Extracellular space compartmental

Other processes that lead to nonlinear compartmental models are processes dealing with transport of materials across cell membranes that represent the transfers between compartments. The amounts of various metabolites in the extracellular and intracellular spaces separated by membranes may be sufficiently distinct kinetically to act like compartments. It should be mentioned here that Michaelis-Menten kinetics also apply to the transfer of many solutes across cell membranes. This transfer is called facilitated diffusion or in some cases active transport (cf. Chapter 2). In facilitated diffusion, the substrate combines with a membrane component called a carrier to form a carrier-substrate complex. The carrier-substrate complex undergoes a change in conformation that allows dissociation and release of the unchanged substrate on the opposite side of the membrane. In active transport processes not only is there a carrier to facilitate crossing of the membrane, but the carrier mechanism is somehow coupled to energy dissipation so as to move the transported material up its concentration gradient. 

The average adult body contains about 42 L of fluids, which accounts for two-thirds of the total body weight. Most of these fluids are compartmentalized in three regions of the body the interior of cells, tissue spaces between cells (inclnding the lymph vessels), and the blood vessels. The majority, about 28 L, is located inside the cells and is called intracellular fluid. All body fluids not located inside the cells are collectively known as extracellular fluids. Thus, fluids in two of the fluid compartments are extracellular the interstitial fluid, which flUs the space between tissue cells and moves in lymph vessels, and the fluid of the bloodstream— plasma. Interstitial fluid constitutes about 25% (10.5 L) of the total body fluid, and the plasma (nearly 3.5 L) makes up about 8% of the total. 

Naked monosodium urate crystals stimulate oxygen radical release by human polymorphonuclear leukocytes. Very recently, two papers dealing with superoxide anion generation by human neutrophils exposed to monosodium urate have been published. From the comparison of the data derived from nitroblue tetrazolium and cytochrome c reduction, it has been suggested that radical production in response to urate crystals is compartmentalized and occurs predominantly in the intracellular space. Microcrystalline sodium urate-induced oxygen consumption and nitroblue tetrazolium reduction were present for at least 15 min after stimulation of the cells. To enhance extracellular radicals neutrophils were converted to secretory non phagocitic cells by use of cytochalasin... 

Altered compartmentation of leached minerals since the free space of the leaves is leached preferentially. Decreased buffer capacity, in particular of the extracellular compartment. 

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