Urinary System

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

Overview

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