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ASK A SCIENCE TEACHER
250 Answers to Questions You've Always Had About How Everyday Stuff Really Works
By Larry Scheckel The Experiment, LLC
Copyright © 2013 Larry Scheckel
All rights reserved.
ISBN: 978-1-61519-087-4
CHAPTER 1
The Magnificent Human Body
1. How many cells are in your body?
* There is no real consensus on the number of cells in the human body. Estimates put the number between ten trillion and one hundred trillion. A trillion is a million million—it's a word that crops up when we talk about the size of our national debt! The number of cells depends on the size of the person: bigger person, more cells. Also, the number of cells in our body keeps changing as old cells die and new ones form.
Cells are so small that most can only be seen through a microscope. Every cell is made from an already existing cell. Each cell in the body behaves like a little factory and has two major components, the cytoplasm and the nucleus. The cytoplasm contains the structures that consume and transform energy and perform many of the cell's specialized functions, including storing and transporting cellular materials, breaking down waste, and producing and processing proteins. The nucleus is the control center and contains the genetic information that allows cells to reproduce. The mitochondrion (plural mitochondria) in the cell is the factory where food and oxygen combine to make energy. Human cells and other animal cells have a membrane that holds the contents together. This membrane is thin, allowing nutrients to pass in and waste products to pass out. Food is the energy the cell needs. Each cell needs oxygen to burn (metabolize) the nutrients released from food.
The body has some cells that do not experience cell division. And red blood cells and outer skin cells have cytoplasm but do not have a nucleus.
In the cell, the process is called respiration. Oxygen breaks down the food into small pieces. The oxidizing of the food molecules is turned into carbon dioxide and water. Water makes up about two-thirds of the weight of the cell. The energy released is used for all the activities of the cell. The cell membrane has receptors that allow the cell to identify surrounding cells. Different kinds of cells release different chemicals, each of which causes certain other types of nearby cells to react in certain ways. Within each of these different cells are found twenty different types of organelles, or structures.
Slightly over two hundred different kinds of cells make up the human body. The shape and size of each type of cell is determined by its function. Muscle cells come in many different forms and have many different functions. Blood cells are unattached and move freely through the bloodstream. Skin cells divide and reproduce quickly. Some cells in the pancreas produce insulin, others produce pancreatic juice for digestion. Mucus is produced in cells in the lining of the lung. Our lungs also contain alveolar cells that are responsible for taking in gas from the blood. The cells that line the intestine have extended cell membranes to increase the surface area, helping them absorb more food. Cells in the heart have a large number of mitochondria to help them process a lot of energy, because they have to work very hard.
Nerve cells generate and conduct electrical impulses; for the most part, they do not divide. Each nerve cell has a specific place in our nervous system. Nerve cells outside of the brain are very long and have the task of passing signals between the brain and the rest of the body, allowing us to move our muscles and sense the world around us. The rest of our nerve cells—about one hundred billion of our body's cells—are brain cells.
Brain cells are the most important cells in our bodies. It is our brain that defines who we are. Brain cells in children under five do have the ability to reproduce, to some extent. However, we are naturally losing brain cells all the time. The best estimate of normal brain cell loss is put at nine thousand per day. That may seem like a large number, but remember that the brain has 100 billion cells, so a nine-thousand-cell loss per day is not that great. Inhalants, such as glue, gasoline, and paint thinner, cause brain cell loss at thirty times the normal rate. Excessive alcohol use is a big contributor to brain cell damage.
Cells that all do the same job make up tissue, such as bone, skin, or muscle. Groups of different types of cells make up the organs of the body. Different organs grouped together form a system, such as the digestive system or the circulatory system. All the systems working together make up a healthy human body.
Cells live, of course, but cells also die. Liver cells last about a year and half. Red blood cells live for 120 days. Skin cells are good for 30 days. White blood cells survive for thirteen days. And it turns out that the great majority of cells in the human body are bacterial cells, and most are beneficial. It is hard to believe that the average adult loses close to 100 million cells every minute. The good news is that the body, through cell division, is replacing those lost 100 million cells every minute. And in any case, even 100 million cells is only a small fraction of the trillions of cells that make up our bodies.
2. Why do the young and the elderly get sick more easily?
* Babies get sick more often than older children or adults because their immune systems are not fully developed and functioning at full capacity. The common cold, which is an infection of the respiratory system caused by a virus, is the most frequent malady. Doctors say that normal, healthy babies get up to about seven colds before they reach their first birthday. Another common affliction is the flu, caused by a different family of viruses, which bring on high fever, chills, fatigue, and sometimes digestive symptoms like vomiting and diarrhea, in addition to the respiratory symptoms of a cold.
Another reason babies get sick so often is that they are frequently around other children, often siblings, and this exposes them to viruses and bacteria in school and daycare. Children in schools and daycare get more colds, runny noses, and ear infections than children cared for at home. However, their earlier exposure to these diseases also leads them to develop immunity earlier.
Babies are also curious about the wide, wonderful world they are born into. So they will stick anything and everything into their mouth as a means of exploring that world. You can imagine the enormous amount of germs that ride along.
Furthermore, babies have not developed the immunity to the many different viruses that cause colds, because they haven't had time to acquire the antibodies to fight off viruses. Babies do have some of their mothers' antibodies when they are born, which were transmitted through the placenta during pregnancy. This kind of immunity isn't permanent, but breastfeeding can extend it, because many of the mother's antibodies are present in her milk. This is why breast-fed babies tend to have fewer colds and flu symptoms than bottle-fed babies. Babies, like other people, also develop their own antibodies in response to germs they are exposed to; in fact, it's a mistake to try to eliminate all pathogens from a baby's environment.
Winter is the toughest time for babies, because it is the season when colds spread nationwide. Also, in winter people spend more time indoors, where viruses are more likely to spread from one person to another. The less humid air of indoor heating dries nasal passages, which allows viruses to thrive.
All people, both adults and children, are susceptible to bacterial and viral infections. Bacterial infections include meningitis, cholera, bubonic plague, tuberculosis, diphtheria, and anthrax. Vaccines for these dreaded ailments were developed decades ago. But when the very young and very old get sick, it is most often from viruses. A prime example is the common cold.
There is no cure for the common cold, because many different viruses cause colds and even if a medicine is developed for one of them, people would still catch colds from other viruses. Many people who have colds, or whose children have colds, ask their doctors for antibiotics, because they don't understand that these drugs don't work against viruses. But there are medicines that can relieve the symptoms of colds and flu so babies can get better sooner and not suffer as much. Recent research has developed medicines against some viruses; for example, the vaccine that helps prevent the flu can also treat it if given soon enough after a person develops symptoms.
Elderly people get sick more often because their immune systems are weakened or breaking down. They also tend to have existing conditions that make them more vulnerable. Some have heart disease, kidney problems, asthma, diabetes, and a whole host of illnesses that no one looks forward to. Many of these diseases, as well as their treatments, suppress the immune system.
That's why the Centers for Disease Control and Prevention (CDC) advises that children under five years of age and people over sixty-five years of age have flu shots when each new strain begins to spread. Most people who contracted the H1N1 swine flu virus in 2009 came down with a mild illness, but the fatality rate was high. According to the World Health Organization (WHO), 284,500 died from the H1N1 virus, the majority being from Africa and Southeast Asia.
3. What are birthmarks?
* A birthmark is a colored spot on or just under the skin. Most birthmarks show up when a baby is born. Some are noticed shortly after the baby is born. Some birthmarks fade away as the child grows up, but some stay and get bigger, thicker, and darker.
Nearly all birthmarks are harmless and painless. They can be almost any size, shape, or color.
Birthmarks have two primary causes: blood vessels that bunch together or do not grow normally and extra pigment-producing cells, or melanocytes, in the skin. Doctors don't know what's responsible for these two causes, but many think there is a genetic component involved.
The most common birthmark is the port-wine stain. The stain is usually pink-red at birth and tends to become red or purple as a person ages. Port-wine stains, caused by blood vessels that do not grow normally, can have various sizes and shapes. Port-wine stains most often show up on the face, back, or chest. The strawberry birthmark is another that is found on newborns. It is also caused by a clumping of blood vessels that do not grow normally. Mongolian spots are benign congenital birthmarks found mostly on East Asians. Originating on the lower back, these bluish spots disappear by the time the child reaches age five. A salmon patch is a very common birthmark, occurring on 75 percent of newborns. It is caused by dilation of tiny blood vessels. Most salmon patches disappear by age one or two. Stork marks appear on the back of the neck, middle of the forehead, or upper eyelids. They vanish by the time the child is two years old.
The downside of birthmarks is that kids have to live with the teasing, ribbing, and cruel remarks of classmates. Some kids can go through a miserable childhood enduring the slings and arrows of their peers. But there is some good news. Makeup creams can hide many birthmarks on the face and neck or make them less noticeable. Others can be removed by surgery or lightened with a laser, but these treatments can be painful. Since most birthmarks are harmless, most are not treated.
4. Why is blood red?
* Blood is red because hemoglobin, a protein in red blood cells that binds oxygen and carbon dioxide, contains chemical compounds called hemes, and a heme is a blood pigment that contains iron, which is reddish in color. There are about thirty-five trillion red blood cells—tiny, round, flat disks—circulating in our blood at any one time—that's thirty-five followed by twelve zeroes. And each red blood cell typically has more than 250 million hemoglobin molecules, each with four heme groups!
Blood is pumped by the heart and circulated around the body through blood vessels. Blood is bright red when the hemoglobin picks up oxygen in the lungs. The red blood cells carry the oxygen, bound to their hemoglobin, to the rest of the body through arteries and capillaries. Carbon dioxide from the body's cells returns to the heart through capillaries and veins. The darker venous blood carries the carbon dioxide from the tissues to the lungs, which expel them.
The blood coursing through our body's plumbing of arteries, veins, and capillaries contains many different materials and cells. Plasma, the liquid part of blood, is a light yellow color, denser than water, and carries proteins, antibodies to fight diseases, and fibrinogen, which helps the blood clot. Plasma also has carbohydrates, fats, and salts. Young red blood cells mature in the marrow of the bone. Red blood cells have a life expectancy of about four months. Then they are broken up in the spleen and replaced by new blood cells. New cells are constantly replacing old cells. Our blood also contains several types of white blood cells. When a germ infects the body, some white blood cells race to the scene and produce protective antibodies that overpower the germs, while other white blood cells surround and devour them.
The average adult has between eight and twelve pints, or four to six quarts of blood. If a person loses a significant portion of their blood supply, they go into shock and die. This can be prevented by transfusing blood from another person with a matching blood type (see page 13). The first blood transfusion on record took place in 1665. Richard Lower of Oxford, England, took blood from one dog and put it in another dog. The first known human-to-human blood transfusion took place in 1795 in Philadelphia.
5. Why are we attracted to unhealthy foods?
* Some short answers: lots of junk foods have loads of sugar. Many junk food items are brightly colored, which attracts our (especially children's) attention. People like finger foods, such as burgers, hot dogs, and fries. Advertisers target children, making junk food more attractive than is healthy from a young age. Deep-fried foods are tastier than bland foods, and children and adults develop a taste for such foods. Fatty foods cause the brain to release oxytocin, a powerful hormone with a calming, antistress, and relaxing influence, said to be the opposite of adrenaline, into the blood stream; hence the term "comfort foods."
We may even be genetically programmed to eat too much. For thousands of years, food was very scarce. Food, along with salt, carbs, and fat, was hard to get, and the more you got, the better. All of these things are necessary nutrients in the human diet, and when their availability was limited, you could never get too much. People also had to hunt down animals or gather plants for their food, and that took a lot of calories. It's different these days. We have food at every turn—lots of those fast-food places and grocery stores with carry-out food.
But that ingrained "caveman mentality" says that we can't ever get too much to eat. So craving for "unhealthy" food may actually be our body's attempt to stay healthy.
Food manufacturers put color additives in their foods. Bright, vibrant, saturated colors look more appealing to consumers. A bright red apple is more appealing than a dull red or green apple. A key to survival in olden times was the ability to recognize foods that contained usable energy or nutrition. People needed to be able to recognize foods that contained many calories, would support healthy brain function, harbored healing medicines, and boosted the immune system. Many of those natural foods often appeared in bright colors, such as apples, oranges, bananas, carrots, and berries. Color was a reliable indicator of a healthful food. Indeed, when apples, bananas, or berries spoil, they lose their bright colors. So food-manufacturing companies are exploiting what was once a well-based notion that colorful foods are healthy foods!
Additives make foods taste better, look better, and last longer on the shelf. Experts agree that all those additives can't be good for us. Some additives come from coal tar and petrochemicals. Our bodies are not made to ingest crude oil. Some additives have been shown to be safe, but many have not even been tested. There is growing suspicion that all those additives are responsible in part for a rise in child obesity, attention deficit hyperactivity disorder (ADHD), and questionable behavior patterns. Some food dyes, such as Blue #2, Yellow #5, and Red #40, have been linked to cancer and ADHD.
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Excerpted from ASK A SCIENCE TEACHER by Larry Scheckel. Copyright © 2013 Larry Scheckel. Excerpted by permission of The Experiment, LLC.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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