Anatomy: Lymphatic and Immune Systems

Lymphatic system function

A system of vessels and nodes that returns excess tissue fluid to the blood
Needed because plasma tends to leak out of blood capillaries
Note: most cells get oxygen and nutrients directly from interstitial fluid
Filters pathogens to be targeted by immune system

Pathway of flow

Throughout most of the body, tissue fluid (interstitial fluid) enters lymphatic capillaries- The fluid is now called lymph
Moves through lymph vessels and lymph nodes
Returned to the blood at veins a base of the neck

Structures

Very low pressure system- uses valves to maintain flow direction
Lymphatic capillaries: Wall= Endothelium (simple squamous epithelium); Minivalves formed by loose edges of cells
Larger lymph vessels- has valves (similar to those of veins)
Lymph nodes- contains reticular CT (with reticular fibers); lymph flows through; pathogens are filtered out by immune cells

Pathology

Lymphedema= accumulation of interstitial fluid due to poor lymphatic drainage
Example (extreme): elephantitis- caused by parasitic worm

Immune system

System of cells, tissues, and organs that is dispersed widely throughout the body to defend against pathogens

Leukocytes

White “blood” cells- most are not in blood
Examples:
Macrophages- engulf foreign materials/ debris
NOT specific to one type of antigen
Presents antigens on cell surface

Lymphocytes

Recognizes and attacks one specific type of antigen
Must be activated first (e.g. by macrophage)

Lymphoid tissue

Reticular connective tissue with lots of lymphocytes
Common in places where pathogens may enter
E.g. MALT= mucous-associated lymphoid tissue

Lymphoid organs

Mostly lymphoid tissue
Primary lymphoid organs (where lymphocytes are made)
thymus and red bone marrow

Secondary lymphoid organs

Contain mature lymphocytes
Lymph nodes
Tonsils
Appendix
Spleen
peyer’s patches