Tissue membrane

Major structural components of soft parts C, H, N, 0, P, S Organic compounds Components of blomolecules that comprise tissues, membranes, organelles, organic exoskeletons... 

The pleura are connective tissue membranes composed of matrix, mesotheli-al cells, and fibroblasts. There are two types of pleural responses benign responses, such as thickening of the matrix, formation of plaques (which may calcify) or effusions, and fluid accumulation in the interpleural spaces between the visceral and parietal pleurae and neoplastic disease, or the malignancy known as mesothelioma. 

Retina The ten-layered nervous tissue membrane of the eye. It is continuous with the optic nerve and receives images of external objects and transmits visual impulses to the brain. Its outer surface is in contact with the choroid and the inner surface with the vitreous body. The outer-most layer is pigmented, whereas the inner nine layers are transparent. [NiH]... 

Distribution is the delivery of drug from the systemic circulation to tissues. Once a drug has entered the blood compartment, the rate at which it penetrates tissues and other body fluids depends on several factors. These include (1) capillary permeability, (2) blood flow-tissue mass ratio (i.e., perfusion rate), (3) extent of plasma protein and specific organ binding, (4) regional differences in pH, (5) transport mechanisms available, and (6) the permeability characteristics of specific tissue membranes. 

Tab. 1.5 Protein to lipid ratios of rat tissue membranes. (Reprinted from Table 1.5 of ref. 2, with permission from Macmillan)...

The distribution of drugs depends on both the physicochemical properties of the drug molecules and the composition of tissue membranes. These factors can either result in a uniform or uneven distribution of dmgs into the various body compartments and fluids. In the extreme, distribution may tend toward an accumulation of drugs in particular tissues or to an almost complete exclusion of the drag from a particular compartment in a defined length of time. One unique compartment that has to be considered in this respect is the brain, which is separated from the capillary system of the blood by the blood-brain barrier, whose membrane has a special structure. It consists of a cerebral capillary network formed by a capillary endothelium that consists of a cell layer with continuous compact intercellular junctions. It has no pores, but special cells, astrocytes, which support the stability of the tissues, are situated at the bases of the endothelial membrane separating the brain and CSF from the blood. The astrocytes form an envelope around the capillaries. 

The form in which elastin is laid down varies considerably in the different types of elastic tissue. Membranes with a very high elastin content are found in the walls of the larger arteries, in some parts of the heart, and in the trachea and bronchi. In the larger arteries the structural units of the elastic tissue formation are concentric lamellae which are often of rather variable thickness and always contain many irregular openings. In the ligamentum nuchae of some animals, particularly the ox, the structure is quite different and thick longitudinal elastic fibers, of almost circular cross section, form most of the tissue. 

To be taken up into the body and finally carried to the cell, a pollutant must pass through a number of biological membranes. These include not only the peripheral tissue membranes but also the capillary and cell membranes. 

Bioassays are based on observations of physiological responses specific for the hormone being measured. In vivo bioassays usually involve the injection of test materials (such as blood or urine from a patient) into suitably prepared animals target gland responses, such as growth or steroidogenesis, are then measured. In vitro bioassays involve the incubation of tissue, membranes, dispersed cells, or permanent cell lines in a defined culture medium, with subsequent measurement of an appropriate hormone response. Most in vitro bioassays measure responses proximal or distal to a second messenger, such as stimulation of cAMP formation. Bioassays tend to be imprecise and are rarely necessary in clinical medicine. 

The theory that volatile anesthetics may act by specific binding to lipoprotein components of nerve tissue membranes or of the membrane itself has some experimental evidence. The use of 19F nuclear magnetic resonance spectroscopy with halothane indicated that saturable anesthetic sites for halothane exist in living rats at 2.5% inspired gas. The authors consider this to support the idea that volatile anesthetics do act specifically even stereospecifically (Moody etal., 1994). 

If it is assumed that only unbound, unionized drug can cross a tissue membrane by passive diffusion then the steady state drug concentration ratio of a tissue to plasma (T/P) is given by the following relationship... 

While neurotoxins effectively stop nerve and muscle function without causing microscopic damage to the tissues, membrane-damaging toxins destroy or damage tissue directly. For these toxins, prophylaxis is important, because the point at which the pathological change becomes irreversible often occurs within minutes to a few hours after exposure. 

In an in vitro experiment using rat liver cells, more n-6 DPA than DHA was esterified in total PL, but this was reversed in their incorporation into triacylglycerol (TG). A higher amount of DHA than DPA found in tissue membranes is therefore mainly the result of more efficient synthesis of DHA (15). 

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