starts over again and the heart valves open and close as dictated by the laws of nature.

Just as a clogged fuel line can reduce the flow of gas and compromise engine function, resulting in loss of power to a car, so too, diminished blood flow through any of the heart valves can compromise cardiac output resulting in loss of power to the body. In addition, just as leaky valves in one or more cylinders of a car engine can cause poor compression and loss of power, so too, leaky heart valves that allow blood to go back in the wrong direction, can reduce the efficiency of cardiac function and result in loss of power to the body.

If our earliest ancestors had any of these heart valve defects they never could have survived to reproduce. How do we know this? Valvular Heart Disease.

Just like the guy-wires used to stabilize a tent, or the mast of a ship, the mitral valve is attached to muscles anchored in the ventricle to strengthen it. However, degeneration of the valve or ischemic injury to its supporting muscles can weaken it and when the left ventricle contracts, instead of all of the blood going through the aortic valve into the aorta, some of it goes through the mitral valve back into the left atrium. This is called mitral regurgitation, and it reduces cardiac efficiency and output, particularly during exercise, because only some of the blood goes where it is supposed to go. Most people with this condition have fatigue, lack of energy and shortness of breath with limited exertion.

Anyone who has tried to blow up a balloon can appreciate the effect of obstruction to flow and the kind of force needed to overcome it. The aortic valve area is normally 3-4 cm². When degeneration, thickening, and hardening of the valve occurs, this causes its opening to narrow resulting in aortic stenosis.

The smaller the opening, the harder the left ventricle has to work to pump blood into the systemic circulation. An area of 1-1.5 cm² is considered moderate, and less than 1 cm², severe, aortic stenosis. Since blood flow to the systemic circulation is compromised, people who have this condition are prone to angina, dizziness and syncope (passing out), weakness, and shortness of breath, often with very limited activity.

It is important to keep in mind that in addition to mitral regurgitation and aortic stenosis, other less common valve problems, like mitral stenosis and aortic and tricuspid regurgitation, can occur. In fact, it is not unusual for one or more of these valve disorders to be present together.

In my last two articles we looked at how, when it comes to coronary blood flow and heart valve function, real numbers can lead to debility. But there are two more components of cardiac function that still need to be considered when trying to explain how our ancient ancestors had the ability to survive within the laws of nature: heart muscle contractility and the heart’s electrical system.

Keep in mind that in real life, it is not unusual for the heart to suffer from a defect involving all four of these factors, which together would have made survival impossible for our earliest ancestors.

Image: � Carl Keyes / Dollar Photo Club.