b. In micturition, the detrusor muscle contracts and
the external urethral sphincter relaxes.
c. Micturition reﬂ ex
(1) Distension stimulates stretch receptors in the
urinary bladder wall.
(2) The micturition reﬂ ex center in the
sacral portion of the spinal cord sends
parasympathetic motor impulses to the
(3) As the urinary bladder F
lls, its internal
pressure increases, forcing the internal urethral
(4) A second reﬂ ex relaxes the external urethral
sphincter, unless its contraction is voluntarily
(5) Nerve centers in the brainstem and cerebral
cortex aid control of urination.
LIFE-SPAN CHANGES (PAGE 803)
The kidneys, ureters, and urethra change with age, but
nephrons are so numerous that a healthy person is usually
unaware of kidney shrinkage and slowed cleansing of the
1. With age, the kidneys appear grainy and scarred.
2. G±R drops signiF
cantly with age as glomeruli atrophy,
ll with connective tissue, or unwind.
3. Renal tubules accumulate fat on their outsides and
become asymmetric. Reabsorption and secretion may
slow or become impaired. Drugs remain longer in the
circulation as a person ages.
4. Changes in the cardiovascular system slow the rate of
processing through the urinary system. The kidneys
slow in their response to changes, and are less
cient at activating vitamin D.
5. The urinary bladder, ureters, and urethra lose
elasticity, with effects on the urge and timing of
10. Renal clearance
a. Renal clearance is the rate at which a chemical is
removed from the plasma.
b. The inulin clearance test, creatinine clearance test,
and para-aminohippuric acid test can be used to
ELIMINATION OF URINE (PAGE 798)
a. The ureter is a tubular organ that extends from
each kidney to the urinary bladder.
b. Its wall has mucous, muscular, and F
c. Peristaltic waves in the ureter force urine to the
d. Obstruction in the ureter stimulates strong
peristaltic waves and a reﬂ
ex that decreases urine
2. Urinary bladder
a. The urinary bladder is a distensible organ that
stores urine and forces it into the urethra.
b. The ureters and urethra open at the three angles of
the trigone in the ﬂ
oor of the urinary bladder.
c. Muscle F bers in the wall form the detrusor muscle.
d. A portion of the detrusor muscle forms an internal
a. The urethra conveys urine from the urinary
bladder to the outside.
b. In females, it empties between the labia minora.
c. In males, it conveys products of reproductive
organs as well as urine.
(1) Three portions of the male urethra are
prostatic, membranous, and penile.
(2) The urethra empties at the tip of the penis.
a. Micturition is the process of expelling urine.
Explain why the urinary system is necessary for survival.
Identify the organs of the urinary system and list their
general functions. (p. 775)
Describe the external and internal structure of a kidney.
List the functions of the kidneys. (p. 777)
List in correct order the vessels through which blood
passes as it travels from the renal artery to the renal vein.
Distinguish between a renal corpuscle and a renal tubule.
Name in correct order the structures through which F
passes from the glomerulus to the collecting duct. (p. 781)
Describe the location and structure of the
juxtaglomerular apparatus. (p. 782)
Distinguish between cortical and juxtamedullary
nephrons. (p. 784)
20.3 Urine Formation
Distinguish among ±
ltration, tubular reabsorption, and
tubular secretion as they relate to urine formation. (p. 785)
Which one of the following is abundant in blood plasma,
but present only in small amounts in glomerular ±
a. sodium ions
e. potassium ions
Explain how the diameters of the a²
erent and e²
ect the rate of glomerular ±
ltration. (p. 788)
Explain how changes in the osmotic pressure of blood
ect the glomerular ±
ltration rate. (p. 789)