The Loop of Henle Establishes the Kidney’s Concentration Gradient
- Imagine you're lost in a desert with limited water.
- How does your body ensure you don't dehydrate?
- The answer lies in the loop of Henle, a structure in your kidneys that conserves water and maintains balance.
What is the Loop of Henle?
Definition
Loop of Henle
The loop of Henle is a U-shaped tube found in the nephron, the kidney’s functional unit. It is responsible for creating a concentration gradient in the medulla, enabling the production of concentrated urine.
- The loop consists of two limbs:
- Descending Limb: Permeable to water but not to solutes.
- Ascending Limb: Impermeable to water but actively transports sodium ions ($Na^+$) out of the filtrate.
The loop of Henle is located in the kidney's medulla, where it creates a high osmotic concentration gradient.
How Does the Loop of Henle Work?
1. The Descending Limb: Water Leaves By Osmosis
- As filtrate moves down the descending limb, water is reabsorbed into the surrounding medulla.
- This occurs because the medulla has a higher solute concentration, drawing water out by osmosis.
- The filtrate becomes more concentrated as it descends.
The descending limb acts like a sponge, squeezing out water into the medulla while retaining solutes in the filtrate.
2. The Ascending Limb: Sodium Ions Leave By Active Transport
- In the ascending limb, the process changes.
- Sodium ions ($Na^+$) are actively transported out of the filtrate into the medulla.
- This creates a high solute concentration in the medulla, but the ascending limb is impermeable to water, so water remains in the filtrate.
- As a result, the filtrate becomes more dilute as it ascends.
Remember: The descending limb is permeable to water, while the ascending limb is impermeable to water but actively transports sodium ions.
