Gross Structure of the Urinary System

The paired kidneys lie on either side of the vertebral column below the diaphragm and liver. Each adult kidney weighs about 160 g and is about 11 cm (4 in.) long and 5 to 7 cm (2 to 3 in.) wide—about the size of a fist. Urine produced in the kidneys is drained into a cavity known as the renal pelvis (= basin), and then it is channeled from each kidney via long ducts—the ureters—to the urinary bladder (fig. 17.1).

Renal artery Renal vein

Renal artery Renal vein

Inferior vena cava

Kidney

Renal vein

Renal artery

Abdominal aorta

Ureter

Urinary bladder

Urethra

Inferior vena cava

Kidney

Renal vein

Renal artery

Abdominal aorta

Ureter

Urinary bladder

Urethra

■ Figure 17.1 The organs of the urinary system. The urinary system of a female is shown; that of a male is the same, except that the urethra runs through the penis.

A coronal section of the kidney shows two distinct regions (fig. 17.2). The outer cortex is reddish brown and granular in appearance because of its many capillaries. The deeper region, or medulla, is striped in appearance due to the presence of microscopic tubules and blood vessels. The medulla is composed of eight to fifteen conical renal pyramids separated by renal columns.

Kidney stones (renal calculi) are composed of crystals and proteins that grow until they break loose and pass into the urine collection system. Small stones that are anchored in place are not usually noticed, but large stones in the calyces or pelvis may obstruct the flow of urine. When a stone breaks loose and passes into a ureter, it produces a steadily increasing sensation of pain. The pain often becomes so intense that the patient requires narcotic drugs. Most kidney stones contain crystals of calcium oxalate, but stones may also be composed of crystals of calcium phosphate, uric acid, or cystine. These substances are normally present in urine in a supersaturated state, from which they can crystalize for a variety of reasons. The stones may be removed surgically or broken up by a noninvasive procedure called shock-wave lithotripsy.

Clinical Investigation Clues

Remember that Emily had pain in her lower back, between the twelfth rib and the lumbar vertebrae. From which organ might the pain originate? Is it likely that Emily has a kidney stone?

Physiology of the Kidneys

Renal cortex

Renal medulla

Renal pyramid

Renal cortex

Renal medulla

Renal pyramid

Renal column

Renal pelvis Renal papilla

Distal convoluted tubule

Collecting duct

Loop of Henle

Renal column

Renal pelvis Renal papilla

Distal convoluted tubule

Collecting duct

Loop of Henle

■ Figure 17.2 The structure of a kidney. The figure depicts (a) a coronal section of a kidney and (b) a magnified view of the contents of a renal pyramid. (c) A single nephron tubule, microscopic in actual size, is shown isolated.

The cavity of the kidney is divided into several portions. Each pyramid projects into a small depression called a minor calyx (the plural form is calyces). Several minor calyces unite to form a major calyx. The major calyces then join to form the funnel-shaped renal pelvis. The renal pelvis collects urine from the calyces and transports it to the ureters and urinary bladder (fig. 17.3).

The urinary bladder is a storage sac for urine, and its shape is determined by the amount of urine it contains. An empty urinary bladder is pyramidal; as it fills, it becomes ovoid and bulges upward into the abdominal cavity. The urinary bladder is drained inferiorly by the tubular urethra. In females, the urethra is 4 cm (1.5 in.) long and opens into the space between the labia minora (see chapter 20). In males, the urethra is about 20 cm (8 in.) long and opens at the tip of the penis, from which it can discharge either urine or semen.

Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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