8.3 LYMPHATIC SYSTEM AND IMMUNITY

Lymphatic circulatory system = network of vessels throughout the body
o maintains a steady flow of water and other substances between the
blood, the interstitial fluid, and the lymphatic system
o works with white blood cells to protect the body against infection

lymph is what circulates in the lymphatic vessels
o plasma from the capillaries of the
circulatory system escapes or leaks out to
become part of the interstitial fluid
bathing cells and is taken up by lymphatic
vessels
o lymph rejoins the main circulatory system
through ducts that empty into the large
veins near the heart

Lymphatic vessels have valves to ensure one-way
flow (like veins)

Blood circulates in a continuous circuit of
cardiovascular vessels and is pumped by the
heart, while lymph forms in closed-ended tubes in the capillary bed.
IMMUNE RESPONSE

three lines of defense of the immune system:
1. barriers – prevent from entering body
2. non-specific immune responses (cell-mediated immunity) – involves
white blood cells
3. specific immune responses (antibody-mediated immunity) – involves
production and release of antibodies
1.
Barriers
Barrier
Chemical or Physical
How it works
Eyelashes
physical
trigger reflex blinking
may catch airborne particles
contain antibodies and lysozyme (antibacterial enzyme)
Tears
Cilia of the
respiratory tract
chemical
physical
cilia sweep dust, bacteria, and other airborne particles
towards the mouth, preventing them from entering lower
respiratory tract
Stomach acid
chemical
kills pathogens
Skin
chemical and physical
Bactericides in skin make it inhospitable for microbes to
grow; perspiration acidic
outer layer made of keratin which is waterproof and
indigestible
2. Non-Specific Immune Response (Cell-Mediated)
 includes the white blood cells: lymphocytes, macrophages, Killer T cells
(cytotoxic T cells) and other T cells
 white bloods cells find and destroy pathogens (bacteria, viruses, cancer) through
the process of phagocytosis = engulf and digest pathogen
 engulfing and digestion of a pathogen leads to antibody-mediated immunity
3. Specific Immune Response (Antibody-Mediated)
 Cells produce antibodies = proteins that can recognize specific foreign
substances the body and neutralize and destroy them
 Include the lymphocytes (white blood cells) made in the thymus gland (T cells –
mission is to seek out intruder and signal B Cells to attack) and in the bone
marrow (B cells – mission is to produce antibodies) *** note T cells also in
Cellular-Mediated Immunity ******
 Antibodies are proteins that recognize antigens (identifier molecules that are
found on the surface of all cells) on foreign substances
 Antibodies bind with antigens to produce an antigen-antibody complex which is
larger and more easily identified so it can be engulfed by macrophages
 Once body recognizes foreign antigens it builds up immunity after each exposure
due to specialized memory cells that recognize another encounter with the
foreign antigen

More antibodies
produced after second exposure

It took less time to
produce antibodies in second exposure
HOW THE SECOND AND THIRD LINE OF DEFENSE WORKS:
Pathogen (with antigen marker)
enters body and is engulfed by
macrophage
Macrophage displays antigen
marker on cell surface
stimulates
Helper T cells bind to macrophage
and release chemical that activates
other T cells and B cells
Killer T Cells (cytoxic T
cells) puncture cell
membranes of pathogen
Stimulates
production of
Memory T
Cells to
recognize
more
pathogens
Stimulates
production of
more active Killer
T Cells and
suppressor T cells
(inhibit immune so
normal tissues not
destroyed
Activated B cells enlarge
and produce memory B
cells and plasma cells
Plasma cells
produce more
antibodies
Memory B
cells remain in
blood for next
exposure
Antibodies bind with antigens
(antigen-antibody complex)
and are recognized and
destroyed by macrophages