Test 3 Flashcards
Proximal Convoluted Tubule
Highly permeable to H2O and reabsorbs 65% of NaCl
Thin Descending Limb of Loop of Henle
Highly permeable to H2O but impermeable to NaCl and Urea (Concentrating Segment)
Thin Ascending Limb of the Loop of Henle
Passively reabsorbs NaCl but impermeable to H2O
Thick Ascending Limb of the Loop of Henle
Actively reabsorbs most of the NaCl absorbed in loop, impermeable to H2O (diluting segment), and contains macula densa located between afferent and efferent arterioles.
Tubuloglomerular feedback
Signal sent from macula densa to afferent arteriole of same nephron causing vasoconstriction when amount of NaCL leaving the Loop is too high. Vasoconstriction –> decrease GFR
Distal Convoluted Tubule
Actively transports NaCl but is impermeable to H2O (diluting segment)
Collecting Duct
Fine control of ultra filtrate composition, controlled by aldosterone (increased NaCl and H2O reabsorption) and ADH (increased H2O reabsorption)
Chloride Reabsorption
Generally follows Na, Symport with K+ in proximal tubule and thick ascending limb, Antiport with Na+/HCO3- in proximal tubule, and Cl- channels in thick ascending limb, DCT, and Collecting Duct
Renal handling of Potassium
80-90% absorbed in proximal tubule via diffusion, paracellular pathways are used in thick ascending limb, DCT and Collecting duct K+ secretion by a conductive pathway.
Renal Handling of Calcium
70% reabsorbed by proximal tubule but passive diffusion through a paracellular route, 25% is absorbed by thick ascending limb, remaining 5% is reabsorbed in DCT by transcellular pathway.
Renal Handling of Inorganic Phosphate
Largely reabsorbed by proximal tubule (80%)
Renal Handling of Magnesium
Bulk reabsorbed in Thick ascending limb via paracellular pathway, 20-25% reabsorbed in proximal tubule, 5% is by DCT and collecting duct
Relationship between sodium reabsorption and potassium secretion in the Collecting Duct
More Na+ reabsorbed = More potassium excreted, More sodium in collecting duct –> more compensation –> more K+ excretion (hypokalemia).
Targets of Diuretics
Diuretics target Na+ transporters and channels on the luminal side of tubules –> more Na+ excretion in urine (natriuresis) –> More H2O excretion in urine (Diuresis)
Prototype Carbonic Anhydrase Inhibitor
Acetazolamide
Site of action of Carbonic Anhydrase Inhibitors
Proximal Tubule
Mechanism of Action of Carbonic Anhydrase Inhibitors
Competitive inhibitors of luminal and cytosolic carbonic anhydrase, Causes decreased reabsorption of HCO3-, decreased secretion of H+ –> decreased Na+ reabsorption.
Efficacy of Carbonic Anhydrase inhibitors
Modest because distal segments of nephron can compensate for increased Na+ concentration.
Renal hemodynamic effects of Carbonic Anhydrase inhibitors
-Because of increased Na+ concentration at macula densa, afferent vasoconstriction –> decreased GFR
Adverse effects of Carbonic Anhydrase Inhibitors
-Hypokalemia (potassium wasting) due to compensation by Na+/K+ exchange in distal nephron -Urinary alkalization due to increased HCO3- excretion –> metabolic acidosis. -Renal stone formation b/c Ca2+ is insoluble at alkaline pH
Therapeutic Uses of Carbonic Anhydrase Inhibitors
-Rarely used as diuretic -Open-angle glaucoma -Altitude sickness -Epilepsy
Urinary Electrolyte changes due to Carbonic Anhydrase inhibitor (Acetazolamide)
-Increase pH due to increased HCO3- excretion -Increased Na+ excretion due to decreased H+/Na+ antiport action -Increased K+ excretion due to increased K+/Na+ antiport action caused by increased [Na+] in distal nephron
Prototype Loop Diuretic
Furosemide
Loop Diuretic Site of Action
Thick ascending limb of Loop of Henle