Principles of organisation of the lymphoid system

===Lecture Details===
Paul McMenamin; Week 11 MED1011; Anatomy
===Lecture Content===
Lymphatic obstruction causes elephantitis, obstructed by microfiliarial worms. Lymph drains and filters tissue fluid, recognises foreign antigens, produces antigen specific cells. Tissue fluid is produced in capillary beds, is ECF that does not return to venous system. It is low in cells/leukocytes and has a lower protein count than plasma. It is present in all tissues except avascular tissues and some vascular tissues (brain with CSF and internal eye with aqueous humor). A lot of fluid is driven to lymph by hydrostatic pressure.
Lymphatic capillary has poorly developed basal lamina, devoid of pericytes. Lymphatic endothelium is highly attenuated. Cells are connected directly to interstitial collagen by anchoring filaments. They also have flap like minivalves caused by no tight junctions in endothelial overlap and are blind ending tubes. They can be difficult to identify histologically but can be seen as beaded clear tubes with numerous valves. All fluid is recycled to systemic vascular system. Most channels have no smooth muscle but do have valves to give unidirectional flow. It returns to the vascular system by muscle activity, adjacent artery pulses, pressure in compartments. 
Lymph nodes remove cell debris, filter foreign particles, recognise foreign proteins (T proliferate in response to Ag, B produce Ab in response to Ag). Sentinel nodes are site of first spread of tumour. Chyle is fatty lymph drainage. Lymph nodes are designed to maximise opportunity for Ags to encounter T cells in cortical zone and B cells in medullary zone. Nodes contain a complex meshwork of reticular fibres with cells attached. Nodes have a rich blood supply. All lymph must pass through one node before entering blood.
Thoracic duct drains all body except right upper limb, right side of H and N, right side of chest which all go to the right lymphatic duct. Superficial lymphatics follow veins, deep follow arteries. Lymphatic plexus can mean lymph can take several pathways
===Readings===
====Eizenberg Ch 10 and 11====