The human kidneys are a pair of reddish-brown, bean-shaped organs that act as filtration systems for the body, removing metabolic waste and regulating fluid balance. To describe the kidney’s position and structure, anatomists use the term “pole,” which refers to the rounded extremity of the organ. The upper pole is the superior, or topmost, end of the kidney, while the lower pole is the corresponding inferior aspect.
Defining the Kidney’s Structure
The kidneys are situated in the posterior abdomen, positioned outside of the peritoneal cavity in a space known as the retroperitoneum. They extend vertically from the level of the twelfth thoracic vertebra (T12) down to the third lumbar vertebra (L3). The right kidney generally sits slightly lower than the left due to the liver directly above it.
The upper poles of both kidneys are angled slightly more medially and posteriorly compared to their lower poles. Each organ measures about 10 to 12 centimeters in length, with the superior pole often protected by the eleventh and twelfth ribs. The kidney is defined by a convex lateral edge and a concave medial edge, where the renal hilum—the entry point for the renal artery and exit point for the renal vein and ureter—is located.
The kidney tissue is composed of two main layers: the outer cortex and the inner medulla. The upper pole is covered by a dense, fibrous sheath called the renal fascia. This fascia separates the kidney from surrounding structures and securely encloses the organ.
The Adrenal Gland’s Position
The most distinguishing anatomical feature of the upper pole is its close relationship with the adrenal gland, also known as the suprarenal gland. These two endocrine organs sit like a cap directly over the superior, medial aspect of each kidney. The right adrenal gland is typically pyramidal in shape, while the left one is more crescent-shaped, and both are entirely separate from the kidney tissue itself.
These glands are enclosed within the same superior layer of the renal fascia, which helps secure them in their position above the upper pole. The adrenal glands are functionally linked to the kidney’s role in maintaining homeostasis. They are tasked with producing and releasing a variety of hormones directly into the bloodstream, which regulate metabolism, the immune system, and blood pressure.
Among the hormones produced are cortisol, which aids the body’s response to stress, and aldosterone, which signals the kidneys to regulate sodium and potassium levels. The adrenal glands are highly vascularized, possessing an extensive blood supply to support the rapid release of these hormones. This close proximity and shared fascial sheath make the upper pole an important anatomical landmark for understanding the placement of these hormone-producing glands.
Clinical Relevance of the Upper Pole
Understanding the specific anatomy of the upper pole is important for various medical procedures and diagnostic imaging. Imaging modalities like ultrasound and CT scans often focus on this region to assess the adrenal glands for masses or nodules. Because the adrenal gland sits immediately above the kidney, any issues with the gland directly involve the upper pole’s anatomical space.
Surgical procedures, particularly the removal of an adrenal gland (adrenalectomy), require precise knowledge of the upper pole’s location and its surrounding vascular structures. The anatomical location is also crucial in managing kidney transplant procedures, especially when dealing with accessory blood vessels that supply the superior portion of the organ. Surgeons must often reconstruct or carefully manage these upper pole arteries to preserve kidney tissue.
The upper pole’s position, situated high in the retroperitoneum, also places it near the diaphragm and the lower ribs. Furthermore, conditions like cysts or masses within the kidney often originate in the poles, making their superior location a factor in determining treatment or monitoring.