Lymphatic System and Immune Tissue

Study Notes

The lymphatic system is composed of lymph nodes, lymphatic vessels, and lymphatic ducts.
It collects excess interstitial fluid and returns it to the circulatory system.
Lymph is the clear, colorless fluid found in most lymphatic vessels. Chyle is milky lymph, containing fats from the small intestine.
Lymphatic vessels are absent in the brain, bone marrow, and avascular tissues (like epithelia and cartilage).
Lymphatic flow is unidirectional and maintained via valves within the vessels.

Lymphoid organs are composed of two major parts:
- Stroma: supportive connective tissue framework (capsule and trabeculae, fine reticular fibers).
- Parenchyma: functional cellular component (outer cortex, inner medulla, etc.)

A primary lymphoid organ where T lymphocytes mature.
The thymus begins to involute, or shrink, after puberty.
It continues to function into adulthood.
The thymus is composed of a cortex and a medulla; septa divide the lobes into incomplete lobules.
Hassall's corpuscles are a characteristic feature of the medulla, increasing in number with age.

Small, oval, encapsulated structures along lymphatic vessels.
They have a convex outer surface and a concave hilum (containing efferent and afferent lymphatic vessels, and blood vessels).
Divided into three zones: cortex, paracortex, and medulla (containing primary and secondary nodules, B and T lymphocytes, macrophages and plasma cells).

Lymphangitis and lymphadenitis are inflammations of lymphatic vessels and lymph nodes, respectively, often resulting from infection.
Lymphedema occurs when lymph flow is obstructed, leading to fluid buildup.
Cancerous lymph nodes can be surgically removed, potentially leading to secondary lymphedema.