What are arteries, veins and capillaries - Human body for kids

Even in the most developed countries in the world, we can’t find a transport system, whose performance is comparable to the efficiency of the blood system in the human body.
Great “roads” and “highways” connect all kinds of big "cities", and food and other necessary supplies are delivered to them.
Such large pathways in the body are the arteries - vessels that carry blood from the heart and veins through which the blood returns to the heart.
However, in the “small towns” and “villages” there is also need for food and supplies. Small roads and streets (the capillaries) reach to the villages and houses in the human body, even to the smallest stations.
What are arteries, veins and capillaries

Circulatory system (Source: Wikipedia)

What are Arteries?

The arteries lie deep in the tissues, except in the area of the wrist, on the upper side of the foot, at the temples and on the sides of the neck.
From any of these places, we can feel the pulse, which is very important for the doctors.
Major arteries have valves at the places from where they come out from the heart.
These vessels are built from many elastic fibers and muscles that can expand and contract.
Arterial blood is bright red and moves through the arteries in waves.

What are Veins?

Veins lie near the surface of the skin and blood in them is darker and moves smoothly: they have valves at certain distances along their whole length.
Far from the heart, into all parts of the body, large blood vessels become tiny, thin as hairs, and there are called capillaries.

What are Capillaries?

Capillary is 50 times thinner than the thinnest of human hairs!
It is so thin that blood cells pass through the capillaries just one after the other, which means that the blood passes through the capillaries very slowly.
What happens when blood flows through a capillary? 
Blood leaves the capillary, but the capillary wall is thin and consists of a single layer of cells. Through the wall of the blood gives up its oxygen to the surrounding tissues, and on return it receives carbon dioxide which is released from the tissues around the capillaries. At the same time, the blood exchanges other substances that provide food to the tissue, and “unnecessary” products enter into the capillary.

Interesting facts about the human heart

  • Adult heart is the size of a fist, and weighs about 300 grams, yet it for 24 hours can produce energy sufficient to lift about 70 tons (or one locomotive) to 33 centimeters above the ground!
  • During the day, the heart tightens and relaxes approximately 100,000 times.
  • The heart of adult men in 24 hours, can pump 16.5 liters of blood.

How can you find out what your blood type is?

All people do not have the same blood. It was only recently discovered, and until then, the blood, in emergency was given by immediate transfusion regardless of the so-called blood type.
This is why half of the patients were worse and many of them died.
To determine the blood groups, are needed the red blood cells of the donor and recipient's blood serum. Serum is one part of blood plasma.

What happens if we mix different blood groups?

If one drop of blood from one type is mixed with blood or serum from other blood type, red blood cells are glued to each other and this is called agglutination. In that case, the red blood cells usually fall apart and cause hemolysis of the blood.
This is why it is important to determine blood groups.

Using agglutination tests, it is showed that the people have four blood types: O, A, B and AB.

Red blood cells of O do not agglutinate with the serum of any group.
In other words, the blood group O can be given to anyone for the purposes of transfusion, regardless of their blood type.
human blood types
That's why people with a group O are known as general blood donors.
In the group AB the serum does not agglutinate the red blood cells of any group, so that people with this blood type can receive blood of any group.

These are called “common” recipients of blood.

We all inherit our blood type, and we can’t change it in the course of our life.
An interesting observation is that across the planet there is a certain scheme of blood groups. From west toward east Europe the number of people with blood group A declines, while the number of people who have group B rises.
In England, 43 percent of people have group A, and 30 percent of the Russia, and Iran, only 15 percent.

Refraction of Light Experiment for Kids - What is Refraction?

When light passes from one substance to another, it may also change direction.
When light rays pass from air to water or from water to air, they bend as they pass through the surface of the water.
This bending is called refraction.

Refraction of Light Experiment: Can you bend a pencil?

Can you bend a pencil without breaking it?
You can make a pencil look as if it has been bent, by putting it in water.

You will need:

  • a glass
  • water
  • a pencil

1. Fill the glass halfway with water Put a pencil in the glass and lean it against the side.
Refraction of Light Experiment: Can you bend a pencil? - Part 1

2. Look at the water from the side The pencil will look bent.
Refraction of Light Experiment: Can you bend a pencil? - Part 2

3. Now take the pencil out of the water. Nothing has happened to it after all!
Refraction of Light Experiment: Can you bend a pencil? - Part 3

Refraction of Light Experiment: Can you bend a pencil? - Part 4

Light rays pass through other substances, as well as air and water.
They travel at different speeds as they pass through these substances.
As rays pass out of one substance and into another, they are refracted.
The amount that light is refracted depends on two things.
The first is the color of the light. 
Red light bends less than other colors, and violet light bends more.
The second is the angle at which the light reaches the surface of the second substance.
This is called the angle of incidence.
The angle at which the light leaves the second substance is called the angle of refraction.
Try your experiment again, looking at the pencil from a number of different angles.
You will see that the pencil seems to bend more at some viewing angles than at others.

Electrical Circuits for Kids - What is Electric Circuit?

  • Do you have a flashlight? 
  • Have you ever looked inside it? 

A flashlight won't light up unless there are batteries inside.
When you switch it on, the batteries make an electric current flow.
This current flows through the bulb and makes it light up.
When you switch on a flashlight, the batteries inside create an electric current by making electrons move. The electric current flows out of one end of the battery, through the bulb, and then back into the battery.
As long as the current can move freely around this pathway, the bulb will light up.
We call this kind of pathway an electric circuit.
While the flashlight is switched on, the current continues to flow around and around the circuit. Turning the switch off makes a break in the circuit. Now the current can't flow, and the light goes out.

Electric Circuit experiment

You will need:

  • two pieces of plastic-coated wire, about 8 inches (20 cm) long, with bare ends
  • a screwdriver 
  • masking tape 
  • a 1.5-volt("D") battery
  • a 1.5 volt battery bulb holder

Which bulb will light up?
An electric current won't flow if it can't make a complete trip around a circuit.
You can test this for yourself.
Set up the simple circuits shown below.
Can you guess which one will make the bulb light up?

1. Tape one end of a piece of wire to the top battery terminal.
Connect the other end of this wire to one side of the bulb holder.
Does the bulb light up?
Electric Circuit experiment for kids Part 1

2. Now connect the other circuits shown here.
Electric Circuit experiment for kids Part 2

Which one is a complete circuit?

Positive and negative terminals

A battery has two connections where the electric current flows in or out.
These connections are called terminals.
Sometimes, as in most flashlight batteries, the terminals are on either end of the battery. Other batteries have both terminals on one end.

  • One terminal is marked + (plus). 
  • The other terminal is marked — (minus). 

The electric current flows out of the terminal marked plus, the positive terminal.
The current flows into the terminal marked minus, the negative terminal.

Crystals for Kids - How do Crystals Form

If we look very closely at some grains of salt, we will see that each grain has the same shape.
Salt grains are shaped like tiny cubes.
Regular shapes like this are called crystals.
Many elements and compounds form crystals. The crystals in salt are easy to see. But other crystals are so small that you need to look through a microscope to see them.
Sugar and ice form crystals.

The atoms in different crystals join together to form different patterns. 
There are seven basic patterns of crystal.

The atoms of garnet form isometric crystals.
The atoms of garnet form isometric crystals.

The atoms of quartz form rhombohedral crystals.
The atoms of quartz form rhombohedral crystals.

The atoms of zircon form tetragonal crystals.
The atoms of zircon form tetragonal crystals.

The atoms of beryl form hexagonal crystals.
The atoms of beryl form hexagonal crystals.

The atoms of topaz form orthorhombic crystals.
The atoms of topaz form orthorhombic crystals.

The atoms of gypsum form monoclinic crystals.
The atoms of gypsum form monoclinic crystals.

The atoms of feldspar form triclinic crystals.
The atoms of feldspar form triclinic crystals.
Many rocks and metals in the earth's surface are found as crystals, too. The crystals of each element or compound are the same. Crystals are made when liquids cool or solutions dry out. Some of the atoms move closer together.
The crystals form in regular shapes because the atoms in the crystals arrange themselves in patterns. Crystals can grow larger over time as they attract more particles towards them. But each different crystal will always keep the same shape.

Atoms can be arranged in a variety of repeating patterns to make different crystals
Atoms can be arranged in a variety of repeating patterns to make different crystals

Aluminum Manufacturing Process - How is Aluminium Produced?

Like many metals, aluminum is a very useful element.
It is found in rock as bauxite, which is an aluminum ore containing oxygen.
The oxygen has to be removed before the aluminum can be used.
The oxygen and the aluminum are joined so firmly that ordinary smelting does not remove the oxygen as it does with other metals.
The best way to separate the aluminum and the oxygen is to pass electricity through them.
This is called electrolysis.
First of all, rock and sandy particles are removed from the aluminum ore.
This leaves a white powder called aluminum oxide.
It is made up of aluminum atoms joined to oxygen atoms.
The powder is dissolved in a tank of chemicals and heated to about 1742 °F (950 °C).
This makes the aluminum oxide melt and become a liquid.
Molten aluminum collects at the bottom of the tank.
Any impurities in the aluminum collect at the top, where the aluminum oxide cools to form a crust.
Rods made of carbon are lowered into the molten aluminum oxide.
An electric current flows through the molten liquid.
The current enters the liquid through one of the rods and leaves through the carbon lining of the tank.
As this happens, the current breaks up the molten aluminum oxide into aluminum and oxygen.
The molten aluminum metal sinks to the bottom of the tank, and the oxygen combines with the carbon, to be released as carbon dioxide gas.
The pure, molten aluminum is drawn off into a crucible and then poured into molds to cool.
The cool aluminum hardens into ingots.

What are the Primary Colors of Light and What is Color Spectrum?

The colors of the rainbow are red, orange, yellow, green, blue, and violet.
But these are not the only colors in the rainbow.
If you look carefully at a rainbow, you can see that there are colors in between the red and the orange bands that are mixtures of the two.
This is true for all the other main colors as well.
The whole range of these colors is called the spectrum.
The three most important colors of the spectrum are red, green, and blue.
These are the primary colors of light.
All the other colors you can see are mixtures of these three.
If there are equal amounts of red, green, and blue light, you see this mixture as white light.

Colors and wavelength

Try to think of light as something that travels like waves.
White light can be split up into different colors because each color is made up of waves of a particular length. The distance between the top of one wave and the top of the next wave is called the wavelength, and each color has its own wavelength.
The color blue has the shortest wavelength.
Red has the longest wavelength.
When red and green lights are mixed, the result is yellow light.
A mixture of blue and green light forms blue-green light, and blue and red lights form purple light. Combining all three primary colors in light in the proper proportions results in white light.

How much calcium is in human body?

The average human body contains about 1.5 kg of calcium. Major part of the calcium is in the bones as a major part of bone mass.
Bone structure, we could compare with reinforced concrete.
Bone has fibers called collagen fibers, similar to the flexible and iron wires that are placed in reinforced concrete. Calcium makes mass which surrounds the collagen fibers.
The amount of calcium in our bones changes with age. 
During the first year of life the child bones have very little calcium and are very flexible. The child can bend in all sorts of directions without breaking any bones. But when one experiences the age of 80, his bones can contain nearly 80 percent of calcium, and are easily breakable.
To young children we give a lot of milk, among other things, because the milk is very rich in calcium, and young organism is, of course, in need a lot of calcium. One liter of cow's milk contains more than 1.5 g of calcium. Cheese, cream and yogurt also contain large amounts of calcium.
In those parts of the world where the food does not have enough calcium people do not have healthy teeth and often suffer from bone fractures.

What Is Crop Rotation And What Are The Benefits Of Crop Rotation

The land that we need for growing food is very important. We can't afford to spoil it. There are many ways in which farmers could make better use of the land and grow good crops without the help of factory-made chemicals.
If it is farmed with care, the land will go on giving us enough food to eat for thousands of years to come.
One method of careful farming is called crop rotation.
Different kinds of plants take different nutrients from the soil and leave others behind. The same crop planted year after year takes out the same nutrients.
But different crops, like corn and alfalfa, can be planted on the same piece of land.
One year, corn is planted. This will take out certain nutrients from the soil. The following year, alfalfa will be planted. The alfalfa will put back the nutrients absorbed by the corn.

Health Care Careers List - List of Jobs in The Medical Field

Medical specialists are medical professionals who have knowledge, education, and training in a particular field of medicine.
In the following lists are presented some types of medical specialists and their areas of expertise.

List of medical careers


Area of expertise: Treatment of allergies


Area of expertise: Administration of anesthetics for surgery


Area of expertise: Diseases of the heart and circulatory system

Pulmonary Specialist

Area of expertise: Diseases of the lungs and chest


Area of expertise: Diseases of skin, hair, and nails

Emergency Medicine Specialist

Area of expertise: Emergency treatment of acute illnesses and injuries


Area of expertise: Causes, transmission, and control of infectious diseases

Family Physician

Area of expertise: Ongoing health care for persons of all ages


Area of expertise: Diseases of the digestive system

General Surgeon

Area of expertise: Surgical treatment of diseases of the abdomen, breast, and other areas


Area of expertise: Diseases of the female reproductive organs


Area of expertise: Diseases of the blood, bone marrow, and lymph tissues


Area of expertise: Nonsurgical treatment of diseases of the internal organs


Area of expertise: Diseases of the kidney


Area of expertise: Diseases of the brain and nervous system


Area of expertise: Surgical treatment of diseases of the brain and spinal cord 


Area of expertise: Health care for pregnancy, labor, and childbirth


Area of expertise: Treatment of cancer


Area of expertise: Diseases of the eye


Area of expertise: Diseases of the bones, joints, and muscles


Area of expertise: Diseases of the ear, nose, throat, and neck


Area of expertise: Study of biopsy specimens and body fluids


Area of expertise: Health care of infants, children, and adolescents


Area of expertise: Rehabilitation of patients following illness or injury

Plastic Surgeon

Area of expertise: Cosmetic surgery and surgical reconstruction


Area of expertise: Disorders of the foot


Area of expertise: Diseases of the anus, rectum, and colon


Area of expertise: Treatment of mental disorders


Area of expertise: Study of X ray and ultrasound


Area of expertise: Treatment of rheumatic diseases


Area of expertise: Diseases of the urinary tract and the male reproductive organs

Vascular Surgeon

Area of expertise: Surgical treatment of diseases of blood vessels

What is Tallying? - Tallying and Tally Marks

Can you imagine a time when people did not use numbers?
The first people on earth lived by hunting wild animals and collecting wild fruit and nuts.
They had no need to count.
Numbers did not matter to them.
But then, about 11,000 years ago, herdsmen began to keep flocks of sheep and goats.
They had to be able to count so that they would know if any of their animals were missing.
The first calculations were made by counting in ones—'1 and 1 and 1,' and soon.

This method of counting is called tallying. 

One way herdsmen used to tally was to put a stone on a pile for each animal.
Other ways were to tie knots in a length of rope, cut notches in sticks, or make scratches on a rock. Each stone, knot, notch, or scratch represented one sheep or goat.

Space Probes Information - Voyager 1 and Voyager 2 - Voyage of discovery

On August 20, 1977, Voyager 2 was launched into space.
Two weeks later, Voyager 1 set off. 

The two Voyagers were types of unmanned spacecraft called space probes.
Their mission was to travel to the more distant planets of the solar system and send information about them back to earth.
No spacecraft had ever traveled so far into space before.
Voyagers 1 and 2 each carried 11 instruments. 
These included remote-controlled computers, television cameras, ray detectors, infrared and ultraviolet sensors, and a magnetometer.
These instruments recorded and sent back information about our solar system.
Technology has developed quickly since the Voyager probes were launched. That equipment is now out of date. A modern, desktop computer is more powerful than the Voyager computers. Scientists have updated the probes' computer programs and made repairs from earth by remote control.
In 1980, three years after its launch, Voyager 1 reached Titan, Saturn's largest moon.
The probe sent back information to earth. It found chemicals like those on earth. But Titan is too cold for these chemicals to develop into living things as they have done on earth.

The journey of Voyager 2

1. On August 20, 1977, Voyager 2 was launched from earth at a speed of just over 24,800 miles (40,000 kilometers) per hour. The idea was to use the gravity, or pull, of each planet it passed to catapult the space probe faster and faster through space, from one planet to the next.
2. On July 9 1979, Voyager 2 came closest to Jupiter and discovered it has three more moons. The planet’s gravitational pull increased the speed of Voyager 2 to around 30.700 miles (48.000 kilometers) per hour.
3. It was August 25, 1981, and Voyager 2 passed Saturn at a speed of 33,700 miles (54,400 kilometers) per hour. Then we learned that Saturn has nine more moons that it was known to have.
4. At Uranus, on January 24, 1986, Voyager 2 discovered 10 new moons. Its speed was now 36,700 miles (59,200 kilometers) per hour.
5. Mission completed! On August 25, 1989, Voyager 2 passed within 3,000 miles (4,800 kilometers) of Neptune's cloud top.
We learned that this planet is a hostile world.
No living thing could survive here.
Twelve years after it left Earth, Voyager 2 reached Neptune. It had traveled nearly 4.4 billion miles (7.1 billion kilometers) and arrived four minutes early!
Voyager 2 carries its own message—a record of voices and other sounds from earth— just in case there is life beyond our solar system.
Voyager 2 is expected to enter interstellar space within a few years of 2016. It is not headed toward any particular star, although in roughly 40,000 years it should pass 1.7 light-years (9.7 trillion miles) from the star Ross 248.
Voyager 2 is expected to keep transmitting weak radio messages until at least 2025, over 48 years after it was launched.