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LSS Urinary System 

Alexandra Burke-Smith

Principle cells are important in sodium, potassium + water balance (mediated via Na+/K+ pump on basolateral membrane). In the principle cells of the DTC, the apical sodium channel is sensitive to aldosterone, and is linked to a K+ channel also on the apical membrane Intercalated cells exist between each principle cell, and are important in acid-base balance, mediated by an HATP pump on the apical membrane The principal cells of the cortical collecting duct have a tight epithelium, therefore tightly regulate water movement (driven by osmolarity gradient)

Clinical application of knowledge – defects of tubular function 

There are 3 single gene defects which affect tubular function: o Renal tubule acidosis o Bartter syndrome o Fanconi syndrome

Renal tubular acidosis  Caused by an inability to acidify the urine below pH5.5  hypechloremic metabolic acidosis of the blood  Other symptoms include impaired growth + hypokalemia  Mainly a defect in the distal renal tubule  failure of H+ ion secretion even when conditions are favourable for secretion  In a normal tubular cell, H+ secretion occurs simultaneously to HCO3- transport out of the cell into the blood. This is driven by a reaction catalysed by carbonic anhydrase.  failure of H+ secretion has 2 possible causes:  malfunction of bicarbonate transport out of tubular cell into blood  accumulation of product therefore limiting carbonic anhydrase activity.  A mutation in the carbonic anhydrase enzyme could also occur Bartter syndrome  Definition = excessive electrolyte secretion  Caused by mutation in the Na/Cl/K co-transporter on ascending limb of Henle, or mutation in the K+ channel  Causes severe salt loss, moderate metabolic alkalosis, hypokalemia, renin + aldosterone hypersecretion  Antenatal barter syndrome = more severe form of disease  premature birth +polyhydramnios Fanconi Syndrome  Defined by an increased excretion of low molecular weight proteins caused by a failure of protein reabsorption  Also increased excretion of uric acid + glucose phosphate  Caused by a defect in a Cl- channel involved in protein-receptor vesicle recycling  reduction of protein receptors therefore proteins cannot be reabsorbed  E.g. of detrimental consequence = excessive amounts of cytokines flowing through tubular system  immune response


Alex's Urinary  

Alex's Urinary