The human body
The human body is a sophisticated and multifaceted structure made up of different systems that cooperate to sustain life and health. It is made up of systems, tissues, organs, and cells, each of which carries out specific tasks. The body is composed of trillions of cells, which are the fundamental building blocks of life, at the cellular level. Tissues including muscle, neuron, and epithelial tissues are formed by the combination of these cells.
Organs are structures made up of various tissues that cooperate to carry out particular functions. The kidneys filter waste, the lungs help with breathing, and the heart pumps blood. These organs are components of bigger systems, such as the respiratory, urinary, and circulatory systems, in that order.
The neural and endocrine systems, which control and coordinate biological processes using hormones and electrical impulses, are also present in the human body. The skeletal system offers support and structure, and the immune system guards against illness. The digestive system breaks down food to provide energy and nutrients, whereas the muscular system permits movement.
The body’s capacity to keep its internal environment steady, or homeostasis, is essential to life. The complex interplay of feedback mechanisms that react to changes both internally and externally is how this balance is established and ensures optimal bodily function.
Why do we need oxygen?
Animals can go for weeks without food, and for days without water. But without oxygen they die in a few minutes.
Oxygen is a chemical element. It is the most abundant element on earth and it is all around you. It makes up about one-fifth of the air (most of the rest of the air is nitrogen).
Oxygen combines with almost all other elements. In living creatures, oxygen is combined with hydrogen, carbon, and other substances. In a human being it accounts for two-thirds of body weight.
At normal temperatures oxygen combines with other elements very slowly. When oxygen combines with other elements, new substances, called oxides, are formed. The combining process is called oxidation.
Oxidation goes on all the time in living creatures. Food is the fuel of living cells. As food is oxidized, energy is released. This energy is used for moving the body and for building new body substances. The slow oxidation in living creatures is often called internal respiration.
The human body, oxygen is breathed in through the lungs. From the lungs, oxygen passes into the bloodstream and is carried to all parts of the body. The breathing process supplies the cells with oxygen for respiration. So, we need oxygen for the energy to keep the body functioning.
People who have trouble breathing are often placed in oxygen tents. Here the patient breathes in air that is from 40 to 60 percent oxygen. The patient thus uses little energy to get the oxygen he needs.
While oxygen is continually being removed from the air, the supply of oxygen never seems to get used up. Plants give off oxygen as they make food, and this helps keep up the supply of oxygen.
How does the brain send messages to the human body?
The brain can get signals, add them up, and signal back for action in a split second. Different parts of the brain do different things.
The medulla, at the top of the spinal cord, controls nerves that are in charge of certain muscles and glands. The medulla keeps your heart beating, your lungs taking in air, and your stomach digesting food.
The cerebellum controls body movement and balance. The cerebrum is where thinking, learning, remembering, deciding, and awareness take place. The sensations of seeing, hearing, smelling, tasting, and touching are centered here. So are body feelings.
Scientists still do not understand how the brain does its work. But they have learned that the messages that travel through the nervous system—to and from the brain—are weak electrical charges.
Nervous are made up of nerve cells. A nerve cell consists of a central cell body with a number of threadlike parts reaching out from it. Message are passed from cell to cell through these threads.
The billions of nerve cells in the body from a huge network that leads towards the spine. Along the way nerves from different parts of the body come together in thick bundles. A thick cable of nerves from runs up the hollow of the spine to the brain. One set of nerves in the cable carries message from the senses to the brain. Another set carries messages from the brain to the muscles and glands. The brain sorts out the signals and makes the right connections.
How fast does our blood flow?
Blood doesn’t flow through the human body the way water flows through a regular series of pipes. The vessels through which blood is pumped out of the heart to all parts of the body are the arteries. But the arteries that are some distance from the heart keep on dividing and dividing until they become tiny vessels called capillaries. And the blood flows much more slowly through these vessels than it does through arteries.
Capillaries are fifty times thinner than a human hair, so that the blood corpuscles pass through them in signal file. It takes a quantity of blood about one second to flow through a capillary.
Blood is constantly flowing through the heart. It takes about 1.5 seconds for a given quantity of blood to pass through the heart, blood flows from the heart to the lung and back to the heart. This takes about 5 to 7 seconds.
Blood flows from the heart to the brain and back to the heart. This takes about eight seconds. The longest trip the blood has to make is from the heart through the trunk and the legs to the toes and then back to the heart. This takes about 18 seconds.
The time required for the blood to circulate through the entire body—that is, from the heart to the lung to the heart to the body to the heart – is about 23 seconds.
But the condition of the body has an effect on how fast the blood flows. For example, fever or work can increase the number of heartbeats and make the blood flow twice as fast. A single blood cell makes about three thousand round trips through the body’s circulation in one day.
Do we keep the same skin all our life?
The skin consists of two tissue layers. One is a thick, deeper layer of fibres called the corium. On top of this is a delicate layer of cells called the epidermis.
The epidermis contains no blood vessels. In fact, it is made up of dead cells. Only the button layer of these cells receives nutrition and is alive. These cells are very busy. It is their job to produce cells. The growth of the epidermis takes place as a result of the cells that are being produced by the cells of the deeper layers.
The new cells are pushed upward by the other cells, and so are removed from sources of nutrition and die. As a result, a chemical change takes place in them and they become a horny material. So, the lower half of the epidermis consists of cells that produce cells, the upper half of cells that have died and have been changed into horn.
The top layers of cells are detached at the same rate at which the lower layers produce new cells. So, our skin manufactures many billions of new cells daily and sheds as many billions of dead horn cells. Have you ever noticed how when you take off a pair of black stocking at night they are covered with these tiny dead cells?
This process goes on without interruption and is why our skin continues to look young year after year. So we do not actually keep the same skin all our life—we are always getting a new skin.
This is also why stains on our skin, such as ink, grease, iodine, tar, or rust, all disappear very soon. The top layer of cells is removed, a new one takes its place. And there are thirty layers of these horn cells, and when one is rubbed off, a new one pushes up from the lowest layer. We can never run out of layers of these cells.
Why is hair different colors?
Our hair has a very interesting structure. It develops from the horn layer of the skin, actually growing downward. It strikes root and then shoots upward through the layers of the skin.
Hair, like the epidermis from which it is derived, has a tissue of cells which form the “soil” in which it grows, and a horny shaft which is nourished and pushed upward by this “soil.”
Among the cells at the root of the hair are cells that contain a pigment called melanin. These cells (like the others) multiply and move upward with the hair shaft as it grows. They die and leave the granules of pigment in the hair.
The pigment granules are all shades of brown, from a reddish color to a deep black-brown. The horn substance of the hair, in which the pigment is embedded, is yellow. The color of the horny materials and that of the pigment granules mix together. And that’s how all the different colors of human hair develop, from blond to black. Our genes, which we inherit, help decide what shades the pigment granules will be, and so what the color of our hair will be.
The average person has from 300,000 to 500,000 hairs in his skin. Blond persons have finer hair and more hairs and more hairs than others. Dark persons have coarser hair and about a quarter less hair. Red-haired persons have the coarsest hair and the fewest hairs.
Your hair grows at the rate of about 13 millimeters a month. And it grows at a different rate at various times of the day.
What makes a boy’s voice change?
To produce what we call a “voice,” three things are used in the body. One is the vocal cords, which vibrate. The second is air, which normally serves for breathing, as a source of energy to set the vocal cords vibrating. And the third is the cavities of the throat (pharynx), mouth, and nose to reinforce, or resonate, the sounds.
The vocal cords are located in the larynx, or voice box. A voice has volume, pitch, and quality. Volume is related to the energy of the stream of air and to the type of resonance provided. The vibration of the cords produces vocal tone. The pitch is related to the tension, length, and thickness of the vocal cords.
Now that we see how a voice is produced, we can understand what makes a boy’s voice change. A child has a small larynx (voice box) with short vocal cords. When the vocal cords vibrate, they produce short air waves, and this results in a high-pitched voice.
At puberty the larynx begins to grow and the vocal cords become longer. And this is what makes the voice change; it becomes deeper. In boys the growth is so rapid and the difference in size of the whole voice mechanism in the throat is so great, that boys cannot get used to it quickly and often lose control of the voice. This is what people sometimes call “the breaking of the voice.” This happens with boys and not with girls because in an adult male the vocal cords are about 50 percent longer than in the adult female. Girls’ vocal cords don’t grow as fast nor as long.
While the general pitch of the adult voice depends on the length of the vocal cords, each voice has a certain range which decides to which class it belongs, such as bass, baritone, tenor, soprano, and so on.
Why haven’t they found a cure for cancer?
First, what is cancer? Basically, it is when the process of cell division in the body gets out of hand. As the new “wild” cells continue to divide, they form a larger and larger mass of tissue. So, cancer is an uncontrolled growth (and spread) of body cells.
Cancer can occur in any kind of cell. Since there are many different kinds of cells, there are many different kinds of cancer. In man alone there are hundreds of different kinds of cancer—so cancer is not one disease but a large family of diseases. This is one of the problems in finding a cure for cancer.
One approach in dealing with the problem of cancer is to learn what agents cause cancer. Scientists also need to know exactly how such agents cause normal cells to produce cancerous cells. In this way they hope to be able to prevent the disease. Other lines of research involve the search for agents to destroy the cancer cells in the body, just as modern antibiotics destroy bacterial cells.
Scientists have found many cancer-causing agents that are chemicals. Steps have been taken by governments to keep such chemicals out of food and to prevent other forms of contact with them. Such actions do help prevent cancer.
Because of the close links between cancer and viruses in certain animals, more and more scientists are coming to believe that many types of cancer are caused by viruses. But exactly how a virus can produce cancer in the human body is still not known.
So, the search for the causes of cancer is a difficult one, but much progress is being made. Eventually, it may be discovered that the different kinds of cancer have little in common. Or it may be that all the different agents work in the same way. But at present we still don’t know.
How is body temperature controlled?
A thermostat controls the temperature in a room or building by controlling the amount of heat the furnace produces. There is a part of the brain called the thalamus, which acts like a human thermostat. It controls the amount of heat in the body and keeps it at about 37 degrees Centigrade.
The body burns fuel and oxygen to make energy, which is mostly heat. Since the body makes heat all the time, it must have ways of letting some heat off, or it would keep getting hotter and hotter. The job of the thermostat is to control the amount of heat let off so that the body temperature stays at about 37 degrees.
Air from the lings carries off some heat. Waste passing out of the body also carries off heat. The body lets off much more heat through the skin. It always lets off some heat this way, which is why the skin is warm to the touch.
But the thalamus can make the skin give off more—or less—heat as needed. If the body is getting too warm, more blood than usual flows to the surface of the skin; it gives off heat to the skin surface, which gives off heat to the air. If the body is getting cold, the capillaries under the surface of the skin become smaller; less blood passes near the skin and so less heat is given off.
When the body becomes very warm, we begin to sweat. Sweat is a salty liquid produced by the sweat glands. Little tubes lead from the sweat glands to the pores in the skin. From the pores sweat spreads over the skin. Sweating speeds up the escape of heat from the body because the liquid evaporates.
The liquid changes to a gas and is carried away by the air. At the same time, it carries away heat. That is why you feel colder when you are wet than when you are dry.
Why is water good for you?
If you asked a biologist to list the most essential things for life, water would be right at the top. Water is absolutely essential to every form of life that we know. Every living cell–of plant and animal alike—depends on this substance.
As you may know, of every 4.5 kilograms of your weight, about 3 kilograms is nothing but water. Much the same is true of other living things. Without water to drink, human beings die in a short time.
Why is this so? Why is water necessary to life? The reason every living thing needs a certain amount of water is because the cells—the basic units that make up living things—have water molecules in them. Without water these basic units would be very different and of no use to life as we know it.
In the course of a day, an adult human being takes in about two liters of water, as fluids, and one liter in what we call solid foods, such as fruit, vegetables, bread and meat. These are really not dry, since they are thirty to ninety percent water.
Besides these three that enter the body from outside in the course of a day, about ten liters of water pass back and forth within the body between the various organ systems.
There are about five liters of blood in the vessels of the body, and three liters of this is water. And this remains unchanged. Even if a person feels “dried out” after a long hike in the summer heat, or has drunk four liters of beer, his blood vessels still contain three liters of water. No matter how much water you drink, you cannot dilute the blood.
What vitamins do we need?
The answer is simple: we need them all. When we don’t get a particular vitamin, the conditions that result are known as deficiency diseases.
Vitamins are very different from each other in structure. But each vitamin is a substance that the body cannot manufacture, but must have. So a vitamin is essential for some vital function of the body and must be supplied by food.
Here is a brief description of what vitamins do for us. Vitamin A is essential for growth, for vision, and for healthy skin and mucous membranes. It is supplied by milk and milk products, eggs, liver, fruits and vegetables.
Vitamin B1 (thiamine) makes possible the proper use of carbohydrates and is required by the nerves. It is found in whole-grain bread, milk, vegetables, beans, nuts, and pork. Vitamin C prevents scurvy and is essential for healthy teeth, gums, and blood vessels. It is obtained from fresh fruits and vegetables.
A vitamin called niacin is needed to prevent pellagra, a disease that causes great suffering in undernourished people. It is supplied by meat, vegetables, and whole-grain cereals. Vitamin D prevents rickets. It is manufactured in the body through the action of sun on skin. Vitamin D is now made synthetically in chemical factories and is often added to the milk you buy.
Other vitamins such as E and K and riboflavin have been isolated. Each one has a special duty to perform. That’s why one should have a well-balanced diet to ensure an adequate intake of all vitamins.
