Transitional epithelium or urothelium lines all of the following structures of the urinary system, EXCEPT:
**Core Concept**
Transitional epithelium, also known as urothelium, is a specialized type of epithelial tissue that lines the urinary system, particularly the parts that are exposed to urine. It is characterized by its ability to stretch and expand to accommodate changes in urine volume.
**Why the Correct Answer is Right**
Transitional epithelium is found in the renal pelvis, ureters, bladder, and proximal part of the urethra. It consists of multiple layers of cells that can flatten and stretch to accommodate changes in urine volume. The unique structure of transitional epithelium allows it to prevent urine from leaking into the surrounding tissues.
**Why Each Wrong Option is Incorrect**
* **Option B:** The glomerulus is a tuft of capillaries within the nephron where filtration of the blood takes place. It is lined by specialized endothelial cells, not transitional epithelium.
* **Option C:** The collecting duct is a part of the nephron where water and electrolytes are reabsorbed or secreted. It is lined by simple cuboidal epithelium, not transitional epithelium.
* **Option D:** The renal calyces are cup-like structures that collect urine from the renal pyramids and channel it into the renal pelvis. They are lined by transitional epithelium.
**Clinical Pearl / High-Yield Fact**
Transitional epithelium is highly resistant to chemical and physical damage, which is why it can withstand the constant flow of urine and the varying pH levels of the urinary system.
**Correct Answer:** B. The glomerulus is lined by specialized endothelial cells, not transitional epithelium.