Transcript Exercise 35
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