Overall effect: increase in systemic blood pressure and blood volume and restoration of normal GFRNatriuretic peptidesReleased by heart in response to stretched walls due to increased blood volume or pressureAtrial natriuretic peptide (ANP) is released by atriaTrigger dilation of afferent glomerular arterioles and constriction of efferent glomerular arteriolesIncrease glomerular pressures and increase GFRANP also decreases sodium reabsorptionNet result is increased urine production and decreased blood volume and pressure3. Autonomic regulation of GFR-Mostly consists of sympathetic postganglionic fibersSympathetic activation:Constricts afferent glomerular arteriolesDecreases GFRSlows filtrate productionSympathetic activation can override local regulatory mechanisms that act to stabilize GFRFiltration at renal corpusclePassiveSolutes entering capsular space include:Metabolic wastes and excess ionsGlucose, free fatty acids, amino acids, and vitamins
Useful materials are reabsorbed in renal tubules and collecting systemThree functions of renal tubule1. reabsorbing useful organic nutrients in filtrate2. reabsorbing more than 90% of water in filtrate3. secreting any wastes that did not enter filtrate at glomerulusPrinciples of reabsorption and secretionReabsorption: recovers useful materials from tubular fluid and returns them to blood99% of filtrate is reabsorbed in renal tubulesSecretion: adds substances from blood to tubular fluidReabsorption and secretion: occur in every segment of renal tubule and in collecting systemInvolve diffusion, osmosis, leak channels (channel-mediated diffusion), and carrier-mediated transportTypes of carrier-mediated transport1. Facilitated diffusion2. Active transport3. cotransport4. countertransportCharacteristics of carrier-mediated transportA specific substance binds to a carrier protein that facilitates movement across membraneA given carrier protein typically works in one direction onlyDistribution of carrier proteins can vary in different regions of cell surfaceThe membrane of a single tubular cell contains many types of carrier proteinsTransport maximum (Tm)If nutrient concentrations rise in tubular fluid,Reabsorption rates increase until carrier proteins are saturated (until transport maximum is met)A concentration higher than transport maximum exceeds reabsorptive abilities of nephronDetermines renal thresholdRenal thresholdPlasma concentration at which a specific compound or ion begins to appear in urineVaries with substance involvedIf plasma glucose is higher than 180 mg/dL, glucose appears in urine (glucosuria)Renal threshold for amino acids is 65 mg/dLOsmotic concentration (osmolarity)
total number of solute particles per literexpressed in osmoles per liter or milliosmoles per literbody fluids have an osmotic concentration of about 300 mOsm/LIon concentrations are reported in milliequivalents per literConcentrations of large organic molecules are reported in mass per unit volumeReabsorption and secretion at PCTPCT cells normally reabsorb 60-70% of filtrate volume produced in renal corpuscle
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- Fall '19