Exploring the World of Medicine

Everything your kids (and you!) wanted to know about the medical field, presented in clear, understandable language, with beautiful visual aides. This fascinating book will keep children interested for hours and will surely become their go-to reference book for everything related to their bodies, the medicine they take, and what happens at their doctor's visits.

Send in e-mailSend in e-mail
Send in e-mailSend in e-mail
Immune System blood

Exploring the World of Medicine


Did You Know?

To make sure that we stay healthy, our body has a sophisticated, efficient system of cells and organs that operates round the clock. This system is our:


Why Our Immune System Is So Sophisticated and So Efficient

Our immune system can tell the difference between cells that make up the tissue and organs in our body, and between cells such as germs, viruses and parasites that invade our body and can make us sick. When our immune system discovers these invaders, it launches a defensive response intended to ward them off and destroy them.

The Roles of Our Immune System

The roles of our immune system are:

         To detect “invaders” such as germs, viruses, parasites, fungi and toxic substances, and to prevent them from entering our body and spreading.

         To protect the systems in our body against infections and, in this way, assure that they function properly.

         To mobilize a full-scale defense system to fight the invaders and destroy them.

Important Facts:

Proteins are normally the building material of living cells.

Proteins that are not the building material of living cells are perceived as foreign substances, and can provoke an immune reaction, and are called:


Viruses, parasites, germs, fungi and poisonous substances can operate as antigens, triggering a defensive response by our immune system.

Our Immune System Is Our Defense System

Let’s compare our immune system to a defense system. It has two lines of defense:

1) An external line of defense, consisting of our skin and of the tissue that covers the lumen of our respiratory and digestive tracts.

2) An internal line of defense, consisting of our body’s inner cells and organs. They function as “factories” that produce defense mechanisms against foreign invaders managing to penetrate our external line of defense.

Our Body’s External Line of Defense


Our Body’s External Line of Defense Consists of:

1. Our skin, which is our body’s largest organ. Our skin separates the inside of our body from the outside world. So, it is a kind of “protective shield” against invisible invaders.

2. The tissue that cover the lumen of our respiratory and digestive tracts. It is equipped with mechanisms that prevent foreign invaders from penetrating our body through it.

Our Body’s Internal Line of Defense

Our body’s internal line of defense is a kind of “factory” that produces defense mechanisms against foreign invaders. This “factory” has five platoons:

The Five Platoons That Manufacture Our Body’s Defense Mechanisms

1. Marrow Platoon

The Marrow Platoon is the tissue inside our bones that produces the cells of our blood system: red blood cells, platelets and leukocytes (which are different types of white blood cells).

2. Spleen Platoon

The Spleen Platoon is an internal organ that serves as a meeting place for different types of white blood cells.

3. Thymus Platoon

The Thymus Platoon is the organ through which part of our white blood cells pass. As they do so, they acquire special characteristics that enable them to fight invaders.

4. Lymphatic System Platoon

Flu Virus

The Lymphatic System is made up of the lymphoid organs of the immune system, which are distributed throughout our body and linked to one another by lymphatic vessels.

The Lymphatic System Consists of:

(A) A network of capillaries and lymphatic vessels is draining to lymph nodes platoon.

(B) Lymph, or lymphatic fluid, which circulates throughout our lymphatic system until it reaches our bloodstream. It transports cells of our immune system to our body’s tissues

How Interesting!

Our body movements and muscle contractions press on the lymphatic vessels carrying lymphatic fluid, causing it to move and to circulate throughout our body. In contrast, it is only the contractions of our heart that cause our blood to circulate throughout our body.

5. Lymph Nodes Platoon

Lymph Nodes consist of the immune system’s “fighter” cells. Our lymphatic and blood vessels carry these cells, which gather in large quantities along the vessels, concentrating in particular in our groin, belly, under our armpit and round our neck. That is how node-like structures, called lymph nodes, are formed. These lymph nodes become a meeting place for different “fighter” immune cells.

Important Information

Our immune system is made up of a group of organs and tissues functioning together as a unit and sharing a common goal: to protect our body against “invaders”.

T Cell

Useful Information

Sometimes, when we have a cold, we feel painful little lumps in our neck. These lumps are lymph nodes. They are swollen because the immune cells inside them just fought the invaders.

The Active Cells Platoon in Our Body’s Internal Line of Defense Operates in This Way:

The defense cells, which are our immune cells, set out to protect our body.

They leave our bone marrow and thymus gland,

travel through our blood vessels,

and pass through our lymph vessel system,

reaching our lymph nodes and spleen.

From there, they wander with our bloodstream throughout our body, “on patrol”.

Wherever they find an infection, as the result of the penetration of an invader,

they rush to locate it

and to carry out their duty.

The platoons on guard set out to take defensive action.

The first to set out to defend our body is the white blood cell platoon, which is made up of cells called macrophages. Their defense mechanism identifies the invader as a foreign protein, swallow it and present it, or parts of it, to the other white blood cells.

Neutrophils form another white blood cell platoon. They wander with our bloodstream, reach infected areas in our body, detect invaders, and kill the germs directly.

Lymphocyte Blood Cell Platoon:

This is the main platoon that defends our body against invaders.

The Lymphocyte Blood Cell Platoon Is Divided into Two Parts:

T-Cell (T-Lymphocyte) Platoon

B-Cell (B-Lymphocyte) Platoon

The membranes of T-cells and B-cells have special molecules called receptors.

These receptors are the defense mechanisms of T-cells and B-cells, and they can detect invaders that have penetrated our body. Each receptor is adapted to the identity of a specific invader. They can be likened to field scouts, because their role is to find out what is going on in our body and who has invaded it.

Important Information

What is a molecule?

A molecule is a tiny particle from which all material is built.
T-Cells and B-Cells Embark on Defensive Action Against the Invaders


When T-cells embark on defensive action, they have several roles:

They form contact with macrophages cells that have already met the foreign protein and swallowed it.

After familiarizing themselves with the foreign protein,

additional fighter T-cells directly kill various viruses and parasites with the help of cells called killer cells.

Other defender T-cells start to release substances that activate B-cells.

Another small group of T-cells multiply rapidly, and remain in our bloodstream as memory T-cells.


When B-cells embark on defensive action, they also have several roles:

They detect the invaders and, following their familiarity with them, start to produce antibodies against them.

These antibodies, which are Y-shaped protein molecules, are released into our lymphatic system and bloodstream.

Each B-cell produces one type of “fighter” antibody that is specially adapted to a particular antigen, and against which it embarks on defensive action.

A small group of B-cells turn into memory B-cells.

What Do Memory Cells Remember?


If the same foreign protein penetrates our body again, our memory T-cells remember its chemical signal. They quickly detect it, and in this way can respond far more swiftly than the first time.


If the same invader penetrates our body a second time, memory B-cells remember it, based on its chemical signal, and swiftly detect it. At once, they accelerate antibody production to a much greater extent compared to their first encounter with the foreign protein.

What I Would Like To Know:

Can You Catch the Same Infection More than Once?

This is a very interesting question. For some insight, read this historical story:

A Story from the Past

The ancient Greeks realized that people who recovered from the plague did not catch this fatal disease again for the rest of their lives. Their body remembered the agent that caused it the first time, and was able to respond to its presence far more efficiently when it returned a second time.

How Is This Story from the Past Connected to Modern Medical Knowledge?

In the past, people did not know the causes of diseases. Today, medical science has shown that the immune system, whose role it is to keep our body safe, remembers every type of invader that ever infected us, thanks to memory T-cells and memory B-cells.

Important Information

Our body has different types of cells. Each cell is designed to perform duties specific to only it.

All our cells cooperate by transmitting information by means of chemical signals produced by a variety of molecules.

This reciprocity between the different cells and organs in our body allows them:

         to build a sophisticated, complex information network

         to respond swiftly and precisely to any invader penetrating our body.

Think about This

Every B-cell produces antibodies, releasing them into our bloodstream at the astonishing rate of approximately 2,000 per second, or 120,000 per minute.

Calculate how many antibodies are released into our bloodstream in 10 minutes, in 60 minutes, and in as many minutes as you like.

This Is Important

How is it possible that you got the flu or caught a cold once again this year?

Yes, there is a reason that you got the flu again this year even though you had it last year. It is because the flu virus you caught this year is a different kind. So, your body’s memory T-cells and memory B-cells did not recognize it, and could not respond appropriately.

Similarly, if you caught a cold again this year, that is because the common cold is caused by many different types of viruses, and your memory T-cells and memory B-cells are unfamiliar with the particular type that invaded your body this time round.


Sometimes, there are different types of pathogens that your memory cells are unacquainted with. That is why this year you may catch a different version of the very same illness that you came down with last year.

However, if you are ever exposed to the very same “invaders” again, it is more likely that you will not fall ill this time round, or that this time you will catch the mildest form of the illness.

Does Our Immune System Ever Fail To Perform its Duty?

When our body’s “defense system”, which is our immune system, fails to perform its duty and has difficulty responding to invaders, it is due to a condition called an Immunodeficiency Disorder.

There are two kinds of immunodeficiency disorders:

1.  Congenital Immunodeficiency:

This condition appears in babies born with defects in their immune system.

2. Acquired Immunodeficiency:

This condition appears when a person was born with a healthy immune system, but it was harmed in the course of life.

The severest form of acquired immunodeficiency appears in people who have contracted the human immunodeficiency virus (HIV) and now suffer from acquired immunodeficiency syndrome (AIDS).

How Do People Who Have AIDS Cope with Their Disease?

People who have AIDS cope with the help of medications. Before specific medications were developed, it was fatal. Today, research, focusing in several directions, has enabled the development of a range of effective medications.

However, in spite of the fact that these medications:

         delay the multiplication of the HIV virus,

         and  halt the progress of AIDS in infected people,

it does not rid the body completely of the disease.

Deadly HIV Virus Sneaks into T-Cell:

White blood cell (to left): Virus particle, colored blue, destroys immune system.

I Am Curious

Why Is it so Hard for Scientists To Develop a Vaccine against the HIV Virus?

It is difficult for scientists to develop a vaccine against the HIV virus because it is so different than all other known viruses.

The reason that the HIV virus is different from any other known virus is because it constantly changes its genetic features, that is, mutates, at an incredible speed. That is its special “trick”.

More on the “Trick” that the HIV Virus Uses

The “trick” that the HIV virus uses in order to continue multiplying is to constantly change its protein shell (capsid), and at an incredible speed.

The protein shell of all viruses is composed of antigens, which trigger the body’s immune response. However, the shell of the HIV virus changes with such dizzying swiftness that even the body’s T-cells and B-cells, whose receptors are the immune system’s unique protective mechanism, cannot manage to adapt themselves quickly enough. As a result, the immune system fails in its duty to protect the body, and collapses.

The challenge that science faces is to develop a vaccine that will quell the incredibly swift, constant mutation of the HIV virus and, in so doing, immunize the body against it.

Important Information

Since the mid-1990s, significant progress has been made in the treatment of AIDS patients and of HIV carriers (people who have a dormant form of the HIV virus).

What Happens When the Immune System Overreacts to Environmental Antigens?

Did you ever start sneezing, and could not stop?

Do your eyes water at times?

Do your hands start itching the moment you touch grass or trees?

These are typical reactions of the immune system when something is wrong with it.

Sometimes, our immune system reacts very strongly to common substances in our environment that normally do not trigger an immune response.

This reaction is known as an allergic response.

Many people are allergic to some antigen or other in our environment.

Invaders that Trigger an Allergic Reaction by Our Immune System

         The pollen of various flowers, grass, weeds and trees, which fly in the air.

         Cigarette smoke, substances emitted into the air by industrial plants, sawdust, trees, flour, etc.

         Milk products, eggs, peanuts and nuts.

         Seasonal weather changes, transitional seasons (spring and autumn), winds and dampness.

         The hair, fur and feathers of animals such as cats, dogs, poultry, birds and horses.

         House dust mites, which are microscopic organisms found mainly in bedding.

Cancer and the Immune System

How does a Cancer develop?

Sometimes the control mechanisms of a cell are damaged. Something goes wrong with one cell.

If that cell starts to multiply uncontrollably, it causes the section of the tissue in which it is located to grow and to turn into what is known as a tumor.

In the first stage, when the tumor is benign, it does not damage the body.

When Do Tumors Damage the Body?

When the cells in which something went wrong not only create tumors locally, but also invade neighboring tissue.

The tumor cells use the body’s fluids to travel to other parts of the body, where they multiply and create additional tumors.

These tumors are called cancerous tumors.

How the Immune System Copes with Cancer

The moment the immune system detects cancerous antigens, the immune cells embark on the offensive.

They set out to fight back.

Macrophages cells surround the antigens on the surface of the cancerous cells.

As a result,

the T-cell system is activated:

Some T-cells embark on direct action,

and kill the cancerous cells.

Other T-cells activate the B-cell system:

The B-cells produce antibodies against the antigens on the cancerous cells, and in this way help to destroy them.

Sometimes, the immune system has a hard time coping with cancer. In such cases, the medical profession comes to the rescue.

How the Medical Profession Helps Sick People Cope with Cancer

There are different kinds of medical treatments for malignant tumors. Their goal is the destruction of the malignant cells, and the restriction of damage to other tissue.

The Advantages of Medical Treatment:

1. The number of people recovering from cancer increases.

2. The life expectancy of many sick people rises.

The Disadvantages of Medical Treatment:

1. When the malignant cells are destroyed, healthy tissue is damaged.

2. Sometimes, the malignant cells are totally destroyed, while at others only partly.

The medical profession has been conducting research on cancer for decades. It aspires to:

1. develop more focused, effective methods of destroying malignant cells that are multiplying, while restricting the damage to other tissue.

2. detect the basic fault causing healthy cells to become cancerous, and divide and multiply unceasingly.

This Is Very Important

The biggest challenge that cancer researchers face is to:

         outline ways to prevent the development of cancerous cells

         improve treatment methods

         improve the methods for early detection of cancer

Medical advice: Dr. Yael Levy

More about the World of Medicine