Lymphatic system Macrophages

The lymphatic system of the skin extends up and into the papillary layers of the dermis. A dense, flat meshwork of lymphatic capillaries is found here [11]. Lymph passes into a deeper network at the lower boundary of the dermis. Serum, macrophages, and lymphocytes readily negotiate through the skin s lymphatic and vascular networks. 

Similar experiments with PEG-phosphatidyl ethanolamine mixed micelles with a core-incorporated amphiphilic " In- or Gd-loaded chelating agent PAP demonstrated fast and efficient gamma and MR visualization of different compartments of the lymphatic system. Upon subcutaneous administration, the micelles penetrate the lymphatics and effect visualization (Figure 6). Micelles mostly stay within the lymph fluid rather than accumulate in the nodal macrophages (because of protective effect of surface PEG fragments) and rapidly move via the lymphatic pathway. 

The lymphatic system, lined with epithelial cells, contains a highly proteinaceous (albumin) fluid with prominent electrolytes, which are characterized by the associated cations of Na , K, and Ca. In health as well as most disease states lymphatic fluid contains no red cells or cells directly derived from the circulating blood system in addition to the lymphoid cells, it does contain macrophages, another major cell type. 

There are two important defense mechanisms against inhaled particles. The first of these involves the mucociliary escalator and consists of the trapping of particles in mucus followed by the upward movement of the mucus brought about by the upward beating of cilia on the airway epithelial airway cells. The material is then either swallowed or expectorated. The second mechanism is macrophage mediated. Macrophages engulf particles and either deposit them on the mucociliary escalator or enter the lymphatic system. 

The alveoli are not ciliated, and particles deposited in the P region remain there until they dissolve in lung fluid, or are engulfed by wandering cells called macrophages, which transport them to the ciliated bronchioles or to the lymphatic system of the lung. 

The main cells of the viable epidermis are keratinocytes. They get their growth factors and nutrients by passive diffusion via the interstitial fluid, which is estimated to represent about 15% of the total volume of the epidermis and drains into the lymphatic system. The viable epidermis also contains melanocytes, Langerhans cells, migrant macrophages, and lymphocytes. The top two layers of the viable epidermis, the stratum lucidum and the stratum granulosum, are physiologically very important. Removal of these three epidermal layers results in water loss and an enhancement of skin permeability [8],... 

The basic difference between silica dusts and those of other materials like clay, coal, and silicon carbide, is that when the latter reach the lungs the particles are engulfed by macrophages and carried through the lymphatic system to the lymph nodes of the... 

Figure 9.12 Photomicrograph of section of lung tissue 2 weeks after instillation of amorphous sihca. Large numbers of particle-bearing macrophages are present in the perivascular sheath, most likely being cleared through the lymphatic system. The lung architecture is undamaged. [Adapted from Jones et al. (37).]...

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