Immune System

the natural defense system, present in the body of a VERTEBRATE animal which helps to protect it against diseases caused by micro-organisms and parasites. There are two types of immunity provided by the immune system:

1) natural (known as innate)--this is present from birth and is wide ranging, operating against almost any foreign substance that threatens the body.

2) acquired immunity--this type of immunity occurs as a result of an attack by a particular foreign substance. The immune system builds up its defenses against that particular substance and uses them again in any future attack.

Taken from Dictionary of Science

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An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumour cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own healthy cells and tissues in order to function properly. Detection is complicated as pathogens can evolve rapidly, producing adaptations that avoid the immune system and allow the pathogens to successfully infect their hosts.

To survive this challenge, multiple mechanisms evolved that recognize and neutralize pathogens. Even simple unicellular organisms such as bacteria possess enzyme systems that protect against viral infections. Other basic immune mechanisms evolved in ancient eukaryotes and remain in their modern descendants, such as plants and insects. These mechanisms include antimicrobial peptides called defensins, phagocytosis, and the complement system. Jawed vertebrates, including humans, have even more sophisticated defense mechanisms. The typical vertebrate immune system consists of many types of proteins, cells, organs, and tissues, which interact in an elaborate and dynamic network. As part of this more complex immune response, the human immune system adapts over time to recognize specific pathogens more efficiently. This adaptation process is referred to as "adaptive immunity" or "acquired immunity" and creates immunological memory. Immunological memory created from a primary response to a specific pathogen, provides an enhanced response to secondary encounters with that same, specific pathogen. This process of acquired immunity is the basis of vaccination.

Disorders in the immune system can result in disease. Immunodeficiency occurs when the immune system is less active than normal, resulting in recurring and life-threatening infections. Immunodeficiency can either be the result of a genetic disease, such as severe combined immunodeficiency, or be produced by pharmaceuticals or an infection, such as the acquired immune deficiency syndrome (AIDS) that is caused by the retrovirus HIV. In contrast, autoimmune diseases result from a hyperactive immune system attacking normal tissues as if they were foreign organisms. Common autoimmune diseases include Hashimoto's Thyroiditis, rheumatoid arthritis, diabetes mellitus type 1 and lupus erythematosus. Immunology covers the study of all aspects of the immune system which has significant relevance to human health and diseases. Further investigation in this field is expected to play a serious role in promotion of health and treatment of diseases.

Taken from Wikipedia

Parabolic Velocity

in astronomy, the velocity a body would need to make a parabola about the centre of attraction (also called ESCAPE VELOCITY).

Taken from Dictionary of Science

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The velocity which an object at a given point would require in order to describe a parabola about the center of attraction. This is also the escape velocity since it is the upper limit of velocity on a closed curve. It is obtained by multiplying the velocity of an object moving in a circular orbit by the square root of 2 (approx. 1.414). For example, if the Earth's mean velocity around the Sun of 29.8 km/sec. (18.5 miles/sec.), in a near circular orbit, were increased to 42 km/sec. (26 miles/sec.), the Earth would move to a parabolic path and escape from the solar system.

Taken from The Internet ENCYCLOPEDIA OF SCIENCE

Bacterium

(plural bacteria) a MICRO-ORGANISM (one that cannot be seen with the naked eye but only with the aid of a MICROSCOPE), which usually has a body made of only one cell (unicellular). Bacteria are believed by many scientists to be the first organisms to have existed on Earth and they have always been extremely important in all life processes. Bacteria occur in water, air, soil and rotting plant or animal debris, and even in extremely inhospitable environments such as hot springs full of chemicals. They are vitally important in the breakdown and decomposition of ORGANIC material--without bacteria, nothing would rot away. Most bacteria need oxygen in order to live and are called aerobic, but others do not and are termed anaerobic. The surrounding layer around a bacterial cell is called the cell wall. Two types of bacteria, which each have a different cell wall structure (Gram positive or Gram negative) are identified by a test known as Gram's stain. Some bacteria have a protective, slimy outer layer called a capsule, and others may have hairs called filaments which cause movement. Bacteria occur in a number of different shapes and forms which help to identify them. These are spiral (plural spirilli, singular, spirillus), spherical or round (plural cocci, singular coccus), rod-like (plural bacilli, singular, bacillus), comma-shaped (vibrio) and corkscrew-shaped (spirochaetae). Bacteria usually reproduce by asexual reproduction and a few are responsible for extremely serious diseases in plants, animals and man, e.g. typhoid, tuberculosis, diphtheria and cholera. These diseases can be treated with ANTIBIOTICS although there is a problem of resistance of some bacteria to certain antibiotic drugs.

Taken from Dictionary of Science

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The bacteria ([bækˈtɪərɪə]; singular: bacterium) are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals. Bacteria are ubiquitous in every habitat on Earth, growing in soil, acidic hot springs, radioactive waste, water, and deep in the Earth's crust, as well as in organic matter and the live bodies of plants and animals. There are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh water; in all, there are approximately five nonillion (5×10³⁰) bacteria on Earth, forming much of the world's biomass. Bacteria are vital in recycling nutrients, with many steps in nutrient cycles depending on these organisms, such as the fixation of nitrogen from the atmosphere and putrefaction. However, most bacteria have not been characterized, and only about half of the phyla of bacteria have species that can be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology.

There are approximately ten times as many bacterial cells in the human flora of bacteria as there are human cells in the body, with large numbers of bacteria on the skin and as gut flora. The vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, and a few are beneficial. However, a few species of bacteria are pathogenic and cause infectious diseases, including cholera, syphilis, anthrax, leprosy and bubonic plague. The most common fatal bacterial diseases are respiratory infections, with tuberculosis alone killing about 2 million people a year, mostly in sub-Saharan Africa. In developed countries, antibiotics are used to treat bacterial infections and in agriculture, so antibiotic resistance is becoming common. In industry, bacteria are important in sewage treatment, the production of cheese and yoghurt through fermentation, as well as in biotechnology, and the manufacture of antibiotics and other chemicals.

Once regarded as plants constituting the class Schizomycetes, bacteria are now classified as prokaryotes. Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and rarely harbour membrane-bound organelles. Although the term bacteria traditionally included all prokaryotes, the scientific classification changed after the discovery in the 1990s that prokaryotes consist of two very different groups of organisms that evolved independently from an ancient common ancestor. These evolutionary domains are called Bacteria and Archaea.

Taken from Wikipedia

Haemoglobin

an iron-containing red pigment, which is found within the red blood cells (called ERYTHROCYTES) of vertebrates and which is responsible for the transport of oxygen around the body. In actively metabolizing tissue such as the muscles, haemoglobin exchanges oxygen for carbon dioxide (CO₂), which is then carried in the blood back to the heart and pumped to the lungs, where the haemoglobin loses the CO₂ and regains oxygen.

Taken from Dictionary of Science

Eclipse

the total or partial disappearance of one astronomical body by passing into the shadow of another. A solar eclipse occurs when the new moon passes between the earth and the sun. A lunar eclipse occurs when the moon moves into the shadow of the earth, i.e., the earth is situated between the sun and the moon.

Taken from Dictionary of Science

Zenith Distance

the angular distance of a heavenly body from the ZENITH.

Taken from Dictionary of Science

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The term zenith distance is more often used in astronomy and is the complement of the elevation. That is: 0° in the zenith, 90° on the horizon, up to 180° at the nadir.

Taken from Wikipedia

Mach number

the speed of a body expressed as a ratio with the SPEED OF SOUND. Mach I is sonic speed, and thus below I is subsonic and above I is supersonic.

Taken from Dictionary of Science

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Mach number (Ma or M) (generally pronounced /ˈmɑːk/, sometimes /ˈmɑːx/ or /ˈmæk/) is the speed of an object moving through air, or any fluid substance, divided by the speed of sound as it is in that substance. It is commonly used to represent an object's (such as an aircraft or missile) speed, when it is travelling at (or at multiples of) the speed of sound.

where

is the Mach number

is the speed of the source (the object relative to the medium) and

is the speed of sound in the medium

Facts about Fluids

More than half of the human body is water (59.5%), as compared to 16% protein, 16% fat, 6% minerals, 1.5% carbohydrates and 1% miscellaneous. Dehydration can result in damage to tissues. Therefore, when you sweat heavily during the hot season or after exercising strenuously, you have to replace the water lost through sweating (as well as via urinating and breathing). To restore your body's fluid balance, the best drink is still plain water.

A cold beer won't do the job, because the carbohydrates and the electrolytes (salt and potassium) in the beer have to be broken down by the body before the water content can be absorbed. Besides, the alcohol content can be metabolized only by using more body water. How about soft drinks and sports drinks? They, too, contain glucose and electrolytes that need to be broken down before they can refresh you.

Taken from The Bosconian Forum

FACTS ABOUT YOUR BODY

HOW FAST DOES AIR TRAVEL WHEN YOU SNEEZE?

A hundred miles per hour.


WHAT MAKES YOUR KNUCKLES CRACK?

Bubbles popping! There is fluid around the joints of your finger bones. When you stretch your fingers, the pressure on the fluid changes, little bubbles form in the fluid and they pop. Want to crack the same knuckles again? You have to wait about 15 minutes.


HOW DO YOU GET "GOOSE BUMPS"?

Each hair on your body grows in its own shaft, called a follicle. If you get cold or scared, the smooth muscles around the follicles contract. This gives you goose bumps and makes the hairs stand upright.


HOW LONG DOES AN EYELASH LIVE?

About 150 days.


WHY DO SOME PEOPLE HAVE DIMPLES?

Dimples are caused by muscles on your face. These muscles are unusual because they are attached to the skin; most muscles are attached to bones. When people smile, certain muscles make dimples.


WHAT IS THE LARGEST BONE IN THE BODY?

The largest bone in the body is the thigh bone.


WHEN ARE PEOPLE THE HEALTHIEST?

People are the healthiest between the ages of five and 15.


WHEN DO KIDS STOP GROWING?

Boys achieve 98% of their height when they reach the age of 17 and three-fourths. Girls reach 98% of their height when they are 16 and a half.


HOW LONG DOES IT TAKE TO BLINK YOUR EYES?

About three-fourths of a second.


WHAT IS THE HEAVIEST ORGAN IN THE BODY?

The liver. It weighs three and a half pounds in an adult, or about five times more than the heart.


WHEN IS YOUR EYE STILL?

Never! The eye is always moving, even when you are staring at something. The tiny muscles in the eye move about 100,000 times a day to let you see. For your leg muscles to get the same exercise, you would have to walk 50 miles.


HOW MANY SOUNDS CAN YOU HEAR?

You can hear between 350,000 and 400,000 different sounds.


HOW MUCH AIR DO THE LUNGS USE IN ONE DAY?

About 12,500 quarts.


WHY DO PEOPLE YAWN?

In the lungs are millions of tiny air sacs called alveoli. Changes in the alveoli cause you to yawn. When you are sleepy, you are not breathing deeply enough oxygen. The alveoli are not filled with air. So your brain sends out a message telling you to take a long breath. That long breath is a yawn.


WHAT IS THE HARDEST SUBSTANCE IN THE BODY?

If you guessed that it is the bones, you are wrong. The hardest substance is the enamel that covers your teeth. However, like other parts of the body, the enamel cannot fix itself when it is damaged.


HOW MANY DIFFERENT SMELLS CAN HUMANS SMELL?

The average person knows 4,000 different smells. Some people with a very special sense of smell know 10,000 different scents. People who test perfumes have this talent.


HOW MANY MUSCLES DOES IT TAKE TO SMILE?

It takes 17 muscles to smile. Forty-three muscles are used when you frown.


HOW IMPORTANT IS THE THUMB?

The thumb does 45% of all the work done by your hand.

Condensed from Macmillan Illustrated Almanac for Kids