Glomerular capsule glucose and other organic solutes

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Glomerular capsule Glucose and other organic solutes Osmotic water flow Carrier protein Countertransport pump Reabsorption Secretion Water reabsorption Solute reabsorption PCT is primary site of reabsorption: > 99% organic materials (glucose, amino acids, other nutrients) Ions, electrolytes (Na + , K + , HCO 3 - , Mg 2+ , phosphate, sulfate) Water (~108 L/day) As reabsorption occurs: Solute concentration decreases in tubular fluid Water moves back into peritubular capillary (peritubular fluid) Mechanisms of reabsorption Carrier proteins Protein pumps Diffusion Osmosis Reabsorption (24.10) Figure 24.10 1
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Urine storage and elimination Cells of distal convoluted tubule Peritubular capillary Peritubular fluid Tubular fluid Toxins, drugs Toxins, drugs Distal convoluted tubule Proximal convoluted tubule Nephron loop Collecting duct Glomerular capsule KEY Diffusion A K + K + Na + K + Na + Na + H + Na + Na + Na + H + H + Glomerulus Carrier protein Countertransport pump Reabsorption Secretion Secretion occurs in DCT & PCT Further modifies solute composition of tubular fluid In DCT, protein pumps allow reabsorption & secretion to occur in combination Na + in exchange for K + Stimulated by aldosterone Na + in exchange for H + Carrier proteins secrete toxins, drugs Nitrogenous wastes, ammonia PCT secretes Nitrogenous wastes, ammonia, H+, some drugs Secretion (24.10) Figure 24.10 2
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The Nephron Loop Produces a Concentration Gradient in the Medulla (24.11) Kidney’s ability to concentrate urine depends on salt gradient in renal medulla 4x saltier in medulla than cortex Nephron loop performs countercurrent multiplication Countercurrent: Fluid flows in opposite directions in adjacent tubules of nephron loop Multiplication: Continuous flow of fluid causes ongoing materials exchange with surrounding tissues Continually & actively transports salt into renal medulla Ascending limb reabsorbs NaCl Salt accumulates in renal medulla Causes higher salt concentration in medulla than cortex Sets up diffusion gradient for water reabsorption Descending limb reabsorbs water 600 600 900 900 900 1200 1200 100 Na + Cl Na + Cl Na + Cl 300 Na + Cl H 2 O H 2 O H 2 O 300 300 Thin descending limb: permeable to water impermeable to solutes solute concentration increases Sodium and chloride ions are pumped out Na + Cl Na + Cl Thick ascending limb: impermeable to water selectively permeable to Na + and Cl solute concentration decreases Renal medulla Figure 24.11 3
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Urea concentration increases in tubular fluid as it moves through nephron Concentration of ions, toxins, wastes, drugs also increases Due to water reabsorption along nephron & collecting system Water reabsorption in DCT & collecting duct variable Urea concentration at papillary duct = ~450 mOsm/L Urea Is Concentrated in Urine (24.11) KEY KEY Renal cortex Renal medulla H 2 O H 2 O 900 1200 1200 1200 100 300 300 300 300 1 2 3 H 2 O H 2 O = Impermeable to water = Impermeable to solutes = Impermeable to urea;
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