The Lymphatic System
Introduction

The ability to ward off pathogens
that produce disease is called
resistance
Introduction

Lack of resistance is called
susceptibility
Lymphatic System





Consist of;
lymph (fluid)
lymphatic vessels
lymphatic organs and tissues
bone marrow
Lymphatic System

1.
Functions;
Drain interstitial fluid
Lymphatic System
2. Return leaked plasma proteins to
the blood
Lymphatic System
3. Protects against invasion by
nonspecific defenses and specific
immune responses
Lymphatic Circulation

Interstitial fluid drains into lymphatic
capillaries thus forming lymph
Lymphatic Circulation

Lymph capillaries merge to form
larger vessels, called lymphatic
vessels
Lymphatic Circulation

Convey lymph into and out of
structures called lymph nodes
Lymphatic Capillaries
Lymphatic capillaries are found
everywhere except;
1. Avascular tissue

Lymphatic Capillaries
2. CNS
Lymphatic Capillaries
3. Portions of the spleen
Lymphatic Capillaries
4. Red bone marrow
Lymphatic Capillaries

Lacteal – lymphatic capillary in the
villus of the small intestine which
transport fats
Lymph Trunk and Ducts
1.
2.
Thoracic Duct
Right Lymphatic Duct
Thoracic Duct

Main collecting duct of the lymphatic
system
Thoracic Duct

Receives lymph from the left side of
the head, neck, and chest, the left
upper extremity and the entire body
below the ribs
Thoracic Duct

It drains lymph into venous blood via
the left subclavian vein
Right Lymphatic Duct

Drains lymph from the upper right
side of the body
Right Lymphatic Duct

It drains lymph into venous blood via
the right subclavian vein
Flow of Lymph
1. Fluid flows from arteries and blood
capillaries to interstitial spaces
(interstitial fluid)
Flow of Lymph
2. To lymph capillaries (lymph)
Flow of Lymph
3. To lymphatic vessels
Flow of Lymph
4. To lymph trunks
Flow of Lymph
5.To the thoracic duct or right
lymphatic duct
Flow of Lymph
6. To the subclavian veins (blood)
Lymphatic Organs and Tissues

Lymphatic organs are classified as
primary or secondary
Primary Lymphatic Organs


Red bone marrow
Thymus gland
Secondary Lymphatic Organs



Lymph nodes
Spleen
Lymphatic nodules
Thymus Gland

Lies between the sternum and the
heart
Thymus Gland

Functions in immunity as the site of
T cell maturation
Thymus Gland

Large in the infant and after puberty
it is replaced by adipose and areolar
connective tissue
Lymph Nodes

Are encapsulated oval structures
located along lymphatic vessels
Lymph Nodes

Contain T cells, macrophages,
follicular dendritic cells, B cells, and
plasma cells
Lymph Nodes

Lymph enters nodes through afferent
lymphatic vessels and is filtered to
remove damage cells and
microorganisms
Lymph Nodes

Exits through efferent lymphatic
vessel
Lymph Nodes

Foreign substances filtered by the
lymph nodes are trapped by nodal
reticular fibers
Lymph Nodes

Macrophages destroys foreign
substances by phagocytosis
Lymph Nodes

Lymphocytes bring about the
destruction of others by immune
response
Lymph Nodes


Site of proliferation of plasma cells
(from B cells) and T cells
Plasma cells make antibodies
Spleen

Largest mass of lymphatic tissue in
the body
Spleen

Located between the stomach and
diaphragm
Spleen

Made up of white and red pulp
White Pulp

Lymphatic Tissue
White Pulp

Its T lymphocytes directly attack and
destroy antigens in blood
White Pulp

Its B lymphocytes develop into
antibody producing plasma cells, and
the antibodies inactivate antigens in
blood
White Pulp

Macrophages destroy antigens in
blood by phagocytosis
Red Pulp

1.
2.
Consists of;
Venous sinuses
Splenic cords
Red Pulp

Venous sinuses are filled with blood
Red Pulp

1.
2.
3.
4.
5.
Splenic cords consist of;
RBCs
Macrophages
Lymphocytes
Plasma cells
granulocytes
Red Pulp

Macrophages remove deffective
RBCs, WBCs, and platelets
Red Pulp

Stores blood platelets
Lymphatic Nodules

Oval-shaped concentrations of
lymphatic tissue
Lymphatic Nodules

Scattered throughout the mucous
membranes lining the GI tract,
respiratory airways, urinary tract,
and reproductive tract
Peyer’s patches

Lymphatic nodules in the ileum of
the small intestine
Tonsils

Multiple aggregations of large
lymphatic nodules at the junction of
the oral cavity and the pharynx
Tonsils

1.
2.
3.
Include;
Pharyngeal
Palatine
Lingual tonsils
Tonsils

Participate in immune responses by
producing lymphocytes and
antibodies
Nonspecific Resistance to Disease
Involves a
1. First line of Defense
2. Second line of Defense
First Line of Defense
Involves
1. Mechanical Protection
2. Chemical Protection
Mechanical Protection
Include
1. Epidermis layer of the skin

Mechanical Protection
2. Mucous membranes in the nose
and trachea
Mechanical Protection
3. Lacrimal apparatus
Mechanical Protection
4. Saliva
Mechanical Protection
5. Mucus
Mechanical Protection
6. Cilia
Mechanical Protection
7. Epiglottis
Mechanical Protection
8. Flow of urine
Mechanical Protection
9. Defecation
Mechanical Protection
10. Vomiting
Chemical Protection
1. The skin produces sebum, which
has a low pH
Chemical Protection
2. Lysozyme in sweat has
antimicrobial properties
Chemical Protection
3. Gastric juice in the stomach has
a low pH
Chemical Protection
4. Vaginal
acidic
secretions are also
Second Line of Defense
Involves
1. Antimicrobial proteins
2. Phagocytic and natural killer cells
3. Inflammation
4. Fever
Antimicrobial Proteins
1.
2.
Interferons
Complement System
Interferons

Body cells infected with viruses
produce proteins called interferons
(IFNs)
Interferons

IFN diffuses to uninfected cells and
binds to surface receptors
Interferons

This induces uninfected cells to
synthesize antiviral proteins that
inhibit viral replication
Complement System

A group of 20 proteins present in
blood plasma and on cell membranes
Complement System

When activated, these proteins
enhance immune, allergic, and
inflammatory reactions
Natural Killer Cells

Lymphocytes that lack the
membrane molecules that identify T
and B cells
Natural Killer Cells

Can kill a variety of infectious
microbes and some tumor cells
Natural Killer Cells

Sometime release perforins that
insert into the plasma membrane of
a microbe and make the membrane
leaky so that cytolysis occurs
Natural Killer Cells

Sometimes they bind to a target cell
and inflict damage by direct contact
Phagocytes

Neutrophils and macrophages
Inflammation
Four symptoms
1. Redness
2. Pain
3. Heat
4. Swelling
Inflammation
Three stages
1. Vasodilation and increased
permeability
Inflammation
2. Emigration of phagocytes from the
blood into interstitial fluid
Inflammation
3. Tissue Repair
Inflammation

Vasodilation and increased
permeability are responsible for heat,
redness, and swelling
Inflammation

Pain results from injury to neurons
and from toxic chemicals released by
microbes
Fever

When macrophages respond to an
infection, they release interleukin
-1
Fever

Interleukin-1 stimulates the
hypothalamus to initiate a fever
Fever

Inhibits some microbial growth and
speeds up body reactions that aid
repair
Major Histocompatibility Complex
Antigens

Unique to each person’s body cells
Major Histocompatibility Complex
Antigens

All cells except rbc display MHC class
I antigens
Major Histocompatibility Complex
Antigens

Antigen presenting cells
(macrophages) also display MHC
class II antigens
Pathways of Antigen Processing

For an immune response to occur, B
and T cells must recognize that a
foreign antigen is present
Pathways of Antigen Processing

Antigens are chemical substances
that are recognized as foreign by
antigen receptors when introduced
into the body
Pathways of Antigen Processing

The body contains millions of
different T and B cells each capable
of responding to a specific antigen
Cell-Mediated Immunity

Refers to destruction of antigens by
T cells
Cell-Mediated Immunity
Three main steps
Cell-Mediated Immunity
1. T cells recognize antigen fragments
associated with MHC II class
molecules on the surface of an
antigen presenting cell
(macrophage).
Cell-Mediated Immunity

Although CD8 cell receptors bind to
the antigen associated with MHC
class I molecules on the virus
infected cell
Cell-Mediated Immunity
2. A small number of T cells
proliferate and differentiate into a
clone of effector cells
Cell-Mediated Immunity
2 continued …
Clone of effector cells – a pop. of
identical cells that can recognize the
same antigen
Cell-Mediated Immunity
3. Antigen (intruder) is eliminated
Types of T Cells
1.
2.
3.
Helper T (TH) cells
Cytotoxic T (TC) cells
Memory T cells
Helper T cells

T4 cells
Helper T cells

Display CD4 proteins
Helper T cells

Recognize antigen fragments
associated with MHC-II molecules
Helper T cells

Secrete interleukin-2 which as a
costimulator
Helper T cells

Proliferation of T cells requires
costimulation
Cytotoxic T cells

Fight foreign invaders by killing the
target cell
Cytotoxic T cells

Target cell – the cell that bears the
same antigen that stimulated
proliferation
Cytotoxic T cells

One killing mechanism uses perforin
to cause cytolysis of the target cell.
Cytotoxic T cells

The second mechanism uses
lymphotoxin to activate damaging
enzymes within the target cells
Cytotoxic T cells

Main targets are virus infected cells
Memory T cells

Programmed to recognize the
original invading antigen
Antibody-Mediated Immunity

Refers to destruction of antigens by
antibodies
Antibody-Mediated Immunity
There are 4 steps
Antibody-Mediated Immunity

1. An antigen binds to the surface of
B cells
Antibody-Mediated Immunity
2. Some antigen is taken into the B
cell, broken down into peptide
fragments and combined with the
MHC-II self antigen, and moved to
the B cell surface
Antibody-Mediated Immunity
3. Hepler T cells recognize the
antigen-MHC-II combination and
secrete interleukins
Antibody-Mediated Immunity

The interleukins deliver the
costimulation needed for B cell
proliferation
Antibody-Mediated Immunity
4. Some activated B cells become
antibody-secretion plasma cells.
Others become B cells
Antibodies

A protein that can combine
specifically with the antigenic
determinant on the antigen that
triggered its production
Antibodies

1.
2.
3.
4.
5.
Five classes
IgG
IgA
IgM
IgD
IgE
IgG

It binds to bacteria and viruses
IgG

It crosses the placenta until it can
begin secreting its own.
IgA

It is in blood, breast milk, tears,
saliva, and intestinal secretions.
IgA

Levels decrease during stress
IgA

Protects our mucous membranes
against infections with bacteria and
viruses
IgM

First antibody to be secreted by
plasma cells after exposure to
antigens
IgM

Antibodies to A and B red cell
antigens are IgM
IgM

Cannot cross the placenta
IgD

Activate B cells
IgE

On the surface of mast cells and
basophils
IgE

Involved in allergic reactions
IgE

When a person with pollen allergies
inhales pollen, it combines with the
IgE on their mast cells
IgE

Causes mast cells to release
histamine
AIDS

A condition in which a person
experiences infections as a result of
the progressive destruction of cells
by the humon immunodeficiency
virus
HIV

The only documented transmissions
are by way of blood, semen, vaginal
secretions, and breast milk
HIV

A recent study in San Fran showed
that 8% of their HIV-infected
patients acquired it via oral sex
HIV

Form of a retrovirus with a protein
coat
HIV

HIV enters CD4 positive T
lymphocytes and macrophages
where it sheds its protein coat
HIV

New HIV DNA is produced in the T
cell along with new protein coats and
then released
HIV

The T cells are ultimately destroyed
HIV

Progression to AIDS occurs because
of reduced numbers of T cells and
resulting immunodeficiency
AIDS

Person now susceptible to
opportunistic infections
HIV

Treatment of HIV infection with
reverse transcriptase inhibitors has
shown to delay the progression of
HIV infection to AIDS