Lymphatic vessels

Synthesis. Histamine [51-45-6] 2-(4-imidazolyl)ethylarnine (1) is formed by decarboxylation of histidine by the enzyme L-histidine decarboxylase (Fig. 1). Most histamine is stored preformed in cytoplasmic granules of mast cells and basophils. In humans mast cells are found in the loose connective tissue of all organs, especially around blood and lymphatic vessels and nerves. These cells are most abundant in the organs expressing allergic diseases the skin, respiratory tract, and gastrointestinal tract. 

Airway cross-sections have the nominal anatomy shown in Fig. 5.16. Airway surface liquid (AST), primarily composed of mucus gel and water, surrounds the airway lumen with a thickness thought to vary from 5 to 10 mm. AST lies on the apical surface of airway epithelial cells (mostly columnar ciliated epithelium). This layer of cells, roughly two to three cells thick in proximal airways and eventually thinning to a single cell thickness in distal airways, rests along a basement membrane on its basal surface. Connective tissue (collagen fibers, basement membranes, elastin, and water) lies between the basement membrane and airway smooth muscle. Edema occurs when the volume of water within the connective tissue increases considerably. Interspersed within the smooth muscle are respiratory supply vessels (capillaries, arteriovenous anastomoses), nerves, and lymphatic vessels. 

Lymph-gefass, n. lymphatic vessel, -korper-chen, n. lymph corpuscle, leucocyte, lyo-pbil, a. lyophile, lyophil(ic). -phob, a. lyophobe, lyophobic. -trop, a. lyotrope, lyotropic. 

Saug-. suction, sucking, absorbing, absorbent, aspirating, -ader, /. Anat.) absorbing vessel, lymphatic vessel, -aderdriise, /. lymphatic gland, -apparat, m. suction apparatus aspirator. -druck, m. suction pressure, -diise, /. suction nozzle Venturi tube. 

Wasser-gang, m. aqueduct drain waterway. -gas, n. water gas, -gasteer, m. water-gas tar, -geblkse, n, water blast, -gefass, n. water vessel (Med.) lymphatic vessel, -gehalt, m, water content, moisture content. 

Lymphangiogenesis is the growth of lymphatic vessels, which is critically controlled by the interaction of VEGF-C and VEGF-D with the receptor VEGF-R3 on lymphatic endothelial cells. 

Microorganisms that escape phagocytosis in a local lesion may now be transported to the regional lymph nodes via the lymphatic vessels. If massive invasion occurs with which the resident macrophages are unable to cope, microorganisms may be transported through the thoracic duct into the bloodstream. The appearance of viable microorganisms in the bloodstream is termed bacteraemia and is indicative of an invasive infection and failure of the primary defences. 

Lymphatic capillaries join together to form larger lymphatic vessels that have valves within them to ensure the one-way flow of lymph. The lymph is moved along by two mechanisms. Automatic, rhythmic waves of contraction of the smooth muscle in the walls of these vessels are the primary mechanism by which lymph is propelled through the system. Second, the contraction of skeletal muscles causes compression of lymphatic vessels. As in the veins, this pumping action of the surrounding skeletal muscles contributes to movement of the lymph. Ultimately, the lymph is returned to the blood when it empties into the subclavian and jugular veins near the heart. 

Mucosa. The innermost layer of the wall is the mucosa, which consists of a mucous membrane, the lamina propria, and the muscularis mucosa. The mucous membrane provides important protective and absorptive functions for the digestive tract. The nature of the epithelial cells lining the tract varies from one region to the next. Rapidly dividing stem cells continually produce new cells to replace worn out epithelial cells. The average life span of these epithelial cells is only a few days. The lamina propria is a thin middle layer of connective tissue. This region contains the capillaries and small lymphatic vessels that take up the digested nutrient molecules. The muscularis mucosa is a thin layer of smooth muscle. Contraction of this muscle may alter the effective surface area for absorption in the lumen. 

This is a diffnse and loosely dehned system which encompasses those cells and tissnes that are phagocytic. These include the endothelia of blood and lymphatic vessels (which are only weakly phagocytic), reticnlar cells of the spleen, endothelial cells, sinnsoids in the liver and lymph nodes, macrophages and drcnlating phagocytes. 

Chylomicrons are discharged from the enterocytes by exocytosis into lacteals, which are lymphatic vessels that originate in the intestinal villi, drain into the cisternae chyli, and follow a course through the thoracic ducts to enter the bloodstream through the left subclavian vein. 

To achieve a reasonable degree of absorption, peptide and protein pharmaceuticals may need permeation enhancers to promote passage across mucosal cells. Another concern is that studies of insulin and enkephalin in animals suggest that protease activity may be high, especially in the rectal cavity [5,6]. On the other hand, the density of lymphatic vessels and drainage therein at these sites may be advantageous compared with other routes of administration. 

These lipids are then packaged into spherical lipoproteins, particles of lipids and proteins, known as chylomicrons, which are secreted into lymphatic vessels and subsequently enter the blood stream. Once in the circulatory system the triacylglycerol components of the chylomicrons are degraded to fatty acids and glycerol by the enzyme lipoprotein lipase, which is attached to the luminal (inner) side of capillary vessels in heart, muscle, adipose (commonly... 

The epithelial mucous membrane surface has a specific bottom layer that contains capillary vessels and lymphatic vessels for absorption, with smooth muscle and the neuroplexus. Large numbers of lymphatic nodules, derived from the reticular tissue of the mucous membrane, are localized in this layer. The blood vessel system is extensively related to absorption and secretion of water and substances in the intestinal tract. However, we cannot ignore the simultaneous contributions of the lymphatic and blood vessel systems. The lymphatic vessel... 

We now turn to an anatomical description of lymph nodes. The lymph node is surrounded by a thick, fibrous capsule and is subdivided into compartments by trabeculae. Inside the capsule is the subcapsular or marginal sinus, which forms the entry point of lymphatic fluid into the node, via the afferent vessel. The lymph node cortex, which lies beneath the subcapsular sinus, is the location of the primary and secondary lymphoid follicles. The primary follicles are comprised of B-lymphocytes. An immune response stimulates B-cells to replicate and differentiate, converting the primary follicle into a secondary follicle or germinal center, surrounded by a zone of small lymphocytes. The paracortex surrounds the germinal centers and primary follicles and contains mostly T-lymphocytes. The medulla is composed of medullary cords, consisting of macrophages and plasma cells, and medullary sinuses. The medullary vessels include the arteries and veins, and the afferent and efferent lymphatic vessels, respectively, deliver the lymphatic fluid into and out of the lymph node. 

---