Spatial arrangement and shape of the kidneys
The kidneys have a characteristic bean-like shape with a convex lateral border and a concave medial border, where the hilum (hilum renalis) is located. The longitudinal axes of the organs are not parallel: they converge at the upper poles and diverge at the lower poles.
The kidneys are characterized by marked skeletal asymmetry in their positioning:
- Left kidney: lies higher; its upper pole reaches the upper margin of the 11th rib, and the hilum projects onto the 12th rib.
- Right kidney: is displaced downward; its upper margin is at the level of the 11th intercostal space, and the hilum descends below the 12th rib.
The hila of both kidneys face anteriorly and medially — toward the abdominal aorta and inferior vena cava, projecting at the level of the LI body.
Syntopy: organ relations of the kidneys
The posterior surface of both kidneys lies against the muscular mass (lumbar part of the diaphragm, quadratus lumborum muscle, m. psoas major) via the fascia retrorenalis. It is important to remember that the upper half of the kidney (above the 12th rib) is in contact with the costodiaphragmatic recess (recessus costodiaphragmaticus) of the pleura, creating a risk of its injury during surgeries.
Anterior syntopy differs radically:
- On the right: the liver is adjacent to the upper pole, the right colic flexure lies laterally, and the descending part of the duodenum is adjacent to the medial border and hilum.
- On the left: the fundus of the stomach is located at the upper pole, the spleen and left colic flexure lie laterally, and the tail of the pancreas approaches the hilum.
Anatomy of the renal pedicle and vessels
The renal pedicle includes the artery, vein, pelvis, lymphatic vessels, and nerves surrounded by adipose tissue. The elements are arranged in a strict order (from posterior to anterior):
- Renal pelvis (the most posterior structure).
- Renal artery (superior and anterior to the pelvis).
- Renal vein (the most anterior and superior element).
Arteries (aa. renales): branch off the aorta. The right artery is longer and passes posterior to the inferior vena cava. The left is shorter and lies in close proximity to the tail of the pancreas. Intrarenally, the artery divides into anterior (supplying 4 segments) and posterior (1 segment) branches.
Veins (vv. renales): drain into the inferior vena cava. The left vein is longer, crosses anterior to the aorta, and receives the left testicular/ovarian vein. The renal veins form important portocaval anastomoses with the portal venous system.
Topography of the suprarenal glands
The suprarenal glands lie above the upper poles of the kidneys (level of TXI–TXII) within the renal fasciae. Posteriorly, they rest on the diaphragm.
- Right suprarenal gland is anteriorly bordered by the extraperitoneal bare area of the liver and is tightly adjacent to the inferior vena cava medially.
- Left suprarenal gland is anteriorly covered by the peritoneum of the omental bursa, inferiorly contacts the pancreas and splenic vessels, and medially contacts the aorta and celiac plexus.
The blood supply to the glands is unique — each receives branches from three sources: the inferior phrenic artery (superior), directly from the aorta (middle), and from the renal artery (inferior). Venous drainage occurs via a single vein (v. suprarenalis).
Briefly: answers to topical questions
Which muscles are adjacent to the posterior surface of the kidneys, forming the renal bed?
Four muscular structures adjacent to the posterior surface of the kidneys form the renal bed. These include:
- Lumbar part of the diaphragm — located in the upper part.
- Quadratus lumborum muscle (m. quadratus lumborum).
- Aponeurosis of the transversus abdominis muscle.
- Psoas major muscle (m. psoas major).
What are the names of the five renal segments into which the kidney is divided?
The kidney is divided into five segments corresponding to the intraorgan branching of the anterior and posterior branches of the renal artery. The following segments are distinguished:
- 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.
Which sheaths (capsules) sequentially surround the kidney?
The kidney is sequentially surrounded by three sheaths arranged from outward to inward. These include:
- Connective tissue fascia — the outermost layer.
- Adipose capsule (capsula adiposa renis or perinephric fat) — a layer of loose adipose tissue located beneath the fascia and enclosing the kidney on all sides.
- Fibrous capsule (capsula fibrosa) — a thin, smooth membrane that directly adheres to the organ parenchyma and contains smooth muscle elements.
Which nerve plexuses participate in the innervation of the kidneys?
Kidney innervation is provided by the renal nerve plexus (plexus renalis). Its formation involves branches of the celiac plexus (4–6 branches), the lesser splanchnic nerve (n. splanchnicus minor), and the aortorenal ganglion. The renal plexus is connected with the lumbar sympathetic trunk, superior mesenteric, and intermesenteric plexuses.
To memorize the syntopy of the renal pedicle elements (from anterior to posterior), use the acronym VAP: Vein (anterior), Artery (middle), Pelvis (posterior).
Class and exam questions
Why is the right kidney positioned lower than the left?
The asymmetry is caused by the pressure of the massive right lobe of the liver, which closely abuts the anterior surface of the upper pole of the right kidney.
What is the surgical significance of accessory renal arteries?
They occur in 1/3 of patients, often penetrate the renal poles (especially the lower one), and can have a large diameter. Their accidental ligation or injury will lead to ischemia of that part of the organ.
Where does venous blood drain from the suprarenal glands?
Drainage occurs via a single central vein. The left suprarenal vein always drains into the left renal vein, while the right drains into the right renal vein or directly into the inferior vena cava.
What else to study on this topic
- Segmental structure of the kidney: topography of 5 vascular segments
- Extraorgan arterial anastomoses of the kidney and their role in vascular occlusion
- Portocaval anastomoses via the renal vein system (splenorenal anastomosis)
- Sources of formation of the renal and suprarenal nerve plexuses
- Lymphatic drainage pathways from the kidneys and suprarenal glands to the cisterna chyli
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