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The Lymphatic System
 Lymphatic system functions
 Transport fluids from body tissues back to
bloodstream
 Play essential roles in body defense and
resistance to disease
 Consists of two semi-independent parts:
 Lymphatic vessels
 Lymphoid tissues and organs
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Lymphatic Characteristics
 Lymph – excess tissue fluid carried by
lymphatic vessels
 Pale white fluid, similar composition to
blood plasma, but with more leukocytes,
lymphocytes, and triglycerides
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Lymphatic Vessels
 Lymphatic vessels
 Carry lymph towards the heart, never
away
 No pump, moved by “milking” action of
muscles
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Lymphatic Vessels
 Lymphatic vessels
 Fluid leaks into
lymphatic capillaries
from body tissue
 Lymphatic collecting
vessels collect it from
lymph capillaries
 Carries lymph to and
away from lymph
nodes
Figure 12.1
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Lymphatic Vessels
Figure 12.2
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Lymphatic Vessels
 Lymphatic collecting
vessels (continued)
 Returns fluid to
circulatory veins
near the heart
Figure 12.1
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Lymph
 As lymph seeps into lymph capillaries,
harmful materials are carried with it:
 Bacteria
 Viruses
 Cancer cells
 Cell debris
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Lymph Nodes
 Lymph nodes filter lymph
before it is returned to the
blood
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Lymph Nodes
 Leukocyte defense cells within lymph nodes:
 Macrophages – engulf and destroy foreign
substances
 Lymphocytes – provide immune response
to antigens
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Other Lymphoid Organs
 Several other organs
contribute to
lymphatic function
 Spleen
 Thymus
 Tonsils
 Peyer’s patches
Figure 12.5
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The Spleen
 Spleen:
 Filters out and destroys worn out blood
cells
 Acts as a blood reservoir
 Synthesizes antibodies, filters antibodycoated cells from blood
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The Thymus
 Thymus:
 Produces hormones (like thymosin) to
program (“educate”) certain lymphocytes
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Tonsils
 Tonsils:
 Small masses of lymphoid tissue around
the pharynx
 Trap and remove bacteria and other
foreign materials
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Peyer’s Patches
 Peyer’s Patches:
 Found in the wall of the small intestine
 Capture and destroy bacteria in the
intestine
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Body Defenses
 The body is constantly in contact with
bacteria, fungi, and viruses
 The body has two defense systems for foreign
materials: nonspecific and specific
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Body Defenses
 Nonspecific defense system
 Mechanisms protect against a variety of
invaders
 Responds immediately to protect body
from foreign materials
 Specific defense system
 Specific defense is required for each type
of invader
 Also known as the immune system
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Body Defenses
Figure 12.6
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Nonspecific Body Defenses
 First Line of Defense:
 Body surface coverings and their secretions
 Intact skin - physical barrier, acidic pH
 Mucous membranes - mucus, proteindigesting enzymes, HCl (in stomach)
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Nonspecific Body Defenses
 Second Line of Defense:
 Non-specific defense cells
 Phagocytes (like macrophages) - engulf &
digest foreign matter
 Natural killer (NK) cells - lyse & destroy
cancerous or virus-infected cells
 Antimicrobial chemicals
 The inflammatory response
 Fever
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Antimicrobial Chemicals
 Two kinds:
Complement,
Interferon
 Complement
 Plasma
proteins
 Lyse
microorganism
, enhance
phagocytosis
Figure 12.10
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Antimicrobial Chemicals
 Interferon
 Secreted proteins of virus-infected cells
 Bind to healthy cell surfaces to inhibit
viruses binding
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Inflammatory Response
 Inflammation: an increase in blood flow, tissue fluid,
and clotting proteins in a specific area
 Prevents spread of foreign agents to neighboring
tissues, disposes of pathogens & debris, promotes
tissue repair, releases chemicals that attract immune
cells
 Triggered when body tissues are injured
 Signs: redness, heat, swelling, pain
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Steps in the Inflammatory Response
Figure 12.8
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Fever
 Abnormally high body temperature
 Hinders pathogens with temperature
preferences
 Increases mobility of leukocytes, rate of
phagocytosis, production rate of certain
lymphocytes
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings