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Renal Notes.doc

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Physiology 3120
Tom Stavraky

Renal Notes Functions of the kidney: Ion regulation and osmoregulation, waste management, hormone production, gluconeogenesis Glomerular Filtration – the bulk flow of protein-free plasma from the glomerulus into Bowman’s space. Glomerular Filtration Rate – the volume of fluid filtered per unit time into Bowman’s space expressed in ml/min or L/day. In humans is about 180 L/day. The GFR is very constant because of the myogenic principle and tubulo-glomerular feedback Clearance – the total volume of plasma that is completely cleared of a substance and passed out in the urine and is expressed in L/day U V C Q Q - substance must be freely filtered, not absorbed and not secreted PQ - Can use inulin, or creatinine ([C] is slightly over-estimated and is secreted to a minor extent) (creatinine excretion stays constant) - Tubulo-glomerular feedback, higher transport of Na or Cli in the macula densa cells causes formation of adenosice which is released and constricts the afferent arteriole Filtered Load = plasma concentration x GFR Amount Reabsorbed = Filtered Load – Amount Excreted Fractional Excretion = residual fraction of a solute that is not reabsorbed is obtained by subtracting % reabsorbed from 100. Paracelluar reabsorption – In the case of Ca++ and Mg++ uses paracellin-1. Expressed primarily in thick ascending limb cells. Non-regulated Transporters  Na+/Glucose co-transporters (proximal tubule), Na+/a.a. co- transporter (proximal) Non-regulated Channels  AQI (proximal), AQIII, AQIV (collecting duct basolateral) Hormone Regulated Transporters  Na+/H+ exchanger (proximal, upregulated by AGII and down regulated by ANF), Na+/Phosphate co-transporter (proximal tubule), Na+/K+/2 Cl- co- transporter (thick ascending limb, stimulated by ADH, inhibited by loop diuretics), Na+ channels (collecting ducts), AQII (collecting duct, ADH) Exception  Na+/K+ ATPase, regulated everwhere except descending loop and distal convoluted tubule Secretion  K+ channels, regulated by aldosterone in collecting duct - Transporters have max rate of transport Proximal Tubule – handles 2/3 salt and water reabsorption, volume gets put to 35% of its initial volume Collecting Duct – can have 16% final volume or 1% final volume depending on stimulation - osmolytes are secreted in the medulla to artificially increase the osmolality. Includes myo-inositol and betaine. Cells making up capillaries and medulla also make osmolytes to survive. ADH – synthesized and released from the hypothalamus, plasma osmolality sense by osmoreceptor cells. Baroreceptors will also lead to ADH secretion if blood pressure drops (must be significant drop). ADH interacts with cell surface receptors on the basolateral membrane of collecting duct cells causing AQII channels to get put in the apical membrane. Will also increase the activity of the Na+/K+/2Cl- co-transporter Loop Diuretics – e.g. Furosemide block Na+/K+/2Cl- transporter. Used to treat hypertension. - Alcohol inhibits ADH release while caffeine blocks ADH bindin
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