Topography and External Structure
The kidneys are located in the retroperitoneal space (retroperitonealiter). They lie on either side of the vertebral column. Topographically, their position projects from the twelfth thoracic (Th12) to the third lumbar (L3) vertebra. An important anatomical feature is asymmetry: the right kidney normally lies slightly lower compared to the left.
Externally, the organ resembles a bean. Its anatomy traditionally features several key landmarks:
- Surfaces: anterior (facies anterior) and posterior (facies posterior).
- Poles (extremities): superior (extremitas superior) and inferior (extremitas inferior).
- Borders: lateral border (margo lateralis), which is convex, and medial border (margo medialis), which is concave.
At the concave medial border lies the renal hilum — hilum renale. Extending deep into the substance of the organ, the hilum opens into a spacious cavity — the renal sinus (sinus renalis). The renal pedicle is formed within the region of the hilum. The following structures pass through the hilum renale:
- Renal artery (a. renalis).
- Renal vein (v. renalis).
- Renal pelvis (pelvis renalis).
- Lymphatic vessels and nerve plexuses.
Fixation Apparatus: Renal Sheaths
To maintain the organ in its proper anatomical position and protect it, a system of fascial and adipose layers surrounds the kidney. Proceeding sequentially from the parenchyma outward, three layers are distinguished:
- Fibrous capsule (capsula fibrosa) — closely adheres directly to the renal parenchyma.
- Adipose capsule (capsula adiposa) — surrounds the organ, serving as a cushioning pad to protect it from mechanical trauma.
- Renal fascia (fascia renalis) — the outermost layer, which helps anchor the organ in the retroperitoneal space.
Internal Structure and Urine Excretory Pathways
On cross-section, the organ's tissue (parenchyma) is clearly divided into two layers. The outer layer is the renal cortex (cortex renis). The inner layer is the renal medulla (medulla renis).
頬he medulla is organized into specialized structures called renal pyramids (pyramides renales). Their bases face the cortex, while their apices point toward the renal sinus. The apices of the pyramids form the renal papillae (papillae renales).
The intrarenal urine-collecting system represents a sequential cascade of structures:
- The papillae (papillae renales) open into minor renal calyces (calices renales minores).
- Several minor calyces fuse together to form major renal calyces (calices renales majores).
- The major calyces unite to form a single expanded cavity — the renal pelvis (pelvis renalis).
The functional basis of this entire complex system is the nephron (nephron), the main structural and functional unit of the organ.
Blood Supply and Innervation
The organ features an extremely high rate of blood flow. Arterial blood is supplied by the renal artery (a. renalis), which is a major branch of the abdominal aorta (aorta abdominalis).
After passing through the microvasculature of the organ, venous blood collects into the renal vein (v. renalis). This vein drains directly into the inferior vena cava (v. cava inferior).
Nervous regulation of the organ is provided by the renal plexus (plexus renalis). This is a mixed plexus containing both sympathetic and parasympathetic nerve fibers that control vascular tone and organ function.