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The Lymphatic &
Immune Systems
 Consists of two semi-independent parts
 A meandering network of lymphatic vessels
 Lymphoid tissues and organs scattered throughout
the body
 Returns interstitial fluid and leaked plasma proteins
back to the blood
 Lymph – interstitial fluid once it has entered
lymphatic vessels
Lymphatic System: Overview
Lymphatic System:
Overview
Lymphatic
System:
Overview
 A one-way system in which lymph flows toward the
heart
 Lymph vessels include:
 Microscopic, permeable, blind-ended capillaries
 Lymphatic collecting vessels
 Trunks and ducts
Lymphatic Vessels
 Similar to blood capillaries, with modifications
 Remarkably permeable
 Loosely joined endothelial minivalves
 Withstand interstitial pressure and remain open
 The minivalves function as one-way gates that:
 Allow interstitial fluid to enter lymph capillaries
 Do not allow lymph to escape from the capillaries
Lymphatic Capillaries
Lymphatic Capillaries
Lymphatic
Vessels and
Valves
Figure 22–3
Lymphatic Trunks & Ducts
 The lymphatic system lacks an organ that acts as a
pump
 Vessels are low-pressure conduits
 Uses the same methods as veins to propel lymph
 Pulsations of nearby arteries
 Contractions of smooth muscle in the walls of the
lymphatics
Lymph Transport
General circulation of lymph
 Lymphocytes are the main cells involved in the
immune response
 The two main varieties are T cells and B cells
Lymphoid Cells
Lymphocytes
 T cells and B cells protect the body against antigens
 Antigen – anything the body perceives as foreign
 Bacteria and their toxins; viruses
 Mismatched RBCs or cancer cells
Lymphocytes
 T cells
 Manage the immune response
 Attack and destroy foreign cells
 B cells
 Produce plasma cells, which secrete antibodies
 Antibodies immobilize antigens
 Macrophages – phagocytize foreign substances and
help activate T cells
 Dendritic cells – spiny-looking cells with functions
similar to macrophages
 Reticular cells – fibroblastlike cells that produce a
stroma, or network, that supports other cell types in
lymphoid organs
Other Lymphoid Cells
Lymphoid
Nodules
Figure 22–6
 Lymph nodes are the principal lymphoid organs of
the body
 Nodes are imbedded in connective tissue and
clustered along lymphatic vessels
 Aggregations of these nodes occur near the body
surface in inguinal, axillary, and cervical regions of
the body
Lymph Nodes
 Their two basic functions are:
 Filtration – macrophages destroy microorganisms
and debris
 Immune system activation – monitor for antigens
and mount an attack against them
Lymph Nodes
Lymph Nodes
 Range from 1–25 mm diameter
Figure 22–7
Lymph node
Structure
Structure of a Lymph Node
 The spleen, thymus gland, and tonsils
 Peyer’s patches and bits of lymphatic tissue
scattered in connective tissue
 All are composed of reticular connective tissue and
all help protect the body
 Only lymph nodes filter lymph
Other Lymphoid Organs
The Thymus
Structure of the Spleen
 Innate (nonspecific) system responds quickly and
consists of:
 First line of defense – intact skin and mucosae
prevent entry of microorganisms
 Second line of defense – antimicrobial proteins,
phagocytes, and other cells
 Inhibit spread of invaders throughout the body
 Inflammation is its hallmark and most important
mechanism
Immunity: Two Intrinsic Defense Systems
 Adaptive (specific) defense system
 Third line of defense – mounts attack against
particular foreign substances
 Takes longer to react than the innate system
 Works in conjunction with the innate system
Immunity: Two Intrinsic Defense Systems
The 7 Nonspecific
Defenses
Figure 22–10
 Skin, mucous membranes, and their secretions make
up the first line of defense
 Keratin in the skin:
 Presents a formidable physical barrier to most
microorganisms
 Is resistant to weak acids and bases, bacterial
enzymes, and toxins
 Mucosae provide similar mechanical barriers
Surface Barriers
 Mucus-coated hairs in the nose trap inhaled particles
 Mucosa of the upper respiratory tract is ciliated
 Cilia sweep dust- and bacteria-laden mucus away
from lower respiratory passages
Respiratory Tract Mucosae
 The body uses nonspecific cellular and chemical
devices to protect itself
 Phagocytes and natural killer (NK) cells
 Antimicrobial proteins in blood and tissue fluid
 Inflammatory response enlists macrophages, mast
cells, WBCs, and chemicals
 Harmful substances are identified by surface
carbohydrates unique to infectious organisms
Internal Defenses: Cells and Chemicals
Natural Killer Cell Function
Figure 22–11
 Macrophages are the chief phagocytic cells
 Free macrophages wander throughout a region in search of
cellular debris
 Kupffer cells (liver) and microglia (brain) are fixed
macrophages
 Neutrophils become phagocytic when encountering
infectious material
 Eosinophils are weakly phagocytic against parasitic worms
 Mast cells bind and ingest a wide range of bacteria
Phagocytes
Mechanism of Phagocytosis
 Inflammation is caused by:
 Pathogens
 Mechanical irritation or
damage
 Chemical irritants
 Extreme temperatures
 Marked by four “cardinal
signs”
 Redness
 Pain
 Swelling
 Heat
Inflammation
 Vasodilation & increased capillary permeability
 Release of:
 Histamine – attract leukocytes (chemotaxis), cause
further vasodilation and increased permeability
 Kinnins – Similar to histamine
 Prostaglandins – synergistic with the above.
Trigger pain.
 Leukotrienes – allow adherence of phagocytes to
pathogens
 Complement – more histamine, and a bunch of
other stuff (about which more later)
Overview of inflammatory response
Neutrophils and
Monocytes
respond to
“Chemotaxis”
 Caused by resetting of hypothalamic thermostat
 Bacterial toxins
 Triggers release of cytokines & interleukin-1
(endogenous pyrogens)
 Increases interferon effects
 Increases metabolic rate to enhance tissue repair and
increase immune response
 Makes environment hostile to microbes
Fever
Adaptive (Specific) Defenses
 The adaptive immune system is a functional system
that:
 Recognizes specific foreign substances
 Acts to immobilize, neutralize, or destroy foreign
substances
 Amplifies inflammatory response and activates
complement
The Immune Response
Figure 22–15 (Navigator)
Antigens
 Substances that can mobilize the immune system
and provoke an immune response
 The ultimate targets of all immune responses are
mostly large, complex molecules not normally
found in the body (nonself)
Antigens & Antigenic
Determinants (epitopes)
Lymphocytes
 Immature lymphocytes released from bone marrow
are essentially identical
 Whether a lymphocyte matures into a B cell or a T
cell depends on where in the body it becomes
immunocompetent
 B cells mature in the bone marrow
 T cells mature in the thymus
Cell-mediated
and Antibody
mediated
defenses
 The MHC is a group of genes that code for proteins
that act as an ID badge for your cells
 The “self antigens” are glycoproteins that are also
called human leukocyte antigens (HLA)
 There are two classes, MHC-I & MHC-II
 MHC-I is on all cells (except erythrocytes)
 MHC-II is found on antigen-presenting cells (APCs)
Major Histocompatability Complex and
recognition of “self”
Antigen processing
Antigen Presentation
Figure 22–16b
 Helper T Cells (CD4)
 Secrete interleukin-2 (IL-2)
 Helps activate cytotoxic T Cells, B Cells and/or NK
cells
 Involved in both cell and antibody mediated responses
Types of T Cells
 Cytotoxic T Cells (CD8) a.k.a. “killer T Cells”
 Attack virally or bacterial infected cells and cancerous
cells directly
 Memory T Cells provide for a prolonged protection
against specific antigens (immunity in the true sense)
Types of T Lymphocytes
T lymphocyte
activity:
The cell
mediated
response
Pathways of T Cell Activation
Figure 22–19
B Cells
 B cells become immunocompetent and self-tolerant
in bone marrow
 Some self-reactive B cells are inactivated (anergy)
while others are killed
 Other B cells undergo receptor editing in which
there is a rearrangement of their receptors
Humoral Immunity Response
 Antigen challenge – first encounter between an
antigen and a naive immunocompetent cell
 Takes place in the spleen or other lymphoid organ
 If the lymphocyte is a B cell:
 The challenging antigen provokes a humoral
immune response
 Antibodies are produced against the challenger
Antibody structure
7 Functions of Antigen–Antibody Complexes
1. Neutralization of antigen binding sites
2. Precipitation and agglutination:
 formation of immune complex Activation of
complement
3. Attraction of phagocytes
4. Opsonization:
 increasing phagocyte efficiency
7 Functions of Antigen–Antibody Complexes
6. Stimulation of inflammation
7. Prevention of bacterial and viral adhesion
Summary
Body Responses to Bacterial InfectionFigure 22–24
Combined
Immune
System
Responses
Figure 22–25