CH 20

Lymph Node Anatomy

James F. Thompson, Ph.D.

The Lymph Nodes•Anatomy

– oval, bean shaped structures scattered throughout body along lymph vessels

– may be deep or superficial

– concentrated along the respiratory tree and GI tract, in the mammary glands, axillae, and groin

– filter lymph fluid to trap foreign organisms, cell debris, and tumor cells

Lymphatic Organs – Lymph Nodes•Covered by a fibrous connective tissue capsule

•Trabeculae extend from cortex to medulla•Stroma – the internal supportive connective tissue network of

reticular fibers

Structure of a Lymph Node• outer cortex - filled

with lymph follicles– outer edge of follicle

contains more T cells– inner germinal

center is the site of B-cell proliferation

• inner medulla - medullary cords of lymphocytes, macrophages, plasma cells (activated B cells)

Cortex

Medulla

Structure of a Lymph Node

• Medullary cords extend from the cortex and contain B cells, T cells, and plasma cells

• Throughout the node are lymph sinuses crisscrossed by reticular fibers

• Macrophages reside on these fibers where they phagocytize foreign matter

follicles withgerminal centers

Histology of Lymph Nodes

Circulation in the Lymph Nodes• Lymph enters via a number of

afferent lymphatic vessels• It then enters a large

subcapsular sinus and travels into a number of smaller sinuses

• It meanders through these sinuses and exits the node at the hilus via efferent vessels

• The node acts as a “settling tank,” because there are fewer efferent vessels, lymph stagnates somewhat in the node

• This allows lymphocytes and macrophages time to carry out their protective functions

Only lymph nodes filter lymph!

• fluid enters cortex through afferent vessels– filter and trap damaged

cells, microorganisms, foreign substances, tumor cells by reticular fibers

– macrophages phagocytize some, lymphocytes destroy some by immune defenses

• exits medulla by efferent vessels at hilus

Lymph Flow Through Lymph Nodes

Blood Flow Through Lymph Nodes

• blood vessels enter and exit at the hilus

• this blood circulation provides nutrition for the node’s tissues and a route for leukocytes to enter into or exit from the lymphatic tissue of the node

End CH 20

Lymph Node Anatomy