Tubular Transport - Na, Cl, Water and HCO3 transport (PCT)

Vocabulary flashcards covering the mechanisms of sodium, water, and bicarbonate transport in the proximal convoluted tubule (PCT) based on the lecture by Dr. Ratnadeep Saha.

Peritubular Starling Forces

The combination of low blood hydrostatic pressure and high blood oncotic pressure in peritubular capillaries that promotes the reabsorption of salt and fluid from the nephron.

Obligatory Water Reabsorption

The passive reabsorption of approximately $2/3$ of filtered water in the proximal convoluted tubule, driven by the osmotic gradient created by solute reabsorption.

Aquaporin 1 (AQP1)

Specific water channels located in the proximal tubule that facilitate the passive movement of water during obligatory water reabsorption.

Na+ / K+ ATPase pump

A pump located on the basolateral surface of tubular cells that uses energy to maintain low intracellular $Na^+$ levels, driving the transport of sodium from the lumen into the cell.

Na+ / H+ Exchanger

An apical membrane transporter vital for bicarbonate ($HCO3^-$) absorption and blood $pH$ regulation by exchanging luminal $Na^+$ for intracellular $H^+$.

Carbonic Anhydrase

A key enzyme (Type 4 on the brush border and Type 2 intracellularly) that facilitates the conversion of $H_2CO_3$ to $H_2O$ and $CO_2$ to allow for $85\%$ of bicarbonate reabsorption in the PCT.

Na+ / Glucose Cotransporter

A secondary active transport mechanism in the early PCT that reabsorbs sodium moves down its concentration gradient to pull glucose into the cell.

Paracellular Transport

The movement of substances (like $Na^+$ and $Cl^-$) between tubular cells through "leaky" tight junctions, which becomes the predominant mechanism for sodium reabsorption in the late PCT.

Claudin proteins

Proteins that regulate the permeability of tight junctions; lower levels of these proteins result in "leaky" junctions that allow for ion permeability.

Solvent Drag

The process by which the movement of water from the interstitium into the blood peritubular capillaries carries dissolved solutes along with it.

Na+ / HCO3- Cotransporter

A basolateral transporter that moves sodium and bicarbonate out of the tubular cell and into the interstitium together.

Proximal Convoluted Tubule (PCT)

The segment of the nephron where approximately $67\%$ ($2/3$) of filtered sodium and water is reabsorbed.

Glut1 and Glut2

Glucose transporters located on the basolateral surface of the proximal tubule cells that facilitate the exit of glucose into the interstitium via passive diffusion.