Lymph Circulation
Recall that more fluid filters out of blood capillaries (net outward flow) than returns to them by reabsorption. The excess filtered fluid is ~ 20-25L per day and drains into lymphatic vessels and becomes lymph.
Like veins, lymphatic vessels contain valves ensuring one-way movement of lymph.
The sequence of fluid flow is therefore:
Blood capillaries (blood) → interstitial spaces (interstitial fluid) → lymphatic capillaries (lymph) → lymphatic vessels (lymph) → lymph node lymphatic vessels lymphatic trunk → lymphatic duct junction of the internal jugular and subclavian veins (blood) Vena cava The lymphatic system doesn’t have a central pump like the heart for the circulatory system. The same two “pumps” that aid venous return also aid flow of lymph: Skeletal Muscle Pump, Respiratory Pump.
Lymphatic Organs and Tissues
Primary Lymphatic Organs : sites where stem cells divide and become immunocompetent (mature) which is capable of mounting an immune response.
The primary lymphatic organs are: Red Bone Marrow & Thymus .
The Secondary Lymphatic Organs and tissues are the sites where most immune responses occur.
They include lymph nodes, spleen, lymphatic nodules (follicles).
The thymus, lymph nodes, and spleen are considered organs because they are surrounded by a CT capsule.
Red Bone Marrow
Found in the epiphyses of long bones and within flat bones Pluripotent stem cells in red bone marrow give rise to mature, immunocompetent B cells and immature T cells. B cells enter the blood stream and migrate to other lymphatic tissue Immature T cells travel to the thymus
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