All are true about the trigone on the base of the urinary bladder, except ?
**Core Concept**
The trigone is a triangular area on the base of the urinary bladder, formed by the fusion of the two ureteric orifices and the internal urethral orifice. It plays a crucial role in the storage and voiding of urine. The trigone is a significant anatomical landmark in urology and is often used as a reference point for various surgical procedures.
**Why the Correct Answer is Right**
The trigone is a muscle-free area, which means it does not contain any smooth muscle fibers. This is because the trigone is formed by the fusion of the ureteric orifices and the internal urethral orifice, which are lined by transitional epithelium. The absence of smooth muscle in the trigone allows for the unimpeded flow of urine from the ureters into the bladder during voiding. Additionally, the trigone is a relatively fixed area, which helps to prevent the ureters from kinking or twisting during bladder contractions.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the trigone is not a highly vascularized area. While the trigone does receive some blood supply from the bladder, it is not as richly vascularized as other areas of the bladder.
**Option B:** This option is incorrect because the trigone is not a site of significant innervation. The trigone receives some innervation from the pelvic nerves, but it is not a primary site of innervation for the bladder.
**Option C:** This option is incorrect because the trigone is not a common site for bladder tumors. While tumors can occur in the bladder, the trigone is not a high-risk area for neoplastic growth.
**Clinical Pearl / High-Yield Fact**
The trigone is often used as a reference point for various urological procedures, such as transurethral resection of the bladder (TURB) and bladder biopsy. Surgeons often use the trigone to locate the ureteric orifices and the internal urethral orifice, which helps to avoid damaging these structures during surgery.
**Correct Answer: D. The trigone is a highly vascularized area.