Lymphatic System
• Tissues, organs, vessels
and a fluid called lymph
– similar to interstitial fluid
• Diffuse lymphatic tissue
– Tonsils, mucosa associated
lymph tissue and red bone
marrow
• Organs involved
– thymus
– spleen
– lymph nodes
Functions of the Lymphatic System
• Draining excess interstitial fluid & plasma
proteins from tissue spaces
• Transport of some nutrients and hormones
• Immunity –specific defense
– recognize microbes or abnormal cells &
respond by killing them directly or secreting
antibodies that cause their destruction
Formation & Flow of Lymph
• Fluid & proteins filtered
from blood capillaries are
collected by lymphatic
capillaries & returned to
the blood
• Muscle contraction and
breathing promote flow of
lymph
• Lymphatic vessels empty
into veins in shoulders
Lymph Circulation
• Lymphatic capillaries
– Capillaries are closed-ended tubes in tissues
– One-way valves
– Pickup fluid (lymph) from Tissues
Lymph Circulation
• LymphaticVessels
–
–
–
–
Lymph passes from capillaries into lymph vessels
Resemble veins with thin walls & valves
Afferrent lymphatics carry lymph to nodes
Efferent lymphatics carry lymph from nodes
• Lymphatic Trunks
– Lymph passes from lymphatic vessels into trunks
– *Bronchomediastinal, jugular, subclavian, intestinal
and lumbar trunks
Lymph Circulation
• Lymphatic ducts
– Two ducts drain lymph from lymphatic trunks
into the subclavian veins
– Thoracic Duct: Larger one that drains most of
body lymph into the left subclavian vein
– Right Lymphatic Duct: Smaller one that
drains right side of head, right shoulder and
right arm into the right subclavian vein
Lymph Circulation
Right Lymphatic Duct-------------------------Thoracic Duct
Right Lymphatic Duct------
Thoracic Duct----------------------------
Lymphatic Pathways
Interstitial fluid  Lymph Capillaries 
Afferent Lymphatic vessels  Lymph Nodes
Efferent Lymphatic vessels  Lymphatic
Trunks Lymphatic Ducts  Subclavian
Veins
Lymphocytes
• B-cell lymphocytes
– Respond to antigens by dividing to produce
• Plasma cells: Antibody secreting cells
• Memory B-cells
• T-cell lymphocytes
– Respond to antigens by dividing to produce
• Cytotoxic T-cells that kill antigen-bearing cells
• Helper T-cells that help activate other T-cells and B-cells
• Memory T-cells
• Natural killer (NK) lymphocytes can kill invading
cells and tumor cells without need to respond to
antigens – nonspecific defense
Diffuse Lymphatic Tissues
• Lymphatic nodules – MALT (Mucosa
Associated Lymph Tissues)
– lymphatic nodules within the digestive and
respiratory systems
– Small intestine -Peyer's patches
– Appendix
– Bronchi of respiratory tract
Diffuse Lymphatic Tissues
• Tonsils
– Located in and around throat
– Tonsilar crypts
– Functions
• Crypts Trap microbes
• Mount immune response against inhaled and
ingested microbes
Lymph organs
• Lymph nodes
– Structure
– Location
• Throughout body
but concentrated in
groin, neck, armpit
– Functions
• Filter Lymph
• Mount immune
response
Lymph Node Distribution
Lymph Organs
• Thymus
– Located in
mediastinum above
heart
– Large in infants
atrophying with age
– Function
• Thymosin hormones
for T-cell maturation
Spleen
• Located in upper
left quadrant to
left of stomach
• Functions
– Filters blood
– Produces
lymphocytes
– Stores iron and
platelets
Defense
• Non-specific Defense
– First Line Defense: External
•
•
•
•
•
Skin
Mucous Membranes
Tears
Saliva
Stomach acid
Non-specific Defense
• Second Line Defense: Internal
• Antimicrobial proteins
– Interferons – antiviral
– Complement – immunity, allergies and inflammation
• Natural killer (NK) cells
– Lymphocytes
– kill microbes and tumor cells
• Phagocytes
– Wandering phagocytes
– Fixed phagocytes
Non-specific Defense
• Second Line Defense: Internal
• Inflammation
– Mast cells and basophils release chemicals
– Arterioles vasodilate – more blood to site
– Increased capillary permeability – more fluid into
tissues
Non-specific Defense
• Inflammation results in
– Redness
– Heat
– Swelling (edema)
– Pain
– Healing
Specific Defense: Immunnity
• Study of immunity is immunology
• Immunity versus non-specific defense
– Specificity: responds to specific antigens
– Memory: Second exposure to antigen causes a
stronger response
• Antigens
– Foreign (non-self) chemicals
– Cause immune response
Immunity
• B-cell and T-cell lymphocytes responsible for
immunity
• Two types of immune responses
– Cell mediated immunity: T-cells respond to
intracellular antigens such as virus infected cells and
tumor cells
– Antibody mediated immunity: B-cells respond to
extracellular antigens such as bacteria
Cell Mediated Immunity
• T-cells processed by thymus gland
• Two types of T-cell lymphocytes
– CD4 cells (Helper cells)
• Activated when antigen presented by antigen
presenting cell (APC) cell
• Develops into helper T-cells and memory cells
• Helper T-cells must stimulate CD8 cells for them to
become fully activated killer T’s
– CD8 cells (Cytotoxic cells)
• Activated by contact with virus infected body cell
• Develop into killer t-cells and memory cells
Cell Mediated Immunity
• Cytotoxic T’s leave lymphatic tissue to search for
and destroy virus infected cells, tumor cells and
tissue transplant cells on contact
Cell Mediated Immunity
Antibody Mediated Immunity
• B-cell lymphocytes stay in lymph tissues
• Extracellular antigen enters lymph tissue
and binds to B-cell receptors
• B-cells become activated
– B-cells divide (clone) to form plasma cells and
memory cells
– Helper T-cells bind to antigen on B-cells and
“help” stimulate plasma cell and memory cell
formation
Antibody Mediated Immunity
• Plasma cells secrete various types of
antibodies
• Antibodies bind to the specific antigen that
activated its parent B-cells
• Antibodies cause the destruction of the
antigen
Antibody Mediated Immunity
• Antibodies destroy antigens by
– Neutralizing antigens such as toxins
– Agglutinating (clumping) and precipitating
(removing from solution) antigen bearing cells
– Activating the complement proteins that
destroy the antigen by various means
– Enhancing phagocytosis
Antibody Mediate Immunity
Immune Response
Primary Response
• After an initial exposure to an antigen a
slow rise in antibodies production occur
first as immunoglobulin M (IgM) then (IgG)
Secondary Response
• After a subsequent exposure the antibodies
production is far greater and is mainly (IgG)
Summary of Cell and Antibody Mediated Immunity