All the cells in the body consist of matter. They each need oxygen, water, glucose and other chemicals to live, grow and work properly. The respiratory system brings in oxygen and the gastrointestinal system brings in water, glucose and the other atoms and molecules the body needs to live. These important chemicals are put into the bloodstream so they can be transported to the cells in the tissues. However, like all matter, blood has mass and therefore is subject to the laws of nature. It is subject to inertia, the force that keeps an object still if it is at rest. The more mass an object has the more energy is needed to move it or change its speed. The heart is a muscular organ that uses energy to pump the blood with enough pressure throughout the body so you can live and stay active. Blood is also subject to gravity, the force that makes an object fall to the ground. The higher something is above the heart, the more energy is needed to pump blood to it. When you stand up quickly your heart must contract harder and faster to pump enough blood to your brain so you donít pass out. Finally, just as friction slows the movement of an object on the ground, blood meets its counterpart, vascular resistance, in the blood vessels. As the larger arteries branch into smaller ones, and from there into even smaller arterioles, the flow of blood comes up against vascular resistance. Think of blood travelling through the arterial system to the tissues like rush hour traffic on a highway as all the cars and trucks slow down to exit to their destinations. However, in the case of blood flow, itís like all of the vehicles are trying to enter the exit ramps at the same time. Obviously, most of them are going to meet resistance and will have to slow down or stop and wait their turn. Having increasingly smaller sized arterial blood vessels results in vascular resistance which slows the blood down significantly by the time it reaches the capillaries in the tissues. By applying its understanding of the relationship between blood pressure, blood flow and vascular resistance, your body is able to control the blood flow to its various organs and tissues so that it matches their energy needs no matter what it might be doing. Letís review what your body must already know about these natural phenomena and then see how it takes control so you can live within the laws of nature.
Pressure is defined as “the force per unit area applied in a direction perpendicular to the surface of an object”. In other words, pressure is the weight or stress applied at a right angle to a given surface. Press your thumb, first lightly, and then harder and harder against the back of your wrist and youíll see what I mean. Think about how much energy you have to use as you perform this action. The heart uses energy to pump blood into the arterial system so it can flow to the capillaries to feed the tissues of the body. After the blood leaves the capillaries, it flows into the venous system back to the heart. http://www.youtube.com/watch?v=PgI80Ue-AMo As the blood circulates throughout the cardiovascular system it exerts pressure against the walls of the different blood vessels in which it is contained. This can be a large or small artery, an arteriole, a capillary, a venule, or a small or large vein. In general, a personís blood pressure is understood to be the force of blood exerted against the walls of a large artery, like the brachial artery in the arm. This is measured by inflating a cuff that is wrapped around the upper arm until there is no blood flow and then, as the pressure in the cuff is reduced, listening at the inner aspect of the elbow with a stethoscope for the return of blood flow. Since the heart contracts to pump blood out, and then relaxes to fill up again, the blood pressure in the brachial artery ranges between a higher one, called the systolic pressure, and a lower one called the diastolic pressure. The blood pressure is usually measured in units called “millimeters of mercury” (mmHg) and a normal reading is about 120 mmHg/80 mmHg, which is usually expressed simply as 120/80. The mean (average) blood pressure can be calculated by taking 1/3 of the systolic pressure and adding it to 2/3 of the diastolic pressure, since the heart is in the contraction (systolic) phase about 1/3 of the time and the relaxation (diastolic) phase about 2/3 of the time. A brachial artery blood pressure of 120/80 results in a mean blood pressure of about 95 mmHg. http://homepage.smc.edu/wissmann_paul/anatomy1/1bloodpressure.html As the blood flows through the different blood vessels of the cardiovascular system and uses up energy, the pressure within them gradually drops. When the blood first leaves the left ventricle into the systemic circulation the mean blood pressure is about 100 mmHg. As it moves into the brachial artery it has dropped to about 95 mmHg, and by the time it enters the arterioles it is about 85 mmHg. From here to when it actually enters the capillaries the blood pressure usually has dropped to about 30 Ė 35 mmHg. And by the time the blood travels through the capillaries and the veins back to the right side of the heart the blood pressure is usually about 0-5 mmHg.
So, the heart imparts enough energy to the blood to move it, against the random forces of nature such as inertia, gravity and vascular resistance (friction), through the cardiovascular system. This energy causes the blood to exert a pressure against the walls of the different blood vessels through which it flows. As the blood travels from the left side of the heart, through the arterial system, the capillaries in the tissues, the veins, and back to the right side of the heart, this energy is gradually used up. This gradual reduction in energy causes the pressure exerted by the blood against the walls of the successive blood vessels to decrease as it flows through the circulation.
Blood flow can be defined as “the volume of blood that passes a given point in the circulation within a certain amount of time”. It is usually measured in “milliliters per minute” (mL/min). At rest, the heart pumps out about 5,000 mL/min of blood. This is called the cardiac output. One can then say that, at rest, the total systemic blood flow throughout the body is about 5 L/min (Liters/minute). At extreme levels of activity the heart pumps much harder and faster and is usually able to quintuple its output to about 25 L/min of blood flow. This amount applies to the right side of the heart, which pumps blood to the lungs so it can pick up oxygen and drop off carbon dioxide, and the left side of the heart that pumps it to the rest of the organs and tissues of the body.
The blood flow to a given organ or tissue is dependent, not only on its mass, but also its energy needs, in other words, what itís doing. The brain of a 70 Kg man has a mass of only 1500 gm, about 2% of the total. But at rest the brain receives 750 mL/min, or 15% of his total cardiac output (750/5,000 = 0.15). The brain needs a large amount of blood flow, over and above what one would expect for its size, because even though the body may be physically at rest the brain is always working. It must maintain your consciousness, integrate billions of bits of data about your body function and whatís going on around you and control vital functions like your breathing and circulation. In fact, no matter how little or how much you exert yourself, the amount of blood flow to your brain must stay at about 750 mL/min for it to work properly. The heart, with a mass of only about 300 gm, less than 1% of the bodyís total, is another organ that must constantly work, even when the body is at rest. At rest, the heart receives about 250 mL/min of the cardiac output, or about 5% of the total blood flow (250/5,000 = 0.05). In contrast, the skeletal muscle, which is connected to and moves our bones so we can be active, with a mass of about 30 Kg, or 40% of the bodyís total, at rest, receives only 15% of the cardiac output, or 750 mL/min. So far we have accounted for about 35% of the total systemic blood flow that comes out of the left side of the heart every minute when the body is at rest. The remaining blood flow mostly goes to the liver and gastrointestinal system (25%), the kidneys (20%), the fat (5%), the bones (5%), the skin (5%), and the lungs (2.5%).
When the body is very active, such as when our hominid ancestors were running to find food, or trying to avoid becoming food, the cardiac output is about 25L/min. The majority of this quintupling of blood flow must go to the skeletal muscle and the heart muscle so the body can do what it needs to do to survive. In fact, compared to what it receives at rest, during extreme physical exertion the amount of blood flow to the skeletal muscle increases about 28-fold to about 21 L/min, or 85% of the total cardiac output. During this activity the blood flow to the heart muscle quadruples, going from 250 mL/min at rest, to about 1,000 mL/min or about 4% of the total cardiac output. The brain is able to maintain its usual blood flow of 750 mL/min but most of the other organs and tissues of the body see a decrease in blood flow. For example, the blood flow to the liver and gastrointestinal system drops about 60%, going from about 1.25 L/min to about 500 mL/min (only 2% of the cardiac output), and the blood flow to the kidneys drops 75%, going from 1,000 mL/min to only 250 mL/min (only 1% of the cardiac output).
So, at rest, the cardiac output of 5 L/min, and with extreme exercise 25 L/min, from the left ventricle of the heart represents the total systemic blood flow. The amount of blood flow that is needed by a given organ or tissue is related to, not only its mass, but also its activity level. Even when the body is physically at rest, organs like the brain and the heart must continue to work, and therefore must receive much more blood flow than their size would seem to demand, whereas the skeletal muscle receives much less. Vital organs, like the brain and the heart, must always have enough blood flow, no matter the circumstances, so they can meet their energy needs to allow the body to stay alive. However, it is important to remember that when our hominid ancestors were very physically active, either running after food or trying to avoid becoming food, their cardiac output would have risen to about 25 L/min. In order to be able to do what they needed to do to survive, most of this increase in systemic blood flow had to be directed to their heart and skeletal muscle while the blood flow to their brains was maintained.
Vascular resistance can be defined as “the force that slows the blood flow within the vessels of the cardiovascular system”. Remember, at rest, a typical blood pressure in the brachial artery is 120 mmHg/80 mmHg, which translates into an average blood pressure of 95 mmHg, and the total systemic blood flow is 5 liters/min. However, unlike blood pressure and blood flow, the vascular resistance cannot be measured directly. But if we consider what happens to the energy present within the blood vessels as the blood flows within them, we can identify a relationship between blood pressure, blood flow and vascular resistance. This will allow us to see how each of these affects each other. Blood enters a blood vessel with a certain amount of energy. This energy is reflected in how much pressure it exerts against the walls. As the blood travels along the vessel some of this energy is used up for blood flow, and some of it is taken up by the resistance to blood flow within the vessel. This difference in the pressure from when the blood first enters and then leaves the blood vessel is called the perfusion pressure, since it is the driving force that pushes the blood through it. So, by the time the blood leaves a particular blood vessel and branches into other ones, the pressure it exerts against its walls has been reduced due to the blood flow and vascular resistance that has taken place. Since these two processes occur at the same time the relationship between the perfusion pressure, the blood flow and the vascular resistance can be expressed by the equation P = Q x R, where P is the perfusion pressure, Q is the blood flow, and R is the vascular resistance.
This may not mean much to you, but it does mean a lot to your body. For, by understanding this relationship the flow of blood to its different organs can be controlled so that life may continue. Experience teaches us that when we work harder, so does our heart and our muscles. In fact, without this happening our hominid ancestors would never have been able to survive. One then has to wonder how the body makes sure that enough of the extra blood that is being pumped by the heart goes to where it is really needed, the skeletal muscles and the heart muscle. By taking a closer look at the relationship between perfusion pressure, blood flow and vascular resistance we can figure out what the human body, by necessity, has known since it first appeared on the world scene. For without this knowledge, and our bodyís ability to use it properly, we would not exist.
Adequate Blood Flow = Proper Organ Function = Life
Your carís gas tank may be full, but if the fuel line is clogged so that the gas cannot flow into the engine, your car is as good as dead. The same can be said for the human body. Since each of our cells needs enough oxygen, water and glucose to live, if there isnít enough blood flowing to them to provide them with these, and other necessities, they are as good as dead. And if a vital organ, like the brain, or the heart, has a major reduction in blood flow due to blockages in some of the arteries feeding it, then, once again, you are as good as dead. Since it is really blood flow (Q) that is the bodyís main concern for survival it is important then to notice that if P = Q x R, then to solve for Q (blood flow) we can turn this equation around and see that Q = P/R. This means that blood flow (Q) is directly related to the perfusion pressure (P) and is inversely related to the vascular resistance (R). In other words, if the perfusion pressure increases, so does the blood flow and if the perfusion pressure decreases, then blood flow drops as well. Whereas, if the vascular resistance increases, the blood flow drops and if the vascular resistance decreases, then blood flow rises. This should make sense because the energy that causes blood to exert pressure against the walls of the blood vessel is the driving force for blood flow. Therefore, an increase in the perfusion pressure should result in an increase in blood flow while a decrease in the perfusion pressure should result in less blood flow. Also, since vascular resistance, by definition, is the force that slows blood flow, it should make sense then that an increase in vascular resistance should result in less blood flow and a decrease in vascular resistance should result in more blood flow.
In real life the blood flow to the different organs and tissues of the body is always changing due to there being constant variations in the blood pressure. This can happen for many different reasons. It can be due to changes in the bodyís position with respect to gravity. Standing up makes more blood drop to your legs and away from your heart. Lying down makes more blood return from your legs to your heart. Bending over makes more blood rush to your head. All three of these maneuvers, and others like them, affect where the blood in the circulation naturally tends go, which can affect the blood pressure. The changes in blood pressure can also be due to your fluid balance as well. If youíve been working hard outside, sweating in the heat, not having had a chance to replace your fluid loss, then your body is low in water. The total amount of water present in your body affects how much fluid remains within the circulation and therefore affects the blood pressure as well. Finally, the changes in blood pressure can be due to changes in the bodyís level of activity. How active you are often determines how hard and fast your heart pumps which affects how much blood comes out of your heart per minute and directly affects the blood pressure. And depending on whether you are at rest, have just eaten a big meal, or are running away from danger, this can affect the distribution of blood flow and the perfusion pressure within the different organs and tissues as they continue to do what they need to do.
Since Q = P/R, a change in perfusion pressure can therefore directly affect blood flow as well. As noted above, if the perfusion pressure increases, so will blood flow and if it decreases, the blood flow will decrease as well. Maintaining the blood flow within the right range is very important for an organ to receive enough of what it needs to live and function properly without at the same time causing damage to the tissues. For example, if the blood flow to your brain drops too low, you will begin to feel dizzy and weak, have blurring or loss of vision, become confused and may even pass out. If this progresses you may have a seizure, lapse into a coma and even die. This can happen from profound hypotension (low blood pressure) and shock. However, too high of a perfusion pressure, resulting in too much blood flow into the tissues, can also cause the brain to malfunction as well. Too much blood entering the capillaries can result in the leakage of too much fluid into the brain tissue causing swelling which can lead to headaches, dizziness, and confusion. And if not corrected this can also progress to seizures, coma and even death. When this happens it is called a hypertensive crisis. Since we know that the perfusion pressure and blood flow to our organs (especially the brain) are always changing, but, no matter what weíre doing, we donít usually experience symptoms of too little or too much blood flow, we can conclude that the body must have a mechanism in place to keep things working properly. By looking at the equation Q = P/R, what do you think the body would have to do to keep Q relatively constant if P is always changing by either going up or down?
The answer to this question is that to keep the blood flow (Q) stable within a given organ or tissue the body must be able to adjust the vascular resistance (R), up or down, to compensate for the changes in perfusion pressure (P). Remember Q = P/R. So, for example, if P increases, causing a rise in Q, the body must increase R just enough to offset this increase in P so as to bring Q back to normal again. Conversely, if P decreases, causing a drop in Q, the body must decrease R just enough to offset this decrease in P so as to bring Q back to normal again. But how does the body adjust the vascular resistance? To answer this question we must first learn about the main factor that affects vascular resistance.
Vascular Resistance Redux
Common sense tells us that the wider the channel is for a fluid to move along, the less resistance and more flow, and the narrower the channel, the more resistance and less flow. What do you think would happen to rush hour traffic if all of the exit ramps on the highway went from being two lanes to four lanes? Traffic would move a lot better wouldnít it? What if they all went from being two lanes to just one lane? Traffic would have to slow down more. The main factor that affects the vascular resistance is the width of the channel within which the blood flows in the blood vessel. This channel is called the lumen and the width, or caliber of the lumen, is known as the luminal diameter. In fact, the vascular resistance is inversely related to the 4th power of the luminal diameter. This means that if the luminal diameter doubles, the vascular resistance diminishes by a factor of 16 (2 x 2 x 2 x 2). And if the luminal diameter is cut in half, the vascular resistance increases by a factor of 16. But the really important thing to notice here is how a change in the luminal diameter affects blood flow (Q). We know that Q = P/R, which means that blood flow (Q) is inversely related to the vascular resistance (R). But we now also know that R is inversely related to the 4th power of the luminal diameter. So, if R is inversely related to the 4th power of the luminal diameter, and Q is inversely related to R, then, like with a double negative, Q must be directly related to the 4th power of the luminal diameter. This means that if the luminal diameter of the blood vessel doubles, the blood flow increases by a factor of 16, and if the luminal diameter is halved the blood flow decreases by a factor of 16. What experience teaches us is borne out by these equations, the larger the channel, the less resistance and more flow, and the smaller the channel, the more resistance and less flow. But how does the body adjust the luminal diameter to change the vascular resistance? To answer this question we must now look at the anatomy of the arteriole.
The Anatomy of Control
The arterioles that feed the capillaries in the vascular beds of the different organs and tissues are surrounded by muscle. http://www.wesapiens.org/file/2534015/Structure+of+arteriole The luminal diameter depends on how much the muscles around the arterioles are contracted. The more contraction there is, the smaller the caliber of the arteriole (vasoconstriction), and the less contraction there is, the larger the caliber of the arteriole (vasodilation). Since the vascular resistance is inversely related to the fourth power of the luminal diameter, this means that the amount of muscle contraction around the arteriole also determines the vascular resistance as well. With vasoconstriction there is more vascular resistance and with vasodilation there is less vascular resistance. Finally, since blood flow is inversely related to the vascular resistance, this means that the amount of muscle contraction around the arteriole in addition to determining the vascular resistance also determines the blood flow. Vasoconstriction causes not only an increase in vascular resistance but also a decrease in blood flow. And vasodilation causes not only a decrease in vascular resistance but also an increase in blood flow. Recall that at rest, the skeletal muscle receives only 750 mL/min of blood flow (15% of the cardiac output). But with very heavy exercise this rises 28-fold to about 21,000 mL/min (85% of the cardiac output). In addition, the blood flow to the heart muscle quadruples from 250 mL/min to 1,000 mL/min. However, at the same time, the blood flow to the brain remains constant while there is a 60% drop in blood flow to the liver and gastrointestinal system and an 75% drop to the kidneys. So, how does the body control the muscle tone around the arterioles and with it the vascular resistance and blood flow into the vascular bed of a specific organ or tissue? To answer this question we must now look at what factors affect the muscle contraction of the arterioles and how the body takes control to make sure its organs and tissues receive the right amount of blood flow so they can do what they need to do.
Controlled Blood Flow = Survival of the Fittest
The muscles surrounding the arterioles respond to several different factors. Some of these factors are intrinsic to what is going on inside the arterioles and the nearby tissues. The pressure of the incoming blood stretches the vessel walls and affects the degree of muscle contraction around the arterioles. In addition, the presence of certain chemical byproducts from the metabolism of the tissues also impacts the vascular tone as well. In addition, there are extrinsic factors that affect the vascular tone which come from outside the arterioles and their surrounding tissue. These include various hormones that are released by distant gland cells and travel in the bloodstream, and neurotransmitters that are released by nerve cells. These molecules attach to specific receptors on the muscle cells and affect how much they contract. Remember, the muscle tone around the arterioles determines not only the vascular resistance but also the blood flow that runs through them. Therefore, if your body can control the vascular tone of the arterioles feeding a specific organ or tissue it can control the amount of blood flow to it as well.
When the body is at rest, one main extrinsic factor that affects the blood flow to its various organs and tissues is the sympathetic nervous system. Except for in the brain, the sympathetic neurotransmitter, norepinephrine, attaches to receptors on the muscle cells of most of the other arterioles in the body and tells them to stay contracted. The resulting vasoconstriction causes limited blood flow throughout most of the organs and tissues of the body when it is at rest. Another very important and intrinsic mechanism that helps to control blood flow, particularly to the brain and the heart muscle, is autoregulation. Recall, Q = P/R, so an increase in pressure naturally causes an increase in blood flow. And a decrease in pressure naturally causes a decrease in blood flow. But the change in pressure also causes a change in the amount of muscle stretch as well. With autoregulation, an increase in pressure and stretch, which causes an increase in blood flow, automatically causes the muscle to contract. This reflexive vasoconstriction results in an increase in vascular resistance and a decrease in blood flow which helps to bring the blood flow back toward normal. Similarly, a decrease in pressure and stretch, which causes a decrease in blood flow, automatically causes the muscle to relax. This reflexive vasodilation results in a decrease in vascular resistance and an increase in blood flow which helps to bring the blood flow back toward normal. Thus, autoregulation helps the body accomplish exactly what is needed to keep the blood flow relatively constant despite the changes in perfusion pressure. So, at rest, the blood flow to the various organs and tissues of the body is regulated, not only by the sympathetic nervous system but also autoregulation as well.
Human survival requires that the body be able to rest when it needs to. But it also requires that the body be able to work and do various other activities as well. At rest the cardiac output is about 5 L/min, and it rises to 7 L/min on walking slowly, 12 L/min on walking fast, 18 L/min when jogging, and 25 L/min with running fast and doing other vigorous pursuits. The heart muscle needs some of this increased blood flow so it can increase the cardiac output for these actions. However, most of this increase in blood flow travels to the skeletal muscle so it can perform these activities. The main intrinsic factor that facilitates this blood flow to the heart and the skeletal muscle during exercise is called metabolic or functional hyperemia. The increase of several chemical byproducts from the metabolism required for muscle activity causes the relaxation of the muscles surrounding the arterioles. This vasodilation results in a decrease in vascular resistance and an increase in local blood flow. In addition, the extrinsic mechanism that controls the cardiac output so that it matches the activity level is also responsible for helping the blood flow to go to the heart and muscle as well. Recall, to control something you must have a sensor to detect what needs to be controlled, an integrator to take the data, compare it with a standard and decide if changes need to be made, and an effector(s) to make the changes that are needed. An increase in physical exertion results in more nerve messages from the muscles being sent to the brain due to an increase in muscular activity and the chemical changes brought on by an increase in their metabolism. The brain responds quickly to this information by stimulating the sympathetic nerves and the adrenal glands. This causes the release of more norepinephrine, and from the adrenals, epinephrine. Together, these sympathetic neurotransmitters attach to receptors on the heart muscle to cause a rapid increase in heart rate and ventricular contractility resulting in an increase in cardiac output. However, in addition to affecting heart function, norepinephrine and epinephrine also affect the vascular tone of the arterioles as well. As noted above, norepinephrine causes vasoconstriction in most of the vascular beds of the body except for the brain. But the arterioles leading to the heart and skeletal muscle are unique in that they both have epinephrine receptors as well. The epinephrine attaches to these receptors and causes vasodilation which helps to counteract the effects of norepinephrine and facilitates the increase in blood flow to the heart and skeletal muscle. Therefore, during exercise, the vasoconstrictive effect of norepinephrine, which reduces the flow to most of the other organs of the body, like the liver and kidneys, is more limited in the heart and the skeletal muscle by the vasodilating effects of epinephrine. So, with increasing exertion, the sympathetic nervous system tends to facilitate blood flow to the heart and the muscles, at the expense of most of the other organs of the body, while preserving blood flow to the brain.
In summary, the intrinsic factors of autoregulation and functional hyperemia, with the extrinsic effects of the sympathetic nervous system, work together to help control the blood flow so that it matches the metabolic needs of the various organs and tissues of the body. Without this control mechanism in place the bodyís ability to survive within the laws of nature would be impossible.
Points to Ponder
Just because a car has a fuel system and wheels that are attached by different parts to the engine doesnít automatically mean that it can accelerate up a steep incline. The engine must receive enough gas and have the horsepower to allow the car to overcome the natural forces of inertia, gravity, friction, and wind resistance. So too, just because our body has a cardiovascular system and muscles doesnít automatically enable us to move quickly and have the strength to survive. Our heart must receive enough blood flow so it has the power to increase its output and most of that increase in output has to be directed to our muscles so they can overcome the same forces of nature. As noted above, too little or too much blood flow, particularly in the brain, can cause significant injury and even death. Without being able to control the blood flow so that it matches the metabolic needs of the various organs and tissues of the body, life, as we know it, would be impossible.
Think of what parts and reactions are needed to control blood flow; sensors to detect muscle activity, the chemical byproducts of metabolism and blood pressure, the sympathetic nerves and adrenal glands that send out norepinephrine and epinephrine, specific receptors on, and the muscles surrounding, the arterioles, in addition to autoregulation and functional hyperemia, just to name a few. Then consider that the body must inherently know that Q = P/R, otherwise how could it direct these parts and reactions to always do the right thing so that the control of blood flow can be maintained? Then ask yourself if evolutionary biology has even come close to providing an adequate explanation for how this all came into being while continuing to have the capacity to survive each step along the way? Not only must every part have been in the right place, doing the right thing and at the right time (irreducible complexity) but they also must have been doing enough of it as well (survival capacity). As opposed to Darwin, who only knew what life looked like and not how it actually worked, modern scientists now know that there are objective benchmarks that must have been met for human life to have survived. Just like the car that needs to be given enough gas and have enough horsepower to accelerate up a steep incline, so too, for our hominid ancestors to have been active enough to prey on others, rather than being preyed upon, required that they be able to increase their cardiac output enough while directing most of the increase in blood flow to their skeletal and heart muscle and maintaining enough blood flow to their brain. The human body must take into account and fight against the random forces of nature to survive. The random forces of nature do not produce life. When left to their own devices they cause death. Inertia, gravity and vascular resistance all play their own part in preventing enough blood from flowing to the various organs and tissues of the body. However, by being able to increase the cardiac output enough while at the same time adjusting the vascular resistance within its various organs and tissues according to the equation Q = P/R, the human body has been able to survive without the help of its intellect. It is indeed a pity that many now use that intellect to convince themselves that their lives have come about, not despite the random forces of nature, but solely because of them.
Howard Glicksman M. D. graduated from the University of Toronto in 1978. He practiced primary care medicine for almost 25 yrs in Oakville, Ontario and Spring Hill, Florida. He now practices palliative medicine for a Hospice organization in his community. He has a special interest in how the ethos of our culture has been influenced by modern science’s understanding and promotion of what it means to be a human being. Comments and questions about this column or any of the previous ones are welcome at firstname.lastname@example.org
Copyright 2013 Dr. Howard Glicksman. All rights reserved. International copyright secured.