I as in Immune System
The immune system, which is made up
of special cells, proteins, tissues, and organs, defends people against germs
and microorganisms every day. In most
cases, the immune system does a great job
of keeping people healthy and preventing infections, but sometimes problems
with the immune system can lead to
illness and infection.
The immune system is the body's
defense against infectious organisms and other invaders. Through a series of steps called the immune response, the immune
system attacks organisms and substances that invade body systems and cause
disease.
The immune system is made up of a
network of cells, tissues, and organs that work together to protect the body. The cells involved are white blood cells, or
leukocytes, which come in two basic types that combine to seek out and destroy
disease-causing organisms or substances.
Leukocytes are produced or stored in many locations in the body, including
the thymus, spleen, and bone marrow. For
this reason, they're called the lymphoid organs. There are also clumps of lymphoid tissue
throughout the body, primarily as lymph nodes, that house the leukocytes.
The leukocytes circulate through the body between the organs and nodes via
lymphatic vessels and blood vessels. In
this way, the immune system works in a
coordinated manner to monitor the body for germs or substances that might cause
problems.
The two basic types of leukocytes are:
·
phagocytes, cells that chew up invading organisms
·
lymphocytes, cells that allow the body to remember and recognize previous invaders and
help the body destroy them
A number of different cells are considered phagocytes. The most common type is the neutrophil,
which primarily fights bacteria. If
doctors are worried about a bacterial infection, they might order a blood test
to see if a patient has an increased number of neutrophils triggered by the
infection. Other types of phagocytes
have their own jobs to make sure that the body responds appropriately to a
specific type of invader.
The two kinds of lymphocytes are B lymphocytes and T lymphocytes. Lymphocytes start out in the bone marrow and
either stay there and mature into B cells, or they leave for the thymus gland,
where they mature into T cells. B
lymphocytes and T lymphocytes have separate functions. B cellss are like the body's military
intelligence system, seeking out their targets and sending defenses to lock
onto them. T cells are like the
soldiers, destroying the invaders that the intelligence system has identified.
Here's how it works:
When antigens (foreign substances that invade the body) are detected,
several types of cells work together to recognize them and respond. These cells trigger the B lymphocytes to
produce antibodies, specialized proteins that lock onto specific antigens.
Once produced, these antibodies continue to exist in a person's body, so
that if the same antigen is presented to the immune
system again, the antibodies are already there to do their job. So if someone gets sick with a certain
disease, like chickenpox, that person typically doesn't get sick from it again.
This is also how immunizations prevent certain diseases. An immunization introduces the body to an
antigen in a way that doesn't make someone sick, but does allow the body to
produce antibodies that will then protect the person from future attack by the
germ or substance that produces that particular disease.
Although antibodies can recognize an antigen and lock onto it, they are not
capable of destroying it without help.
That's the job of the T cells, which are part of the system that
destroys antigens that have been tagged by antibodies or cells that have been
infected or somehow changed. (Some T
cells are actually called "killer cells.") T cells also are involved in helping signal
other cells (like phagocytes) to do their jobs.
Antibodies also can neutralize toxins (poisonous or damaging substances)
produced by different organisms. Lastly, antibodies can activate a group of
proteins called complement that are also part of the immune system. Complement assists in killing bacteria,
viruses, or infected cells.
All of these specialized cells and parts of the immune
system offer the body protection against disease. This protection is called immunity.
Humans have three types of immunity — innate, adaptive, and passive:
Innate
Immunity
Everyone is born with innate (or natural) immunity, a type of general
protection. Many of the germs that
affect other species don't harm us. For
example, the viruses that cause leukemia in cats or distemper in dogs don't
affect humans. Innate immunity works
both ways because some viruses that make humans ill — such as the virus that
causes HIV/AIDS — don't make cats or dogs sick.
Adaptive
Immunity
The second kind of protection is adaptive (or active) immunity, which
develops throughout our lives. Adaptive
immunity involves the lymphocytes and develops as people are exposed to diseases
or immunized against diseases through vaccination.
Passive
Immunity
Passive immunity is "borrowed" from another source and it lasts
for a short time. For example,
antibodies in a mother's breast milk provide a baby with temporary immunity to
diseases the mother has been exposed to.
This can help protect the baby against infection during the early years
of childhood.
Problems of the Immune System
Disorders of the immune system fall
into four main categories:
·
immunodeficiency disorders (primary or acquired)
·
autoimmune disorders (in which the body's own immune system attacks its own
tissue as foreign matter)
·
allergic disorders (in which the immune
system overreacts in response to an antigen)
·
cancers of the immune system.
By now we all know that a healthy lifestyle, eating healthy, vitamin rich
foods, and moving in fresh air can help our immune
system work properly, but sometimes it is a long way from "knowing"
to "doing".
Here's an excellent overview from Harvard Medical School about your immune system:
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