Renal pyramids

Where are the renal pyramids located?

The pyramids are located in the renal medulla (medulla renis), which lies deep to the renal cortex (cortex renis).

The kidney (renes) itself is a paired bean-shaped organ. It is located retroperitoneally (retroperitonealiter) on either side of the vertebral column, predominantly at the level from the twelfth thoracic (Th12) to the third lumbar (L3) vertebrae. The right kidney is usually situated somewhat lower than the left.

Anatomical landmarks of the organ containing the pyramids:

• Surfaces — anterior and posterior (facies anterior et posterior).
• Borders — convex lateral (margo lateralis) and concave medial (margo medialis).
• Poles — superior and inferior (extremitas superior et inferior).

Renal capsules: fibrous capsule (capsula fibrosa), adipose capsule (capsula adiposa), and renal fascia (fascia renalis).

Structure and urine outflow pathways

The structural and functional unit of the organ is the nephron (nephron). Urine formation occurs through the interaction of the vascular system and the epithelial tubule system.

Pathway from the renal pyramids to the urinary tract structures:

• Renal papillae (papillae renales) — the apices of the renal pyramids, opening into the minor renal calyces.
• Minor renal calyces (calices renales minores) — structures into which the papillae open.
• Major renal calyces (calices renales majores) — formed by the confluence of the minor calyces.
• Renal pelvis (pelvis renalis) — formed where the major calyces transition into the pelvis.

The renal pelvis, along with blood vessels, nerves, and lymphatic vessels, passes through the renal hilum (hilum renale) located on the medial border. The hilum opens into the renal sinus (sinus renalis).

Blood supply to the renal parenchyma

Renal blood circulation has a specific hemodynamics: blood sequentially passes through two capillary networks. The first network is represented by capillary glomeruli surrounded by a capsule, while the second surrounds the epithelial tubules.

Intrarenal circulation is provided by the following vessels:

• Interlobar arteries and veins (aa. et vv. interlobares renis).
• Arcuate arteries and veins (a. et v. arcuata).
• Interlobular arteries (a. interlobularis).

The renal artery divides into branches in the renal sinus area, and the renal vein collects tributaries from the sinus area. The suprarenal (v. suprarenalis) and testicular (v. testicularis) veins also drain into the left renal vein.

Features in newborns

In newborn infants, renal morphology has several distinct features:

• The kidneys are relatively large, located low, and retain fetal lobulation.
• The cortical layer is thinned, and the pelves have an intrarenal position.
• The tubular system and loops of Henle are shortened, and their lumens are narrowed.
• The concentrating ability of the kidneys is reduced: they poorly excrete excess salts (sodium), which easily leads to edema syndrome upon water or salt loading.
• The ureters are wide and tortuous, with an underdeveloped muscular and elastic framework. This predisposes to vesicoureteral reflux.
• Daily urine output is about 250 ml with a high frequency of urination (20–25 times a day).
• There is a close lymphatic connection between the kidneys and the intestine, which is a risk factor for the translocation of infection from the gastrointestinal tract into the urinary tract.

Class and exam questions

What else to study on this topic

• Nephron
• Blood supply to the kidney
• Renal pelvis and calyces
• Renal topography

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.