Lymphatic Vessels - Anatomy & Physiology
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Lymphatic vessels are part of the lymphatic system and transport lymph.
Development
The lymphatic system develops after the circulatory system and similarly to blood vessels, lymphatic vessels develop from mesoderm via angio & vasculogenesis.
Structure
Unlike the circulatory system for blood the lymphatic system is open and does not have a central pump. Lymph flows through the system in one direction.
The smallest lymphatic vessel is called a lymphatic capillary and these are blind ending vessels consisting of endothelium with a highly perforated basal lamina. This means that lymphatic capillaries are thinner and more permeable than their blood counterparts.
The capillaries feed into larger vessels called lympathic vessels and these have smooth muscle their walls and they pass through lymph nodes. These vessels eventually feed into two large ducts, the thoracic and the tracheal, which empty into the jugular veins. The thoracic duct empties into the veins of the left side while the tracheal to those on the right.
The smaller vessels generally travel with blood vessels and nerves. Valves in the vessels prevent back flow and keep the flow of lymph unidirectional. As there is no central pump the movement of lymph is largely dependant on skeletal muscular activity.
Function
Due to their structure lymphatic capillaries are more permeable than vascular capillaries and this mean that they can not only more effectively remove fluid from tissue but also take up large molecules. This allows the lymphatic system to transport large proteins as well as chylomicrons for the transport of fats. The interstitial fluid filtered into the lymphatic vessels is called lymph. As the vessels pass through lymph nodes the lymph is surveyed by immune cells before returning to the blood ensuring that antigens/pathogens from tissues are removed.