Maintenance of the Body
sis; “water in the kidney”). Hy-
dronephrosis can severely damage the kidney, leading to necro-
sis (tissue death) and renal failure.
Internal Gross Anatomy
A frontal section through a kidney reveals three distinct regions:
. Te most superﬁcial
, is light-colored and has a granular ap-
pearance. Deep to the cortex is the darker, reddish-brown
, which exhibits cone-shaped tissue masses called
. Te broad
of each pyra-
mid faces toward the cortex, and its apex, or
points internally. Te pyramids appear striped because they are
formed almost entirely of parallel bundles of microscopic urine-
collecting tubules and capillaries. Te
extensions of cortical tissue, separate the pyramids. Each pyra-
mid and its surrounding cortical tissue constitutes one of ap-
of a kidney.
, a funnel-shaped tube, is continuous with
the ureter leaving the hilum. Branching extensions of the pelvis
form two or three
lih-sēz; singular: calyx).
Each major calyx subdivides to form several
cup-shaped areas that enclose the papillae.
Te calyces collect urine, which drains continuously from
the papillae, and empty it into the renal pelvis. Te urine then
ﬂows through the renal pelvis and into the ureter, which moves
it to the bladder to be stored. Te walls of the calyces, pelvis,
and ureter contain smooth muscle that contracts rhythmically
to propel urine by peristalsis.
tis) is an infection of the renal pelvis and caly-
ces. Infections or inﬂammations that aﬀect the entire kidney are
tis). Kidney infections in females
are usually caused by fecal bacteria that spread from the anal re-
gion to the urinary tract. Less oFen they result from bloodborne
Position of the kidneys against the posterior
Cross section viewed from inferior direction. Note
the retroperitoneal position and the supportive tissue layers of the
Posterior in situ view showing relationship of the kidneys
to the 12th ribs.