Kidney Function and Nephron Processes kidney lec 2

Flashcards for reviewing kidney function, reabsorption, and secretion processes.

Renal Threshold

The concentration of a substance dissolved in the blood above which the kidneys begin to shift it into the urine.

Glucose Renal Threshold

Approximately 180 mg/dl, which is the concentration above which glucose starts appearing in the urine.

Proximal Tubule Reabsorption

Reabsorbs 100% of glucose and amino acids, 90% of bicarbonate, 65% of Na+ and Cl-, and 65-70% of H2O and phosphate.

Thin Descending Loop of Henle Reabsorption

Primarily reabsorbs H2O.

Thick Ascending Loop of Henle Reabsorption

Reabsorbs 10-20% of Na+, K+, and Cl-; also paracellular reabsorption of Mg2+ and Ca2+.

Distal Convoluted Tubule Reabsorption

Reabsorbs 3-5% of Na+ and H2O.

Collecting Ducts Reabsorption

Reabsorbs H2O.

Effect of PTH on Phosphate Reabsorption

PTH inhibits phosphate reabsorption in the proximal tubule.

Effect of Angiotensin II on Reabsorption

Stimulates Na+, H2O, and HCO3 reabsorption.

Reabsorption in the Loop of Henle

Reabsorbs via medullary hypertonicity (counter-current multiplier and counter-current exchanger) and makes urine hypertonic.

Permeability of Thick Ascending Loop of Henle

Impermeable to H2O; urine becomes less concentrated as it ascends.

Aldosterone's Effect on Sodium Uptake

Na+ uptake regulated by aldosterone in the distal convoluted tubule.

ADH Mechanism

Acts on the V2 receptor and inserts aquaporins on the luminal side of the collecting ducts.

Paracellular Route

Transport between tight junctions in the proximal tubule.

Transcellular Route

Includes transapical, transbasal, and travelateral pathways.

Determinants of Net Solute Flux

Area of exchange, permeability of intercellular junctions and cell membrane, and electrical and chemical gradient.

Transport Maximum (Tm)

Plasma/filtrate concentration of a substance actively transported, which overwhelms cellular transport systems.

SGLT2

Sodium-glucose cotransporter in the early proximal tubule that can accumulate glucose to a high concentration ratio.

SGLT1

Sodium-glucose cotransporter in the late proximal tubule that couples glucose to two Na+ ions and can establish a very high concentration ratio.

Protein Uptake in Proximal Tubule

Proteins like albumin are reabsorbed via endocytosis, forming coated vesicles and multivesicular bodies, then broken down into free amino acids.

Mandatory Water Reabsorption

Occurs in the proximal tubule (70% of filtrate).

Regulated Water Reabsorption

Occurs in the collecting ducts (up to 20%), varies based on ADH.

Cortical Nephron Loop of Henle

Loop of Henle outside of medulla: limited water reabsorption, water elimination dominates.

Juxtamedullary Nephron Loop of Henle

Effective counter-current exchanger: water reabsorption.

Counter-current Multiplier

Accumulation of Na+ and urea in the interstitium of the kidney medulla to create high osmotic pressure.

Effect of Aldosterone on Na+ Transport

Aldosterone stimulates transcription resulting in the synthesis of Na+ channels, mitochondrial enzymes and Na-K pumps.

ADH/AVP Mechanism

Increases water permeability by causing the insertion of AQP2 aquaporins into the luminal membrane of collecting duct cells.

Calcium Uptake in Proximal Tubules

70% of Ca2+ uptake occurs in the proximal tubules

Proximal Tubule Calcium Transport

Calcium is transported via paracellular absorption, solvent drag, and Na-Ca exchanger.

Glutamine Metabolism in Proximal Tubule

Glutamine is converted to glutamate, then to 2-ketoglutarate, producing NH4+ and HCO3- for acid-base balance.

HCO3- Reabsorption

Involves reclamation of filtered HCO3- in the early proximal tubule (PCT) and bicarbonate renewal