Transcript Contraction of lymphatic vessels

The Lymphatic System
and Body Defenses
Chapter 12
The Lymphatic System
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Consists of two semi-independent parts
 Lymphatic vessels
 Lymphoid tissues and organs
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Lymphatic system functions
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Transport fluids back to the blood
Approx. 30 L of fluid pass from blood
capillaries to interstitial fluid, but only
27 L fluid come back to blood
capillaries
Extra 3 L fluid stays in interstitial fluid
Returns back to blood capillaries by
lymphatic system
Play essential roles in body defense
and resistance to disease
Lymphatic Vessels
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Properties of
lymphatic vessels
One way system
toward the heart
 Begins in tissues and
deposit in superior
vena cava
 No pump
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 Mechanism
for movement of lymph through L. vessel:
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Contraction of lymphatic vessels:
- Lymph moves into chambers formed by unidirectional
valve by smooth muscle contraction
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Contraction of Skeletal muscles:
- Lymphatic vessels get compressed when surrounding
muscle contracts, cause lymph movement
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Thoracic Pressure changes:
- During inspiration, pressure decreases, vessels expand, lymph
flows in
- During expiration, pressure increases, vessels compressed,
cause lymph movement
Lymph
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Lymph – excess tissue fluid carried by lymphatic
vessels
Materials returned to the blood
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Water
hormones, enzymes, waste products from blood cells
Some proteins from plasma
Harmful materials that enter lymph vessels
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Bacteria
Viruses
Cancer cells
Cell debris
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Lymph vessels include:
 Lymphatic capillaries
 Lymphatic collecting vessels
 Trunks and ducts
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Microscopic, permeable, dead-ended capillaries
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Found between the tissue cells and blood capillaries
 Found in all parts of the body except nervous system,
bone marrow, and tissues without blood vessels
(cartilage, cornea, epidermis)
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Similar to blood capillaries, with modifications:
 Very permeable
 endothelium lack basement membrane
 And adjacent cells overlap, forms minivalves
Function of mini – valve : Act as one-way gate
 Allow interstitial fluid to enter lymph capillaries
 Do not allow lymph to go back to interstitial space
Lymphatic Vessels
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Lymphatic collecting
vessels
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Collects lymph from
lymph capillaries
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Carries lymph to and
away from lymph
nodes
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Deposit into venous
system by two major
vessels
Right lymphatic duct:
right arm and right side
of head and thorax
Thoracic duct : rest of
the body
Lymphatic Organs
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Lymph Nodes
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Principal lymphoid organs of the body
Distributed along the lymphatic
vessels
Approx. 450 lymph nodes found
throughout body
Filter lymph before it is returned to the
blood
Functions:
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Filtration – Macrophages present
within lymph nodes engulf and
destroy microorganisms and debris
that enter the lymph
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Provide Immune Response –
Lymphocytes monitor for antigens
and attack on them
Structure of a Lymph Node
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Lymph nodes are small,
round or kidney-shaped, less
than 1 inch long & surrounded
by a fibrous capsule
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Strands from fibrous capsule
called trabeculae extend
inward and divide the node
into no. of compartments
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Lymph nodes have two
distinct regions:
cortex
medulla
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Lymph Node Structure
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Cortex
 Outer part
 Contains follicles –
collections of
lymphocytes
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Medulla
 Inner part
 Contains phagocytic
macrophages
Lymph Node Structure
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Lymph enters the convex side
through afferent lymphatic vessels
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Lymph flows through a number of
sinuses inside the node
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Lymph exits through efferent
lymphatic vessels
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Because there are fewer efferent
vessels than afferent vessels, the
flow of lymph is very slow in the
node
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This allows time for lymphocytes
and macrophages to carry out
protective functions
Other Lymphoid Organs
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Several other
organs contribute to
lymphatic function
Spleen
 Thymus
 Tonsils
 Peyer’s patches
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Spleen
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Largest lymphoid organ,
located on the left side of the
abdominal cavity beneath the
diaphragm, curves around left
side of stomach
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Filters blood
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Destroys worn out blood cells
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Acts as a blood reservoir
Thymus
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Located low in the throat,
overlying the heart
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Functions at peak levels
only during childhood
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Produces hormones (like
thymosin) to program
lymphocytes
Tonsils:
Small masses of lymphoid
tissue around the pharynx
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Trap and remove bacteria
and other foreign materials
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Tonsillitis is caused by
congestion with bacteria
Peyer’s patches:
 Found in the wall of the
small intestine
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Resemble tonsils in
structure
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Capture and destroy
bacteria in the intestine
Mucosa-Associated Lymphatic Tissue (MALT)
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Includes:
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Peyer’s patches
Tonsils
Other small accumulations
of lymphoid tissue
Protect respiratory and
digestive tracts
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Found in mucous membrane
linings of digestive,
respiratory tracts
Body Defenses
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The body is constantly in contact with
bacteria, fungi, and viruses
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The body has two defense systems for
foreign materials
Innate (Nonspecific) defense system
 Adaptive (Specific) defense system
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Body Defenses
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Nonspecific defense system
Mechanisms protect against a variety of
invaders (harmful microorganisms)
 Responds immediately to protect body from
foreign materials
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Specific defense system
Specific defense is required for each type of
invader
 Also known as the immune system
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Nonspecific Body Defenses
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Body surface coverings
 Intact skin
 Mucous membranes
Specialized Cells
Chemicals produced by the body
Surface Membrane Barriers – First Line of
Defense
 The
skin and Mucous membranes
Skin is physical barrier to foreign materials
 Mucous membranes provide protective
secretions
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pH of the skin is acidic to inhibit bacterial growth
Sebum is toxic to bacteria
Vaginal secretions are very acidic
Surface Membrane Barriers – First Line
of Defense
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Stomach mucosa
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Secretes hydrochloric acid
Has protein-digesting enzymes
Both kill pathogens
Saliva and lacrimal fluid contain lysozyme
An enzyme that destroys bacteria
Mucus traps microogranisms in digestive and
respiratory pathways
Cells and Chemicals:
Second Line of Defense
Phagocytes
 Natural killer cells
 Inflammatory response
 Antimicrobial proteins
 Fever
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Cells and Chemicals:
Second Line of Defense
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Phagocytes
(neutrophils and
macrophages)
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Engulfs foreign
material into a vacuole
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Enzymes from
lysosomes digest the
material
Events of Phagocytosis
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Microbe attaches to the
phagocyte
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Microbe is engulfed by the
phagocyte
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Lysosome is fused with
phagocytic vesicle
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Microbe is killed and digested
by lysosomal enzyme
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Undigested material is
removed by exocytosis
Cells and Chemicals:
Second Line of Defense
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Natural killer (NK) cells
Can lyse and kill cancer cells
 Can destroy virus- infected cells
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Cells and Chemicals: Second Line of Defense
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Inflammatory response
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Triggered when body tissues are injured
Produces four cardinal signs
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Redness
Heat
Swelling
Pain
Results in a chain of events leading to protection
and healing
Steps in the Inflammatory Response
Cells and Chemicals: Second Line
of Defense
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Functions of the inflammatory response
Prevents spread of damaging agents
 Disposes of cell debris and pathogens
through phagocytosis
 Sets the stage for repair
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Cells and Chemicals: Second Line of
Defense
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Fever
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Abnormally high body temperature
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Hypothalmus heat regulation can be reset by pyrogens
(secreted by white blood cells)
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High temperatures inhibit the release of iron and zinc
from liver and spleen needed by bacteria to multiply
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Fever also increases the speed of tissue repair by
increasing metabolic rate of cells
Cells and Chemicals: Second Line of
Defense
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Antimicrobial proteins
Attack microorganisms
 Hinder reproduction of microorganisms
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Most important antimicrobial proteins are:
Complement proteins
 Interferon
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Cells and Chemicals: Second Line of
Defense
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Complement Proteins
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A group of at least 20
plasma proteins
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Activated when they
encounter and attach to
foreign cells (complement
fixation)
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Damage foreign cell
surfaces
Cells and Chemicals: Second Line of
Defense
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Interferon
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Proteins secreted by virus-infected cells
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Bind to healthy cell surfaces to inhibit viruses
binding
Adaptive Body Defenses: Third Line of
Defense
Three aspects of adaptive defense:
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Antigen specific– recognizes and acts against particular
foreign substances
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Systemic – not restricted to the initial infection site
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Has memory – recognizes and mounts even stronger
attack on previously encountered pathogens
Antigens (Nonself)
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Any substance capable of exciting the immune
system and provoking an immune response
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Examples of common antigens
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Foreign proteins
Nucleic acids
Large carbohydrates
Some lipids
Pollen grains
Microorganisms
Self-Antigens
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Human cells have many surface proteins
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Our immune cells do not attack our own proteins
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Our cells in another person’s body can trigger an
immune response because they are foreign
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Restricts donors for transplants
Allergies
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Many small molecules (called haptens or incomplete
antigens) are not antigenic, but link up with our own
proteins
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The immune system may recognize the combination as
foreign and attack
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The immune response is harmful rather than protective
because it attacks our own cells
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Chemicals that act as haptens are found in some drugs,
detergents, hair dyes, cosmetics
Adaptive Defense System: Third Line of
Defense
Types of Immunity
 Humoral immunity
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Antibody-mediated immunity
 Provided
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by antibodies present in body fluids
Cellular immunity
Cell-mediated immunity
 Targets virus-infected cells, cancer cells, and
cells of foreign grafts
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Cells of the Immune System
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Lymphocytes
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Originate from hemocytoblasts in the red bone
marrow
B lymphocytes become immunocompetent (capable
of responding to specific antigen) in the bone marrow
T lymphocytes become immunocompetent in the
thymus
Macrophages
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Arise from monocytes
Become widely distributed in lymphoid organs
Promote phagocytosis
Humoral (Antibody-Mediated) Immune
Response
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B lymphocytes with
specific receptors bind to
a specific antigen
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The binding event
activates the lymphocyte
to undergo clonal
selection
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A large number of clones
are produced (primary
humoral response)
Humoral (Antibody-Mediated) Immune
Response
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Most B cells become
plasma cells
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Produce antibodies to
destroy antigens
Activity lasts for four or
five days
Some B cells become
long-lived memory
cells (secondary
humoral response)
Primary and Secondary Response
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Primary response: exposure to
antigen stimulating the B cells
Generates memory cells
Secondary response: when body is
exposed to the same antigen the
second time
Stimulate B memory cells
Memory cells are long-lived
A second exposure causes a rapid
response
The secondary response is stronger
and longer lasting
Active Immunity
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Occurs when B cells
encounter antigens and
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produce antibodies
Active immunity can be
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Naturally acquired during
bacterial and viral
infections
Artificially acquired from
vaccines
Passive Immunity
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Occurs when antibodies are obtained from someone
else
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As a result Immunological memory does not occur
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Protection provided by “borrowed antibodies”
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Conferred naturally from a mother to her fetus
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Conferred artificially when one receives immune
serum ( eg. Antivenom, antitoxin)
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Or gamma globulin, administered after exposure to
hepatitis
Antibodies (Immunoglobulins) (Igs)
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Soluble proteins
secreted by B cells
(plasma cells)
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Carried in blood plasma
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Capable of binding
specifically to an antigen
Antibody Structure
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Four amino acid chains linked
by disulfide bonds
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Two identical amino acid
chains are linked to form a
heavy chain
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The other two identical chains
are light chains
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Have variable (V) and
constant (C) region
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V: variable region that helps in
binding to antigen
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Forms specific antigenbinding sites
Antibody Classes
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Antibodies of each class have slightly
different roles
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Five major immunoglobulin classes
IgM – can fix complement
 IgA – found mainly in mucus
 IgD – important in activation of B cell
 IgG – can cross the placental barrier
 IgE – involved in allergies
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Immunoglobin Classes
Antibody Function
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Antibodies inactivate antigens in a number
of ways
Complement fixation
 Neutralization
 Agglutination
 Precipitation
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Antibody Function
Cellular (Cell-Mediated) Immune Response
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Antigens must be presented by macrophages to
an immuno-competent T cell (antigen
presentation)
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Antigen-presenting cell self protein binds with antigen nonself
molecules and displays them on the cell surface
Helper T cells recognize and bind to the self-nonself complex
Binding activates helper T cells
Cellular (Cell-Mediated) Immune
Response
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T cells Activated helper
promote the immune
response, particularly
secretion of stimulatory
proteins
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Make helper T cells grow
and divide, producing
memory cells and
additional helper T cells
Help activate B cells,
stimulating humoral
immunity
Stimulate activity of
cytotoxic T cells
(cell-mediated immunity)
Cellular (Cell-Mediated) Immune
Response
Cytotoxic T cells: destroy infected
body cells
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Like helper T cells, cytotoxic T
cells recognize and bind with
self-nonself complexes on
infected cells
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Mechanism of cytotoxic T cell
action
 Binding to infected cell
stimulates cytotoxic T cell
to synthesize the protein perforin
 Perforin makes holes in
infected cell's membrane,
and T cell enzymes enter
 Infected cell is destroyed
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Cellular (Cell-Mediated) Immune
Response
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Suppressor T cells
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Release chemicals to suppress
the activity of T and B cells
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Stop the immune response to
prevent uncontrolled activity
A few members of each clone are
memory cells
Disorders of Immunity:
Immunodeficiencies
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Production or function of immune cells or complement is
abnormal
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May be congenital
Eg. Severe combined immunodeficiency disease (SCID):
Deficit of both B and T cells
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or acquired
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Eg. AIDS – Acquired Immune Deficiency Syndrome, by
interfering with the activity of helper T cells
Disorders of Immunity: Autoimmune
Diseases
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The immune system does not distinguish
between self and nonself
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The body produces antibodies and
sensitized T lymphocytes that attack its
own tissues
Autoimmune Diseases
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Multiple sclerosis – white matter of brain and spinal
cord are destroyed
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Myasthenia gravis – impairs communication between
nerves and skeletal muscles
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Juvenile diabetes – destroys pancreatic beta cells
that produce insulin
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Rheumatoid arthritis – destroys joints
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Systemic lupus erythematosus (SLE) – affects
kidney, heart, lung and skin