The lymphatic system consists of lymph, lymphatic vessels, lymph nodes, and lymphatic organs. It functions to maintain fluid balance, absorb fats, and aid the immune system. Lymph is clear fluid that forms from tissue fluid and is transported through lymphatic vessels and lymph nodes before draining into the bloodstream. The right lymphatic duct drains the right side of the body while the larger thoracic duct drains the rest of the body before both vessels drain into large veins in the neck. Lymph nodes filter lymph and contain immune cells that fight pathogens. Disease can spread through the lymphatic system as lymph nodes indicate metastasis and infections can occur in vessels.

1. Notes on lymphatics 1
C. Riedinger 2011
LYMPHATIC SYSTEM
Consists of:
lymph - lymphocytes - lymphatic vessels - lymph nodes - lymphatic organs
Function:
- maintains fluid balance (prevent oedema)
- absorbs facts from small intestine
- proliferation, development and storage of immune cells
- defends against microorganisms and foreign substances
- =part of circulatory and immune system!
Lymph:
- formed from interstitial fluid (derived from blood)
- consistency similar to blood plasma (cellular components of blood cannot
leave the capillaries)
- taken up by passive diffusion and transient negative pressures in their lumina,
generated by contractile activity of smooth muscles in largest lymphatic vessel
walls (or by movement of other tissues)
- clear and colourless, but from small intestine: dense and milky due to
chylomicrons
- lymph in lacteals (because lymph here is white!) of small intestine is called
chyle
Lymphatic vessels:
- parallel circulatory system
- originates in peripheral tissues as blind-ended endothelial tubes (simple
squamous with valves)
- not present in cornea, cartilage, thymus, CNS, PNS, bone marrow, epidermis
and very few in endomysium of skeletal muscles
- collect excess fluid form the interstitial spaces (10%)
- smallest = lymph capillaries
o resemble capillaries but endothelial lining permeable to larger
molecules, such as colloidal proteins and particulate material (cell
debris, microorganisms)
o have funnel-shaped valves
o area between two valves: lymphangion
o intercellular junctions lack tight junctions
o no intrinsic contractility
o extrinsic forces for propulsion: respiratory movement, muscle
contraction, pulse pressure of adjacent arteries
- terminal lymphatic vessels in mucosa of small intestine: lacteals
- lymphatic capillaries join into larger vessels which pass to local lymph nodes
- lymph passes through series of nodes until it reaches a major collecting duct
(few drain directly, such as thyroid, oesophagus, coronary and triangular
ligaments of liver to thoracic duct)
- largest lymphatic vessels (200um) like small veins, but with more valves
(semilunar)
- lymph drains into large veins in the root of the neck
- almost all reach either thoracic or right lymphatic duct

2. Notes on lymphatics 2
C. Riedinger 2011
Right lymphatic duct:
- Drains right half of head and neck, right arm and right hemithorax
Thoracic duct:
- Similar to medium-sized vein, but more prominent smooth muscle in tunica
media.
- Drains rest of body
- Ascends in the posterior mediastinum between the descending thoracic aorta
and the azygos vein
- Length 38-45cm
- From L2 to root of the neck
capillaries  afferent vessels  lymph node  efferent vessels  lymph trunk 
terminal vessels (TD, right lymphatic duct)  great veins
Lymph nodes:
- filter lymph
- have convex cortex into which afferent vessels open
- also have medulla and hilum (concave surface), through which efferent vessel
exits
- are encapsulated centres of antigen presentation and lymphocyte activation,
differentiation and proliferation
- generate antigen-primed B and T cells
- filter particles (i.e. microbes) from the lymph by phagocytic macrophages
- ~450 in total
o 60-70 head and neck
o 100 thorax
o 250 abdomen and pelvis
- mainly close to viscera, in mesenteries
- lymph flows through channels in lymph nodes after entering from afferent
vessels
- reticulin to support sinus macrophages
- superficial lymph nodes: inguinal region, axilla, neck
o receive lymph from skin, mucous membranes, serous linings
o superficial system drains to the deep system
- deep lymphatic vessels: preaortic, para-aortic, bronchomediastinal
o drain organs
o accompany arteries or veins
Lymphatic organs:
- clusters of lymphocytes and other cells (macrophages) in framework of short
branching connective tissue fibres
- lymphocytes from bone marrow, but proliferate within lymphatic organs
- tonsils, spleen, thymus gland
Spread of disease:
- easy for tumour to enter, slow flow does little damage to foreign cells
- presence of metastases in lymph nodes indicates metastases to distant organs
- lymphadenitis: inflammation, lymphangitis: infection of vessels (red line
under skin) lymphoma: cancer of lymphocytes