807
CHAPTER TWENTY
Urinary System
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
detrusor muscle.
(3) As the urinary bladder F
lls, its internal
pressure increases, forcing the internal urethral
sphincter open.
(4) A second refl ex relaxes the external urethral
sphincter, unless its contraction is voluntarily
controlled.
(5) Nerve centers in the brainstem and cerebral
cortex aid control of urination.
20.5
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
blood.
1. With age, the kidneys appear grainy and scarred.
2. G±R drops signiF
cantly with age as glomeruli atrophy,
F
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
efF
cient at activating vitamin D.
5. The urinary bladder, ureters, and urethra lose
elasticity, with effects on the urge and timing of
urination.
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
calculate G±R.
20.4
ELIMINATION OF URINE (PAGE 798)
1. Ureters
a. The ureter is a tubular organ that extends from
each kidney to the urinary bladder.
b. Its wall has mucous, muscular, and F
brous layers.
c. Peristaltic waves in the ureter force urine to the
urinary bladder.
d. Obstruction in the ureter stimulates strong
peristaltic waves and a refl
ex that decreases urine
production.
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
urethral sphincter.
3. Urethra
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.
4. Micturition
a. Micturition is the process of expelling urine.
20.1 Introduction
1
Explain why the urinary system is necessary for survival.
(p. 775)
2
Identify the organs of the urinary system and list their
general functions. (p. 775)
20.2 Kidneys
3
Describe the external and internal structure of a kidney.
(p. 776)
4
List the functions of the kidneys. (p. 777)
5
List in correct order the vessels through which blood
passes as it travels from the renal artery to the renal vein.
(p. 779)
6
Distinguish between a renal corpuscle and a renal tubule.
(p. 781)
7
Name in correct order the structures through which F
uid
passes from the glomerulus to the collecting duct. (p. 781)
8
Describe the location and structure of the
juxtaglomerular apparatus. (p. 782)
CHAPTER ASSESSMENTS
9
Distinguish between cortical and juxtamedullary
nephrons. (p. 784)
20.3 Urine Formation
10
Distinguish among ±
ltration, tubular reabsorption, and
tubular secretion as they relate to urine formation. (p. 785)
11
Which one of the following is abundant in blood plasma,
but present only in small amounts in glomerular ±
ltrate?
(p. 788)
a. sodium ions
b. water
c. glucose
d. protein
e. potassium ions
12
De±
ne
f
ltration pressure.
(p. 788)
13
Explain how the diameters of the a²
erent and e²
erent
arterioles a²
ect the rate of glomerular ±
ltration. (p. 788)
14
Explain how changes in the osmotic pressure of blood
plasma a²
ect the glomerular ±
ltration rate. (p. 789)
amed
lar
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