62. Physiology - Proximal Tubule non-Tm Mechanisms and Osmotic Diuresis

The process of reclaiming bicarbonate from the filtrate in the proximal tubule, primarily driven by Na+ exchange for H+.

In the proximal tubule, about 80% of filtered bicarbonate is reabsorbed.

An enzyme that catalyzes the conversion of CO2 and H2O into H2CO3, speeding up the reaction.

A secondary active transporter that facilitates the secretion of H+ into the tubular fluid, crucial for HCO3- reabsorption.

The amount of bicarbonate filtered into the kidney tubules, calculated by multiplying GFR by the bicarbonate concentration.

A transporter that moves HCO3- into the interstitial fluid, allowing its reabsorption.

The carbonic anhydrase type found inside the cells of the proximal tubule.

The concentration of bicarbonate in the tubular fluid, reducing from 25 mM to approximately 5 mM by the end of the proximal tubule.

A process where bicarbonate (HCO3-) is reabsorbed from the tubular fluid (TF) in the proximal tubule of the kidney, but HCO3- itself does not directly cross the apical membrane.

The membrane facing the tubular fluid in kidney tubules.

Transport of hydrogen ions (H+) from the intracellular fluid (ICF) across the apical membrane into the tubular fluid, against its electrochemical gradient.

Enzyme that catalyzes the interconversion of carbon dioxide (CO2), water (H2O), and carbonic acid (H2CO3).

Filtered HCO3- reacts with secreted H+ to form H2CO3, which then dissociates into CO2 and H2O in the presence of carbonic anhydrase (CA IV).

The fluid inside the cells.

The fluid within the renal tubules.

The process of reclaiming a substance from the tubular fluid and returning it to the blood.

The transport of a substance from the plasma into the tubular fluid, where it ends up in the urine.

The removal of a substance from the body, typically through urine.

An enzyme that speeds up the reaction converting carbon dioxide and water into carbonic acid, impacting the rate of bicarbonate reabsorption in the kidneys.

A drug that blocks carbonic anhydrase activity, decreasing bicarbonate reabsorption and urine flow.

The process of reclaiming bicarbonate from the kidney's filtrate, primarily through sodium exchange.

Partial pressure of carbon dioxide in the blood. Affects bicarbonate reabsorption.

Amount of bicarbonate filtered into the kidneys, influencing the rate of H+ secretion.

The kidney’s initial segment where 80% of bicarbonate and 70 mosmol solute is reabsorbed per eight minutes.

Maximum transport rate for reabsorption of certain solutes in proximal tubule

Increased urine output due to osmotic imbalances in the kidney.

Water is reabsorbed as required for solute balance along the proximal tubule., primarily through osmosis.

In the early proximal tubule, chloride's movement from the tubular fluid to interstitial fluid is hindered by unfavorable electrical gradient and insufficient chemical gradient. Water reabsorption causes increased tubular fluid chloride concentration, leading to slight chloride movement between cells.

In the late proximal tubule, chloride reabsorption occurs primarily through the cells (transcellularly). A slightly positive lumen potential facilitates chloride movement into the cell, in exchange for another intracellular anion (aided by Sodium-Hydrogen Exchanger).

Concentration gradient drives movement of a substance from an area of higher concentration to lower concentration in transport.

Electrochemical gradient is the driving force for the movement of an ion that considers both concentration and electrical gradients.

Chloride is reabsorbed in high quantities compared to other solutes in the proximal tubule, through both paracellular and transcellular routes.

Sodium is reabsorbed with Chloride in the proximal tubule.

Increased excretion of salt and water due to a non-reabsorbable substance (e.g., mannitol) in the filtrate.

About 80% of filtered solutes and water are reabsorbed isotonically in the proximal tubule.

The potassium concentration in the tubular fluid. Must be > 4 mM for electrochemical equilibrium across the apical membrane.

Glomerular Filtration Rate, the rate at which fluid is filtered from the blood into the Bowman's capsule.

A non-reabsorbable substance.

The process of reclaiming sodium from the nephron filtrate in the proximal tubule.

Catecholamines, Angiotensin II, and Atrial Natriuretic Hormone influence Na+ reabsorption in the proximal tubule.

K+ is passively reabsorbed in the proximal tubule, primarily through solvent drag and electrodiffusion.

Water reabsorption pulls along other substances such as K+.

Movement of K+ down the electrical and concentration gradients.

Maximum transport rate for a substance in the proximal tubule, typically in the ranges of 20-30 mosmol/min.

Movement of chloride from the filtrate to the blood, via solvent drag or active transport.