In which part of the kidneys are casts formed?

Casts are formed in the lumen of the distal and collecting tubules of the kidneys. These structures are essentially molds of the renal tubules and reflect the conditions within these segments. When there is an accumulation of proteins, cells, or cellular debris in the renal tubules, the fluids can gel and solidify, leading to the formation of casts.

The specific environment of the distal and collecting tubules provides the conditions necessary for this process. This includes factors such as concentrated urine, specific pH levels, and the presence of certain substances that can precipitate within the tubular lumen.

While casts may accumulate materials that originate from other parts of the nephron, their formation occurs in the lower segments, specifically the distal and collecting tubules, rather than the glomerulus, proximal tubules, or kidney cortex.