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ACE inhibitor drugsblock the action of angiotensin-converting enzyme and aldosterone receptor blockerstreat hypertension and heart failureAtrial Natriuretic Peptide and ReabsorptionAtrial natriuretic peptide (ANP) is involved in homeostatic control of bodily water and Na
15ANP reduces water and Na loads and thus lowers BP (opposite of RAAS)ANP is released by atrial myocytes (muscles cells) fromgranules in the atria of the heart in response to high BP,hypervolemia, and exerciseOther stimulants for ANP release include sympatheticstimulation, elevated Na concentration, angiotensin II, andendothelin (vasoconstrictor) ANP directly inhibits Na reabsorption in the distal nephronand increases excretion of NaANP also inhibits renin secretion from kidneys and aldosterone secretion from the adrenal cortexANP increases GFR through dilation of the afferent arteriole, raising glomerular capillary BPMore water and salt are filtered leading to more in the urineIt decreases cardiac output and reduces vascular resistance by inhibiting the sympathetic nervous system to heart and blood vesselsA deficiency of ANP can lead to hypertensionGlucose and Amino AcidsTransferred by secondary active transportCotransport carriersonly in the proximal tubule bring Na andthe organic molecule into the cellThis concentration gradient is maintained by the sodium-potassium pump without the direct expenditure of energyActively Reabsorbed SubstancesCarriers are specific for the substance it transportsTubular Maximum (Tm)– all carriers are fully saturatedAny amount of substance filtered beyond the Tmis excretedin the urine (all actively reabsorbed substances have atubular max except Na due to aldosterone)Glucose and the KidneysThe quantity of any substance filtered per minute is called the filtered loadFiltered load = plasma concentration of substance x GFRGlucoses filtered load is 125mg/minTubular Maximum for GlucoseAverages 375mg/minThe filtered load is well below the transport max so usually none appears in the urineRenal Threshold for GlucoseRenal Threshold– plasma concentration at which Tmis reached and the substance begins to appear in the urineFor glucose, it is 300mg/100mL
16Beyond Tmreabsorption is constant at its max rate and any additional increase in the filtered load leads directly to an increase in the amount excretedHigh glucose concentration can occur in diabetes mellituswhere you have inadequate insulinoInsulin is a pancreatic hormone that allows glucose transport into cellsReason That the Kidneys Do Not Regulate GlucoseThey don’t maintain glucose at a specific plasma concentrationIt’s regulated by the endocrine and liver mechanismsThe same occurs with AAs and water-soluble vitaminsPhosphate and the KidneysKidneys directly involved in regulation of many electrolytes like phosphate and calcium because the renal thresholds equal their plasma concentrations