The urinary system consists of two kidneys, two ureters, a urinary bladder, and a urethra .
Urinary
System
After studying this chapter, the reader should be able to:
1. Describe the location and structural features of the
kidneys.
2. Describe the structure of the nephron.
3. Identify and describe the major factors responsible for the
production of urine.
4. Describe how antidiuretic hormone and aldosterone influence
the volume and concentration of urine.
5. List and describe the factors that influence filtration
pressure.
6. Describe the structure and functions of the ureters,
urinary bladder, and urethra.
7. Differentiate between the contents of different substances
in the plasma and urine.
8. Describe the normal characteristics and composition of
urine.
9. List the most important waste products that are excreted
from the kidneys.
10. Describe
the micturition reflex center
The urinary system consists of two kidneys, two ureters, a urinary bladder, and a urethra (FIGURE
22-1). The urinary system has three major functions: (1) excretion, which is the removal of
organic wastes from body fluids; (2) elimination,
which is the discharge of these wastes into the envi-ronment; and (3) homeostatic regulation of the volume and
solute concentration of blood plasma. The urinary system filters approximately
200 liters of fluid from the bloodstream every day.
The kidneys help to maintain homeostasis by reg-ulating the
composition, pH or acid-base balance,
and volume of the extracellular fluid. This is accomplished by their removal of
metabolic wastes and toxins from the blood and diluting them with water and
electrolytes. This process forms urine, which the kidneys excrete. The other
important functions of the kidneys are:
■■ Secretion of the hormone
erythropoietin, which helps to control red blood cell production
■■ Helping with the activation of
vitamin D
■■ Helping to maintain blood volume
and pressure via secretion of the enzyme renin
■■ Carrying out gluconeogenesis while fasting for long periods
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