Transcript lymphatic system

Chapter 22
The Lymphatic System
Lecture Outline
INTRODUCTION
• The ability to ward off the pathogens that
produce disease is called resistance.
• Lack of resistance is called susceptibility.
• Resistance to disease can be grouped into
two broad areas.
• Nonspecific resistance to disease includes
defense mechanisms that provide general
protection against invasion by a wide
range of pathogens.
• Immunity involves activation of specific
Chapter 22
The Lymphatic System
• Resistance is the ability to ward off
disease
– lack of resistance is termed susceptibility
• Nonspecific resistance to disease
– general defensive mechanisms effective on a
wide range of pathogens (disease producing
microbes)
• Specific resistance or immunity is ability to
fight a specific pathogen
– cell-mediated immunity
LYMPHATIC SYSTEM
STRUCTURE AND FUNCTION
• The lymphatic system consists of a fluid
called lymph flowing within lymphatic
vessels, several structures and organs
that contain lymphatic tissue (specialized
reticular tissue containing large numbers
of lymphocytes), and bone marrow, which
is the site of lymphocyte production
(Figure 22.1).
• Interstitial fluid and lymph are very similar.
• Their major difference is location.
Functions of the Lymphatic System
• Draining excess interstitial fluid & plasma
proteins from tissue spaces
• Transporting dietary lipids & vitamins from
GI tract to the blood
• Facilitating immune responses
– recognize microbes or abnormal cells &
responding by killing them directly or
secreting antibodies that cause their
destruction
Formation and Flow of Lymph
• Interstitial fluid drains into lymph
capillaries.
• The passage of lymph is from arteries and
blood capillaries (blood) to interstitial
spaces (interstitial fluid) to lymph
capillaries (lymph) to lymphatic vessels to
lymph trunks to the thoracic duct or right
lymphatic duct to the subclavian veins
(blood) (Figure 22.4).
• Lymph flows as a result of the milking
Lymphatic Organs & Tissues
• Widely distributed throughout the body
• Primary lymphatic organs
– provide environment for stem cells to divide &
mature into B and T lymphocytes
• red bone marrow gives rise to mature B cells
• thymus is site where pre-T cells from red marrow
mature
• Secondary lymphatic organs & tissues
– site where most immune responses occur
• lymph nodes, spleen & lymphatic nodules
• Large organ in infants
(70 g) but atrophied as
adult (3 g)
• 2 lobed organ located in
mediastinum
• Capsule & trabeculae
divide
it into lobules
• Each lobule has cortex
&
medulla
• Cortex
– tightly packed
Thymus
Gland Figure
22.5
Lymph Nodes - Overview
• Lymph nodes are encapsulated oval structures
located along lymphatic vessels (Figures 22.1a and
22.6).
• They contain T cells, macrophages, follicular
dendritic cells, and B cells.
• Lymph enters nodes through afferent lymphatic
vessels, is filtered to remove damaged cells and
microorganisms, and exits through efferent
lymphatic vessels.
• Foreign substances filtered by the lymph nodes are
trapped by nodal reticular fibers.
• Macrophages then destroy some foreign
substances by phagocytosis and lymphocytes bring
Spleen
Figure
22.7
• 5 inch organ between stomach & diaphragm
• Hilus contains blood & lymphatic vessels
• Stroma consists of capsule, trabeculae, fibers &
fibroblasts
• Parenchyma consists of white pulp and red pulp
– white is lymphatic tissue (lymphocytes & macrophages)
around branches of splenic artery
– red pulp is venous sinuses filled with blood & splenic tissue
•
First Line of Defense: Skin and
Nonspecific
resistanceMembranes
refers to a wide variety of
Mucous
body responses against a wide range of pathogens
(disease producing organisms) and their toxins.
• Mechanical protection includes the intact epidermis
layer of the skin (Figure 5.1), mucous membranes,
the lacrimal apparatus, saliva, mucus, cilia, the
epiglottis, and the flow of urine. Defecation and
vomiting also may be considered mechanical
processes that expel microbes.
• Chemical protection is localized on the skin, in
loose connective tissue, stomach, and vagina.
• The skin produces sebum, which has a low pH due
to the presence of unsaturated fatty acids and lactic
Second Line of Defense:
Internal Defenses
• The second line of defense involves
internal antimicrobial proteins, phagocytic
and natural killer cells, inflammation, and
fever.
Antimicrobial Proteins
• Body cells infected with viruses produce
proteins called interferons (IFNs).
– Once produced and released from virusinfected cells, IFN diffuses to uninfected
neighboring cells and binds to surface
receptors, inducing uninfected cells to
synthesize antiviral proteins that interfere with
or inhibit viral replication.
– INFs also enhance the activity of phagocytes
and natural killer (NK) cells, inhibit cell growth,
and suppress tumor formation; they may hold
Antimicrobial Proteins
• A group of about 20 proteins present in
blood plasma and on cell membranes
comprises the complement system
– when activated, these proteins “complement”
or enhance certain immune, allergic, and
inflammatory reactions.
Natural Killer Cells & Phagocytes
• NK cells kill a variety of microbes & tumor
cells
– found in blood, spleen, lymph nodes & red
marrow
– attack cells displaying abnormal MHC antigens
• Phagocytes (neutrophils & macrophages)
– ingest microbes or particulate matter
– macrophages developed from monocytes
• fixed macrophages stand guard in specific tissues
– histiocytes in the skin, kupffer cells in the liver, alveolar
macrophages in the lungs, microglia in the brain &
Phagocytosis
• Phagocytes are cells specialized to
perform phagocytosis and include
neutrophils and macrophages.
– The four phases of phagocytosis include
chemotaxis, adherence, ingestion, digestion
and killing. (Figure 22.9).
– After phagocytosis has been accomplished, a
phagolysosome (Figure 22.9) is formed.
– The lysosome in the phagolysosome, along
with lethal oxidants produced by the
phagocyte, quickly kills many types of
Stages of Inflammation
• The three basic stages of inflammation are vasodilation and
increased permeability of blood vessels, phagocyte
migration, and tissue repair (Figure 22.10).
• Vasodilation & increased permeability of vessels
– caused by histamine from mast cells, kinins from
precursors in the blood, prostaglandins from damaged
cells, and leukotrienes from basophils & mast cells
– occurs within minutes producing heat, redness & edema
– pain can result from injury, pressure from edema or
irritation by toxic chemicals from organisms
– blood-clotting factors leak into tissues trapping microbes
• Phagocyte emigration
– within an hour, neutrophils and then monocytes arrive and
leave blood stream (emigration)
SPECIFIC RESISTANCE:
IMMUNITY
• Immunity is the ability of the body to
defend itself against specific invading
agents.
– bacteria, toxins, viruses, cat dander, etc.
• Differs from nonspecific defense
mechanisms
– specificity----recognize self & non-self
– memory----2nd encounter produces even
more vigorous response
• Antigens are substances recognized as
Maturation of T Cells and B
Cells
• Both T cells and B cells derive from stem
cells in bone marrow (Figure 22.11).
• B cells complete their development in
bone marrow (Figure 22.11).
• T cells develop from pre-T cells that
migrate to the thymus.
• Before T cells leave the thymus or B cells
leave bone marrow, they acquire several
distinctive surface proteins; some function
as antigen receptors, molecules capable
Types of Immune Response
• Cell-mediated immunity (CMI) refers to
destruction of antigens by T cells.
– particularly effective against intracellular
pathogens, such as fungi, parasites, and
viruses; some cancer cells; and foreign tissue
transplants.
– CMI always involves cells attacking cells.
• Antibody-mediated (humoral) immunity
(AMI) refers to destruction of antigens by
antibodies.
Antigens
• Molecules or bits of foreign material
– entire microbes, parts of microbes, bacterial toxins,
pollen, transplanted organs, incompatible blood cells
• Required characteristics to be considered an
antigen
– immunogenicity = ability to provoke immune response
– reactivity = ability to react to cells or antibodies it
caused to be formed
• Get past the bodies nonspecific defenses
– enter the bloodstream to be deposited in spleen
– penetrate the skin & end up in lymph nodes
– penetrate mucous membrane & lodge in associated
CELL-MEDIATED IMMUNITY
• Begins with activation of T cell by a
specific antigen
• Result is T cell capable of an immune
attack
– elimination of the intruder by a direct attack
• In a cell-mediated immune response, an
antigen is recognized (bound), a small
number of specific T cells proliferate and
differentiate into a clone of effector cells (a
Overview of Mature T Cells
1. Helper T (TH) cells, or T4 cells, display
CD4 protein, recognize antigen fragments
associated with MHC-II molecules, and
secrete several cytokines, most
important, interleukin-2, which acts as a
costimulator for other helper T cells,
cytotoxic T cells, and B cells (Figure
22.14).
2. Cytotoxic T (TC) cells, or T8 cells, develop
from T cells that display CD8 protein and
Antibody-Mediated Immunity
• The body contains not only millions of
different T cells but also millions of different B
cells, each capable of responding to a
specific antigen.
• B cells sit still and let antigens be brought to
them
– stay put in lymph nodes, spleen or peyer’s
patches
• Once activated, differentiate into plasma cells
that secrete antibodies