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Chapter 21:
The Immune System
Hans Buchner – German bacteriologist who in the 1880s
proposed that anti-bacterial proteins existed in blood….
start of the modern understanding of immunity
Figure 21.1: Overview of innate and adaptive defenses, p. 789.
Surface barriers
• Skin
• Mucous membranes
Innate
defenses
Internal defenses
• Phagocytes
• Fever
• NK cells
• Antimicrobial proteins
• Inflammation
(a)
Humoral immunity
• B cells
Adaptive
defenses
Cellular immunity
• T cells
(b)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Figure 21.2: Phagocytosis, p. 791.
1 Microbe adheres to phagocyte.
2 Phagocyte forms pseudopods that
eventually engulf the particle.
Innate defenses
Internal defenses
Lysosome
Phagocytic vesicle
containing antigen
(phagosome).
3 Phagocytic vesicle is
fused with a lysosome.
Phagolysosome
Acid
hydrolase
enzymes
4 Microbe in fused vesicle
is killed and digested by
lysosomal enzymes within
the phagolysosome, leaving
a residual body.
Residual body
5 Indigestible and
residual material
is removed by
exocytosis.
(a)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
(b)
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Figure 21.4: Phagocyte mobilization, p. 794.
Innate defenses
Internal defenses
Inflammatory
chemicals diffusing
from the inflamed
site act as chemotactic
agents
4 Positive
chemotaxis
1 Neutrophils enter blood
3 Diapedesis
from bone marrow
2 Margination
Capillary wall
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Endothelium
Basement membrane
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Figure 21.12: Types of acquired immunity, p. 806.
Acquired
immunity
Naturally
acquired
Artificially
acquired
Active
Passive
Active
Passive
Infection;
contact
with
pathogen
Antibodies
pass from
mother to
fetus via
placenta;
or to infant
in her milk
Vaccine;
dead or
attenuated
pathogens
Injection
of immune
serum
(gamma
globulin)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Figure 21.14: Mechanisms of antibody action, p. 809.
Adaptive defenses
Humoral immunity
Antigen
Antigen-antibody
complex
Inactivates by
Neutralization
(masks dangerous
parts of bacterial
exotoxins; viruses)
Agglutination
(cell-bound
antigens)
Antibody
Fixes and activates
Precipitation
(soluble antigens)
Enhances
Phagocytosis
Complement
Enhances
Leads to
Inflammation
Cell lysis
Nucleus
Chemotaxis
Histamine
release
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
The Immune Response in the
body occurs in two ways:
Nonspecific Immunity
Specific Immunity