Renal physiology concept

Drug clearance principles are similar to the clearance concepts of renal physiology. Clearance of a drug is the factor that predicts the rate of elimination in relation to the drug concentration ... 

Acetazolamide (Diamox) is the prototype of a class of agents that have limited usefulness as diuretics but have played a major role in the development of fundamental concepts of renal physiology and pharmacology. Proximal tubular epithelial cells are richly endowed with the zinc met-alloenzyme carbonic anhydrase, which is found in the luminal and basolateral membranes (type IV carbonic anhydrase. 

There are a number of reasons to try to characterize dopamine receptor in addition to the fact that it is fashionable. Two of the major reasons well described by Goldberg and Kohli are (1) the importance of dopamine receptors subtypes responsible for physiological and pharmacological actions and (2) the utilization of the concept of selective dopamine receptors in the design and characterization of new drugs for cardiovascular and renal therapies. 

It is now well established that l,25-(OH)2D3 is the active hormonal form of vitamin D3 [32], The production of l,25-(OH)2D3 in the kidney is regulated by dietary calcium and phosphate and also by changes in serum calcium and parathyroid hormone, which clearly highlight the hormonal nature of this compound. Functionally, the three classical actions of l,25-(OH)2D3 are to stimulate intestinal calcium and independently phosphate absorption, the mobilization of calcium from bone, and increase renal reabsorption of calcium. The focus of this review will be to explore the most recent concepts of vitamin D in regard to its metabolism and physiology, and with respect to the medicinal applications of vitamin D3 metabolites and analogues. 

The clearance concept has been used in defining the pharmacokinetics of drugs since the mid-1970s. " The elearanee eoneept is based in physiology, where it is used as a measure of renal funetion (ereatinine elear-ance). Creatinine is formed from muscle breakdown at a constant rate, and thus a constant creatinine concentration in plasma results. The magnitude of this concentration is dependent on the elimination rate of ereatinine and the size of the muscle pool (formation rate). By measuring the plasma concentration and the renal excretion of ereatinine, renal clearance can be estimated and thereby kidney function indicated, as ereatinine is mainly filtered into the urine... 

Nowadays, this definition can be considered as classical. Because all of these criteria are rarely met simultaneously, the concept of uremic toxins has changed. In the new concept, substances that damage normal physiological functions, or interfere with physiological defense mechanisms in renal failure, have also been recognized as uremic toxins. Some may play a role in the progression of renal disease, inducing uremic symptoms, and may contribute to dialysis-related complications. 

To understand the mechanism of concentration of urine in the kidney under the influence of antidiuretic hormones, it is necessary to briefly review some elementary concepts in kidney physiology. Although the osmolarity of the glomerular filtrate is equal to that of plasma, the osmotic pressure of the interstitial tissue in the renal medulla and papilla is greater than that of plasma. Vasopressin changes the permeability of the limiting membrane and facilitates the reabsorption of water from the tubular lumen (isosmotic) toward the interstitial tissue of the hyperosmotic medulla and papilla. 

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