Renal system tubules

Hydration -These drugs reach high concentrations in the renal system keep patients well hydrated to minimize chemical irritation of tubules. 

The Na+ gradient established by the (Na+, K+)-ATPase is utilized in the transport of a number of solutes into animal cells via Na-solute cotransport or symport.68 This is well known for glutamate. Renal Na+ cotransport systems for mono- and di-carboxylic acids and for various amino acids have been functionally reconstituted in proteoliposomes. These transport systems are polypeptides solubilized from brush border membranes of renal proximal tubules. The establishment of Na+ gradients (high Na+ outside) resulted in increases in concentrations of substrate inside the proteoliposomes.69... 

Tyson CA, Dabbs IE, Cohen PM, Green CE, Melnick R (1990) Studies of nephrotoxic agents in an improved renal proximal tubule system. Toxicol in Vitro 4-5 403 108 Ullrich KJ, Greger R (1985) Approaches to the study of tubule transport functions. In Seldin DW, Giebisch G (eds) Physiology and Pathophysiology. Raven Press, New York, pp 427 169... 

Oxalic acid may have a direct corrosive effect on the eyes, skin, and digestive tract after contact. However, once absorbed (or produced as a result of the metabolism of other compounds), oxalic acid and other soluble oxalates react with calcium in the plasma to form insoluble calcium oxalate. Systemic formation of calcium oxalate may produce hypocalcemia directly. Precipitation of calcium oxalate in the renal system (proximal tubules of the kidney) may lead to local necrosis of the tubular epithelium, producing kidney dysfunction and electrolyte imbalance. Precipitation of calcium oxalate may also occur in the blood vessels, heart, lungs, and liver leading to local effects. 

The renal proximal tubules contain a large array of plasma membrane transport systems. 

The effects of 16-, 17-, 18-, 19-, and 20-HETE have been studied to varying degrees. Activated polymorphonuclear leukocytes (PMNs) are known to produce 16-HETE. In vitro, 16(7 )-HETE inhibits human PMN adhesion and aggregation. Administration of 16-HETE to rabbits with thromboembolic stroke leads to reduction in intracranial pressure [59]. Synthesis of leukot-liene B4, a pro-inflammatory molecule, is also increased by 16(7 )-HETE. Carroll et al. demonstrated that 16(7 )-HETE promotes vasodilation of renal arteries in a COX-dependent manner [60], Furthermore, 16(5)-HETE inhibits the activity of the adenosine triphosphatase (ATPase) in the renal proximal tubule [60], Similarly, 17(iS)-HETE inhibits proximal tubule ATPase activity while 17(i )-HETE is inactive in this system. 

The renal system is composed of functional units called nephrons. Nephrons have two portions, the cortex (i.e., glomerulus. Bowman capsule, and proximal and distal tubules) and the medulla (i.e., the loop of Henle and the collecting tubules). The nephron also contains two primary sections ... 

Acute tubular necrosis (ATN), ischemia, and death of renal tubules are the greatest threats to the renal system after a burn injury. Tubular necrosis will result in impairment of renal function and fluid and electrolyte, as well as acid-base, imbalances owing to impaired renal function in regulation of these areas. 

Sites of endothelin-receptor expression. ETA receptors are expressed in the smooth muscle cells of the vascular medial layer and the airways, in cardiac myocytes, lung parenchyma, bronchiolar epithelial cells and prostate epithelial cells. ETB receptors are expressed in endothelial cells, in bronchiolar smooth muscle cells, vascular smooth muscle cells of certain vessels (e.g. saphenous vein, internal mammary artety), in the renal proximal and distal tubule, the renal collecting duct and in the cells of the atrioventricular conducting system. 

AVP plays a central role in water homeostasis of terrestrial mammals, leading to water conservation by the kidney. OT is primarily involved in milk ejection, parturition and in sexual and maternal behaviour. Both hormones are pqDtides secreted by the neurohypophysis, and both act also as neurotransmitters in the central nervous system (CNS). The major hormonal targets for AVP are the renal tubules and vascular myocytes. The hormonal targets for OT are the myoepithelial cells... 

H)2-D3 is a weak agonist and must be modified by hydroxylation at position Cj for full biologic activity. This is accomplished in mitochondria of the renal proximal convoluted tubule by a three-component monooxygenase reaction that requires NADPFl, Mg, molecular oxygen, and at least three enzymes (1) a flavoprotein, renal ferredoxin reductase (2) an iron sulfur protein, renal ferredoxin and (3) cytochrome P450. This system produces l,25(OH)2-D3, which is the most potent namrally occurring metabolite of vitamin D. 

Effects on Vitamin D Metabolism. Lead interferes with the conversion of vitamin D to its hormonal form, 1,25-dihydroxyvitamin D. This conversion takes place via hydroxylation to 25-hydroxyvitamin D in the liver followed by 1-hydroxylation in the mitochondria of the renal tubule by a complex cytochrome P-450 system (Mahaffey et al. 1982 Rosen and Chesney 1983). Evidence for this effect comes primarily from studies of children with high lead exposure. 

The possible mechanism kidney-induced hypertension is discussed in Section 2.4.2, Mechanisms of Toxicity. Lead appears to affect vitamin D metabolism in renal tubule cells, such that circulating levels of the vitamin D hormone, 1,25-dihydroxyvitamin D, are reduced. This effect is discussed later in this section under Other Systemic Effects. 

The renal tubular dysfunction of galactosemia is very similar to that caused by, e.g., heavy metal poisoning in both cases it seems likely that the inhibition of enzyme systems prevents the cells of the renal tubule... 

An idealised eukaryotic epithelium is represented in Figure 1. This might, for example, be the gut mucosa, the reabsorbing portion of a renal tubule system, or a gill epithelium. The solute must move from the bulk solution (e.g. the external environment, or a body fluid such as urine) into an unstirred layer... 

Expressed in the simplest terms, the glomeruli are filters and the tubules execute active and passive transport between the tubular fluid (glomerular filtrate) and the blood. The combined and coordinated function of the glomeruli and tubules constitutes the renal waste disposal and nutrient recycling system. 

Assuming the capsular pressures opposing the movement of water out of the blood and into the top of the nephron are constant, the net filtration pressure is due largely to the blood pressure. Any fall in blood pressure can have a dramatic effect on the efficiency of filtration and therefore clearance of waste materials. So important is the pressure within the renal vasculature that the kidney is critical in regulating systemic blood pressure via the renin-angiotensin-aldosterone (RAA) axis, a physiological process which relies on transport mechanisms within the renal tubules. 

---