Tuesday, July 31, 2012

The Body’s Cancer Defenses

Out of all the diseases that affect human beings, cancer is particularly hard to grasp. After all, bacteria and viruses had millions of years to evolve into deadly attackers. Cancer cells are just the product of a random cell gone haywire. So how can they possibly account for the second most likely cause of death in the industrialized world?

The answer is bad luck and big numbers. Although cancer-causing mutations are exceedingly rare (on an individual-cell basis), your body has trillions of cells, and it manufacturers millions more every minute. Even a seemingly miniscule rate of cancerous mutation—say, one in a million cell divisions—would guarantee you a terminal case of cancer.

The real question isn’t why we get cancer, but why we don’t get it more often. In fact, the body has countless built-in safety measures to defend against cancerous cells. It has specialized genes that detect suspicious behavior and shut down cell growth or trigger cell destruction. Your immune system even has a class of specialized warriors called natural killer cells that hunt down cancerous cells and release toxic granules that destroy them.

However, none of these mechanisms is completely foolproof, and given enough time (and enough cell mutations), a cancerous cell can start to thrive. Cancer is a particular problem in old age because the body’s cells have had more time to accumulate the right mutations, the natural cancer fighting processes of the body have weakened, and a lifetime of exposure to carcinogens (chemicals in the environment that can damage DNA and spur mutations) has taken its toll. The following chart shows the rate of colon cancer as a function of age, and it tells a clear story—cancer risks skyrocket as time wears on.

It’s all a bit ironic. In one context, sheer mind-boggling odds can turn one mutation in a trillion into the survival advantage that drives the evolution of a species. But in another, a chance combination of deadly mutations can trigger a cancer and destroy an individual.

Source of Information : Oreilly - Your Body Missing Manual

Friday, July 27, 2012


So far, you’ve spent most of your time exploring battles that are relatively clear-cut. They pit your body against outside forces, like invading bacteria and viruses. But now it’s time to consider a subtler enemy—rogue cells in your own body.

The disease is cancer, and it starts with a subtle genetic shift that transforms one of the trillions of ordinary cells in your body into a saboteur. Unlike the cells in the rest of your body, a cancerous cell isn’t bound by the normal rules of human life. It grows without respect for the boundaries between different types of tissue, invades other sites in the body, and refuses to die a natural death. In the end, what begins as a series of simple cellular errors can become an unstoppable process that ravages your body.

How Cancer Starts
Although we often imagine cancer as a single thing, it’s actually a family of diseases that’s characterized by misbehaving cells. The problem begins with a chance mutation in a key regulatory gene—essentially, a cell turns off one of the safeguards that restricts it or over-activates one of the mechanism that drives normal cell growth. However, a single mutation isn’t enough—if it were, you’d be riddled with cancer while you were still in diapers. Instead, cancer needs to develop through a succession of highly improbable mutations, which gradually give the cell and its offspring the ability to defeat several different control mechanisms.

The picture on the next page shows one way this process can unfold:
1. The cell begins its life as normal.

2. Random mutations give the cell the ability to ignore the normal recycling processes of your body, so instead of dying, the cell lives forever. This transformation happens quietly and without event.

3. Next, the cell multiplies, creating similar ill-tempered progeny and crowding healthy cells out of the way. This unchecked growth often creates an abnormal mass of tissue called a tumor, which can cause problems if it presses on one of your vital organs.

4. The real trouble with cancer occurs when the cancerous cells metastasize, or spread to other areas of your body. Once cancer cells have become mobile, they travel far and wide, voyaging through your blood and lymph, and starting new cancer settlements throughout your body. At this point, the odds of successful treatment dwindle quickly.

Because different cancers acquire different mutations, they vary in their virulence. The nastiest forms multiply quickly and travel aggressively, and they can rapidly colonize your body. Other forms are highly treatable and have better survival rates than a heart attack or stroke.

When diagnosing a new cancer in a patient, doctors classify how far it’s advanced by stage. The exact definition of the various stages (and the prognosis of a cancer patient) depends on the type of cancer and its location. But in general, stage I cancers have not yet spread and are usually treatable. Stage II cancers have had some time to develop but have not yet traveled the body, while stage III cancers have made it to nearby lymph nodes. Stage IV cancers are the worst— they’ve spread to organs throughout the body and are usually untreatable.

Ordinarily, cells have a built-in self-destruct sequence. When a cell detects that it’s diseased or damaged (or when other cells detect something suspicious and convince the cell that it’s not quite right), the cell initiates this self-destruct sequence and destroys itself in a calm and orderly fashion. This tidy suicide process is called apoptosis, and it’s as fundamental to the functioning of your body as cell division. However, successful cancer cells don’t obey the shutdown command— they stay alive, multiply, and can develop more dangerous mutations.

Source of Information : Oreilly - Your Body Missing Manual

Tuesday, July 24, 2012

What Is the Deadliest Virus?

When it comes to deadly viruses, Ebola kills in the quickest and most horrific way possible— causing massive bleeding and turning internal organs into a soup of lifeless mush. It’s estimated that 90 percent of Ebola-infected people die from these symptoms. However, HIV (the virus that causes AIDS) is still more effective eventually, virtually everyone who contracts HIV will have their immune systems knocked offline, as the virus infects the very T cells that are supposed to defend the body. Without treatment, a person suffering from AIDS is unlikely to last even a few years, as hundreds of ordinarily harmless microbes ravage the body.

However, neither of these viruses can boast the highest body count through history. That dubious distinction probably belongs to influenza, the virus that causes the flu. Each year, influenza kills hundreds of thousands of people across the globe, most often the very old or the very young. But every few generations, a strain appears that is far deadlier, like the 1918 Spanish flu, which killed tens of millions of people in a single, worldwide outbreak.

Source of Information : Oreilly - Your Body Missing Manual

Saturday, July 21, 2012

Profile of a Cold

One type of virus that your body knows intimately is the one that causes upper respiratory tract infections, which are otherwise known as the common cold. Colds appear to expose a chink in the defenses of your immune system. After all, the average person suffers three or four colds a year, and no matter how many you endure, you’re never rewarded with lasting immunity. The reason for this endless suffering is variety. Scientists recognize more than 200 viruses that cause colds, and it’s likely that there are many more on the loose, unknown and uncataloged.

This diversity raises an obvious question: How can so many different viruses cause essentially the same symptoms when they infect you? The answer is that the symptoms of a cold aren’t caused by the virus itself, but by the inflammatory response that your body greets it with. This often starts with pain and swelling in the throat, followed by a runny nose as your body attempts to wash out virus particles. If the inflammation makes its way deeper into your throat, the next inflammatory symptom is coughing.

The odds are that you’ll spend some time this year battling at least one cold. Here are a few tips to keep in mind:

• Colds aren’t an indication of poor health. We all know someone who makes it through the year without the faintest sniffle—and someone else who spends an entire month bleary-eyed and runny-nosed. The odd truth is that both people may be catching the same cold viruses, but simply experiencing them differently. Before you envy the person who slips by with nary a symptom, remember that a laid-back immune response can allow a cold virus to spread farther and even cause damage before it’s destroyed.

• Vitamin C doesn’t help. It’s an enduring myth, but countless studies show that there’s basically no benefit to the citrus vitamin. The exception is marathon runners and people who perform strenuous exercise in the cold, where vitamin C appears to reduce the risk of catching the cold virus (but still does nothing to cure an existing cold).

• Blowing your nose can be risky. Most scientists agree that blowing your nose doesn’t provide any benefit for your body (other than comfort). However, there’s a darker side to nose blowing. As you learned when you explored nasal mucus, overly vigorous nose
blowing can drive viruses and inflammatory substances into your sinuses, possibly causing additional pain or infection.

• Colds travel through snot. You most commonly pick up the cold virus through airborne droplets of mucus (generated by someone else’s sneeze), or by touching a contaminated surface. Kids are prime transmitters, but even adults are adept at transmitting nearly invisible traces of mucus from their noses to their hands and then to everything else in the surrounding environment. However, the cold virus still needs to jump through a weak point in your body armor, such as your eyes, nose, or mouth. So after you touch any of these vulnerable places, make sure you wash your hands.

• Colds might prime your immune system. There’s no cure for the common cold on the horizon. Even if there were, you might not want to take it. Some researchers believe that a cold-free life might leave people at increased risk for allergies and asthma.

Source of Information : Oreilly - Your Body Missing Manual

Wednesday, July 18, 2012

You Are a Virus

Not long ago, you learned that many of the basic processes of human life require a partnership between your body and the bacteria that calls it home. Now you’re ready to learn another disturbing truth: you have an even more intimate relationship with viruses.

The key players are retroviruses, a broad class of viruses that carries strands of RNA instead of DNA. The interesting and highly technical part is that your body sometimes converts RNA back into DNA. As a result, a virus that holds a piece of RNA is able to fuse itself into your genes, altering your genetic code.

Before you panic, remember that your body has trillions of cells, and virus-infected cells generally don’t last long before white blood cells destroy them. However, there’s always the possibility that a virus will find its way into a germ-line cell—in humans, these are the cells that produce male sperm and female egg. If a virus lands in one of these cells, it has a good shot at being incorporated into the genes of the next generation. And that’s not science fiction, as recent studies suggest that nearly 10 percent of human DNA consists of pasted-in viruses from the past.

Now, it’s important to understand that a virus integrated this way probably isn’t going to infect newly minted babies. That’s because the virus incorporates its DNA in a random place. Usually, it’s in the vast wasteland called junk DNA—segments of your genetic code that don’t appear to do anything at all. However, occasionally a virus lands somewhere important, and the result is usually trouble. Some researchers believe hemophilia and muscular dystrophy are two genetic diseases that cropped up when random, viral DNA blundered into the wrong spot.

Finally, here’s the really interesting part: As you probably know, evolution works when apparently random changes in a creature’s DNA give it a valuable survival advantage. And while viral DNA is more likely to cause a problem than to confer a benefit (and is most likely to do nothing at all), every once in a while a bit gets into a place where it just might do real good. In fact, many scientists believe that viruses have helped shape evolution on our planet by reshuffling genes, pasting in their own contributions, and carrying genes from one species to another. So while life started as mere bacteria, viruses just might have supplied some of the variety that drove evolution forward and led, eventually, to the creation of you.

Source of Information : Oreilly - Your Body Missing Manual

Sunday, July 15, 2012

The Life Cycle of a Virus

To do anything, a virus needs your help. First, it needs to get into your body, and it does that in much the same way as bacteria does—by being inhaled into your lungs, swallowed into your digestive tract, or absorbed through a cut in your skin.

Once inside your body, the virus drifts aimlessly until it comes into contact with the right cell—one that has a coat of proteins that complements those of the virus. When the virus bumps up against this cell, its proteins lock on. (Keep in mind this isn’t a conscious decision for the virus—it’s simply a reaction caused by the fact that it fits the target cell like a fuzzy sweater and a strip of Velcro.)

What happens next is more unsettling. The virus launches the multiple steps of its attack procedure. First, the virus needs to get inside the cell. In some cases, the cell may engulf the virus in the same way that it swallows tiny nutrients, pulling it in. Or the virus may inject its genetic material through the cell wall. Either way, the damage is done. The foreign genetic material finds its way deep into the cell’s working parts, where it quickly takes over.

In the classic case, the virus inserts a short snippet of DNA into the target cell (as shown in step 1 of the figure on page 221). Like all strands of DNA , this DNA contains instructions for building specialized proteins. The target cell cheerily follows these instructions, unaware that it’s helping the enemy.

Once built, these proteins begin to carry out their pre-programmed functions manufacturing thousands of new viruses. (This is what happens in step 2 and step 3.) In this way, the virus hijacks the inner workings of the cell, like a pirate commandeering an ocean liner. But all the while, the virus hasn’t actively done a single thing. It’s just a set of malicious instructions that your body executes, simply because the virus was in the right place at the right time.

Once they’ve taken over a cell, most viruses replicate like Viagra-fuelled rabbits. Eventually, they leak out of the cell through tiny pores or blow it apart like an overfilled water balloon (as you can see in step 4).

There’s a virus for virtually every type of cell. Viruses infect animals, plants, and even bacteria. (In fact, it’s likely that the bacteria that causes cholera would be completely harmless were it not for the presence of a toxinproducing virus embedded inside.) However, the viruses that affect one species are often unable to affect another, or they may have dramatically different effects. HIV is a well-known example—not only is it unable to infect other animals, but the related SIV strains that affect monkeys and chimpanzees rarely cause the compromised immune system and debilitating symptoms of AIDS.

Viruses don’t necessarily correspond to illnesses. In fact, many viruses have no symptoms. They don’t destroy their host cells, reproduce very quickly, or create poisonous compounds. Virtually all people have at least a few harmless viral passengers hiding in their bodies.

Source of Information : Oreilly - Your Body Missing Manual

Wednesday, July 11, 2012


In some respects, the battle between bacteria and your body is refreshingly straightforward. Huge armies of microscopic, foreign creatures flood your body. They wreak havoc—briefly—before your better-armed defensive forces destroy them.

Viruses are a different matter. First, they’re much tinier— about a hundredth the size of
an average bacterium. In fact, viruses are so vanishingly small that even the most powerful optical microscope can’t spot one (although a cutting-edge electron microscope can). Stack viruses and bacteria together, and it’s like comparing a toddler to a brontosaurus.

To get a better feel for the difference in scale, check out www.cellsalive.com/howbig.htm. There you’ll see a simple animation that places you on the head of a pin and increases the magnification until you can spot a dust mite, a particle of pollen, and a red blood cell. Zoom in still more and you’ll be able to make out the much smaller cell of a bacterium, and then, finally, a virus.

There’s another clear difference between bacteria and viruses, but you need to step into their microscopic world to see it. Up close, a bacterium looks like a tiny alien being. It may be small (and ugly), but it’s full of life— feeding, reproducing, and generating energy with some of the same processes your own cells use. Many bacteria are even able to move by propelling themselves with long, whip-like tails, or by gliding along paths of self-produced slime.

By comparison, a virus looks more like a piece of organic debris. Its structure is simple—in fact, a virus consists of little more than a submicroscopic scrap of genetic material (either DNA or its relative, RNA) wrapped in a thin coat of protective protein. On its own, a virus is silent, inert, and completely lifeless. It’s unable to power a single one of the chemical reactions required for life.

If it weren’t for the presence of other life-forms, this is where the story would end. But as you’ll see, viruses have the uncanny ability to turn up at the right place at the right time—namely, in the midst of a normal cell’s manufacturing process.

The lifelessness of viruses makes them dangerous in another way. Because they don’t live on their own, they’re in little danger of dying naturally. In other words, they won’t run out of fuel or burn out from the hard work of cellular life. In fact, some viruses (like anthrax) can linger for years in the outside world. Others can sleep inside their hosts, waiting for the right trigger before they become active.

Source of Information : Oreilly - Your Body Missing Manual

Friday, July 6, 2012

Can You Taste Spoiled Foods?

E. coli and other food-borne bacteria (like salmonella and campylobacter) are tasteless. Contaminated food gives no obvious sign of the single-celled organisms that lurk there, waiting to colonize your body. This raises an excellent question: If dangerous bacteria don’t leave obvious signs, what’s making that week-old package of ground beef smell so bad?

The answer is spoilage bacteria, a family of bacteria that thrives on just about any food. As these bacteria replicate, they coat your food with slime. The waste products they leave behind cause the objectionable changes in smell and taste. However, for all their obvious repulsiveness, eating them probably won’t make you sick. That’s because spoilage bacteria is ideally suited to the world of decaying grocery produce, not the high acid environment of your stomach.

So does this mean that you can add rotten food to your dinner table without harm? Well, not quite. As spoilage bacteria break down food, other organisms hitch a ride. Molds quickly join the party (for example, the fuzzy green fur on forgotten salami). Some are dangerous and create poisonous substances that permeate food, and they remain even after cooking.

Furthermore, if conditions are ideal for spoilage bacteria, it’s a safe bet that they’re good for pathogenic bacteria, too. In other words, if your food is spoiled, it’s also more likely to hold a teeming population of pathogenic bacteria, and therefore to pose a greater health risk.

Source of Information : Oreilly - Your Body Missing Manual

Tuesday, July 3, 2012


The standard way to combat a bacterial infection is with antibiotics, a class of chemicals that kills bacteria. Although we group them into a single category, different antibiotics work in different ways. Some destroy the bacteria’s cell walls, causing them to burst and die. Others disrupt the processes bacterial colonies use to reproduce. Either way, the basic principle is the same—antibiotic drugs interfere with the machinery of bacterial life without affecting the way human cells operate.

Just as antibiotics have no effect on human cells, they also leave viruses, parasites, and fungal infections untouched. You’ll need different types of drugs to battle these attackers—antibiotics will have no effect. And in the case of viruses, you’ll usually be forced to wait and suffer until your immune system ramps up its defenses. (That’s why a trip to the doctor’s office won’t help you cure the average cold or flu.)

Some antibiotics work against certain families of bacteria and are called narrow-spectrum antibiotics. Others destroy wide swaths of bacterial life and are called broad-spectrum antibiotics. But neither sort can distinguish between the bacteria that harm your body and those you’d like to keep. When antibiotics wipe out the beneficial bacteria in your colon and on your skin, they often lead to side effects like diarrhea and fungal infections of the mouth, digestive tract, and vagina.

A more serious problem is antibiotic resistance—the ability of bacteria to evolve immunity to commonly prescribed antibiotics. Antibiotic resistance usually occurs when a colony of bacteria meets up with antibiotic drugs. Although these antibiotics destroy virtually all the bacteria—and they do it quickly—they may leave behind a few rare mutants that have some level of natural immunity. If the antibiotic attack keeps up, these mutants will eventually die along with their weaker relatives. But if the onslaught ends, these mutants will have a chance to establish a new, more resistant colony. Repeat the process a few times, and you’ll gradually breed stronger and more resistant bacteria. And throw in a few different types of antibiotics, and you just might produce a superbug that’s impervious to all forms of standard treatment. Even worse, bacteria have a naughty habit of swapping DNA, which means the antibiotic resistance that develops in one species can leap to another, more virulent strain.

Now that you understand antibiotic resistance, you know why your pharmacist always tells you to finish the full course of your antibiotic prescription. If you have an infection, most antibiotics will destroy the large majority of bacteria in just a couple of days. But if you stop at that point, you may spare a few, resilient stragglers. And like the son who avenges the father in a cult karate movie, those bacterial stragglers just might come back to wreak some serious havoc in your body or someone else’s.

Another way to help prevent antibiotic resistance is to avoid using products that contain unnecessary antibacterial chemicals. The best example is antibacterial soap, a mostly useless product that’s debunked.

Source of Information : Oreilly - Your Body Missing Manual