Page 697 - Atlas of Histology with Functional Correlations

FIGURE 18.1 ■ A sagittal section of the kidney shows the cortex and medulla,

with blood vessels and the excretory ducts, including the pelvis and the ureter.

Each renal papilla is surrounded by a funnel-shaped minor calyx that collects
urine from the papilla. The minor calyces join in the renal sinus to form a major
calyx that, in turn, joins to form a single funnel-shaped renal pelvis. The renal
pelvis leaves each kidney through the hilum, narrows to become a muscular

ureter, and descends toward the bladder on each side of the posterior body wall.

Uriniferous Tubules

The functional unit of each kidney is the microscopic uriniferous tubule. It

consists of a nephron and a collecting duct into which empty the filtered
contents of the nephron. Nephrons produce urine, and the excretory collecting
ducts conduct the urine from the kidneys. Millions of nephrons are present in
each kidney cortex. The nephron, in turn, is subdivided into two components: a

renal corpuscle and renal tubules.

Nephrons of Kidney

There are two types of nephrons, based on their location in the kidney. Cortical

nephrons are located in the upper cortex of the kidney, whereas the
juxtamedullary nephrons are situated near the junction of the cortex and
medulla of the kidney. Although all nephrons participate in urine formation,
juxtamedullary nephrons produce a hypertonic environment in the interstitium of

the kidney medulla that produces concentrated (hypertonic) urine.

Renal Corpuscle

The renal corpuscle consists of a tuft of capillaries, called the glomerulus,
surrounded by a double layer of epithelial cells called the glomerular
(Bowman) capsule. The inner or visceral layer of the capsule consists of
specialized branching epithelial cells called podocytes. These cells are adjacent
to the capillaries, and their long cytoplasmic processes completely invest the

fenestrated glomerular capillaries. From these cytoplasmic processes arise
numerous smaller foot processes or pedicles that interdigitate with pedicles from
adjacent podocytes and form tight-fitting filtration slits. A thin, semipermeable

filtration slit diaphragm spans each filtration slit. The outer, or parietal, layer

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