Thick ascending limb of loop of Henle

The thick ascending limb of loop of Henle (TAL) also known as distal straight tubule, is a segment of the nephron in the kidney. It can be divided into two parts: that in the renal medulla, and that in the renal cortex.

Medullary thick ascending limb

The medullary thick ascending limb remains impermeable to water. Sodium, potassium (K⁺) and chloride (Cl^-) ions are reabsorbed by active transport. K⁺ is passively transported along its concentration gradient through a K⁺ leak channel in the apical aspect of the cells, back into the lumen of the ascending limb. This K⁺ "leak" generates a positive electrochemical potential difference in the lumen. The electrical gradient drives more reabsorption of Na⁺, as well as other cations such as magnesium (Mg²⁺) and importantly calcium Ca²⁺.

Loop diuretics such as furosemide block the K⁺/Na⁺/2Cl^- co-transporter.

This is also the part of the tubule that generates Tamm-Horsfall protein. The function of this protein is not well understood, but is responsible for creating urinary casts.

Cortical thick ascending limb

The difference between the medullary and cortical thick ascending limbs is mainly anatomical. Functionally, they are very similar.

The cortical thick ascending limb...
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