Lymphatic system

Lymphatic system: returns fluids leaked from blood vessels back to blood; consists of:

–Elaborate network of drainage vessels called lymphatic vessels

–Fluid in lymphatic vessels, called lymph

–Structures called lymph nodes that cleanse lymph as it passes through


Lymphatic capillaries- bind ended vessels that weave between tissue cells and blood capillaries


  • In the small intestine lacteals are specialized set of lymphatic capillaries for absorption and transport of digested fat.

Lymphedema- insufficient return of lymph to blood resulting in severe localized edema


  • Lymphatic capillaries drain into increasingly larger and thicker-walled channels



Lymphatic vessels are low presssure conduits; rely on same structures and mechanisms that promote undirectional blood flow through low pressure veins.

Physical activity increases flow of lymph.


Lymphoid cells consists of immune system cells found in lymphoid tisssues together with supporting cells that form “scaffolding” of those tissues



2 types of lymphocytes ( protect body from antigens)

▪T lymphocytes (T cells) – manage immune response; some directly attack and destroy infected cells

▪B lymphocytes (B cells) – B cells produce plasma cells, which secrete antibodies that mark antigens for destruction by phagocytosis or other means
Antigens- anything that triggers an immune response

Macrophages - phagocytize foreign substances and activate T cells

Dendritic cells - capture and deliver antigens to lymph nodes to activate T cells

Reticular cells - fibroblast-like cells that produce reticular fiber stroma (network that supports other cell types) in lymphoid organs and tissues



Lymphoid organs are grouped into two functional categories:

–Primary lymphoid organs: where T and B cells mature

▪B cells mature in red bone marrow

▪T cells mature in thymus

–Secondary lymphoid organs: where mature lymphocytes first encounter their antigens and become activated; include:

▪Lymph nodes and spleen

▪Collections of mucosa-associated lymphoid tissue (M A L T) that form:

–Tonsils, Peyer’s patches in small intestine, and appendix

▪Diffuse lymphoid tissues



Afferent - towards

Efferent- away from