Lymph Drainage - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 177

other hand, the lung, gut, genitourinary tract, and dermis of the skin contain a dense
network of lymphatic vessels.
The lymphatic network not only maintains the fluid balance, but also carries
fat-soluble vitamins, fatty acids, and other lipids from the digestive tract and
delivers these materials to the body's cells. Chyle 4 is an emulsion 5 of lymph
(continuous phase) and immiscible free fatty acids (dispersed phase). In villi
of the small intestine during digestion, fatty foods processed by enzymes of
digestive juices are taken up by enterocytes. In enterocytes, absorbed lipids are
again processed and incorporated in chylomicrons. These lipoproteins enter lacteals
(lymphatic capillaries) and form chyle. The relative low pressure of the lacteals
enables entry of large molecules, whereas the higher pressure in veins allows only
smaller digestion products (e.g., amino acids and sugars) to enter directly blood.
Lymph drainage is involved in immunity. The lymphatic network comprises the
lymphoid tissue, particularly lymph nodes. The lymphoid system also includes all
structures devoted to the production and circulation of lymphocytes (bone marrow,
thymus, spleen, lymphoid follicles such as tonsils, and mucosa-associated lymphoid
tissue, especially in the digestive and respiratory tracts). The lymphatic system
transports leukocytes to and from the lymph nodes. Antigen-presenting cells such as
dendritic cells are transferred by lymph drainage to lymph nodes where an immune
response is launched.
Fluid carried out of the blood stream during normal blood circulation is
filtered not only from blood capillaries, but also lymph nodes. In lymph nodes,
filtered fluid permits to remove microorganisms, abnormal cells, and other materials.
This fluid is then transported back into the blood stream via lymphatic vessels.
Therefore, the lymphatic system assists the immune system in removing waste,
debris, dead blood cells, pathogens, and toxins. However, it also conveys can-
cer cells.
Lymph vessels collect and drain excess tissue fluid and transport lymph into
veins, thereby returning it to blood. Lymphatic capillaries are slightly larger than
blood capillaries. Their wall structure enables interstitial fluid to flow into them,
but not out. Ends of mural endothelial cells overlap. When the interstitial pressure
is greater than the lymphatic capillary pressure, the cells separate slightly and
interstitial fluid enters the lymphatic capillary. When the lymphatic luminal pressure
is greater than the interstitial pressure, endothelial cells strongly, thereby preventing
lymph exit into the interstitial medium.
Unlike the blood circulation, the collecting lymphatic system is an open circuit
with closed upstream ends, as the smallest, thin-walled, lymphatic capillaries
located between cells are closed at one end.

4 Greek

: sap, juice, digestive juice.
5 Latin emulgere: to milk (milk is an emulsion of lipids and water).

χ υλ o ς