Lymphatic System and Non-Specific Defense
 The Lymphatic System
• Anatomy of the Lymphatic System
• Lymphatic Vessels and Flow
• Lymph Nodes
• Other Lymphoid Organs
The Lymphatic System
 Consists of two semi-independent parts
• Lymphatic vessels
• Lymphoid tissues and organs
 Lymphatic system functions
• Transport fluids back to the blood
• Play essential roles in body defense and
resistance to disease
Parts of the Lymphatic System
Lymphatic vessel or duct
• One way system toward the heart
• No pump
• One-way valves restrict flow
• Made of overlapping endothelial
cells; very permeable
• Lymph moves toward the heart
through milking action of skeletal
muscle and rhythmic contraction
of smooth muscle in vessel walls
Lymphatic Vessels
 Lymph Capillaries
• Walls overlap to form flap-like mini-valves
• Fluid leaks into lymph capillaries
• Capillaries are anchored to connective tissue by filaments
• Higher pressure on the inside closes mini-valves
Lymphatic Vessels
 Lymphatic collecting vessels
•
Collects lymph from lymph capillaries
•
Carries lymph to and away from lymph
nodes
•
Returns fluid to circulatory veins near
the heart
•
Thinner walls ,more valves
Lymphatic ducts
•Right lymphatic duct
•Thoracic duct
Return to venous circulation
Lymph Fluid
 Materials returned to the blood
• Water
• Blood cells
• Proteins
 Harmful materials that enter lymph vessels
• Bacteria
• Viruses
• Cancer cells
• Cell debris
Lymph Nodes: Where Are They?
Figure 12.3
Lymph Nodes: Function, Structure, & Flow
 Filtering of lymph before it is returned to
the blood
 Structure
•
Mostly kidney shaped, < 1 inch long
•
Outer Cortex contains follicles – collections
of lymphocytes that respond to antigens,
intense B cell reproduction centers
•
Inner Medulla contains phagocytic
macrophages that engulf and destroy foreign
substances
 Lymph Flow
•
Lymph enters the convex side through
afferent lymphatic vessels
•
Lymph flows through a number of
sinuses inside the node
•
Lymph exits through efferent
lymphatic vessels
•
Fewer efferent than afferent vessels
causes flow to be slowed
Other Lymphoid Organs
 Spleen: Filtering and removal of
old red blood cells; blood reservoir.
Site of lymphocyte proliferation
and immune surveillance and
response.
 Thymus: Hormone production
(thymosin) and maturation and
"education" of T lymphocytes.
 Tonsils: Trap and remove bacteria
and particulate matter; tonsilitis is
bacterial inflammation (Part of
MALT)
 Peyer’s patches: Capture and
destroy bacteria in intestine,
preventing them from breaching the
intestinal wall (Part of MALT).
Generates “memory” lymphocytes
* MALT: Mucosa-Associated
Lymphatic Tissue
Figure 12.5
Cells of the Lymph: Lymphocytes
 Types of Lymphocytes
• T cells (cell-mediated and cytotoxic immunity)
o Manage the immune response
o Attack and destroy foreign cells
• B cells (blood based or humoral immunity)
o Produce plasma cells, which secrete antibodies
 Functions of Lymphocytes
• T cells and B cells protect against antigens
o Anything the body perceives as foreign
 Bacteria and their toxins; viruses
 Mismatched RBCs or cancer cells
Other Lymphoid Cells
 Macrophages phagocytize foreign substances
and help activate T cells
 Dendritic cells capture antigens and deliver
them to lymph nodes
 Reticular cells produce stroma that supports
other cells in lymphoid organs