Introduction to the Urinary System (pp. 656–657)

1. The urinary system consists of two kidneys, two ureters, the urinary bladder, and the urethra.

2. The urinary system maintains the composition and properties of body fluid, which establishes the extracellular environment. The end product of the urinary system is urine, which is voided from the body during micturition.

Kidneys (pp. 657-664)

1. The kidneys are retroperitoneal, embedded in a renal adipose capsule.

2. Each kidney is contained by a renal capsule and divided into an outer renal cortex and an inner renal medulla.
   1. The renal medulla is composed of renal pyramids separated by renal columns.

   2. The renal papillae empty urine into the minor calyces and then into the major calyces, which drain into the renal pelvis. From there, urine flows through the ureter.

3. Each kidney contains more than a million microscopic functional units called nephrons.
   1. Filtration occurs in the glomerulus, which receives blood from afferent glomerular arterioles.

   2. Glomerular blood is drained by efferent glomerular arterioles that deliver blood to peritubular capillaries surrounding the nephron tubules.

   3. The glomerular capsule and distal convoluted tubules are located in the renal cortex.

   4. The nephron loop is located in the renal medulla.

   5. Filtrate from the distal convoluted tubule is drained into papillary ducts that extend through the renal medulla to empty urine into the calyces.

Ureters, Urinary Bladder, and Urethra (pp. 664-668)

1. Urine is channeled from the kidneys to the urinary bladder by the ureters and expelled from the urinary bladder through the urethra. The detrusor muscle of the urinary bladder and the sphincter muscles of the urethra are used in the control of micturition.
   1. Each ureter contains three layers: the mucosa, muscularis, and adventitia.

   2. The lumen of the urinary bladder is lined by transitional epithelium, which is folded into rugae. These structures enhance the ability of the urinary bladder to distend.

   3. The urethra has an internal sphincter of smooth muscle and an external sphincter of skeletal muscle.

   4. The male urethra conducts urine during urination and seminal fluid during ejaculation. The female urethra is much shorter than that of a male and conducts only urine.

   5. The male urethra is composed of prostatic, membranous, and spongy portions.

2. Micturition is controlled by reflex centers in the second, third, and fourth sacral segments of the spinal cord.