Page 1015 - Fundamentals of anatomy physiology

1002 Unit 5 Environmental Exchange
Figure 26–4 The Structure of the Kidney. ATLAS: Plates 57a,b; 61b

Inner layer of Renal cortex Renal
fibrous capsule Renal medulla pyramids
Renal pyramid Renal sinus
Renal sinus
Adipose tissue Connection to Renal pelvis
minor calyx Major calyx
in renal sinus Minor calyx
Renal pelvis Minor calyx Renal papilla
Major calyx
Hilum Kidney lobe
Renal papilla Hilum Fibrous
capsule
Ureter Kidney lobe

a A diagrammatic view of a frontal Ureter
section through the left kidney
Renal columns

Fibrous capsule

b A frontal section of the
left kidney (cadaver)

26 (Figure 26–4a,b). The fibrous capsule is bound to the outer sur- Each kidney has about 1.25 million nephrons, with a com-
faces of the structures within the renal sinus. In this way, it stabi- bined length of about 145 km (85 miles).
lizes the positions of the ureter, renal blood vessels, and nerves.
Blood Supply and Innervation of the Kidneys
The kidney itself has an outer cortex and an inner medulla.
The renal cortex is the superficial portion of the kidney, in The kidneys receive 20–25 percent of the total cardiac out-
contact with the fibrous capsule. The cortex is reddish brown put. In normal, healthy people, about 1200 mL of blood flow
and granular. through the kidneys each minute—a phenomenal amount of
blood for organs with a combined weight of less than 300 g
The renal medulla consists of 6 to 18 distinct triangular (10.5 oz)!
structures called renal pyramids. The base of each pyramid
touches the cortex. The tip of each pyramid—a region known as Each kidney receives blood through a renal artery. This
the renal papilla—projects into the renal sinus. Each pyramid vessel originates along the lateral surface of the abdominal aorta
has a series of fine grooves that converge at the papilla. Bands near the level of the superior mesenteric artery (Figure 21–23,
of cortical tissue called renal columns extend into the medulla pp. 786–787). As it enters the renal sinus, the renal artery
and separate adjacent renal pyramids. The columns have a dis- provides blood to the segmental arteries (Figure 26–5a).
tinctly granular texture, similar to that of the cortex. A kidney Segmental arteries further divide into a series of interlobar
lobe consists of a renal pyramid, the overlying area of renal arteries. These arteries radiate outward through the renal
cortex, and adjacent tissues of the renal columns. ­columns between the renal pyramids. The interlobar arteries
supply blood to the arcuate (AR-ku. -a. t) arteries, which arch
Urine is produced in the kidney lobes. Ducts within each along the boundary between the cortex and medulla of the
renal papilla discharge urine into a cup-shaped drain called a kidney. Each arcuate artery gives rise to a number of cortical
minor calyx (KA. -liks). Four or five minor calyces (KAL-i-se. z) radiate arteries, also called interlobular arteries. They supply the
merge to form a major calyx, and two or three major caly- cortical portions of the adjacent kidney lobes. Branching from
ces combine to form the renal pelvis, a large, funnel-shaped each cortical radiate artery are numerous afferent arterioles.
chamber. The renal pelvis fills most of the renal sinus and is These vessels deliver blood to the capillaries supplying indi-
connected to the ureter, which drains the kidney. vidual nephrons (Figure 26–5b,c).

Urine production begins in microscopic, tubular structures
called nephrons (NEF-ronz) in the cortex of each kidney lobe.