Kidney collecting tubules

Fushimik Fushimi K, Uchida S, Fiara Y, Fiirata Y, Marumo F, Sasaki S. Cloning and expression of apical membrane water channel of rat kidney collecting tubule. Nature 1993 361(6412) 549-552. 

PGE-N, Stimulation of adenylate cyclase via increased laj Thyroid gland Kidney-collecting tubule " Hepatocyte Frog erythrocyte P... 

PGE-Np Stimulation of Ca mobilization, thereby potentiating Ca " "-dependent events Kidney-collecting tubule Vascular smooth muscle ... 

The answer is c. (Katzung, p 493.) Lithium treatment frequently causes polyuria and polydipsia. The collecting tubule of the kidney loses the capacity to conserve water via anti diuretic hormone. This results in significant free-water clearance, which is referred to as nephrogenic diabetes insipidus. 

The smallest functional unit of the kidney is the nephron. In the glomerular capillary loops, ultrafiltration of plasma fluid into Bowman s capsule (BC) yields primary urine. In the proximal tubules (pT), approx. 70% of the ultrafiltrate is retrieved by isoosmotic reabsorption of NaCl and water. In the thick portion of the ascending limb of Henle s loop (HL), NaCl is absorbed unaccompanied by water. This is the prerequisite for the hairpin countercurrent mechanism that allows build-up of a very high NaQ concentration in the renal medulla In the distal tubules (dT), NaCl and water are again jointly reabsorbed. At the end of the nephron, this process involves an aldosterone-controlled exchange of Na+ against 1C or H. In the collecting tubule (C), vasopressin (antidiuretic hormone, ADH) increases the epithelial permeability for water, which is drawn into the hyperosmolar milieu of the renal medulla and thus retained in the body. As a result, a concentrated urine enters the renal pelvis. 

After a single exposure of rabbits to 17 ppm for 6 hours, the sensory trigeminal nucleus was severely affected. Other effects included tubular and focal necrosis in the collecting tubules of the kidney and fatty degeneration of the liver. ... 

Water excretion is further controlled by the antidiuretic hormone from the posterior pituitary gland which acts to increase water resorption in the kidney through making the collecting tubule permeable to water for additional resorption beyond what took place in the tubule. The posterior pituitary gland secretes the hormone as a rapid and sensitive response... 

Mineralocorticoids act by binding to the mineralocorticoid receptor in the cytoplasm of target cells, especially principal cells of the distal convoluted and collecting tubules of the kidney. The drug-receptor complex activates a series of events similar to those described above for the glucocorticoids and illustrated in Figure 39-3. It is of interest that this receptor has the same affinity for cortisol, which is present in much higher concentrations in the extracellular fluid. The specificity for mineralocorticoids at this site appears to be conferred, at least in part, by the presence of the... 

Figure 12.1 Schematic of a single nephron, the functional unit of the kidney. Microsolutes are filtered from blood cells in Bowman s capsules. As the filtrate passes towards the collection tubule most of the microsolutes and water are reabsorbed by a type of facilitated transport process. The fluid finally entering the collecting tubule contains the nitrogenous wastes from the body and is excreted as urine. There are about 1 million nephrons in the normal kidney [1]...

Vasopressin [vay soe PRESS in] (antidiuretic hormone, ADH), is structurally related to oxytocin (Figure 25.5). The chemically-synthesized nonapeptide has replaced that extracted from animal posterior pituitaries. Vasopressin has both antidiuretic and vasopressor effects. In the kidney it binds to the V2 receptor to increase water permeability and resorption in the collecting tubules. Thus the major use of vasopressin is to treat diabetes insipidus. It also finds use in controlling bleeding due to esophageal varices or colonic diverticula. Other effects of vasopressin are mediated by the Vi receptor, found in vascular smooth muscle, liver and other tissues. As might be expected the major toxicity is water intoxication and hyponatremia. Headache, bronchoconstriction and tremor also can occur. Caution must be used in treating patients with coronary artery disease, epilepsy and asthma. 

The effects of aluminofluoride complexes on the kidney were studied using glomerular mesangial cells, proximal tubular cells, and inner medullar collecting tubule cells of rat kidney. 

Although calcitriol is synthesized only in the proximal renal tubule, after the administration of pHJcalcidiol, radioactivity in the kidney accumulates only in the distal and collecting tubules. This is the region in which selective resorption of calcium from the urine occurs and, in response to calcitriol, there is induction of calbindin-D28k. As in the intestinal mucosa, calbindin in the kidney is a cytosolic protein and is presumably involved in the intracellular accumulation and transport of calcium. 

Many studies have shown that AmB can induce a loss of concentrating ability of the kidney [18, 32, 33]. This abnormality is almost invariably present and occurs early (1-2 weeks) in the course of therapy. The impairment in concentrating ability probably reflects direct tubular toxicity since it occurs in the absence of a decrease in GFR, and is temporally unrelated to azotemia. Barbour et al. [34] reported a study of 3 patients whose inabihty to concentrate the urine was associated with a defect in free water reabsorption even under maximal stimuli, and concluded that a tubular functional abnormality was induced because of the failure of the vasopressin response in the medullary collecting tubule. 

Ling BN, Eaton DC. Cyclosporin A inhibits apical secretory K-i-channels in rabbit cortical collecting tubule principal cells. Kidney Int 1993 44 974-984. 

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