Tubular Reabsorption and Secretion

What is tubular reabsorption?

The process by which most of the filtrate is returned to the bloodstream.

What is tubular secretion?

The transfer of substances from the tubule cells and blood into the filtrate.

What are the two main routes of reabsorption?

Paracellular (between cells) and transcellular (through cells).

In transcellular transport, what does the apical membrane face?

The tubular fluid.

In transcellular transport, what does the basolateral membrane face?

The interstitial fluid.

Which types of transport mechanisms are used in reabsorption?

Primary active transport and secondary active transport.

Are symporters and antiporters part of primary or secondary active transport?

Secondary active transport.

What do symporters do?

Move two substances in the same direction across a membrane.

What do antiporters do?

Move two substances in opposite directions across a membrane.

What is transport maximum (Tm) and what condition can it lead to?

The maximum rate of reabsorption; exceeded Tm for glucose leads to glucosuria.

What is solvent drag?

Water moving between cells, carrying dissolved solutes—part of paracellular reabsorption.

What is obligatory water reabsorption?

Water reabsorption that follows solutes, mainly in the PCT and loop of Henle.

What is facultative water reabsorption?

Water reabsorption under hormonal control, primarily in the DCT and collecting duct.