Page 701 - Atlas of Histology with Functional Correlations

descending and ascending segment, and a thick ascending portion called the

distal convoluted tubule. The distal convoluted tubule is shorter and less
convoluted than the proximal convoluted tubule, and it ascends back into the
kidney cortex. Because the proximal convoluted tubule is longer than the distal
convoluted tubule, it is more frequently observed near the renal corpuscles and
in the renal cortex. The distal convoluted tubule then joins to the collecting

tubule. In juxtamedullary nephrons, the loop of Henle is very long. It descends
from the kidney cortex deep into the medulla and then loops back to ascend into
the cortex.

The collecting tubule and the collecting duct are not part of the nephron. A

number of short collecting tubules join to form several larger collecting ducts.
As the collecting ducts become larger and descend further toward the papillae of
the medulla, they are called papillary ducts. Smaller collecting ducts are lined
with a cuboidal epithelium. Deeper in the medulla, the epithelium changes to

columnar. At the tip of each papilla, the papillary ducts empty their contents into
the minor calyx. The area on the papilla that exhibits openings of the numerous
papillary ducts is the area cribrosa.

The kidney cortex also exhibits numerous, lighter-staining medullary rays

that extend vertically from the bases of the pyramids into the cortex. Medullary
rays consist of collecting ducts, blood vessels, and straight portions of a number
of nephrons that penetrate the cortex from the base of the pyramids.

RENAL BLOOD SUPPLY

To understand the functional correlation of the kidney, it is important to
understand the blood supply (see Fig. 18.1). Each kidney is supplied by a large

renal artery that divides in the hilum into several segmental branches, which
branch into several interlobar arteries. These arteries continue in the kidney
between the pyramids toward the cortex. At the corticomedullary junction, the
interlobar arteries branch into arcuate arteries that arch over the base of the

pyramids and give rise to interlobular arteries. These arteries branch further
into the afferent arterioles, which give rise to the capillaries in the glomeruli
of renal corpuscles. Efferent arterioles leave the renal corpuscles and form a
complex peritubular capillary network around the tubules in the cortex and

long, straight capillary vessels, or vasa recta, in the medulla that loops back to
the corticomedullary region. The vasa recta form loops that are parallel to the

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