Topography and external anatomy
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 somewhat lower compared to the left.
Externally, the organ resembles a bean. Its anatomy traditionally distinguishes 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.
It is on the concave medial border that the renal hilum is located — hilum renale. Extending deep into the organ, the hilum leads into a spacious cavity — the renal sinus (sinus renalis). In the area of the hilum, the so-called "renal pedicle" is formed. The following structures pass through the hilum renale:
- Renal artery (a. renalis).
- Renal vein (v. renalis).
- Renal pelvis (pelvis renalis).
- Lymphatic vessels and nerve trunks.
Fixation apparatus: renal capsules
To hold the organ in the correct anatomical position and protect it, a system of capsules exists. Sequentially, from the parenchyma outwards, three layers are distinguished:
- Fibrous capsule (capsula fibrosa) — closely adheres directly to the organ tissue.
- Adipose capsule (capsula adiposa) — surrounds the organ and serves as a cushioning pad, protecting it from mechanical impacts.
- Renal fascia (fascia renalis) — the outermost layer, which participates in fixing the organ in the retroperitoneal space.
Internal structure and urinary pathways
On a cross-section, the tissue of the organ (parenchyma) is clearly divided into two layers. The outer layer is represented by the renal cortex (cortex renis). The inner part is the renal medulla (medulla renis).
The medulla is organized into specific structures — renal pyramids (pyramides renales). Their bases face the cortex, and their apices are directed toward the renal sinus. The apices of the pyramids form the renal papillae (papillae renales).
The intraorgan urinary excretion system is 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, in turn, unite and 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 is characterized by extremely intensive blood flow. Arterial blood enters via 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 plexus is mixed: it includes both sympathetic and parasympathetic nerve fibers that control vascular tone and organ function.
Briefly: answers to topical questions
What is the syntopy of the renal pedicle elements from anterior to posterior?
The syntopy of the renal pedicle elements from anterior to posterior is represented by the vein, artery, and pelvis.
- Renal vein (v. renalis) — the most anterior and superior element.
- Renal artery (a. renalis) — located posterior to the vein, superior and anterior to the pelvis.
- Renal pelvis (pelvis renalis) — the most posterior element, continuing into the ureter.
All elements are surrounded by adipose tissue.
Which organs are in contact with the anterior surface of the right kidney?
The anterior surface of the right kidney is in contact with the liver, colon, and duodenum.
- Liver (hepar) — lies adjacent to the superior pole of the kidney.
- Colon (colon) — the right colic flexure lies adjacent laterally.
- Duodenum (duodenum) — the descending part lies adjacent to the hilum and medial border.
The anterior surface of the kidney is separated from the listed organs by the pre-renal fascia (fascia prerenalis) and loose connective tissue.
Which segments are distinguished in the macroscopic structure of the kidney?
In the macroscopic structure of the kidney, five segments are distinguished, which are supplied with blood by corresponding branches of the renal artery.
- Superior segment — supplied by a. segmenti superioris.
- Superior anterior segment — supplied by a. segmenti anterioris superioris.
- Inferior anterior segment — supplied by a. segmenti anterioris inferioris.
- Inferior segment — supplied by a. segmenti inferioris.
- Posterior segment — supplied by a. segmenti posterioris.
The first four segments belong to the basin of the anterior branch of the renal artery, while the posterior segment is supplied by the posterior branch.
Which specific nerves and ganglia form the renal plexus?
The renal plexus (plexus renalis) is formed by branches of autonomic plexuses, ganglia, and nerves.
It includes:
- branches of the celiac plexus (plexus coeliacus);
- branches of the abdominal aortic plexus;
- splanchnic nerves (nn. splanchnici);
- branches from the aortico-renal ganglion;
- branches from the lower thoracic and upper lumbar ganglia of the sympathetic trunk;
- preganglionic parasympathetic fibers of the vagus nerve (n. vagus).
Which regional lymph nodes drain lymph from the kidneys?
Lymph drainage from the kidneys proceeds to the following regional lymph nodes:
- Lumbar lymph nodes;
- Para-aortic lymph nodes (aortic);
- Paracaval lymph nodes (caval).
The superficial and deep lymphatic systems of the kidney merge at the renal hilum and head toward these regional nodes. Subsequently, lymph drains into the cisterna chyli.
To memorize the sequence of the renal pedicle structures (from anterior to posterior at the hilum): VAN — Vein, Artery, Pelvis (the text simply mentions their presence, but the VAN order is a topography classic).
Class and exam questions
At what vertebral level are the kidneys located?
In the retroperitoneal space on both sides of the spine, extending from the twelfth thoracic (Th12) to the third lumbar (L3) vertebra.
Why is the right kidney positioned lower than the left?
Normally, the right kidney lies slightly lower than the left (in topographical anatomy, this is due to the close relationship with the massive right lobe of the liver).
What is the sequence of urine outflow pathways within the kidney?
Urine passes from the renal papillae into the minor calyces, then into the major calyces, which fuse to form the renal pelvis.
What forms the apices of the renal pyramids?
The apices of the renal pyramids form the renal papillae (papillae renales), which open into the minor renal calyces.
What else to study on this topic
- Histological structure of the nephron (nephron) and its segments
- Syntopy of the anterior and posterior surfaces of the kidneys (facies anterior et posterior)
- Branching of the renal artery (a. renalis) within the organ parenchyma
- Formation and composition of the renal plexus (plexus renalis)
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