Hole’s Human Anatomy
and Physiology
Twelfth Edition
Shier w Butler w Lewis
Chapter
20
Urinary System
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1
20.1: Introduction
• A major part of homeostasis is maintaining the composition,
pH, and volume of body fluids within normal limits (Define
homeostasis)
• The urinary system removes metabolic wastes and
substances in excess, including foreign substances like drugs
and their metabolites that may be toxic
• It consists of a pair of kidneys, a pair of ureters, a urinary
bladder and a urethra
2
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Kidney
Renal
vein
Hilum
Renal
artery
Inferior
vena cava
Abdominal
aorta
Ureters
Urinary
bladder
Urethra
© CNRI/SPL/Photo Researchers, Inc.
3
20.2: Kidneys
• The kidney is a reddish brown, bean-shaped organ with a
smooth surface
• In the adult it is about 12 centimeters long, 6 centimeters
wide, and 3 centimeters thick
• It is enclosed in a tough, fibrous capsule
4
Location of the Kidneys
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Kidney
Adipose tissue
Parietal
peritoneum
Spleen
Inferior vena cava
Aorta
Small intestine
Large intestine
Pancreas
Stomach
(a)
Adrenal gland
Twelfth rib
Liver
Kidney
Parietal peritoneum
Renal fascia
Renal fascia
Hip bone (cut)
Large intestine
5
(b)
Kidney Structure
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Renal capsule
Renal cortex
Renal medulla
Renal corpuscle
Nephrons
Renal
cortex
Minor calyx
Major calyx
Renal
medulla
Renal sinus
Renal column
Fat
in renal sinus
Collecting
duct
Papilla
Renal pelvis
Minor calyx
Renal
tubule
Renal papilla
(b)
(c)
Renal pyramid
Ureter
(a)
6
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Inferior vena cava
Abdominal aorta
Suprarenal artery
Suprarenal vein
Adrenal gland
Renal artery
Renal column
Renal capsule
Renal pelvis
Renal papilla
Renal vein
Renal medulla
Hilum
Renal pyramid
Renal cortex
Ureter
Minor calyx
7
Function of the Kidneys
• The main function of the kidneys is to regulate the volume,
composition, and pH of body fluids
• The kidneys remove metabolic wastes from the blood and
excrete them to the outside of the body, including nitrogenous
and sulfur-containing products of protein metabolism
• The kidneys also help control the rate of red blood cell
production, regulate blood pressure, and regulate calcium ion
absorption
8
Renal Blood Vessels
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Cortical radiate
artery and vein
Proximal
Cortex convoluted
tubule
Arcuate vein
and artery
Medulla Efferent
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Cortical radiate
artery and vein
Afferent arteriole
arteriole
Interlobar
vein and artery
Distal convoluted
tubule
Peritubular
capillary
Renal
artery
Renal
vein
Renal pelvis
Efferent
Afferent
arteriole
arteriole
Glomerulus
(a)
Ureter
Peritubular
capillary
(a)
Renal tubules
Glomerulus
(b)
Glomerular
capsule
(a) : Tissues and Organs: A Text-Atlas of Scanning Electron Microscopy, by R.G. Kessel and R.H. Kardon. © 1979 W.H. Freeman and Company
(b) : Courtesy of R.B. Wilson MD, Eppeley Institute for Research in Cancer, University of Nebraska Medical Center
9
(b)
b: © L.V. Bergman/The Bergman Collection
Nephrons
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Afferent
arteriole
Efferent
arteriole
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Slit pore
Pedicel
Primary process
of podocyte
Blood
flow
Blood
flow
Glomerular
capsule
Parietal layer
of glomerular
capsule
Slit pore
Glomerulus
Proximal
convoluted
tubule
Visceral layer of
glomerular capsule
Pedicel
Primary process
of podocyte
© David M. Phillips/Visuals Unlimited
10
Animation:
Fluid Exchange Across
the Walls of Capillaries
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Glomerular
capsule
Cortical radiate
artery
Cortical radiate
vein
Proximal
convoluted
tubule
Collecting ducts
Glomerulus
Afferent
arteriole
Efferent
arteriole
Distal
convoluted
tubule
Epithelial cell
Renal
cortex
Renal
tubules
Glomerular Glomerulus
capsule
Renal
corpuscle
To renal
vein
Descending
limb
Ascending
limb
Blood vessel
(a)
From renal
artery
Peritubular
capillary
Nephron
loop
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(b)
a: © Biophoto Associates/Photo Researchers, Inc., b: © Manfred Kage/Peter Arnold
Renal
medulla
Collecting duct
12
Juxtaglomerular Apparatus
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Afferent
Glomerular
arteriole
capsule
Glomerulus
Juxtaglomerular
apparatus
Distal
convoluted
tubule
Efferent
arteriole
Proximal
convoluted
tubule
Glomerulus
Podocyte
Afferent arteriole
Nephron loop
(a)
Juxtaglomerular
cells
Macula densa
Glomerular capsule
Juxtaglomerular
apparatus
Ascending limb
of nephron loop
Efferent arteriole
(b)
13
Cortical and Juxtamedullary Nephrons
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Cortical nephron
Renal
cortex
Juxtamedullary
nephron
Renal
medulla
Collecting
duct
14
Blood Supply of a Nephron
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Glomerular
capsule
Renal artery
Cortical radiate
artery and vein
Interlobar artery
Proximal
convoluted
tubule
Glomerulus
Efferent
arteriole
Arcuate artery
Afferent arteriole
Distal
convoluted
tubule
Interlobular artery
Afferent arteriole
Peritubular
capillaries
Glomerular capillaries
Efferent arteriole
Vasa recta
Peritubular capillaries
Interlobular vein
Arcuate vein
Collecting duct
Interlobar vein
15
Nephron loop
Renal vein
20.3: Urine Formation
• The main function of the nephrons and collecting ducts is to
control the composition of body fluids and remove wastes
from the blood, the product being urine
• Urine contains wastes, excess water, and electrolytes
• Urine is the final product of the processes of:
• Glomerular filtration
• Tubular reabsorption
• Tubular secretion
16
Urine Formation
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Arteriole
Venule
Net reabsorption
Blood
flow
Net filtration
Interstitial fluid
(a) In most systemic capillaries, filtration predominates at the arteriolar end
and osmotic reabsorption predominates at the venular end.
Peritubular
capillaries
Afferent
arteriole
Glomerular
capillaries
Efferent
arteriole
Venule
Blood
flow
Glomerular
filtration
Filtered
fluid
Tubular
reabsorption
Tubular
secretion
Tubular fluid
Urine
Renal tubule
(b) In the kidneys, the glomerular capillaries are specialized for filtration. The renal tubule is
specialized to control movements of substances back into the blood of the peritubular
capillaries (tubular reabsorption) or from the blood into the renal tubule (tubular secretion).
17
Glomerular Filtration
• Glomerular filtration
• Substances move from the blood to the glomerular capsule
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Glomerulus
Proximal
convoluted
tubule
Afferent
arteriole
Capillary
endothelium
Podocyte
Glomerular
filtrate
Glomerular
capsule
Fenestrae
Blood
flow
Podocyte
Efferent
arteriole
18
(a)
(b)
Plasma, Glomerular Filtrate, and Urine Components
19
Filtrate Pressure
• The main force that moves substances by filtration through
the glomerular capillary wall is hydrostatic pressure of the
blood inside (Compare to osmotic pressure)
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Hydrostatic
pressure of
blood
Glomerular hydrostatic
pressure
Capsular
hydrostatic
pressure
Plasma colloid
osmotic pressure
Net Outward Pressure
Outward force, glomerular hydrostatic pressure =
Inward force of plasma colloid osmotic pressure =
Inward force of capsular hydrostatic pressure
=
Net filtration pressure
=
+60 mm
–32 mm
–18 mm
+10 mm
20
Filtrate Rate
• Glomerular filtration rate (GFR) is directly proportional to
the net filtration pressure
Net filtration pressure = force favoring filtration
(glomerular capillary
hydrostatic pressure)
–
forces opposing filtration
(capsular hydrostatic pressure
and glomerular capillary osmotic pressure)
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170
160
150
140
130
120
110
Liters
• Normally the glomerular net
filtration pressure is positive
causing filtration
• The forces responsible include
hydrostatic pressure and osmotic
pressure of plasma and the
hydrostatic pressure of the fluid
in the glomerular capsule
180 Liters
180
100
90
80
70
60
50
40
30
20
10
0.6 – 2.5 Liters
0
Urine
Glomerular filtrate
(a)
(b)
21
Control of Filtrate Rate
• GFR remains relatively constant through a process called
autoregulation
• Certain conditions override autoregulation, including when
GFR increases
• Primarily three mechanisms are responsible for keeping the
GFR constant:
• Autoregulation
• Increased sympathetic impulses that decrease GFR by
causing afferent arterioles to constrict
• The hormone-like renin-angiotensin system
• There also is the hormone atrial natriuretic peptide
(ANP) which affects sodium, causing an increase in GFR
22
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Lung capillaries
Kidney
Liver
Renin
Angiotensinogen
Angiotensinconverting
enzyme
Angiotensin I
Angiotensin II
Bloodstream
Release into
bloodstream
Stimulation
• Vasoconstriction
• Increased
aldosterone
secretion
• Increased
ADH secretion
• Increased thirst
23
Effects of Aldosterone
Aldosterone is a hormone secreted by the adrenal cortex.
It helps regulate the concentration of extracellular
electrolytes by conserving sodium and excreting potassium
ions. Its secretion is regulated by concentration of
electrolytes in body fluids and by the renin-angiotensin
mechanism.
24
Effects of ANP
ATRIAL NATRIURETIC PEPTIDE (ANP)
A hormone produced by the heart, atrial
natriuretic peptide (ANP), increases sodium
excretion and decreases blood pressure and blood
volume.
ANP is released into the bloodstream in response
to stretching of the atrial muscle cells by increased
blood volume.
ANP has the following physiological effects:
• Increases glomerular filtration rate by dilating
afferent arterioles
• Inhibits the collecting ducts from reabsorbing
sodium, both directly and indirectly (by
inhibiting aldosterone secretion)
• Inhibits release of renin
The renin-angiotensin system and ANP function
antagonistically in the maintenance of
fluid/electrolyte balance and blood pressure.
25
Tubular Reabsorption
• Tubular reabsorption
• Substances move from the renal tubules into the
interstitial fluid where they then diffuse into the
peritubular capillaries
• The proximal convoluted tubule reabsorbs (70%):
• Glucose, water, urea, proteins, and creatine
• Amino, lactic, citric, and uric acids
• Phosphate, sulfate, calcium, potassium, and sodium
ions
26
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Blood
flow
Blood
flow
Afferent
arteriole
Glomerular
capsule
Efferent
arteriole
Glomerulus
Glomerular
filtrate
Afferent
arteriole
Glomerular
capsule
Efferent
arteriole
Glomerulus
Glomerular
filtrate
Peritubular
capillary
Tubular
reabsorption
Peritubular
capillary
Tubular
secretion
Renal
tubule
Renal
tubule
Blood flow
(a)
Blood flow
(b)
27
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Blood
flow
Glomerulus
Glomerular
capsule
Blood
flow
Glomerular
filtrate
Proximal
convoluted
tubule
Na+
Na+
+
Cl–
–
–
–
–
PO4–3
HCO3–
N+
Cl–
1
Sodium ions
are reabsorbed by
active transport
2
Negatively charged ions
are attracted to positively
charged ions
3
As concentration of ions
(solute) increases in plasma,
osmotic pressure increases
4
Water moves from proximal
tubule to capillary by
osmosis
+
+
–+
–+
+–
–+
Na+
H2O
H2O
Isotonic
tubular fluid
–+
–+
++
– +
+–
– –
++
– –
Peritubular capillary
Blood
flow
28
29
Tubular Secretion
• Tubular secretion
• Substances move from the plasma of the peritubular
capillaries into the fluid of the renal tubules
• Active transport mechanisms function here
• Secretion of substances such as drugs and ions
30
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Peritubular capillary
Blood flow
K+ or H+
Tubular reabsorption
Na+
Na+
Na+
Na+
Tubular secretion
Na+
K+
Na+
Na+
Na+
H+
K+
K+
Na+
Na+
Tubular fluid
H+
Distal convoluted tubule
Na+
K+
Na+
Na+
Ascending limb
of nephron loop
Collecting duct
31
Regulation of Urine
Concentration and Volume
• Hormones such as aldosterone and ANP affect the solute concentration
of urine, particularly sodium (How does this relate to blood pressure?)
• The ability of the kidneys to maintain the internal environment rests in a
large part on their ability to concentrate urine by reabsorbing large
volumes of water
• The distal convoluted tubule and the collecting duct are impermeable to
water, so water may be excreted as dilute urine
• If ADH is present, these segments become permeable, and water is
reabsorbed by osmosis into the extremely hypertonic medullary interstitial
fluid (What is ADH? What does hyper-, hypo- and isotonic mean?)
• A countercurrent mechanism in the nephron loops (the descending and
the ascending limbs) ensures that the medullary interstitial fluid becomes
hypertonic
• This mechanism is known as the countercurrent multiplier
• The vasa recta also contributes as a countercurrent mechanism
32
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Distal convoluted
tubule
Medullary
interstitial fluid
H2O
H2O
H2O
H2O
H2O
Hypertonic
interstitial
fluid
Collecting duct
Hypertonic
interstitial
fluid
H2O
Dilute urine
(a)
low ADH levels
Medullary
interstitial fluid
H2O
H2O
Collecting duct
Concentrated urine
(b)
high ADH levels
33
34
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1
H2O
Na+
Cl–
Salty
Increasing
NaCl
concentration
2
Cl–
Na+
Isotonic fluid
H2O
H2O
Descending
limb
(permeable
to water)
(a)
H2O
Cl–
Na+
Cl–
Na+
H2O
Hypotonic fluid
More
salty
Thick ascending
limb (impermeable
to water)
3
Medullary
interstitial
fluid
Hypertonic
fluid
Na+
Cl–
H2O
Na+
Cl–
Even
more
salty
(b)
35
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Blood
flow
Blood
flow
Increasing
NaCl
concentration
NaCl
NaCl
Medullary
interstitial
fluid
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
Vasa
recta
36
37
Urea and Uric Acid Excretion
• Urea:
• A by-product of amino acid catabolism (Where is it
produced?)
• The plasma concentration reflects the amount or protein
in diet
• It enters the renal tubules through glomerular filtration
• It contributes to the reabsorption of water from the
collecting duct (How?)
• About 80% is recycled
• Uric acid:
• Is a product of nucleic acid metabolism
• It enters the renal tubules through glomerular filtration
• Most reabsorption occurs by active transport
38
• About 10% is secreted and excreted
Urine Composition
• Urine composition reflects the volumes of water and solutes
that the kidneys must eliminate from the body or retain in the
internal environment to maintain homeostasis
• It varies from time to time due to dietary intake and physical
activity, but is:
• About 95% water
• Usually contains urea, uric acid, and creatinine
• May contain trace amounts of amino acids and varying
amounts of electrolytes
• Volume varies with fluid intake and environmental
factors
39
Renal Clearance
• This is the rate at which a chemical is removed from the
plasma
• It indicates kidney efficiency
• Tests of renal clearance:
• Inulin clearance test
• Creatinine clearance test
• Para-aminohippuric acid (PAH) test
• These tests of renal clearance are used to calculate the GFR
(glomerular filtration rate)
40
Animation:
Renal Clearance
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41
20.4: Elimination of Urine
• After forming along the nephrons, urine:
• Passes the collecting ducts to:
• Openings of the renal papillae:
• Enters the minor and major calyces:
• Passes through the renal pelvis:
• Enters into the ureters:
• Enters into the urinary bladder:
•The urethra carries the urine out of the body
42
Ureters
• The ureters:
• Each is about 25 centimeters long
• Extends downward posterior to the parietal peritoneum
(What is this called?)
• Runs parallel to vertebral column
• Join the urinary bladder in the pelvic cavity
• The wall of ureter has three layers:
• The inner mucous coat
• The middle muscular coat
• The outer fibrous coat
43
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Mucous coat
Lumen
Muscular coat
Fibrous coat
Adipose tissue
© Per H. Kjeldsen
44
Urinary Bladder
• The urinary bladder is a hollow, distensible, muscular organ
located within the pelvic cavity, posterior to the symphysis
pubis and inferior to the parietal peritoneum
• It contacts the anterior walls of the uterus and vagina in the
female, and lies posteriorly against the rectum in the male
• The openings for the ureters is the area of trigone
• It has four layers: inner mucous coat, a submucous coat, a
muscular coat, and an outer serous coat
• Smooth muscle fibers comprise the detrusor muscle which
is the muscle of the bladder wall
45
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Ureter
Abdominal wall
Parietal peritoneum
Urinary bladder
Symphysis pubis
Prostate gland
Urethra
Rectum
Rectum
(a)
(b)
46
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Serous coat
Ureter
Urinary bladder
Ureter
Detrusor
muscle
Submucous
coat
Ductus (vas)
deferens
Mucous coat
Openings of
the ureters
Seminal
vesicle
Trigone
Neck
Prostate gland
Internal urethral sphincter
Prostate gland
Urethra
Region of external
urethral sphincter
(a)
Urethra
(b)
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Muscular coat
Mucous coat
Submucous
coat
Lumen
© John D. Cunningham/Visuals Unlimited
48
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Ureter
Urinary
bladder
Trigone
Urethra
External
urethral orifice
(a)
Ureter
Urinary
bladder
Trigone
Prostatic
urethra
Membranous
urethra
Penile
urethra
External
urethral orifice
(b)
Prostate
gland
Bulbourethral
gland
Penis
49
Urethra
• The urethra is a tube that conveys urine from the urinary
bladder to the outside of the body
• Its wall is lined with a mucous membrane and it has a thick
layer of longitudinal smooth muscle fibers
• In a female:
• It is about 4 centimeters long
• It runs obliquely
• In a male:
• It is about 17.5 centimeters long
• It has a dual function for both urination and reproduction
• It has three sections:
• Prostatic urethra
• Membranous urethra
• Penile urethra
50
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Urethral glands
Muscle layer
Lumen of urethra
Mucous membrane
© Ed Reschke
51
Micturition
• Urine leaves the urinary bladder by micturition or urination
reflex
52
Animation:
Micturition Reflex
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53
Micturition
54
Animation:
Renal Process
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55
Overview of Urinary System
Anatomy
http://faculty.ucc.edu/biologypotter/Urinary_System/sld001.htm
56
20.5: Lifespan Changes
• The urinary system is sufficiently redundant, in both structure and
function, to mask age-related changes
• The kidneys become slower to remove nitrogenous wastes and toxins
and to compensate for changes that maintain homeostasis
• Changes include:
• The kidneys appear scarred and grainy
• Kidney cells die
• By age 80 the kidneys have lost a third of their mass
• Kidney shrinkage is due to loss of glomeruli
• Proteinuria may develop (What is this?)
• The renal tubules thicken
• It is harder for the kidneys to clear certain substances
• The bladder, ureters, and urethra lose elasticity
• The bladder holds less urine
57
Important Points in Chapter 20:
Outcomes to be Assessed
20.1: Introduction
 Name the organs of the urinary system and list their general functions.
20.2: Kidneys
 Describe the location of the kidneys.
 Describe the structure of a kidney.
 List the functions of the kidneys.
 Trace the pathway of blood flow through the major vessels within a
kidney.
 Describe a nephron and explain the functions of its major parts.
20.3: Urine Formation
58
 Explain how glomerular filtrate is produced and describe its composition.
Important Points in Chapter 20:
Outcomes to be Assessed
 Explain how various factors affect the rate of glomerular filtration and
identify ways that this rate is regulated.
 Define tubular reabsorption and explain its role in urine formation.
 Identify the changes in the osmotic concentration of the glomerular
filtrate as it passes through the renal tubule.
 Identify the characteristics of the countercurrent mechanism and
explain its role in concentrating the urine.
 Define tubular secretion and explain its role in urine formation.
20.4: Elimination of Urine
 Describe the structures of the ureters, urinary bladder, and urethra.
 Define micturition and explain how it occurs and how it is controlled.59
Important Points in Chapter 20:
Outcomes to be Assessed
20.5: Lifespan Changes
 Describe how the components of the urinary system change with age.
60