1. health and fitness
2. disease
3. aids and hiv

LYMPHATIC SYSTEM AND BODY
DEFENSES
Unit 11
LYMPHATIC SYSTEM
Defense against disease
 Consists of two semi-independent parts:
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Network of lymphatic vessels
 Various lymphoid tissues and organs throughout
body
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Lymphatic vessels transport fluids that have
escaped from the blood vascular system back to
the blood.
 Lymphoid organs house phagocytic cells and
lymphocytes
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LYMPHATIC VESSELS
Fluid is forced out of the blood in the
capillary beds, and most of it is
reabsorbed at the venous ends.
 About 3 L per day are left behind 
this becomes part of the interstitial
fluid, and is now called lymph.
 This fluid must return to the
bloodstream in order to have enough
volume for the cardiovascular system
to function
 If this does not happen, fluid starts
to build up in the tissues, producing
edema (swelling)
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LYMPHATIC VESSELS
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One way system  vessels only flow towards the heart
Low-pressure and pumpless system
Lymph capillaries = microscopic, blind ended vessels
that spread out between tissues cells and blood capillaries
in the loose connective tissues of the body.
Little valves at the end  open when fluid pressure is
higher in the interstitial space, but close up when the
pressure is higher inside the lymphatic vessels  prevents
leaks
LYMPHATIC VESSELS
Large particles like proteins, cell debris, bacteria,
and viruses can’t enter blood capillaries, but they
can enter lymphatic capillaries, especially in
inflamed areas
 Now the bacteria and viruses can travel
throughout the body  how do we solve that
problem?
 Lymph takes “detours” through lymph nodes 
gets cleaned of debris and “examined” by cells in
the immune system
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LYMPHATIC VESSELS
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Lymph moves from lymph capillaries to successively larger
lymphatic vessels (lymphatic collecting vessels),
similar to how blood moves from capillaries to venules to
veins.
Lymph returns to venous system through one of two large
ducts:
Right lymphatic duct – drains lymph from right arm and
right side of head and thorax
 Thoracic duct – receives lymph from the rest of the body
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Both ducts empty into subclavian veins
Lymphatic vessels are thin walled and the larger ones
have valves to prevent backflow, like veins.
Also helped by skeletal muscles “milking” the lymph along
and pressure change in the thorax during breathing.
LYMPH NODES
Help protect the body by removing foreign material
such as bacteria and tumor cells from the lymphatic
stream as well as producing lymphocytes.
 Lymph nodes = filters
 Large clusters can be found in the inguinal (hips),
axillary (armpits), and cervical (neck) regions of body.
 Contain macrophages, which engulf and destroy
bacteria, viruses, and other foreign substances found
in lymph
 Also contain lymphocytes, a type of WBC
 Active infection usually results in swollen glands due
to the trapping function of the nodes.
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LYMPH NODES
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Usually kidney-shaped, less than 1 inch long, and
“buried” in connective tissue that surrounds them.
Each node is surrounded by a fibrous capsule
Trabeculae = strands that extend into the capsule to
divide them into compartments
Cortex = outer part of the node, contains collections of
lymphocytes called follicles
Germinal centers = dark centers of follicles that
enlarge when B lymphocytes generate plasma cells
Medulla = center of lymph node, contains phagocytic
macrophages
Lymph enters through afferent lymphatic vessels,
moves through sinuses, and exits through efferent
lymphatic vessels.
LYMPH NODES
SPLEEN
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Blood rich organ that filters blood
Located on the left side of abdominal cavity,
curls around stomach
Doesn’t filter lymph, it filters blood and cleans
out bacteria, viruses, and other debris
Destroys worn out RBCs and returns their
breakdown products to the liver
Stores platelets and acts as a blood reservoir
(like the liver)
During hemorrhage, the spleen will contract
and empty its stored blood back into
circulation to help keep levels normal
Forms all blood cells in a fetus, but only
lymphocytes are made in adults
THYMUS
Lymphatic mass found low in throat overlying
the heart
 Produces hormones (thymosin and others) that
function in the programming of certain
lymphocytes so that they can protect the body
 Functions at peak levels only during youth
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TONSILS
Small masses of lymphatic tissue that ring the
pharynx (throat)
 Trap and remove any bacteria or other foreign
pathogens entering the throat
 Sometimes they work too well  get congested
with bacteria and become red, swollen, and sore =
tonsillitis
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PEYER’S PATCHES
Resemble tonsils, but found in wall of small intestine
 Macrophages in ideal position to capture and destroy
bacteria  lots of bacteria in intestine
 Help stop bacteria from penetrating intestinal wall
 Peyer’s patches and tonsils are known as mucosaassociated lymphatic tissue (MALT)
 MALT protects upper respiratory and digestive
tracts  never-ending attacks of foreign matter
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LYMPHOID ORGANS
BODY DEFENSES
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Two main systems:
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Nonspecific – responds immediately to protect body
from all foreign substances, reduces workload of
specific defense system
Intact skin and mucous membranes
 Inflammatory response
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Specific – aka immune system, attacks particular
foreign substances
Lymphatic organs
 Blood vessels
 White blood cells
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SURFACE MEMBRANE BARRIERS
First line of defense = skin and mucous
membranes
 Act as physical barriers
 Acid pH of skin inhibits bacterial growth
 Stomach mucosa makes hydrochloric acid and
protein-digesting enzymes, which helps kill
pathogens
 Saliva and tears contain lysozyme, an enzyme
that destroys bacteria
 Sticky mucus traps microorganisms in digestive
and respiratory pathways
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CELLS AND CHEMICALS
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Second line of defense
Phagocytes – engulfs a foreign particle and digests it
Natural killer (NK) cells – lyse and kill cancer cells
and virus-infected cells  can react against any
target. They attack the cell’s membrane and release
chemicals that cause it to disintegrate
Fever – abnormally high body temperature, pyrogens
are chemicals secreted by WBCs that raise body
temperature, fevers can be very dangerous if they get
too hot or last too long
Inflammatory response – triggered when body tissues
are injured  4 cardinal signs = redness, heat,
swelling, and pain.
INFLAMMATORY RESPONSE
Injured cells release histamine and kinins
 Cause blood vessels to dilate and capillaries to
become “leaky”  increased blood flow
 Activate pain receptors
 Attract phagocytes and WBCs to area 
chemotaxis = cells following chemical gradient
 Swelling (edema) is the result  causes more
pain
 The inflammatory response prevents the spread
of damaging agents, disposes of cell debris and
pathogens, and sets the stage for repair
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RECAP
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Lymphatic system defends against disease
Lymphatic vessels
 Various lymphatic tissues and organs
 Lymph

One way system  towards the heart
 1st line of defense = skin and mucus membranes
 2nd line of defense = cells, chemicals, and
inflammatory response
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IMMUNE SYSTEM
Third line of defense
 Immune response – immune system’s response
to a threat; increases inflammatory response and
provides protection against specific antigens
 Recognizes foreign molecules (antigens) and
actively works to destroy them
 Can recognize previously encountered antigens
and trigger immune responses
 Immunology – study of immunity
 Some diseases that result from a malfunctioning
immune system: cancer, rheumatoid arthritis,
AIDS
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THREE IMPORTANT ASPECTS OF IMMUNE
RESPONSE:
1. Antigen specific – recognizes and acts against
particular pathogens or foreign substances
 2. Systemic – Immunity is not restricted to the
initial infection site
 3. “Memory” – recognizes and mounts stronger
attacks on previously encountered pathogens
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TWO KINDS OF IMMUNITY
1. Antibody-mediated immunity (humoral
immunity) = provided by antibodies present in
body’s fluids.
 2. Cell-mediated immunity = Lymphocytes
themselves defend the body, either by directly
lysing foreign cells or indirectly releasing
chemicals that enhance inflammatory response
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ANTIGENS
Any substance capable of exciting our immune
system and provoking an immune response.
 Tend to be large
 Not normally present in our bodies
 Foreign intruders  “non-self”
 Our own cells have self-antigens, which are
recognized by our body, but would trigger an
immune response in someone else (organ
transplant rejections)
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CELLS OF THE IMMUNE SYSTEM
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Lymphocytes
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B lymphocytes (B cells) – produce antibodies and
oversee antibody-mediated immunity
T lymphocytes (T cells) – do not produce antibodies
and oversee cell-mediated immunity
Lymphocytes must be able to recognize body’s
own cells so they won’t attack them
 Lymphocytes get “trained” to recognize one
distinct antigen to attack = immunocompetent
 Since lymphocytes become immunocompetent
before being exposed to antigens, we know it is
our genes, not antigens, that determine what
foreign substances we will be able to resist.
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CELLS OF THE IMMUNE SYSTEM
Macrophages – “big eaters”
 Engulf foreign particles and present fragments of
these antigens on their own surfaces
 Allow these particles to be recognized by
immunocompetent T cells – antigen presenters
 Macrophages secrete monokines, which activate
T cells
 Active T cells release chemicals that turn
macrophages into killer macrophages
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ANTIBODY-MEDIATED RESPONSE
Primary humoral response = Immature B cell
binds to antigen  gets activated and undergoes
clonal selection (mass produces an army of
cells like itself)
 Afterwards, most clones become plasma
 Some become long-lived memory cells and can
respond to the antigen when they encounter it
later = secondary response
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TWO KINDS OF HUMORAL IMMUNITY
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Active immunity = B cells encounter antigens
and produce antibodies against them
Naturally acquired = bacterial and viral infections
 Artificially acquired = vaccinations
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Passive immunity = Antibodies received from
immune human or animal donor  temporary
protection that ends when “borrowed antibodies”
naturally degrade in the body
Naturally acquired = mother’s antibodies cross over
placenta to fetus
 Artificially acquired = After receiving immune serum
or gamma globulin (used for treating rabies,
hepatitis, snake bites, botulism, tetanus, etc.)
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ANTIBODIES
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Also referred to as
immunoglobulins (Igs)
Soluble proteins secreted
by activated B cells in
response to an antigen 
capable of binding
specifically to that antigen
Basic structure – four
amino acid (polypeptide)
chains linked by disulfide
bonds
2 chains = Heavy chains, 2
chains = Light chains
Variable and constant
regions
ANTIBODIES
Five major classes – IgM, IgA, IgD, IgG, IgE
 Remember – MADGE
 Slightly different biological roles
 Antibodies can function through:
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Complement fixation = activated during nonspecific
body defenses, antibodies attached to cellular targets
cause the cell to lyse
 Neutralization = antibodies bind to specific sites on
bacteria or viruses, making them inactive
 Agglutination = cross-linking between antibodies and
antigens causes clumping
 Precipitation = cross-linking makes clumps so big,
they settle out of solution
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CELL-MEDIATED RESPONSE
T cells are activated to form clones after binding with
“recognized” antigen
 Antigens must be “presented” by macrophages
 Different types of T cells:
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Helper T cells = interact directly with B cells bound to
antigens. They liberate lymphokines, chemicals that
enhance the killing activity of macrophages, attract other
leukocytes, or act as helper factors.
 Cytotoxic (killer) T cells = directly attack and lyse infected
and cancerous cells.
 Delayed hypersensitivity T cells = release chemicals that
enhance inflammation and promote a delayed allergic
reaction
 Suppressor T cells = terminate normal immune response
by releasing suppressor chemicals
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IMMUNITY DISORDERS
Allergy/hypersensitivity = overreaction to
otherwise harmless antigen
 Immunodeficiency = abnormalities in any
immune element (AIDS)
 Autoimmune disease = body’s self-tolerance
breaks down, antibodies attack bodies own cells
and tissues
 http://www.youtube.com/watch?v=l-2ilZA_aw&feature=related
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