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  • The human body is a complex and wondrous living machine

  • like any machine our bodies are composed of smaller parts that work together

  • the various tasks that are performed each day

  • such as breathing eating and digesting food

  • and the movement of our blood are performed by specialized structures

  • known as

  • organs. Examples of organs include the lungs

  • stomach, heart and brain.

  • All of these organs and other body parts like our skin and muscles

  • are made of smaller living units called cells.

  • Our lungs are a good example

  • of how many cells work together to perform a specialized task

  • the cells in our lungs work together to allow us to take in oxygen from the air

  • and get rid of waste products such as carbon dioxide.

  • our lungs are composed of many millions of cells

  • working together to accomplish this task

  • cancer is the result of a long process

  • that begins when one of the cells in an organ or tissue

  • becomes damaged or altered in a way that causes it to break free

  • from the normal controls that allow our cells to work together in harmony.

  • A group of misbehaving cells

  • can cause the same kinds of problems in a body

  • that a defective part would cause in any other type of machine.

  • A normal cell will divide only when it receives a chemical signal telling it to

  • do so

  • these signals are interpreted in the nucleus

  • and the cells reproduce their genetic information and divide into two

  • identical daughter cells

  • through a process called my mitosis. Cancer cells do not obey this rule

  • and will divide even if they do not receive appropriate signals

  • in addition to the signals that normal cells receive telling them to divide

  • they are also told when to stop dividing. This prevents too many cells from being

  • made

  • in fact the cell division process

  • is a highly ordered process. This is a critical issue

  • in cancer because cancer cells do not obey

  • or require normal signals for division. This can lead to the formation of a

  • mass of cells

  • that piles up and may form a tumor. Also different from normal cells

  • is the ability of cancer cells to continue dividing indefinitely

  • An important point about cells

  • is that no matter what their job is in the body they all have the same general

  • structure.

  • the cells that make up our lungs, heart

  • or brain are all similar in their overall appearance

  • even though their jobs are quite different. just as the organs that the former made

  • a smaller structures

  • cells themselves are composed of smaller parts that help them perform their jobs.

  • these smaller structures are called organelles.

  • Of particular importance in cancer is the organelle known

  • as the nucleus. The nucleus can be thought of as the brains of a cell

  • it contains the information that acts as the blueprint for

  • each and every one of us just as a manual would contain instructions to

  • assemble a chair.

  • Specifically this information is contained within the chromosomes

  • that reside in the nucleus.

  • individual units have information are called genes.

  • At a chemical level genes are made of deoxyribonucleic acid

  • or DNA. All of our cells contain the same set of information

  • It is only how the information is used that makes them different.

  • For example cells in the lungs use different bits of the blueprint to do

  • their job

  • than the cells in our stomach. In cancer

  • changes to the DNA cause some of the genes to fail to perform

  • or to do their job in a way that causes problems for the affected

  • individual

  • In short all cancers are thought to result from changes to DNA

  • that alter critical genes and change the behavior of the affected cells.

  • If a change occurs to the nucleotide sequence

  • it is like having the letters of a word changed.

  • An alteration in a gene is called the mutation

  • How do all these changes occur? There are actually a number of different things

  • that can cause mutations

  • Examples include chemicals that can be swallowed or inhaled

  • Such as those found in chewing tobacco and cigarette smoke

  • and radiation from the Sun or artificial sources like

  • a tanning bed Sometimes mutations occur without

  • any known external cause They just happen.

  • Certain genes make products that lead cells to reproduce

  • This would be equivalent to the gasoline system in cars

  • The genes that are responsible for making cells divide

  • are known as Proto-Oncogenes. Changes in these normal genes

  • lead to the production of Oncogenes The result may be cells that divide in

  • the

  • absence of proper signals It is the equivalent

  • of a gas pedal that is stuck in the on position

  • Making a car go, even when no foot

  • is pushing down.

  • Genes whose products function as the equivalent of cellular breaks

  • also exist As a group these genes are known as tumor suppressors

  • Humans have two copies of each gene one inherited from each parent

  • If a single copy of a tumor suppressor is damaged

  • the other copy is usually able to stop the cell from behaving abnormally

  • This would be like losing either the front

  • or rear brakes of a car. The car may be damaged

  • but would still be able to stop and but if the second set of brakes is damaged

  • as well

  • the car would not be able to stop. Just as the cell would not be able to stop

  • dividing

  • if both copies of the tumor suppressor genes are damaged

  • The process by which tumors cause the body to provide them with nutrients

  • is known as angiogenesis Like the hungry plant in the Little Shop of Horrors

  • a growing tumors sends out signals that essentially say

  • feed me The messages from the tumors cause nearby blood vessels

  • to send over new extensions that deliver food and oxygen

  • Importantly, the blood vessels

  • also serve as a passageway for the movement of tumor cells to neighboring

  • and distant parts of the body. Spread of tumors to distant locations is of great

  • importance in cancer.

  • About ninety percent of the deaths due to cancer

  • involve tumors that have spread around the body. The movement of tumor cells to

  • other parts of the body

  • is known as metastasis. Metastasis is a complex process

  • During which cancer cells break off the original

  • or primary tumor and move through the body to form tumors at new locations

  • From the point of view of a cancer cell, this is a dangerous

  • and often unsuccessful process A trip through the body is full of hazards that

  • cause the death of most cells that begin the journey

  • even tough cancer cells. To begin the process

  • individual cells must break away from the tumor and invade nearby vessels

  • the cells crawl along the surface of other cells

  • and the fibrous stringy structures surrounding them

  • and then force their way in. Shown here

  • is the invasion of the blood supply. Once inside a blood vessel,

  • the cancer cells may parish from a variety of causes

  • Some cells die simply because they are unable to survive

  • floating around in the bloodstream.

  • Others may become damaged and die when they squeeze through tight spaces

  • or bump into the walls of the blood vessels. Still

  • other migrating cells may be recognized and destroyed

  • by cells of the immune system. How

  • and where the migrating cells stop is different for different cancer types

  • Once the tumor cells are no longer moving

  • they can begin the process of forming a new tumor

  • by leaving the blood vessel and beginning to reproduce in the new

  • location

  • This does not always occur

  • and cells that have made it this far may still die or fail to divide

  • If the new environment is suitable the newly-arrived cell will begin to grow

  • and a new tumor will develop

  • One way that the development of cancer is prevented

  • is via the death of defective cells A cell that becomes mutated or damaged

  • will first attempt to repair the damage. If that is not possible

  • the cells will commit the cellular version of suicide

  • An orderly process called apoptosis

  • leads to the breakdown of key cell parts and the death of the cell

  • Cancer cells lose this critical capability

  • and will continue to divide This can lead to the accumulation of cells

  • that can become more and more abnormal

  • Due to the high rate at which cancer cells accumulate mutations

  • a tumor that originally started as a single abnormal cell

  • is actually made up of many slightly different cells

  • they are all cancer cells and are similar to each other

  • but they may not all have the same sensitivity to any particular cancer

  • drug or treatment

  • When this mixed bag of cells is exposed to a drug,

  • most to the cells will probably die.

  • Those cancer cells that are resistant to the treatment

  • may reproduce to form a new tumor Importantly

  • this new tumor will be unlikely to respond to the same treatment

  • Their mutations make them invulnerable to that drug

The human body is a complex and wondrous living machine

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B1 cancer tumor divide damaged process body

Animated Introduction to Cancer Biology (Full Documentary)

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    潘宇將 posted on 2014/04/16
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