The Book of Blood: From Legends and Leeches to Vampires and Veins

by Hp Newquist

  Your liver works so hard that it filters nearly a third of all your blood every minute. The clean blood from the liver flows back to the heart via the hepatic vein. After the clean blood is gone, the dead and diseased blood cells remain. The liver breaks them down into a substance called bilirubin, which is dark brown due to the color of the used-up RBCs. All of this waste then flows to the large intestine to be sent on its way to the local bathroom. By the way, all those dead RBCs that make up bilirubin are the reason why feces are brown.

  If it wasn’t for your liver, you could never have been born. When a baby is still inside the mother, the baby’s liver helps create new blood cells before the bone marrow has fully developed. So the first blood your body created for itself came from your liver.

  THE SPLEEN

  The spleen is one of those organs you don’t hear much about. Many people don’t even know what it does—even scientists didn’t know a lot about it until recently.

  The spleen is a squishy purplish organ located just to the left of your stomach. Like the kidneys and liver, it spends much of its time acting as a blood filter. It is full of blood, which it stores in open spaces and receives from the heart through the splenic artery.

  Your spleen is small, but it acts as a blood reservoir in times of emergency.

  Rather than filtering out toxins or other substances, the spleen’s real work involves the components of the blood itself. It detects worn-out or damaged red and white blood cells, as well as platelets. Once blood cells are unable to function properly, the spleen destroys them, making them completely useless. The spleen then recycles any usable parts, such as iron, in the blood. The rest is passed on to the liver through the portal vein so it can be removed from the body as waste.

  Because it can hold a lot of blood all at once, the spleen also serves as a miniature blood reservoir. In times when the body is sick or injured and is losing blood, the spleen can squeeze some of its stored-up reserves back into the body so that the proper amount is still flowing through the arteries and veins. When the body’s blood level is back to normal again, the spleen restocks its reservoir.

  The spleen is also one of the first lines of defense for the blood. It produces a very specific type of white blood cell called lymphocytes, which are disease fighters. If the spleen discovers viruses or parasites in the blood, it ramps up the production of these white blood cells. These cells then attack the invaders in the bloodstream in an attempt to kill them off before they can do harm to the rest of the body. Other white cells in the spleen can actually devour bacteria and fungi.

  The spleen is one of the few organs you can live without—although it’s better to have one—because other organs like the liver are able take over some of its duties.

  THE KIDNEYS

  The kidneys are two bean-shaped organs located on the left and right side of your body just above your stomach. Their job is to clean out waste material picked up from cells and organs by the blood as it flows through your body.

  In addition to carbon dioxide, the bloodstream—primarily the plasma—gets filled up with dead cells, cell byproducts, and other junk as it makes its way all over the body. Blood has to be cleaned out somewhere along the line, or it would be full of waste. The kidneys serve as the equivalent of the local garbage dump.

  The kidneys receive almost 20 percent of the blood pushed out from the heart, nearly as much as the brain. The blood enters the kidneys via the renal artery. Since so much blood is entering the kidneys, it is forced through capillaries and hundreds of thousands of tubelike structures called nephrons. As the blood moves through the nephrons, waste products are squeezed out of the plasma, just like a coffee filter that catches the grinds in a coffee maker or a juicer that traps the pulp from oranges. Any nutrients that remain are absorbed back into the bloodstream, since they can still be used.

  The kidneys take out excess molecules that you might have in your blood from eating too much of any particular kind of food.

  This is especially true of foods with a lot of sugar and salt. The remains of used-up medicines also end up in your kidneys.

  The kidneys are the only place where blood makes a jump from arteries directly to veins without going through the intricate mesh of capillaries and venules. The clean blood from the kidneys then flows back into the bloodstream to continue its way to the heart. The leftover waste is mixed with water and other chemicals and discharged from your body as urine.

  This journey around the circulatory system has shown you how blood nourishes and fuels your body. There is a dark side of 9 blood, however, and it can lead to serious problems in your body.

  CHAPTER 7

  The Blood's Battleground

  Your blood is more responsible for keeping you alive than anything else in your body. You’ve just seen how blood makes its way from place to place, working every second of every day of your life to make sure your body functions as it is supposed to.

  That’s the nice, normal part of blood. And when things are going well for our bodies, we can go months or years without thinking about what blood does for us.

  It’s only when we get sick or seriously hurt that blood comes rushing back into our thoughts—or rushing out of our bodies.

  From our blood’s perspective, the body is not only something to be serviced, it is also something to be protected. And there are occasions when your blood has to act like an army, going out to attack invaders, fight off infections, destroy bacteria, defend against disease, detect and kill intruders, and stand guard until your body is healed. It sounds violent, and at the microscopic level, it truly is.

  Blood is just as vital to us in times of sickness as it is in health. We can see that when we get something as minor as a simple paper cut or accidentally get poked with a sharp object. That’s when blood comes, literally, to the surface.

  When something sharp cuts your skin, or if you fall on a rough surface that scrapes your skin, it tears through several layers of flesh called the epidermis. Like the rest of your body, there are millions of capillaries of all sizes woven through these layers (except for the very top layers of skin, which is why if you scratch your skin lightly you won’t bleed). This tear, cut, or scrape also rips into the capillaries, opening them up as if you were slicing into a water pipe or a straw. Once that happens, blood leaks out. Some capillaries are bigger than others, so in some places the blood flow is heavier and faster.

  Once the blood hits the air, it turns a very bright bright red, even if it’s already given up much of its oxygen inside the body. That’s because it’s absorbing the oxygen outside your body.

  When a blood vessel is damaged and RBCs are exposed to air, platelets get very busy very quickly. The torn vessel releases a substance called collagen that the platelets react to. Since collagen is inside the walls of the vessel, it is normally kept away from platelets. But once collagen comes into contact with the bloodstream, the platelets start bunching up together, blocking the flow of red and white cells. At the same time, the torn blood vessels squeeze tight, reducing blood flow.

  As platelets get exposed to the air, they break apart and spread out, creating a sticky mass. Little bits of fibrinogen that the liver produces join the mass. They mix with the platelets and form little threads of fibrin. The fibrin weaves around the platelets and creates a net that holds the mass together. Together, they form a blockade that prevents the red and white blood cells from passing through. This is called coagulation.

  Creating a clot: fibrin forms a net that prevents red blood cells from leaking out of the body.

  Once the blood has been sealed off, this blockade forms a clot. The blood changes from a flowing liquid to a sticky and barely moving mass. As this mass hardens, it forms a scab. You’re familiar with scabs; they’re the hard little shells that cover a cut or scrape. A scab gets harder as air dries it out, and it becomes a protective coating for the damaged vessel while the vessel is repaired with new cells.

  When the situation is under control, the collagen stops
seeping into the blood, and blood flow continues as normal. After about two weeks, there is no visible sign that anything even happened to your skin. The body is so good at repairing itself that the damage completely disappears. (In extreme cases, a wound may remove a large and deep section of skin. When this happens, the repair process leaves a scar in the area that it patches up, much like the bunching up that occurs when thread is used to repair a tear in cloth.)

  This is what occurs when you have minor injuries. These almost always involve capillaries. It is rare that you will ever have the kind of injury that would sever a major artery or vein. Most of the vessels are buried deeper in the body, closer to organs and bones. If these are damaged, though, the blood flow is usually too fast for the coagulants to work, and has to be slowed down by other means. Usually this involves pressure being placed on the bleeding area to squish the vessel shut. People giving first aid will accomplish this by using the palms of their hands to press down on the wound. If the injury is extreme, a doctor will wrap a tight bandage, called a tourniquet, around the place where the injury has occurred—say an arm or a leg—so that the artery is pressed shut to stop the blood. Eventually the wound itself has to be closed, and a doctor will seal it with stitches.

  You probably cause minor damage to your body regularly without even thinking about it. Scratching mosquito bites, accidentally biting your lip, bumping your nose, stepping on something sharp—all these are ways that blood makes its way to the outside of your body. Because blood works so well, you usually forget about these incidents shortly after it stops flowing.

  Pressure is one way to prevent blood loss because it squeezes the blood vessels closed.

  Some people aren’t so lucky. They are born without the right kind of elements in their blood to create clots. This condition is called hemophilia. When hemophiliacs get even a tiny cut, their blood can’t stop flowing. Their bodies aren’t able to produce the fibrin that is so important to creating the clots that block blood flow. Without clots, the blood just keeps going and going. Fortunately, hemophiliacs can inject the necessary blood parts into their bloodstream using a medicine that is made of blood obtained from other people. This mixes with their own blood to provide coagulants in case they do start bleeding. But since all blood components eventually break down in the body, hemophiliacs have to take a regular supply of this medicine to avoid any problems should they injure themselves.

  Blood clotting and the resultant scabbing is the only example of blood healing we can see with our own eyes. The rest of it happens inside our bodies. Even then, this happens at the microscopic level, and we couldn’t observe it even if we wanted to. Interestingly, while the repairs we can see happen with RBCs, the repairs that occur inside us are all about the white blood cells.

  ON THE ATTACK

  If RBCs and plasma are the couriers that deliver important packages such as oxygen and nutrients to your organs and tissues, white blood cells are the soldiers that protect those deliveries. Not only do they act as bodyguards for the RBCs, but they serve as scouts that go out to destroy invaders that might want to get into your body and hurt it.

  White blood cells come in five main types, and they are all part of your immune system. The immune system is the name for all the organs, tissues, and chemicals in your body that protect you from sickness. The things that cause sickness come in many different forms. A virus that enters your body can cause pneumonia. Bacteria can bring diseases like anthrax and the plague into your system. A malfunction in your normal body processes can cause cancer. White blood cells have to be prepared for all this and much more.

  Each type of white blood cell focuses on a specific function, although some of the WBCs’ duties overlap. The basic function of white blood cells is to identify a problem or an invading microorganism (like a virus), signal to other white cells for help, and then band together in a large group to attack the invader.

  * * *

  FIVE TYPES OF WHITE BLOOD CELLS

  There are five primary types of white blood cells (WBCs), each with a specific job to do when your body is attacked by disease or becomes infected by a cut. Depending on what your body needs, the amount of any one type of WBC varies. For instance, if you have a bacterial infection, your body will produce more neutrophils than lymphocytes.

  NEUTROPHILS are the most plentiful WBCs, usually accounting for at least half of the WBCs in your body at any given time. They fight off infection from fungi and bacteria and are the primary element of pus.

  EOSINOPHILS make up only about 5 percent of all WBCs. They defend against parasites and cause inflammation during allergic reactions.

  BASOPHILS react to allergy-causing invaders by creating histamines that cause inflammation around the source of the invasion, such as the nose and mouth. They make up less than 1 percent of all WBCs.

  LYMPHOCYTES are the second-largest group of WBCs, sometimes making up 50 percent of your white blood cell count. They are important in killing viruses and cancerous cells.

  MONOCYTES account for a little over 1 percent of your WBCs. Their job is to “eat up" solid particles and cell waste and then remove it from the bloodstream.

  * * *

  Imagine that a simple yet unwanted virus like a rhinovirus has The rhinovirus is one of the most common viruses in the world and is responsible for colds. entered your body. You don’t have to imagine too hard because it’s already happened to you: the rhinovirus causes the common cold. It floats in water droplets in the air when other people who have a cold sneeze, or it lives on their hands or on things they’ve touched, like doorknobs. You might breathe it in, or you might get it from shaking hands and then rubbing your nose or eyes. Once the rhinovirus gets in your body, it digs into your cells and starts reproducing. This usually happens in the lining of breathing passages way up in your nose and sinuses.

  The rhinovirus is one of the most common viruses in the world and is responsible for colds.

  The cells damaged by the virus release chemicals that cause the surrounding blood vessels to swell. This leads to a condition known as inflammation. Inflammation happens because the blood vessels need to handle a larger flow of white blood cells to the infected area. You can see inflammation on your skin when it turns red from an infection, or in the bright redness of your throat when you’re sick. Even sunburn is an inflammation of the skin. Inflammation also occurs internally. Tennis elbow, for example, is caused by an inflammation of the tendons around your elbow from the strain of hitting a ball the same way too many times.

  After the rhinovirus has invaded your cells, it begins multiplying very quickly in the nice, warm, and wet portions of your nose and throat. Inflammation, caused by your blood vessels opening up, brings white blood cells right to where the rhinovirus is. But this makes you feel congested because the blood vessels are swelling, and that irritates the area around your nose and throat. You may also get a fever. Scientists aren’t sure why we get fevers, but they believe that an increase in body temperature helps to kill off invading viruses and also speeds up the reaction of the immune system.

  All of these are symptoms of a cold, but here’s an interesting thing to note: The virus isn’t what makes you feel bad. It’s a sad truth that what makes you so miserable when you have a cold is the violent way in which your body has to act against viruses to make sure they don’t get to your vital organs and cause more damage. The virus just sets off the whole process.

  .

  As soon as white blood cells reach the rhinovirus, they take immediate action. Depending on the kind of white blood cells activated, they go after the virus in a number of ways. Some white blood cells, like neutrophils, eat your infected cells and thus devour the virus within them. Lymphocytes can attack the virus and attempt to chemically break it down, almost like the way acid breaks down metal. White blood cells also release a protein called an antibody. This binds to the virus and keeps it from reproducing, thus isolating it and killing it.

  When you get a cold, blood rushes to the affected are
as, causing inflammation from your nose to your throat.

  The rhinovirus, for its part, keeps trying to reproduce fast enough to stay ahead of the attacking white cells. It, too, wants to survive at any cost.

  After a few days of this battle, the rhinovirus is defeated. All of your body’s defense mechanisms return to normal, and you start to feel better. This is always the case, because you always recover after a cold.

  The rhinovirus is a good example of an invader for several reasons: It is a relatively common virus and ultimately very weak. It rarely causes serious illness because it is easily overwhelmed by your white blood cells and immune system (although it doesn’t feel “easy” while you’re sick). In addition, the common cold and the rhinovirus cannot be “cured” or destroyed by medicine. Science has still not figured out a way to create a drug that can kill the virus once it’s in your body. That’s why you can’t get a shot or take a pill to make a cold go away. The medicines people do take, like aspirin or cough syrup, help ease the symptoms, but they don’t take care of the cause.