 Put
excess fluid in tissue spaces back into
the blood stream
 Immunity
 Lymphatic
capillaries →
Lymphatic vessels →
Lymphatic Trunks →
Collecting Ducts →
Veins
 The
lymph will also pass through
lymph nodes found along these
vessels
 Closed-ended
tubes
 Form network with
blood capillaries
 Thin-walled
 Fluid inside is called
lymph
 Lymphatic
vessels
• Structure is very similar to veins
 Lymphatic Trunks
• Larger vessels than lymphatic vessels; drain into
collecting ducts

Two Main Ducts
• Thoracic Duct- collects
lymph drained from the
lower limbs, the
abdomen, the left upper
limb, and the left side of
the thorax, head, and
neck
• Right Lymphatic Ductcollects lymph drained
from the right upper
limb and the right side
of the thorax, neck, and
head
 Interstitial
fluid surrounding capillaries
 Constant movement in and out of
capillaries
 Generally same composition as plasma
except plasma proteins
 Some excess fluid stays and is not
recollected by capillaries
 Volume
pressure of interstitial fluid
causes some of the fluid to enter
lymphatic capillaries
 Lymph will return to the bloodstream but
will be filtered along the way
 Controlled
by
• Skeletal muscle movement
• Pressure changes due to breathing
 Valves
keep the movement going in one
direction
 Usually
small and bean shaped
 Afferent lymphatic vessels
• carry lymph into lymph node
• Come in at various points along convex surface
 Efferent Lymphatic vessels
• Carry lymph out of lymph node
• Come out at hilum (area on the concave side)
 Blood Vessels and nerves enter at hilum
 Connective
tissue encloses lymph node
and creates sub-compartments inside
 Compartments are lymph nodules
 Space inside the nodule is called a lymph
sinus
 Sinuses are filled with lymphocytes and
macrophages
 Filter
foreign particles from blood before
returning the lymph to the blood stream
 Immune
surveillance
 Bilobed
structure
found in the
mediastenum
 Largest during
childhood
 Creates T-cells
 Also endocrine
gland- releases
thymosins to make Tcells mature after
leaving the thymus






Largest lymphatic organ
Found in upper left
quadrant near stomach
Similar structure to
lymph nodes except
sinuses contain blood
instead of lymph
White pulp- high in
lymphocytes
Red pulp- high in red
blood cells, lymphocytes,
and macrophages
Filters Blood
 Protection
against pathogens
 Pathogens include
• Viruses
• Bacteria
• Fungi
• Protozoans
 Innate
vs Adaptive
 Natural
 Active
vs Artificial
vs Passive
 Species
resistance
 First line of defense- skin and mucous layers
 Second line of defense
• Chemical barriers
 Tears, gastric juices, and sweat
 interferons
• Fever
• Inflammation
• Phagocytosis
 Third
line of defense
 Lymphocytes
 Responds
are responsible
to specific antigen on the
invading pathogen
 Undifferentiated
lymphocytes made by fetal
bone marrow
 T cells
• Lymphocytes travel to thymus and become T cells
• T cells either circulate in blood or are found in
lymph system
B
cells
• Made in marrow
• B cells either circulate in blood or found in the
lymph system
 Cellular
Immune response
• Attack up close
• Performed by T cells
 Humoral
immune response
• Attack from afar
• Performed by B cells
 Antigen-presenting
cells processes and
displays antigen of pathogen
 Displayed antigen must be matched with
a circulating helper T cells antibody
receptor
 Helper T cell is activated
 Cytotoxic T
cells- attack cells infected
virus or cancerous cells
 must be activated by a matching antigen
B
cell must match with an antigen
 Activated Helper T cell secrete cytokines
 Cytokines make B cell proliferate to form
plasma cells and memory cells
 Plasma cell secrete antibodies
 Globular
proteins
 Five Types
• Immunoglobulin G (IgG)- in plasma and tissue fluids;
•
•
•
•
activates complement system
IgA- in exocrine gland secretions
IgM- in plasma; activates complement system
IgD- found on surfaces of B cells; activates B cells
IgE- in exocrine gland secretions; associated with
allergic reaction
 Attack
Directly
• Agglutinate- clump pathogens together
• Precipitate- make pathogen insoluble
• Neutralize- cover or destroy toxic part of antigen
 Activate
compliment
• Done by shape change of IgG and IgM
• Starts a series of rxns that activate the compliments
circulating in the plasma
 Compliment
Function
• Opsonization- coating antigen-antibody complex
• Chemotaxis- bringing macrophages to the area
• Lysis- rupturing membranes
• Agglutination
• Neutralization
 Memory T
and B cells- circulate after
primary immune response
 Body
will be able to respond quickly
during secondary immune response
 Immune
response to everyday, nonharmful antigens (allergens)
 Delayed-reaction allergy
• Exposure to allergen on skin
• Collects T cells and macrophages in the area
• Causes dermatitis
 Immediate-reaction
allergy
• Occurs within minutes
• First exposure- B cells become sensitized; IgE is
attached to basophils and mast cells
• Subsequent exposures- mast cells and basophils
secrete several substances including histamine
• These substances produce the reactions seen in
allergy reactions
 Transplant
tissue or organ
 Antigen is recognized as foreign and
starts immune response
 Tissue matching helps minimize reaction
 Immunosuppressive drugs- suppress
immune reaction
 Cytotoxic T
cells cannot correctly identify
self cells and attacks self cells
 Why?
• “catalogue” is incomplete
• Pathogen borrows self antigens during attack
• Pathogen antigen is very similar to a self antigen