Essentials of Anatomy and Physiology

4. Detrusor muscle—the smooth muscle layer, a
   spherical muscle; contracts to expel urine (reflex).


5. Internal urethral sphincter—involuntary; formed
   by detrusor muscle fibers around the opening of
   the urethra.

Urethra—takes urine from the bladder to
the exterior (see Fig. 18–7)

1. In women—1 to 1.5 inches long; anterior to vagina.


2. In men—7 to 8 inches long; passes through the
   prostate gland and penis.


3. Has the external urethral sphincter: skeletal muscle
   of pelvic floor (voluntary).

The Urination Reflex—also called micturition

or voiding

1. Stimulus: stretching of the detrusor muscle by
   accumulating urine.


2. Sensory impulses to spinal cord, motor impulses
   (parasympathetic) return to detrusor muscle, which
   contracts; internal urethral sphincter relaxes.


3. The external urethral sphincter provides voluntary
   control.

Characteristics of Urine (see Table 18–3)

Abnormal Constituents of Urine (see

Table 18–4)

The Urinary System 437

REVIEW QUESTIONS

1. Describe the location of the kidneys, ureters, uri-
   nary bladder, and urethra. (pp. 421, 431)


2. Name the three areas of the kidney, and state what
   each consists of. (p. 421)


3. Name the two major parts of a nephron. State the
   general function of nephrons. (p. 421)


4. Name the parts of a renal corpuscle. What process
   takes place here? Name the parts of a renal tubule.
   What processes take place here? (pp. 421, 424)


5. State the mechanism of tubular reabsorption of
   each of the following: (pp. 425, 427)
   a. Water
   b. Glucose
   c. Small proteins
   d. Positive ions
   e. Negative ions
   f. Amino acids
   g. Vitamins
   Also explain what is meant by a threshold level of
   reabsorption.


6. Explain the importance of tubular secretion. (p.
   427)


7. Describe the pathway of blood flow through the
   kidney from the abdominal aorta to the inferior
   vena cava. (p. 424)


8. Name the two sets of capillaries in the kidney, and
   state the processes that take place in each. (pp. 424,
   425)
   9. Name the hormone that has each of these effects
   on the kidneys: (pp. 428–429)
   a. Promotes reabsorption of Naions
   b. Promotes direct reabsorption of water
   c. Promotes reabsorption of Ca^2 ions
   d. Promotes excretion of Kions
   e. Decreases reabsorption of Naions


9. In what circumstances will the kidneys excrete H
   ions? What ions will be returned to the blood?
   How will this affect the pH of blood? (p. 428)


10. In what circumstances do the kidneys secrete
    renin, and what is its purpose? (p. 429)


11. In what circumstances do the kidneys secrete ery-
    thropoietin, and what is its purpose? (p. 430)


12. Describe the function of the ureters and that of
    the urethra. (p. 431)


13. With respect to the urinary bladder, describe
    the function of rugae and the detrusor muscle.
    (p. 431)


14. Describe the urination reflex in terms of stimulus,
    part of the CNS involved, effector muscle, inter-
    nal urethral sphincter, and voluntary control.
    (pp. 431)


15. Describe the characteristics of normal urine in
    terms of appearance, amount, pH, specific gravity,
    and composition. (pp. 432–433)


16. State the source of each of the nitrogenous waste
    products: creatinine, uric acid, and urea. (p. 433)