The Structure and Function of the Lymphatic System
The lymphatic system originates from blood plasma and is a constant circulation. It consists of complex capillary networks which collect the lymph in various organs. There is an elaborate system of collecting vessels which travel the lymph from the capillaries through lymphatic vessels, lymph nodes, larger lymphatic vessels to lymph trunks and finally to the large veins of the neck at the junction of the right and left internal jugular and subclavian veins where the lymph drains into the blood stream. Lymph glands or nodes are interspaced in the pathways of the collecting vessels and filter the lymph and remove toxic substances as it passes through them and contribute lymphocytes to the lymph.
The lymphatic system forms a one way flow system towards the heart. The lymph flows through the system coming from blind ended lymphatic capillaries at the endothelium single layer. This single layer has an incomplete basement membrane and there is a gap of 14 micronutres which makes it very permeable to large particles, plasma proteins and carbon particles. The capillaries have a loose overlap of small anchoring filaments which contain elastic fibres. When the external pressure is greater with excess interstitial fluid the anchoring filaments are pulled making the openings between cells even larger so fluid can flow to the lymphatic capillary and help the lymphatic vessel take large particles such as viruses, pathogens and cell debris. When the internal pressure is greater in the capillary the cells adhere more closely together and lymph cannot escape back into the interstitial fluid. The pressure reduces when lymph moves further down the lymphatic capillary.
The capillaries are tiny tubes that have small one way valves which ensure the lymph flow is only in one direction away from the tissues. Each capillary is 10-50 micronutres in diameter, slightly larger than...