Download Chapter 24 - Human Anatomy

The Body’s Defenses
Innate Defenses
Adaptive Defenses
Immune Disorders
© 2010 Pearson Education, Inc.
INNATE DEFENSES
• The immune system is the body’s defense against disease.
• Our bodies defend us against pathogens, disease-causing:
– Viruses and
– Microorganisms
© 2010 Pearson Education, Inc.
• Three lines of defense protect us from invaders of varying types:
– External barriers
– Innate defenses, which are
– Already present
– React regardless of whether or not an invader has been previously
encountered
– Adaptive defenses, activated by exposure to specific invaders
© 2010 Pearson Education, Inc.
THE BODY’S DEFENSES
Innate Defenses
(operate without previous
exposure to pathogen)
Internal innate
defenses
External innate
defenses
• Skin
• Secretions
• Mucous
membranes
• Phagocytic cells
Mucus-producing
cells
• Antibodies
Phagocytic
cell
Colorized SEM
Cilia
Adaptive Defenses
(activated by exposure to
specific pathogens)
•
•
•
Natural killer cells
Defensive proteins
Inflammatory
response
• Lymphocytes
B cell
The Lymphatic System
(involved in internal innate
defenses and adaptive defenses)
T cell
Lymph
node
Figure 24.1
External Innate Defenses
• The body has physical barriers including:
– A tough outer skin layer generally impenetrable to viruses and bacteria
– Mucous membranes covered with sticky mucus
– Secretions (such as tears, sweat, and saliva) with antimicrobial chemicals
– Strong stomach acids that kill most pathogens ingested with food
© 2010 Pearson Education, Inc.
Internal Innate Defenses
• To fight pathogens within the body, an animal’s immune system
must:
– Detect foreign particles and cells
– Distinguish nonself from self
• This second line of defense includes:
– White blood cells
– Defensive proteins
© 2010 Pearson Education, Inc.
INTERNAL INNATE DEFENSES
White Blood Cells
Phagocytic cells
(engulf foreign
cells or
substances)
Natural killer cells
(destroy infected
body cells and
cancerous cells)
Defensive Proteins
Interferons
(protect body
cells against viral
infection)
Complement
proteins
(cause invading
microbial cells to
lyse)
Figure 24.2
White Blood Cells
Phagocytic cells (engulf
foreign cells or substances)
Natural killer cells
(destroy infected body cells
and cancerous cells)
Figure 24.2a
Defensive Proteins
Interferons
(protect body cells against
viral infection)
Complement proteins
(cause invading microbial
cells to lyse)
Figure 24.2b
• Two important types of white blood cells are involved in internal
innate defense:
– Phagocytic cells engulf:
–
Foreign molecules and cells
–
Debris from dead cells
– Natural killer (NK) cells:
–
Recognize virus-infected cells
–
Release chemicals that kill diseased cells
© 2010 Pearson Education, Inc.
• The defensive proteins that aid in internal innate defenses work
indirectly and directly.
– Interferons indirectly help healthy cells resist damage.
– Complement proteins attack pathogens directly.
© 2010 Pearson Education, Inc.
Infected cell releases
Interferon molecules.
Virus
Interferon
molecules
Virus-infected cell
Figure 24.3-1
Infected cell releases
Interferon molecules.
Virus
Interferon molecules
bind to healthy cell.
Interferon
molecules
Virus-infected cell
Healthy cell
Figure 24.3-2
Infected cell releases
Interferon molecules.
Virus
Interferon molecules
bind to healthy cell.
Interferon
molecules
Antiviral
proteins
Virus-infected cell
The binding
stimulates
production
of antiviral
proteins.
Healthy cell
Figure 24.3-3
The Inflammatory Response
• Another example of an internal innate defense is the
inflammatory response, a coordinated set of nonspecific
defenses in response to injury or infection.
© 2010 Pearson Education, Inc.
Skin surface
Blood clot
Swelling
Splinter
Bacteria
Chemical
signals
White
blood cell
Phagocytic
cells
Phagocytic
cells and
fluid move
into area
Blood vessel
Tissue injury;
release of chemical
signals such as
histamine
Dilation and increased
leakiness of local
blood vessels;
migration of
phagocytic cells
to the area
Phagocytic cells
engulf bacteria
and cell debris;
tissue heals
Figure 24.4-3
• Damaged cells release chemicals that:
– Increase blood flow to the damaged area
– Turn the wound red and warm
• Anti-inflammatory drugs, such as aspirin and ibuprofen:
– Dampen the normal inflammatory response
– Reduce swelling and fever
© 2010 Pearson Education, Inc.
The Lymphatic System
• The lymphatic system consists of:
– A branching network of vessels
– Numerous lymph nodes
– Several other organs
• Lymphatic vessels carry lymph, a fluid that is similar to interstitial
fluid surrounding body cells.
© 2010 Pearson Education, Inc.
Tonsil
Lymph nodes
Lymphatic vessels
entering veins
Appendix
Thymus
Lymphatic
vessels
Spleen
Figure 24.5
• The lymphatic system:
– Returns tissue fluid to the circulatory system
– Helps to fight infections
© 2010 Pearson Education, Inc.
ADAPTIVE DEFENSES
• Adaptive defenses:
– Are the third line of defense
– Are activated after exposure to specific pathogens
– Depend upon lymphocytes that:
–
Recognize and
–
Respond to specific invading pathogens
© 2010 Pearson Education, Inc.
• There are two types of lymphocytes:
– B cells, which mature in the bone marrow, and
– T cells, which mature in the thymus, a gland in the chest
• B cells and T cells eventually make their way to:
– Lymph nodes
– Other lymphatic organs
© 2010 Pearson Education, Inc.
EFFECTOR T CELLS
Helper T Cells
•
•
Recognize self-nonself complexes
Activate other cells
activate
•
•
Cytotoxic T Cells
Activated by helper T cells
Bind to infected cells and release
proteins that trigger cell death
Proteins
Self-nonself
complex
Phagocytic
cell
Helper
T cell
Infected
cell
Cytotoxic
T cell
Figure 24.UN5
Bone
marrow
Stem cell in bone marrow
Immature lymphocytes in bone marrow
Via blood to thymus
B cell
(matures in
bone marrow)
T cell
(matures in
thymus)
Figure 24.6-2
Bone
marrow
Stem cell in bone marrow
Immature lymphocytes in bone marrow
Via blood to thymus
B cell
(matures in
bone marrow)
T cell
(matures in
thymus)
Via blood
Lymph nodes, spleen, and other lymphatic organs
Figure 24.6-3
• Antigens:
– Are molecules on the surfaces of viruses or foreign cells
– Elicit a response from a lymphocyte
© 2010 Pearson Education, Inc.
Recognizing the Invaders
• B and T cells develop antigen receptors on their surfaces.
– All the antigen receptors on a particular cell recognize a single specific
antigen.
– The great diversity of B cells and T cells produces enough different
antigen receptors to bind to just about every possible antigen.
© 2010 Pearson Education, Inc.
• When a particular B cell binds to its particular antigen, it gives
rise to other short-lived cells, which secrete a receptor-like
molecule called an antibody.
© 2010 Pearson Education, Inc.
Antigen
Antigenbinding site
Antigen-binding
sites
Computer
model of an
antibody
Antibody
Figure 24.7
• Antibodies:
– Are Y-shaped molecules
– Have binding sites with tremendous variety
– Enable the immune system to react to just about any kind of antigen
– Combine with an antigen to form an antigen-antibody complex
© 2010 Pearson Education, Inc.
• Monoclonal antibodies are:
– Produced by cells descended from a single cell
– Identical and specific for a single antigen
© 2010 Pearson Education, Inc.
Responding to the Invaders
• B cells and T cells carry out a coordinated attack along with the
innate defenses.
© 2010 Pearson Education, Inc.
Clonal Selection: Multiplying Lymphocytes
• Clonal selection:
– Generates B cells and T cells appropriate to the invading antigen
– Is the mechanism that underlies the immune system’s specificity and
memory of antigens
© 2010 Pearson Education, Inc.
Antigens
B cells that
recognize
different
antigens
Antigen
receptor on
cell surface
Clone of identical cells
Antibodies
Clone of effector cells
Clone of memory cells
Figure 24.9-3
Immunological Memory
• Clonal selection also produces memory cells, which:
– Are long-lived, lasting decades
– Respond to subsequent exposures to a previously encountered antigen
– Give rise to:
– Effector cells
– Even more memory cells
© 2010 Pearson Education, Inc.
• In the secondary immune response, memory cells:
– Bind to the antigen faster
– Multiply more quickly
• Thus, in adaptive defenses, but not innate defenses, exposure to
a particular antigen enhances future responses to the same
antigen.
© 2010 Pearson Education, Inc.
Vaccination
• Vaccination confronts the immune system with a vaccine, which
includes a harmless variant of a disease-causing microbe or one
of its parts.
• A vaccine stimulates the immune system to mount defenses
against the actual pathogen possessing the same antigens.
© 2010 Pearson Education, Inc.
• In the United States, vaccinations have virtually eliminated:
– Polio
– Mumps
– Smallpox
© 2010 Pearson Education, Inc.
B Cells and the Humoral Immune Response
• The humoral immune response is:
– The secretion of antibodies into the blood and lymph
– Caused by effector B cells
© 2010 Pearson Education, Inc.
T Cells and the Cell-Mediated Immune Response
• The cell-mediated immune response:
– Reacts to pathogens that have already entered body cells
– Involves two main kinds of effector T cells:
– Helper T cells
– Cytotoxic T cells
© 2010 Pearson Education, Inc.
• Helper T cells:
– Stimulate the activity of cytotoxic T cells
– Help activate B cells
– Grow and divide to produce:
– More activated helper T cells
– Memory T cells
© 2010 Pearson Education, Inc.
Phagocytic cell
breaks microbe into
antigen fragments.
Microbe
Phagocytic cell
Antigen from microbe
(nonself molecule)
Self protein
binds to antigen.
Self protein
Self protein displays
antigen on surface.
T cell
receptor
Colorized SEM
Helper
T cell
Phagocytic cell (yellow)
engulfing a foreign cell
Receptor on helper
T cell binds to the
protein-antigen
combination.
Figure 24.11
• Cytotoxic T cells:
– Are the only T cells that kill other body cells
– Identify and find infected body cells
– Synthesize and discharge proteins that:
– Make holes in the infected cell’s plasma membrane or
– Trigger a process that results in death of the infected cell
© 2010 Pearson Education, Inc.
Infected cell
Foreign
antigen
Perforin
protein
Activated
cytotoxic
T cell
Infected
cell
Hole
forming
Proteins
Other
proteins
Cytotoxic T cell binds
to infected cell,
becoming activated
and producing
perforin.
Cytotoxic
T cell
Perforin makes
holes in
infected cell’s
plasma membrane.
Other proteins
enter target cell
through holes
created by
perforin.
Infected cell
is destroyed
by lysis
(bursting).
Figure 24.13-4
IMMUNE DISORDERS
• If the interplay of immune cells goes awry, problems can arise
that range from mild irritations to deadly diseases.
© 2010 Pearson Education, Inc.
Allergies
• Allergies are sensitivities to harmless antigens in the
environment.
• Allergens are antigens that cause allergies.
• The symptoms of an allergy result from a two-stage reaction
sequence.
© 2010 Pearson Education, Inc.
Colorized SEM
SENSITIZATION: INITIAL EXPOSURE
TO ALLERGEN
Ragweed pollen grains
Effector
B cell
Allergen (pollen
grain) enters
bloodstream.
B cells make
antibodies.
Figure 24.14-2
LATER EXPOSURES TO
SAME ALLERGEN
Colorized SEM
SENSITIZATION: INITIAL EXPOSURE
TO ALLERGEN
Ragweed pollen grains
Effector
B cell
Histamine
Mast
cell
Allergen (pollen
grain) enters
bloodstream.
B cells make
antibodies.
Antibodies
attach to
mast cell.
Allergen binds
to antibodies
on mast cell.
Histamine is
released,
causing
allergy
symptoms.
Figure 24.14-5
• Anaphylactic shock:
– Is an especially dangerous type of allergic reaction
– Can be counteracted with injections of epinephrine
© 2010 Pearson Education, Inc.
Figure 24.15
Autoimmune Diseases
• The immune system:
– Normally reacts only against foreign (nonself) substances but
– May attack:
– Our own tissues
– Tissues transplanted into our bodies
© 2010 Pearson Education, Inc.
• Autoimmune diseases:
– Occur when the immune system improperly attacks the body’s own
molecules
– May lead to serious diseases such as:
– Lupus
– Insulin-dependent diabetes
– Multiple sclerosis
– Rheumatoid arthritis
© 2010 Pearson Education, Inc.
Figure 24.16
Immunodeficiency Diseases
• Immunodeficiency diseases:
– Result when one or more of the components of the immune system are
lacking
– Leave affected people more susceptible to infections
© 2010 Pearson Education, Inc.
• Immunodeficiencies may arise:
– Through inborn conditions such as severe combined immunodeficiency
(SCID)
– From acquired illness such as Hodgkin’s disease, a type of cancer
– From radiation or drug therapies used against many cancers
© 2010 Pearson Education, Inc.
AIDS
• AIDS (acquired immunodeficiency syndrome):
– Infects several million people each year
– Has killed more than 30 million people worldwide
© 2010 Pearson Education, Inc.
• HIV, the virus that causes AIDS:
– Currently infects more than 33 million people worldwide
– Attacks helper T cells
– Cripples humoral and cell-mediated immunity
• Lives can be saved by:
– Reducing promiscuity
– Properly using condoms
© 2010 Pearson Education, Inc.
HIV
Colorized TEM
Human helper T cell
Figure 24.17
INNATE DEFENSES
Internal
External
• Skin
• Mucous
•
membranes
Secretions
White blood cells Defensive proteins
• Phagocytic
•
cells
Natural
killer cells
The inflammatory
response
• Involves chemical
• Interferons
signals and
• Complement
proteins
phagocytic cells
Figure 24.UN1