When a horseshoe kidney develops, the ascent of the kidney is restricted by the:
**Core Concept**
A horseshoe kidney is a congenital anomaly where the two kidneys fuse together at their lower poles, forming a U-shaped structure. This fusion occurs due to the failure of the ureteric buds to migrate laterally during embryonic development. As a result, the ascent of the horseshoe kidney is restricted, leading to its abnormal position.
**Why the Correct Answer is Right**
The correct answer is related to the anatomical structure that restricts the ascent of the horseshoe kidney. During embryonic development, the kidneys normally ascend to their final position in the retroperitoneum. However, in the case of a horseshoe kidney, the fusion of the two kidneys at their lower poles creates a bar that prevents the kidneys from ascending further. This bar is formed by the fused lower poles of the kidneys, which are attached to the inferior mesenteric artery.
**Why Each Wrong Option is Incorrect**
* **Option A:** The mesonephric ducts are involved in the development of the urinary system, but they are not directly responsible for restricting the ascent of a horseshoe kidney.
* **Option B:** The suprarenal glands are located near the kidneys but do not play a role in restricting the ascent of a horseshoe kidney.
* **Option C:** The gonadal arteries are involved in the blood supply of the gonads but are not related to the ascent of the kidneys.
**Clinical Pearl / High-Yield Fact**
A horseshoe kidney is more prone to complications such as hydronephrosis, renal calculi, and hypertension due to its abnormal position and potential ureteropelvic junction obstruction.
**Correct Answer: D. The fused lower poles of the kidneys.**