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Lymphatic System and Immunity [11]
Pathogens – Organisms that cause harm to the
body
 Virus – particles not considered to be
living that attack and multiply within
cells
 Bacteria – prokaryotes that live in tissue
fluid in tissues and produce toxins that
damage cells
 Fungi – surface of the body and
interstitial fluid
 Parasites – burrow into organs or live
between tissues
Parts of the lymphatic system
1. lymph – fluid
2. lymphatic vessels
3. lymphocytes – specialized WBC
4. lymphoid tissues and organs (glands)
Lymphocytes (specific defense) respond to
 Invading pathogens
 Abnormal cells – cancer cells or cells
containing viruses
 Foreign proteins – toxins
Immunity – ability to resist infection and
disease through activation of specific defenses
Other systems involved with the immune
system include: integumentary system,
cardiovascular, respiratory system, digestive
syst.
Functions of the lymphatic system include:
1. Production, maintenance, and distribution
of lymphocytes
2. Return of fluid and solutes from the
peripheral tissues
3. Distribution of hormones, nutrients, and
waste products from tissues of origin to
general circulation.
Lymphatic vessels begin with capillaries which
1. originate as blind pockets
2. larger that blood capillaries
3. very thin walls
4. have a flattened or irregular outline
Larger lymphatic vessels have very thin
walls that periodically have valves similar to
the veins. The lymphatic vessels merge and
empty into the right subclavian vein.
Lymphocytes are specialized WBC
1. T (Thymus dependent cells)
a. Cytotoxic T cells – direct attack on
invaders
b.Helper T cells – stimulate activation
and function of B cells and T cells
c. Suppressor T cells – inhibit activation
and function of B cells and T cells
2. B cells become plasma cells which
produce and secrete antibodies which
react with specific proteins called
antigens
3. NK cells – natural killer cells – attack
foreign cells, cells infected with viruses
and cancer cells
Lymphocytes are formed in the bone marrow,
but some migrate to the thymus where they
mature into T cells.
Some examples of lymphoid tissues include:
1. Pharyngeal tonsils
2. Palatine tonsils and
3. Lingual tonsils
4. MALT in the digestive tract (mucosaassociated lymphoid tissue)
Lymphoid Organs include
1. Lymph nodes –
a. Location- scattered throughout the body,
b.Function – filtering lymph for antigens,
stimulation of macophages to initiate
immune response.
2. Thymus –
a. Location – mediastinum just above the
heart
b.Function secretion of hormones that stimulate
stem cell divisions,
 site for maturation of T-cells
3. Spleen
a. Location - Along the curve of the
stomach
b.Function –
 Removal of abnormal blood cells
 Storage of iron from recycled RBC
 Initiation of B and T cells in response
to antigens in blood
Other cells that participate in Tissue Defense
Table 22-3 (copy from the book) pg.787