Transcript Immune System

Immune System
The body system that fights off
invading pathogens and prevents
the growth and spread of cancers
What are pathogens and how do
we encounter them?
• Every second of everyday, the human body is
exposed millions upon millions of pathogens.
• Pathogens include bacteria, viruses and other
organisms that can cause infectious diseases.
• Our body encounters these pathogens through
air, water, food, and touching many different
pathogen-containing objects (maybe people).
• Luckily, our body has three different lines of
defense to combat these pathogens.
Virus
First line- Skin and Mucous
Membranes
• As long as one’s skin remains intact, it can act
as a barrier against pathogens. Keratin in the
skin makes it tough for pathogens to pentrate
• Sebaceous and sweat glands give off secretions
from a pH from 3-5. This is acidic enough to
prevent pathogenic growth. Saliva, tears, and
mucous membrane secretions “bath” the skin’s
surface and contain antimicrobial proteins. One
protein is lysozyme which breaks destroys the
cell walls of bacteria.
Sebaceous and sweat glands
• Mucus, a fluid from cells of mucous
membranes, trap microbes
• Microbes swallowed in foods or water
must attempt to survive in the acidic
environment of the stomach
Second line- The Inflammatory
Response
• Whenever there is an injury such as a cut, a
pathway is created for pathogenic entrance and
the damaged cells send out chemical
messengers “asking for help.” One chemical
messenger is called a histamine. It increases
blood flow to the injured area and permeability of
the surrounding capillaries, enhancing the ability
to clot.
• Then, white blood cells pass through the
capillaries and to the site of the injury. If bleeding
occurs, platelets and blood-clotting proteins rush
to the damaged tissue and
• “seal it off,” not allowing the entrance of
any pathogens.
• As for the pathogens that have already
entered, white blood cells ingest the
invading organisms (this is called
phagocytosis). White blood cells involved
in phagocytosis are called phagocytes.
Phagocytosis
Types of Phagocytes
• Neutrophil- makes of 50-70% of wbcs. Roams
freely throughout blood vessels and at site of
infection, engulfs and destroys pathogens but
also itself (first to arrive)
• Macrophage- Maybe stationed in tissue waiting
or free floating. Gets rid of worn-out cells and
cellular debris.
• Natural Killer Cells-Attacks cells that have been
infected by pathogen, not the pathogen itself
• Eosinophils- Attach to external wall of larger
parasitic invaders, an inject destructive enzyme
inside of them
Macrophage
More info to know
• Pus (white covering over cuts) is actually the
accumulation of dead white blood cells and
pathogens
• Pathogens often trigger fever because they are
released as chemical signals (pyrogens) by
macrophages and a sign that the body is in the
act of fighting an infection.
• Interferons are proteins that stimulate
neighboring cells to produce viral proteins, that
stop the virus’ reproduction. Helps prevent cellto-cell spread of viruses
Pus
Third Line- Immune System
What are some major organs
involved and what do they do?
• Bone marrow- Found inside long bones,
manufactures new white blood cells daily
• Thymus- A gland in the upper part of the
chest where white blood cells mature
• Lymph nodes- Located throughout the
body in the vessels of the lymphatic
system. Filters pathogens from lymph
which are exposed to wbcs.
• Spleen-Located behind the stomach and
helps filters pathogens from the blood
Components of Immune System
Are there white blood cells in the
immune system?
• Yes, they’re called lymphocytes
• Two types:
• B lymphocytes (B cells)- produced and
mature in bone marrow
• T lymphocytes (T cells)-produced in bone
marrow but mature in thymus
Pathogen recognition
• When a pathogen or foreign invader enters the
body, the lymphocytes must be able to recognize
it as foreign (immune response) and specify it
from the other cells in the body. The substance
that triggers this immune response and is
identified as a pathogen is called an antigen
(basically any recognizable pathogen)
• Lymphocytes have receptor proteins on the
surface of their cell membranes. These proteins
recognize and bind to the antigens that have
their same three-dimensional shape. Our body
produces thousands of different lymphocytes,
each with a different receptor
Antigen
Immune Response
• The Immune response starts when a
macrophage engulfs and kills the
pathogen. After destroying it, it places
fragments of the pathogen’s antigens on
the surface, so it can be identified by a
type of T-cell called a helper T-cell. Once it
is identified, the macrophage releases
interleukin-1, a regulatory protein or
cytokine. In turn, the helper T-cell releases
interleukin-2.
Cell-Mediated Immune Response
• Interleukin-2 in turn activates the division of
helper T cells, cytotoxic T cells, and suppressor
T cells.
• Cyotoxic T cells identify the pathogen antigen
because it is on the affected cell’s surface. They
kill the cell by puncturing its cell membrane
• Suppressor T cells then terminate the immune
response after the pathogen has left the body
Humoral Immune Response
• Another course of action is taken after the helper
T cells releases Interleukin-2. B cells are
produced and “differentiate into plasma cells.”
• Plasma cells create defensive proteins known as
antibodies.
• These antibodies attach to pathogens that fit the
shape of their protein and inactivate it, or
provoke its termination through nonspecific
defenses.
Antibodies
Natural Immunity
• After being infected with a disease, some B and
T cells are still left in the body. These cells are
“the body’s long-term protection against
reinfection by a specific pathogen and are called
memory cells. Memory cells make sure one
doesn’t receive the infection again. Being
exposed to the pathogen a second time triggers
(secondary immune response) the memory cells
to prepare and fight the infection before it can
become effective. The first time the antigen is
encountered by the immune response it is called
a primary immune response.
Artificial Immunity
• Legitimate but weakened microbes or
bacterial toxins, are given in the form of
immunization. They cannot cause disease
but instead create an immune response
triggering the production of memory cells
• Immunizations can wear over time
• There are immunizations for polio, tetanus,
and measles to name few
Polio Immunization
Passive Immunity
• Passive Immunity-antibodies can passed
from one individual to another
• Rabies-one with rabies can get the
antibodies from one who is immune to it
Allergies
• Harmless antigens that may cause
wheezing, watery eyes, or sneezing
• Caused by the release histamines and can
be combated by antihistamines, that
relieve one of their symptoms
AIDS
• Acquired immunodeficiency syndrome
• Caused by the human immunodeficiency
virus (HIV). HIV enters and reproduces
inside the helper T cells. These infected
helper T cells in turn help create large
numbers of new virus particles
• Sexual intercourse and the use of
infected-HIV syringes are the most
common reason for its rapid spread
HIV Virus
• “The body’s three lines of defense are
somewhat analogous to the defenses of a
besieged city: first the city walls, then
ordinary soldiers, and finally intelligence
officers who identify and track down
specific dangerous infiltrators.”