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The Body’s Defenses
Chapter 43
Fig. 43-7
Interstitial fluid
Adenoid
Tonsil
Blood
capillary
Lymph
nodes
Spleen
Tissue
cells
Lymphatic
vessel
Peyer’s patches
(small intestine)
Appendix
Lymphatic
vessels
Lymph
node
Masses of
defensive cells
Pathogen
• Pathogen: An agent of
disease. A disease
producer. The term
pathogen most
commonly is used to
refer to infectious
organisms.
– These include bacteria
(such as staph), viruses
(such as HIV), and fungi
(such as yeast).
– Less commonly,
pathogen refers to a
noninfectious agent of
disease such as a
chemical.
Fig. 43-1
1.5 µm
Fig. 43-2
Pathogens
(microorganisms
and viruses)
INNATE IMMUNITY
• Recognition of traits
shared by broad ranges
of pathogens, using a
small set of receptors
•Rapid response
ACQUIRED IMMUNITY
•Recognition of traits
specific to particular
pathogens, using a vast
array of receptors
• Slower response
Barrier defenses:
Skin
Mucous membranes
Secretions
Internal defenses:
Phagocytic cells
Antimicrobial proteins
Inflammatory response
Natural killer cells
Humoral response:
Antibodies defend against
infection in body fluids.
Cell-mediated response:
Cytotoxic lymphocytes defend
against infection in body cells.
• First Line
of Defense
• Second
Line of
Defense
• Third Line
of Defense
1st line of Defense
• Nonspecific Barrier
– Skin
– Mucous
• Lysozyme
– Cilia
– Stomach Acid
2nd Line of Defense
• 1st line has been penetrated!!!
– Inflammatory Response
• Vasodilation
– Histamine
» Released by: Basophils & Mast Cells
– Prostaglandins – Promotes Blood Flow
– Chemokines – attracts phagocytes
» Neutrophils  destroy microbes
» Monocytes  into Macrophages  large # of
microbes
– Pyrogens – increases temperature
– Interferons – block against viral infections
3rd Line of Defense
• Specific Response
Acquired immunity defends against infection of
body cells and fluids
• Acquired immunity has two branches: the
humoral immune response and the cellmediated immune response
• Humoral immune response involves
activation and clonal selection of B cells,
resulting in production of secreted antibodies
• Cell-mediated immune response involves
activation and clonal selection of cytotoxic T
cells
• Helper T cells aid both responses
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 43-16
Humoral (antibody-mediated) immune response
Cell-mediated immune response
Key
Antigen (1st exposure)
+
Engulfed by
Gives rise to
Antigenpresenting cell
+
Stimulates
+
+
B cell
Helper T cell
+
Cytotoxic T cell
+
Memory
Helper T cells
+
+
+
Antigen (2nd exposure)
Plasma cells
Memory B cells
+
Memory
Cytotoxic T cells
Active
Cytotoxic T cells
Secreted
antibodies
Defend against extracellular pathogens by binding to antigens,
thereby neutralizing pathogens or making them better targets
for phagocytes and complement proteins.
Defend against intracellular pathogens
and cancer by binding to and lysing the
infected cells or cancer cells.
Active and Passive Immunization
• Active immunity develops
naturally in response to an
infection
– It can also develop
following immunization,
also called vaccination
• Passive immunity provides
immediate, short-term
protection
– Breast Milk
– Injection of Antibodies
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings