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

by Hp Newquist

  This is important because there are many times when your blood needs help in attacking a disease. Some viruses, bacteria, and even poisons—from poisonous plants or animals like venomous snakes—are so strong that the blood can’t fight them off by itself. In the days before modern medicine, people died regularly from these infections. The flu, the plague, smallpox, polio, and pneumonia were fatal or permanently crippling diseases for most of human history. They were unstoppable, until the development in the early 1900s of antibiotics—drugs such as penicillin that kill bacteria—gave humans a better chance of surviving disease.

  These drugs either enter the bloodstream through your mouth, in the form of a liquid or pill, or are injected right into your blood. They do much of the same work that white blood cells do. The difference is that these medicines are designed to kill specific viruses, parasites, and fungi by traveling through the blood and killing all the invaders in their path.

  The odd thing in most deadly diseases is that they use the bloodstream to do their dirty work. Once they get into the body, they fight off all the body’s defenses and destroy white blood cells until they can travel freely in the blood and invade organs such as the lungs and the brain. If white blood cells can’t kill them off, these diseases travel in the plasma directly to the places where they can do the most damage.

  Some medicines are injected directly into your bloodstream, where they merge with your blood to fight diseases and infections. The medicine is shown here as blue droplets coming from a hypodermic needle.

  A good example is meningitis. This is an infection of the meninges, the protective layer around the brain. It is usually caused by a bacterium called Neisseria meningitidis. This dangerous form of bacteria is spread from person to person by very close contact such as sneezing, coughing, and kissing. Meningitis is extremely rare, but also extremely deadly because it can eat away your blood vessels and cause damage to your brain.

  Because it is so dangerous, your body responds extremely violently to it. Vomiting, fever, and uncontrollable body movements (called seizures) are all symptoms of meningitis. The bacterium is incredibly strong, and it often defeats all of the white blood cells that try to attack it. Eventually, hordes of bacteria make their way to the brain, where they eat through the blood-brain barrier. This allows the bacteria to get into the brain, and also causes blood to seep into places in the brain where it doesn’t belong. To make matters worse, damaged blood vessels and cells clog up the main blood flow to the brain. The result could be death. However, if meningitis is detected in time, it can be cured with strong medication such as antibiotics.

  Meningitis is only one of many serious diseases carried in the bloodstream. Perhaps the most destructive disease that the blood encounters is septicemia, blood poisoning caused by bacteria. It occurs after another major disease, such as meningitis, has destroyed organs in the body. The bacteria are still alive and look for someplace else to continue growing. That place is the blood. The bacteria invade the bloodstream and start attacking the blood just as they did the rest of the body. The blood starts clotting inside the blood vessels. This restricts the flow of blood to places such as the kidneys and brain. After that, the body shuts down and dies.

  Meningitis is so dangerous because it breaks through the blood-brain barrier and allows blood and bacteria to seep into the brain. Here you can see how the blood has passed through the meninges.

  Many viruses and bacteria produced by nature can destroy the human body. Some of them can be quite ghastly. A rare disease caused by the Ebola virus leads to death by dissolving blood vessels, causing patients to bleed internally and uncontrollably. The disease is found only in Africa, and it is almost always fatal. Researchers have no idea where it comes from or how to stop it. Many other viruses that travel in the blood, such as HIV, cannot be cured. They are just too strong, and too complicated, for science to figure out how to stop them. Yet.

  Some diseases that affect the blood have nothing to do with outside forces such as microorganisms. Diabetes, for example, occurs when the body cannot manage the level of sugar, or glucose, in the blood. Glucose is converted to fuel for our cells, and it needs to remain at a consistent level to keep cells working properly. When *the body mismanages glucose, it causes diabetes. Diabetic blood is too full of sugar, which clogs it up and prevents it from doing its job properly. Diabetes sometimes has to be treated with a medicine called insulin to bring the sugar levels back to normal. Untreated, it can cause heart disease and strokes.

  Many people with diabetes are born with it, but it can also affect people who are overweight or have poor eating habits. Diabetes is a huge health concern in America and Europe, as a poor diet and obesity have caused more people to become diabetic. Nearly 10 percent of all Americans have diabetes, and for people over the age of sixty, the percentage is almost 25.

  Overall, blood is good at handling the most common diseases (meningitis, Ebola, anthrax, and AIDS are all extremely serious, but relatively rare). In fact, many of the diseases in your body happen when your blood is unable to do its job properly. Heart disease, the number-one killer in the United States, occurs because your arteries become clogged by a buildup of something called plaque. This prevents oxygenated blood from getting to your heart.

  Plaque is a hard substance that builds up on the walls of arteries (it is different from the plaque on your teeth, even though it has the same name). The plaque in your blood vessels is caused by minute damage to the artery walls. White cells build up around this damage and then attract fatty substances, which harden over time and eventually block the flow of blood. Plaque can also break off in chunks and clog the heart and its valves, leading to a heart attack. This can cause your heart to stop, a condition called cardiac arrest.

  When a similar blood blockage occurs in the brain, it is called a stroke. This commonly affects older people. Plaque clogs the arteries leading into the brain, limiting the necessary blood supply. The result is a stroke, which injures the part of the brain that isn’t getting enough blood. Stroke victims often experience some paralysis and loss of speech. The arteries in the stroke area can often be cleared with medicine, and many people are able to recover fully if treated properly and in time.

  Plaque buildup in your blood vessels prevents a steady flow of blood, which can cause strokes and heart attacks.

  Of course, the worst thing that can happen to the body’s blood supply is to lose it. Major injuries, such as those from a car crash or a gunshot in battle, can cause blood to flow freely out of a wound. When the body loses a lot of blood, the amount of blood flowing through the heart is reduced. This dramatically lowers the pressure of the blood. Lower blood pressure means that less blood is pumped into places such as the brain, which needs a certain amount of blood—and its oxygen—to function properly. If the brain, or any other organ, doesn’t get enough oxygen, it starts failing. This major loss of blood is called shock.

  You might have heard on the news that an accident victim “went into shock.” Most people think this means “shocked,” as if the victim couldn’t believe the horrible thing he or she had just gone through and it was affecting their emotions. This is completely wrong. Medical shock refers to a blood pressure so low that it affects the operation of the organs. Emotional shock is the way people feel or think after experiencing an extremely disturbing event. It’s a big difference, and medical shock can be fatal.

  Severe accidents can also cause internal bleeding. This occurs if, for instance, an organ is ruptured in a fall or if the body crashes into something. Internal bleeding results from severed blood vessels. An organ that is bleeding is said to be hemorrhaging. This means that blood is flowing out of the circulatory system, but the word is most often used to describe bleeding inside the body. Such bleeding must be treated immediately by a doctor. A hemorrhage can result in low blood pressure. It can also damage organs and tissue because the free-flowing blood interrupts their normal operation.

  A hemorrhage occurs in instances such as a brai
n aneurysm. An aneurysm is a swelling on the wall of a weak blood vessel, kind of like a bubble that you make with bubblegum. If this aneurysm occurs in a brain vessel and the vessel bursts, blood spills into the brain. Suddenly blood is going to places it shouldn’t go instead of through the proper channels. If not treated immediately, a person who experiences an aneurysm can die because the body has no way to repair the broken blood vessel.

  In the cases of people who lose a lot of blood, the body cannot produce enough of its own blood to make up for the loss. This is also true for patients who undergo major surgery, such as heart operations or organ removal. The only way to treat extreme blood loss is to provide patients with blood via a transfusion. Fortunately, transfusions help to save thousands of people every day.

  An aneurysm is like a bursting bubble in the brain.

  Keeping your blood healthy, and inside you, is vital to you every moment of your life. All animals need healthy blood in order to survive. But some animals have stranger blood than others.

  CHAPTER 8

  Red Blood, Blue Blood, Clear Blood, Cold Blood

  The way our blood works in our bodies makes sense to us. It flows from the heart to the other organs. It turns red when it picks up oxygen from our lungs. It travels through arteries and veins and capillaries. It serves as a means to deliver fuel to our cells and remove waste from our bodies. In all, it’s an extraordinarily efficient system for keeping us alive.

  What works for humans, though, doesn’t necessarily work for other creatures. In fact, there are some creatures whose blood systems are so bizarre, they seem as if they would be more suited to life on another planet.

  Start with the simple cockroach. One of the most common insects on earth, the cockroach can survive for weeks after having its head cut off. The reason? It has an open circulatory system, which means that its blood sloshes around inside its body as if it was inside a jar. Once the cockroach loses its head, this blood immediately clots around the wound in a thick liquid, which creates a plug in its neck. If the cockroach had blood vessels like those of humans, the blood would pour out as if from a fire hose.

  It also helps that cockroaches are cold-blooded, which means they don’t have to eat as much as warm-blooded mammals. This is a benefit, since their eating apparatus disappears with their heads.

  Many animals on the planet, with the obvious exception of mammals and birds, are cold-blooded. This includes reptiles, fish, amphibians, arachnids, and insects. Actually, their blood isn’t really cold like ice water or snow. “Cold-blooded” is a term for animals that are ectotherms. This means they can’t regulate their internal body temperature; instead they take on the temperature of their surroundings. That’s why lizards and snakes like to bask on rocks in the sun; it keeps their bodies warm. The heat from the sun is converted to energy and helps them hunt for prey and digest their food. When it’s too cold, though, ectotherms have a hard time moving around; cold weather makes them sluggish.

  A cockroach can live without its head for weeks due to the way its blood clots in its neck.

  Yet, cold-blooded creatures can typically live on less food than warm-blooded creatures of the same size. Warm-blooded animals require more food because they need the fuel to keep themselves warm. Ectotherms adapt to whatever the outside temperature is.

  Interestingly, bats—one of the mammals we often associate with the scarier side of blood—are unable to regulate their internal temperature. They cool off only when they are at rest. This makes them almost a cross between warm- and cold-blooded creatures.

  We use the term “cold-blooded” to refer to particularly nasty or evil people because we associate that nastiness with snakes, alligators, and lizards. These animals aren’t nasty, and they’re not truly cold-blooded, but the term lives on.

  By soaking up the sunshine on a warm rock, this lizard is heating its entire body-something it cannot do by itself.

  There is one animal that we could classify as being truly cold- blooded. It’s the mackerel icefish, and it lives in the frigid waters surrounding Antarctica. The icefish, which looks like a misshapen crocodile, is the only known animal with a backbone (a vertebrate) that doesn’t have hemoglobin in its blood. Instead, the blood of the icefish is made up of a clear kind of antifreeze that keeps ice crystals from forming inside its body. It is believed that since the icefish has no hemoglobin, it absorbs oxygen through its skin.

  The icefish has clear blood that serves as an antifreeze keeping ice crystals from building up in its body.

  While the icefish’s blood is ideally suited to helping it survive in temperatures that drop below freezing, another creature uses its blood to survive attacks by enemies. This is the horned lizard. Found across North America, it is often called the horny toad, but in reality it is a very odd lizard with a unique skill. When the horned lizard is attacked by a predator—such as a coyote or a fox—it squirts blood out of its eyeballs into the face and mouth of the attacker. The streams of blood can reach up to five feet. The horned lizard accomplishes this feat by increasing the blood pressure in the front of its head, which results in blood bursting through the vessels of the eyes. Apparently its blood has a hideous taste that sends predators running in the other direction. The lizard isn’t harmed by this effort, although it looks gruesome with blood covering its face after the streaming stops.

  The horned lizard is one of a few creatures that use their blood as a defensive weapon.

  * * *

  OTHER KINDS AND COLORS OF BLOOD

  Blood has three primary colors in the animal kingdom. Not surprisingly, they are red, blue, and yellow. Most land animals have red blood due to the presence of hemoglobin, a protein that turns red when it bonds with oxygen. The blood of many mollusks, such as squids, octopuses, and slugs, is blue because these creatures have hemocyanin proteins instead of hemoglobin. Hemocyanin turns blue when it is exposed to oxygen. Then there are sea squirts, which live deep in the ocean and spend their lives attached to a single piece of coral or rock. Their blood contains hemovanadin, which turns yellow when it is exposed to oxygen.

  Human blood can turn green if a person suffers from sulfhemoglobinemia, a disease that occurs when hemoglobin absorbs atoms of sulfur instead of oxygen molecules. It is an extremely rare condition, but is so strange that it has been called alien blood by some observers.

  * * *

  The horseshoe crab’s blood is not only blue but kills just about every kind of bacteria it touches.

  We might find this process rather gross, but the horned lizard was revered by some ancient American cultures for its ability to “weep blood.” They saw the positive side of the horned lizard’s unique skill.

  The strangest of all blood systems, though, has to belong to the horseshoe crab. This crab (which is not a crab at all but is closer in evolution to scorpions) has been around since before the age of the dinosaurs, and it has a huge shell that looks like a spiked helmet. One of the most fascinating things about the horseshoe crab is that it has blue blood. This is due to its having copper as a base for its blood instead of iron, which is the basic element in red-blooded creatures. Blue blood uses hemocyanin (“cyan” is another name for “blue”) instead of hemoglobin to help it store oxygen.

  The horseshoe crab’s unusual blood isn’t limited to its color. It has an open circulatory system, which means that its blue blood washes around inside its body without traveling through blood vessels. But what makes the horseshoe crab’s blood really incredible is that it can destroy some of the most potent bacteria on earth. When the crab’s blood is exposed to even a single bacterium, it forms a clot around the bacterium and prevents it from moving into the crab’s body.

  Horseshoe-crab blood is so sensitive that pharmaceutical companies use it to test the purity of medicines that are to be injected into humans. Before the medicine is shipped to a local doctor or pharmacy, it is inserted into a sample of horseshoe-crab blood. If the crab blood clots, it means there are bacteria in the medicine, and it’s not pure eno
ugh. Only when there is no clotting is the medicine ready to be used by people.

  Medical technicians extracting blue blood from horseshoe crabs in a laboratory.

  Horseshoe-crab blood is also the best way to determine the sterility of the instruments that are used during surgery. This is especially important when doctors operate on patients with infectious diseases. Testing the equipment used in the surgical suite with a solution containing horseshoe-crab blood ensures that everything is as sterile as possible. There is no other chemical, material, or test that can detect bacteria as well as the blue blood of a horseshoe crab. Scientists are trying to find a way to synthesize horseshoe-crab blood so that they won’t have to remove blood from living crabs.

  Most animals have fairly normal blood systems—at least by human standards—which makes these creatures so unusual. But there is another group of creatures whose relationship to blood is altogether spooky. That’s because they need human blood to help them survive. You know what they are: mosquitoes, leeches ... and vampires.

  CHAPTER 9

  The Creeps

  We like the thought of our blood staying right where it is—safe and sound inside our bodies. We certainly don’t like the idea that something else might want to take our blood away from us.