Darwinism Vs. the real world.XIX

Vasoconstriction and Platelet Aggregation Defy Evolutionary Explanations

Howard Glicksman November 6, 2015 4:25 AM

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.

To feed the cells of the body so they will live, grow, and work properly, the heart must pump blood with enough pressure through the circulatory system. However, just as water under pressure can leak out of a pipe that has burst, so too a ruptured blood vessel can result in blood loss. Moreover, depending on how much blood is lost and where it takes place in the body, this can lead to significant health risks. Our earliest ancestors needed to live active lives and, just like us, were constantly at risk of blood loss from injury. If the body didn't have the wherewithal to prevent significant blood loss, humanity could never have survived or reproduced.

As I noted in my last article, the process that performs the important task of preventing blood loss is called hemostasis. Hemostasis involves the quick and almost simultaneous actions of the injured blood vessel, the platelets, and the clotting factors to form a fibrin clot to stop the bleeding.

But the body faces another dilemma. A clot in a major vessel like an artery supplying blood to the brain, or the heart, or the lungs, can cause significant damage. In other words, hemostasis and the clots it forms must turn on only when it's actually needed and must turn off and stay offwhen it's not. It's like the sprinkler system in a factory and an air bag in a car. They must deploy only when needed. Let's consider the first two components of hemostasis: blood vessel vasoconstriction and platelet aggregation.

Just like in a garden hose, there is a central channel or lumen through which blood flows in a blood vessel. The tissue that lines the lumen is called the endothelium. The endothelium does much more than just act as a barrier between the blood and the underlying support tissue, which in most blood vessels contains a protein called collagen and is surrounded by muscle. When a blood vessel is injured, local chemical changes related to the endothelium trigger the surrounding muscle to automatically contract in an attempt to close down the lumen to prevent further blood loss.

This short-lived vasoconstriction plays a major role in hemostasis and often in small arteries and arterioles can almost totally shut off the blood vessel, allowing the platelets and clotting factors to work together, forming a clot to permanently seal the injured site. Vasoconstriction acts like the person who has to sit on an over-packed suitcase so the top and bottom can be brought close enough together for the lock (platelet plug and fibrin clot) to be applied. Without vasoconstriction, the task of the platelets and clotting factors would be impossible.

Adequate hemostasis to prevent recurrent serious bleeding would have required our earliest ancestors to have blood vessels with normal function. There are several rare medical conditions in which the body has abnormal blood vessels that have difficulty contracting upon injury. Some chronic illnesses cause significant vascular fragility. These conditions put people at very high risk for bleeding from minimal trauma, resulting in life-threatening hemorrhage if a major organ or blood vessel is involved.

Evolutionary biologists may imagine how blood vessels came into being, but clinical experience shows that the complicated structure of blood vessels must not only allow for adequate blood flow, but also have a mechanism in place that helps to minimize bleeding when injury takes place. For our earliest ancestors, this would be the difference between life and death.

The second action needed for clot formation and hemostasis is the activation of the platelets. Platelets, also known as thrombocytes, are small disc-shaped, cell-like structures in the blood. They are about one-quarter to one-half the size of red blood cells. Platelets form in the bone marrow and, once released into the bloodstream, survive for only about ten days.

Platelet production in the bone marrow is controlled by a hormone called thrombopoietin. This hormone is produced mainly in the liver and the kidneys. It works by attaching to specific receptors on the stem cells in the bone marrow to start the production of platelets. How the body regulates thrombopoietin production has only recently been explored, and where the thrombopoietin receptor on the stem cells originated is still unknown. But rest assured, this lack of knowledge does not deter evolutionists from speculating on how platelets with their important function must have come into being only by chance and the laws of nature alone.

Normally, platelets circulate in the bloodstream without interacting with each other or the blood vessel wall. This occurs because the endothelium releases chemicals that prevent the platelets from sticking to each other and repels them from the vessel wall. Vascular injury activates the platelets by disrupting the secretion of these endothelial chemicals and exposes the platelets to the collagen just below the endothelium as well. This allows the platelets passing by the damaged region to attach to the vessel wall, change shape, and stick together.

Activated platelets also release chemicals that cause further vasconstriction and recruit more passing platelets to the site of injury. This piling on of several layers of platelets sticking to each other is called platelet aggregation, and it ultimately results in the formation of a soft platelet plug. Since the vessel walls on either side of the injury still have an intact endothelium, platelet activation and plug formation tends to be limited mainly to the site of injury. In this way, progression of the platelet plug in either direction from the vessel injury is usually prevented. The total absence of platelets is incompatible with life.

For minor injuries in very small blood vessels, the platelet plug is often all that is needed to stop the bleeding and allow healing to take place. Think of it like what a beaver must do to fix a breach in its dam. If it is very small with only a trickle of water going through, then using small amounts of soft leaves and sticks joined together by thin mud may be all that is needed. But if it is larger and has a torrent of water going through, then lots of large logs and flexible branches combined with solid sticks, soft leaves, and lots of thick mud will be needed to seal the breach.

For most of the traumatic injuries our earliest ancestors encountered in trying to win the battle for survival, it is the latter situation that applied. Next time, we'll look at how the third component needed for adequate hemostasis, the clotting factors, bring about fibrin clot formation to prevent excessive blood loss.

Darwinism Vs. The real world XVIII

Blood Clotting Requires Four Different Processes Working Together
Howard Glicksman October 26, 2015 4:17 AM

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.

Let's review some of the lessons that this series has so far provided about human life. The body is made up of trillions of cells, each of which must control its volume and chemical content while receiving what it needs from the blood to live, grow, and work properly. Since the body is made up of matter, it is subject to the laws of nature, which demand that it have enough energy to do what it needs to do to survive.

The body must constantly take in oxygen through the respiratory system to provide itself with the energy it needs to live because, unlike glucose, oxygen can't be stored for future use. About one-quarter to one-half of the energy the body uses while at rest is just for the sodium-potassium pumps within the plasma membrane of its trillions of cells. These pumps push Na+ ions out of the cell and bring K+ ions back in. This action not only maintains the volume and chemical content of the cell, but also the 2/3:1/3 ratio of water inside and outside the cells.

Combined with the control of its water and sodium content and the production of albumin, this process allows the body to maintain enough blood volume. The sodium-potassium pumps also maintain the electrical resting membrane potential of the cell. This is particularly important for proper heart, nerve, and muscle function.

When the cells in the brainstem die (the ones that tell the body to breathe, control its circulation, and make it conscious of its surroundings) the body is considered dead. However, the commonest cardiopulmonary arrest is the most common cause of death. Without respiration the body can't bring in new supplies of oxygen and get rid of toxic carbon dioxide, and without the heart pumping, there isn't enough blood flow to the brain. Together, this causes it to malfunction.

Since blood has mass, the heart has to pump it throughout the body against natural forces like inertia, friction and gravity that would prevent it from moving. As blood moves through the circulatory system, it applies a pressure against the vessel walls. This represents the energy that is generating its flow.

In clinical practice, the blood pressure is taken in the upper arm and is a measure of the force of blood against the walls of the brachial artery. The blood pressure is dependent on how well the heart pumps, how much blood is in the systemic arteries, and the resistance to blood flow applied by the downstream arterioles that control how much blood enters the capillaries. Blood flow (Q) is directly related to the blood pressure (P) and inversely related to the vascular resistance (R). This law of nature can be expressed as Q = P/R. The more blood pressure the more blood flow and the less blood pressure the less blood flow. The more vascular resistance the less blood flow and the less vascular resistance the more blood flow.

When we stand up and feel momentarily dizzy, our body must inherently know that if Q = P/R, then P = Q x R. In other words, blood pressure is directly related to the blood flow and vascular resistance. More blood flow and vascular resistance increases the blood pressure and less blood flow and vascular resistance decreases the blood pressure.

Standing up allows gravity to prevent blood from returning to the heart from the veins in the chest, abdomen and legs. It also keeps it from going from the heart to the brain, which reduces the blood pressure and blood flow to the brain. That's what makes us feel dizzy. The body detects these changes and reacts by sending out nerve messages to make the heart pump harder and faster, pushes blood from the veins back toward the hear,t and increases the vascular resistance applied by the arterioles by increasing the contraction of their surrounding muscles. The first two actions increase blood flow (Q) and the last one increases the vascular resistance (R), so the blood pressure (P) rises and our dizziness usually resolves in a matter of seconds.

The above demonstrates just some of the ways the body takes control and follows the rules in line with the Goldilocks principle: the real numbers must be "just right." After all, life doesn't take place within a vacuum or the imaginations of evolutionary biologists. As was the case with our earliest ancestors, to survive we must remain active, exposing our body, and our blood vessels, to the random forces of nature.

Experience tell us that when we run, jump, climb, roll, fall, and generally bang into or scrape up against solid or sharp things, natural forces like friction, momentum, pressure, sheer and gravity all contribute to blood vessel damage, bleeding and blood loss. This takes place because, with damage to the blood vessel wall, the pressure that sustains blood flow within it naturally pushes blood out through the opening. Think of it like when a water pipe in your home bursts. The water flowing through it is under pressure and when the walls of the pipe rupture water naturally flows out. Depending on the location and the severity, if the body can't stop the bleeding fast enough it runs the risk of serious problems. So to follow the rules that the laws of nature impose on it, the body must have a mechanism in place to prevent excessive bleeding from its blood vessels when they undergo injury.

Experience teaches that when we cut ourselves, a clot forms at the injured site to stop the bleeding and allow healing to take place over the next several days. This process is called hemostasis (Greek: haima = blood + stasis = halt).

Hemostasis generally involves three actions that occur almost simultaneously. Vasoconstriction is contraction of the muscles surrounding the injured blood vessel, which tries to totally close down the opening in the wall. Platelet aggregation is the formation of a soft plug by the platelets coming together and sticking to each other to fill the gap in the blood vessel wall. And activation of the clotting factors is the formation of thousands of sticky strands of fibrin which wrap around the platelet plug to form a molecular meshwork that entraps red blood cells and plasma to form a fibrin clot which closes off the damage and stops the bleeding.

However, when it comes to preventing blood loss from blood vessel injury through hemostasis, the laws of nature present the body with another dilemma. It's important that the clotting mechanism turn on only when it's needed, not only to not waste the body's supply of platelets and clotting factors, but also to prevent the sudden blockage of blood flow to vital organs. A poorly placed blood clot within an artery supplying blood to the heart muscle can cause a heart attack, or to the brain, a stroke, or to the lungs, a sudden drop in oxygen availability. Any one of these situations can result in serious and permanent debility or sudden death.


So, in addition to being able to turn on at the right time, the body must also have a mechanism in place to take control so that hemostasis will turn off and stay off at the right times. How does the body do it and how does evolutionary biology explain how it works in real life? That's what we'll begin to look at next time.