Transport mechanisms blood flow

There are circumstances, however, where blood flow to the GIT may influence drug absorption. Those compounds absorbed by active or specialized mechanisms require membrane participation in transport, which in turn depends on the expenditure of metabolic energy by intestinal cells. If blood flow and therefore oxygen delivery is reduced, there may be a reduction in... 

H-bonding potential Molecular weight/size PSA Intestinal metabolism Transport mechanisms Native surfactants Intestinal secretions, e.g. mucous, enzymes Intestinal blood/lymph flow Excipient effects... 

Possible explanations for a blood flow-limited uptake in kidney include the existence of specific uptake mechanisms, such as receptor-mediated endocytosis and carrier-mediated transport. Since the former mechanism is initiated by binding of the ligand to the cell-surface receptor, the specific binding of alkylglycoside compounds to isolated tubular plasma membranes was examined [23,24]. 

The transport mechanisms that operate in distribution and elimination processes of drugs, drug-carrier conjugates and pro-drugs include convective transport (for example, by blood flow), passive diffusion, facilitated diffusion and active transport by carrier proteins, and, in the case of macromolecules, endocytosis. The kinetics of the particular transport processes depend on the mechanism involved. For example, convective transport is governed by fluid flow and passive diffusion is governed by the concentration gradient, whereas facilitated diffusion, active transport and endocytosis obey saturable MichaeUs-Menten kinetics. 

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. 

The required properties of such an agent Included (1) selectivity for peripheral vascular dopaminergic receptors versus < -and 6-adrenerglc receptors which could mediate pressor and cardiac effects, (2) absence of central dopaminergic and emetic effects, and (3) potent oral renal vasodilator effects. Dopamine has been associated with diuresis and natriuresls. Possible mechanisms include a direct tubular effect on sodium transport, indirect effects produced by changes in total or regional renal blood flow, or effects resulting from a dopamine Induced decrease in aldosterone release from the adrenal (9). Since diuretics play a key role in antihypertensive therapy, the addition of a natriuretic/diuretic component to the renal vasodilator profile would be valuable and appeared to be feasible. 

In the kidney, filtered solutes such as glucose are recovered from the forming urine primarily by active transport mechanisms in the renal tubules. As in the small intestine, glucose is removed from the tubule lumen by SGLT1 and exits across the basolateral membrane via GLUT2. The low affinity of GLUT2 makes flow from the blood into the tubule epithelial cells minimal at normal blood glucose concen-... 

There are three chapters in this volume, two of which address the microscale. Ploehn and Russel address the Interactions Between Colloidal Particles and Soluble Polymers, which is motivated by advances in statistical mechanics and scaling theories, as well as by the importance of numerous polymeric flocculants, dispersants, surfactants, and thickeners. How do polymers thicken ketchup Adler, Nadim, and Brenner address Rheological Models of Suspensions, a closely related subject through fluid mechanics, statistical physics, and continuum theory. Their work is also inspired by industrial processes such as paint, pulp and paper, and concrete and by natural systems such as blood flow and the transportation of sediment in oceans and rivers. Why did doctors in the Middle Ages induce bleeding in their patients in order to thin their blood ... 

The toxic effect of many xenobiotic compounds in the kidneys is specific to the anatomical locations, i.e. proximal tubules, glomeruli, medulla/papilla, or loop of Henle. The site-selective injury observed in humans when exposed to many compounds is similar to that in domestic animals. The cause of these site-specific target injuries is multifactorial and may include detoxification mechanisms, regenerative ability, difference in blood flow, and transport and accumulation of the chemicals and their metabolites. 

The kidneys receive a large blood flow (approximately a quarter of the total cardiac output of 5 litres per minute) and from this volume of blood approximately 170 litres of filtrate are produced every day Clearly, the body would quickly become dehydrated if this volume of fluid were lost to the sewage system, so most of it is reabsorbed from the kidney tubule and returned to the bloodstream. Small molecules that are dissolved in the glomerular filtrate are also reabsorbed back into the bloodstream, either by passive diffusion (which obeys Fick s law) or by the utilisation of energy in an active transport process similar to the mechanisms for gut absorption discussed previously. It should be realised that reabsorption from the glomerular filtrate and return to the bloodstream are involved in the duration of action of many drugs, and a drug molecule may be filtered and reabsorbed many times before it is finally excreted from the body. 

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