**Core Concept**
Cystocoele refers to the herniation of the bladder into the vagina, which is a type of pelvic organ prolapse. This condition occurs when the supportive tissues and muscles surrounding the bladder weaken, allowing it to protrude into the vaginal canal.

**Why the Correct Answer is Right**
Cystocoele typically results from a combination of factors, including childbirth, menopause, and chronic straining during bowel movements or urination. The weakened pelvic floor muscles and connective tissue provide insufficient support for the bladder, leading to its herniation into the vagina. This condition can cause urinary incontinence, pelvic pressure, and discomfort.

**Why Each Wrong Option is Incorrect**
**Option A:** Rectocoele refers to the herniation of the rectum into the vagina, not the bladder. This is a different type of pelvic organ prolapse.
**Option B:** Enterocele is the herniation of the small intestine into the vagina, which may occur alongside cystocoele but is a distinct condition.
**Option C:** Urethral prolapse refers to the downward displacement of the urethra, which is a separate condition from cystocoele.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that cystocoele is often associated with other pelvic organ prolapses, such as rectocoele and enterocele. A thorough pelvic examination is essential for diagnosing these conditions.

**Correct Answer: D. Bladder.**