Let’s learn about the nephron loop.
The nephron loop or loop of Henle is located in the kidney---specifically in a tiny part of the kidney known as the nephron.
The nephron loop is located between the proximal and distal convoluted tubules of the nephron.
The function of the nephron loop is to create a concentration gradient.
This mechanism is called a countercurrent multiplier.
Let’s take a closer look.
The nephron loop contains a descending limb sometimes called the thin segment…and an ascending limb sometimes called the thick segment .
The descending limb is permeable to water.
The ascending limb actively transports electrolytes into the interstitium
these include sodium, potassium and chloride.
Here’s how it works.
A 300 milliosmole isotonic solution enters the descending limb of the nephron loop.
Water moves out of the descending limb through aquaporins or water channels toward the higher solute concentration in the interstitium.
Since water is moving out, the solution becomes more concentrated.
The solution at the bottom of the nephron loop is very concentrated---up to 1200 milliosmoles.
The solution then moves up the ascending limb.
Let’s take a closer look at the ascending limb.
The ascending limb contains active transport proteins
These are the NKCC proteins or sodium, potassium, chloride co-transport proteins.
These proteins actively transport these electrolytes into the interstitium—maintaining the high concentration of the interstitium.
The NKCC protein uses ATP…so energy is expended in order to maintain the gradient.
Since solute is leaving the ascending limb the solution becomes less concentrated.
The solution leaving the nephron loop is hypotonic…around 100 milliosmoles.
Let’s summarize the process.
A 300 milliosmole isotonic solution enters the descending limb of the nephron loop.
Water moves out of the descending limb increasing the concentration of the solution.
The concentration increases to 1200 milliosmoles.
The solution enters the ascending limb.
The active transporters transport sodium, potassium and chloride out of the ascending limb.
The solution becomes less concentrated until it reaches 100 milliosmoles…a hypotonic solution.
We hope you have learned something about the nephron loop…and…see you next time.