Page 702 - Atlas of Histology with Functional Correlations

long loops of Henle that contain the urinary filtrate. The interstitium around

these tubules and blood vessels is drained by interlobular veins that continue
toward the arcuate veins.

Supplemental micrographic images are available at
www.thePoint.com/Eroschenko13e under Urinary System.

FIGURE 18.3 | Kidney: Cortex, Medulla,

Pyramid, Renal Papilla, and Minor Calyx

(Panoramic View)

In this sagittal section, the kidney exhibits an outer darker-staining cortex and an
inner lighter-staining medulla. Externally, the cortex is covered with a dense
irregular connective tissue renal capsule (1).

The cortex contains both distal and proximal convoluted tubules (4, 11),

glomeruli (2), and medullary rays (3). Present also in the cortex are the
interlobular arteries (12) and interlobular veins (13). The medullary rays (3)
are formed by the straight portions of nephrons, blood vessels, and collecting
tubules that join in the medulla to form the larger collecting ducts (6). The

medullary rays do not extend to the kidney capsule (1) because of the
subcapsular convoluted tubules (10).

The medulla comprises the renal pyramids. The base of each pyramid (5) is
adjacent to the cortex, and its apex forms the pointed renal papilla (7) that

projects into the surrounding funnel-like structure, the minor calyx (16), which
represents the dilated portion of the ureter. The area cribrosa (9) is pierced by
small holes, which represent the openings of the collecting ducts (6) into the
minor calyx (16).

The tip of the renal papilla (7) is usually covered with a simple columnar

epithelium (8). As the columnar epithelium of the renal papilla (7) extends onto
the outer wall of the minor calyx (16), it becomes a transitional epithelium
(16). A thin layer of connective tissue and smooth muscle (not illustrated) under
this epithelium then merges with the connective tissue of the renal sinus (15).

Present in the renal sinus (15) are branches of the renal artery and vein called
the interlobar artery (17) and the interlobar vein (18). The interlobar vessels
(17, 18) enter the kidney and arch over the base of the pyramid (5) at the
corticomedullary junction as the arcuate artery and vein (14). The arcuate

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