PowerLecture:
Chapter 12
The Urinary System
Learning Objectives





Explain how the chemical composition of
extracellular fluid is maintained by
mammals.
Describe the components of the human
urinary system.
Understand the processes of urine
formation and excretion.
Explain the controls that maintain fluid
balance and blood pressure.
Explain why kidney disorders can be so
damaging to human health.
Impacts/Issues
Truth in a Test Tube
Truth in a Test Tube
Urine can be used to determine much about
the general health and habits of human
beings.



Changes to the composition
of urine can indicate
metabolic problems,
infection, or even pregnancy.
Urine can also show the
presence of illegal
performance enhancing
drugs in athletes.
Truth in a Test Tube

Urine is a useful indicator of
health because each day
the kidneys filter all of the
blood in the body a total of
30 times, eliminating excess
water and harmful solutes.
Useful References for Impacts/Issues
The latest references for topics covered in this section can be found at
the book companion website. Log in to the book’s e-resources page at
www.thomsonedu.com to access InfoTrac articles.
 Science
Daily: Early Prostate Cancer
Detected in Molecular-Based Urine Test
 InfoTrac: NCAA Steps Up Steroid Tests:
Organization Is Making a Far-Reaching Effort
to Ensure That College Athletes Stay Clean.
Kansas City Star, June 22, 2006.
How Would You Vote?
To conduct an instant in-class survey using a classroom response
system, access “JoinIn Clicker Content” from the PowerLecture main
menu.
 Do
you think employers should be allowed to
require a person to undergo urine testing
before being hired?


a. Yes, drug users are less safe and productive
employees. Employers have a right to screen
them out.
b. No, unless the job involves public safety, it is a
violation of an employee's privacy.
Useful References for
How Would You Vote?
The latest references for topics covered in this section can be found at
the book companion website. Log in to the book’s e-resources page at
www.thomsonedu.com to access InfoTrac articles.
 InfoTrac:
Reasons to Consider: Drug Testing.
Industrial Safety & Hygiene News, April 2002.
 InfoTrac: Urine – Or You're Out: Drug Testing
Is Invasive, Insulting, and Generally
Irrelevant to Job Performance. Reason, Nov.
2002.
 InfoTrac: Street Smarts: Just Say Yes. Inc.,
Nov. 1, 2004.
Section 1
The Challenge: Shifts in
Extracellular Fluid
Shifts in Extracellular Fluid
Extracellular fluid (ECF) is comprised of
tissue fluid, blood plasma, and other fluids
such as lymph that occurs outside of cells;
intracellular fluid is the fluid inside cells.




There is a constant exchange of gases and
other materials between intracellular and
extracellular fluid.
The volume and composition of the ECF must
remain stable for these exchanges to occur.
The urinary system is responsible for
maintaining relatively stable conditions in the
ECF.
Shifts in Extracellular Fluid
The body gains water from food and
metabolic processes.



Absorption of water from liquids and solid foods
occurs in the gastrointestinal tract.
Metabolism of nutrients yields water as a byproduct.
The body loses water in urine, sweat, feces,
and by evaporation.


Water leaves the body by
excretion in urine, evaporation
from the lungs and skin,
sweating, and in feces.
Shifts in Extracellular Fluid


The body exerts the most control over urinary
excretion, the production of urine.
The least amount of water is lost in feces.
Shifts in Extracellular Fluid
Solutes enter extracellular fluid from food,
metabolism, and other ways.




Solutes enter the body when nutrients and
mineral ions are absorbed from the GI tract.
Living cells secrete substances into tissue fluid
and blood.
The respiratory system brings oxygen into the
blood; respiring cells add carbon dioxide.
food, water intake
oxygen intake
DIGESTIVE
SYSTEM
nutrients,
water,
salts
RESPIRATORY
SYSTEM
oxygen
carbon
dioxide
CARDIOVASCULAR
SYSTEM
elimination
of food
residues
elimination
of carbon
dioxide
URINARY
SYSTEM
water,
solutes
rapid transport
to and from all
living cells
elimination of
excess water,
salts, wastes
Fig. 12.1, p. 213
Shifts in Extracellular Fluid
Solutes leave the ECF by urinary excretion,
in sweat, and during breathing.


Respiratory exhalation rids the body of carbon
dioxide; all other major wastes of metabolism
leave in urine.
•
•
•
Uric acid is formed in reactions that degrade nucleic
acids; too much uric acid in the ECF crystallizes in
joints, causing gout.
Ammonia is formed when amino groups are removed
from amino acids; it is turned into urea in the liver
and either reabsorbed or excreted.
Other products of protein degradation are also
excreted.
Shifts in Extracellular Fluid

The kidneys filter a variety of substances from
the blood, including nitrogen, sodium,
potassium, and calcium.
•
•
Sodium, potassium, and calcium are called
electrolytes because a solution in which they are
dissolved will carry an electric current.
Only 1% of the water that enters the kidneys is
excreted in urine; most is returned to the blood.
Useful References for Section 1
The latest references for topics covered in this section can be found at
the book companion website. Log in to the book’s e-resources page at
www.thomsonedu.com to access InfoTrac articles.
 Medicinenet.com:
Electrolytes
 InfoTrac: Gouty Arthritis: A Primer on LateOnset Gout. Geriatrics, July 2005.
Section 2
The Urinary System—
Built for Filtering and
Waste Disposal
The Urinary System – Built for Filtering
and Waste Disposal
Each kidney is a bean-shaped organ about
the size of a rolled up pair of socks.


A kidney has several internal lobes; an outer
cortex wraps around the central medulla.
•
•
The whole kidney is wrapped in a coat of connective
tissue called the renal capsule.
The central cavity of the kidney is the renal pelvis.
kidney cortex
kidney medulla
renal artery
renal vein
renal pelvis
renal capsule
ureter
Fig. 12.2c, p. 214
The Urinary System – Built for Filtering
and Waste Disposal

Kidneys have several functions:
•
•
•
•

They produce erythropoietin, which stimulates
production of red blood cells.
They aid in calcium absorption from food.
Kidneys make renin, an enzyme that helps regulate
blood pressure.
Their main function is to remove metabolic wastes
and maintain fluid balance.
The urinary system also consists of tubelike
ureters that carry urine to the urinary bladder
for storage until urination; urine leaves the
bladder through the urethra.
heart
POSTERIOR
diaphragm
adrenal gland
kidney
abdominal
aorta
ureter
inferior vena
cava
ANTERIOR
urinary
bladder
urethra
Fig. 12.2ab, p. 214
POSTERIOR
right
kidney
peritoneum
vertebral left
column kidney
abdominal cavity
ANTERIOR
Fig. 12.2b, p. 214
The Urinary System – Built for Filtering
and Waste Disposal
Nephrons are the kidney filters.


Each lobe of the kidney contains blood vessels
and over a million thin tubes called nephrons,
which filter water and solutes from the blood.
•
•
The wall of the nephron balloons around a cluster of
blood capillaries called the glomerulus; the balloon
is called the Bowman’s capsule; the rest of the
nephron is a winding tubule.
Filtrate from the Bowman’s capsule enters the
proximal tubule, passes through the loop of Henle
and into the distal tubule, and finally empties into a
collecting duct.
Bowman’s
capsule
(red)
proximal
tubule
(orange)
distal tubule
(brown)

KIDNEY
CORTEX
KIDNEY
MEDULLA
loop of Henle
(yellow)
The Urinary
System – Built
for Filtering
and Waste
Disposal
collecting
duct
(tan)
Some parts of
the nephron
allow
absorption of
water and
solutes, other
parts do not.
Figure 12.3a
The Urinary System – Built for Filtering
and Waste Disposal
Special vessels transport blood to, in, and
away from nephrons.




An afferent arteriole delivers blood to each
nephron where it enters the glomerulus for
filtration; the glomerular capillaries are much
more permeable than other capillaries.
Glomerular capillaries merge to form an
efferent arteriole.
The efferent arteriole splits to form the
peritubular capillaries, which eventually carry
filtered blood into venules and out of the
kidneys.
efferent
arteriole
afferent
arteriole
glomerular capillaries
inside Bowman’s
capsule
peritubular
capillaries
threading
around tubular
nephron regions
Fig. 12.3b, p. 215
Useful References for Section 2
The latest references for topics covered in this section can be found at
the book companion website. Log in to the book’s e-resources page at
www.thomsonedu.com to access InfoTrac articles.
 InfoTrac:
Renal Anatomy and Overview of
Nephron Function. Nephrology Nursing
Journal, April 2003.
Section 3
How Urine Forms:
Filtration, Reabsorption,
and Secretion
How Urine Forms: Filtration,
Reabsorption, and Secretion
Filtration removes a large amount of fluid
and solutes from the blood.



In filtration, blood pressure forces filtrate out of
the glomerular capillaries into the Bowman’s
capsule, then into the proximal tubule.
Blood cells, proteins, and other large solutes
cannot pass into the capsule; water, glucose,
sodium, and urea, however, are forced out of
the blood.
How Urine Forms: Filtration,
Reabsorption, and Secretion
Next, reabsorption returns useful
substances to the blood.


Reabsorption takes place across the walls of
the proximal tubules.
•
•
•
Water, glucose, and salt diffuse through the tubule
wall; active transport then moves glucose and
sodium ions into the tissue fluid.
Negatively charged ions follow the sodium into the
tissues; water also follows.
Solutes are actively transported from the tissues to
the peritubular capillaries, water follows, and
reabsorption is complete.
How Urine Forms: Filtration,
Reabsorption, and Secretion

Any solutes and water remaining in the tubules
become part of urine.
How Urine Forms: Filtration,
Reabsorption, and Secretion
Secretion rids the body of excess hydrogen
ions and some other substances.



During secretion, urea, excess hydrogen ions,
and excess potassium ions are returned to the
nephrons to add to forming urine.
This process maintains the body’s acid-base
balance and also rids the body of drugs, uric
acid, hemoglobin breakdown products, and
other wastes.
How Urine Forms: Filtration,
Reabsorption, and Secretion
Urination is a controllable reflex.



The internal urethral sphincter (involuntary
control) regulates urine flow from the bladder
into the urethra during urination.
The external urethral sphincter (voluntary
control) opens to void urine from the body.
a Filtration. Occurs
at glomerular capillaries
in Bowman’s capsule.
b Reabsorption.
Occurs all along a nephron’s
tubular parts.
distal
proximal
tubule
tubule
c Secretion.
Starts at proximal tubule
and continues all along
the nephron tubule.
increasing
solute
concentration
peritubular
capillaries
CORTEX
MEDULLA
loop of Henle
d Urine is
concentrated
in loop of Henle
and collecting
loop of
duct.
Henle
Urine flows from
collecting duct
into renal pelvis.
Fig. 12.4, p. 216
efferent arteriole
(to peritubular
capillaries)
glomerular capillaries enclosed
by Bowman’s capsule
Bowman’s
capsule
filtrate to
proximal
tubule
afferent arteriole
(from renal artery)
Fig. 12.5a, p. 217
transport protein
Na+
glucose
Na+,
glucose
Cl–
Cl–
H2O
H2O
interior of
tubule
wall of
tubule
tissue
fluid
peritubular
capillary
Fig. 12.5b, p. 217
H+
H+
K+
K+
urea
urea
interior of
tubule
wall of
tubule
tissue
fluid
peritubular
capillary
Fig. 12.5c, p. 217
Useful References for Section 3
The latest references for topics covered in this section can be found at
the book companion website. Log in to the book’s e-resources page at
www.thomsonedu.com to access InfoTrac articles.
 InfoTrac:
Renal Hemodynamics: An
Overview. Nephrology Nursing Journal, Aug.
2003.
 InfoTrac: Glomerular Filtration: An Overview.
Nephrology Nursing Journal, June 2003.
Section 4
How Kidneys Help
Manage Fluid Balance
and Blood Pressure
How Kidneys Help Manage Fluid Balance
and Blood Pressure


The total volume of body fluids doesn’t vary
much because the kidneys make
adjustments to keep the volume of
extracellular fluid, and blood in particular, in
a normal range.
Water follows salt as urine forms.
How Kidneys Help Manage Fluid Balance
and Blood Pressure

The loop of Henle pulls more water and salts
from the filtrate to return it to the body.
•
•
•
The descending part of the loop sits in salty tissue
fluid; water is drawn out of the tube to be
reabsorbed.
The salt concentration of the remaining fluid in the
loop rises until it matches the concentration of the
surrounding tissues.
In the ascending limb of the loop, water is inhibited
from passing through the wall of the loop, but sodium
is actively transported out of the loop.
Figure 12.6
Na+
Cl–
H2O
kidney
medulla
saltiest
near turn
loop of
Henle
Fig. 12.6, p. 218
How Kidneys Help Manage Fluid Balance
and Blood Pressure


Salt continues to be removed in the distal
tubule, but not water; as salt leaves the filtrate,
salt gradients become steep, driving
reabsorption of solutes into the peritubular
capillaries.
Urea helps boost the gradient by diffusion out of
the collecting duct, taking water with it.
How Kidneys Help Manage Fluid Balance
and Blood Pressure
Hormones control whether kidneys make
urine that is concentrated or dilute.


Antidiuretic hormone (ADH) is secreted by
the brain in response to a decrease in
extracellular fluid; ADH causes the distal
tubules and collecting ducts to become
permeable to water, which moves back into the
blood capillaries.
ADH targets
aldosterone
target
KIDNEY
CORTEX
KIDNEY
MEDULLA
Fig. 12.7, p. 219
a Stimulus
Water loss reduces
blood volume.
Sensors in the
brain trigger
release of ADH.
e Response
Receptors in brain detect
the increase in blood
volume. Signals for ADH
secretion stop.
b ADH makes
distal tubules,
collecting ducts
more permeable
to water.
c Kidneys reabsorb
more water, so less
water leaves in urine.
d The blood
volume rises.
Fig. 12.8, p. 219
a Stimulus
Water loss reduces
blood volume.
Sensors in the
brain trigger
release of ADH.
e Response
Receptors in brain
detect the increase in
blood volume.
Signals for ADH
secretion stop.
b ADH makes
distal tubules,
collecting ducts
more permeable
to water.
c Kidneys reabsorb
more water, so less
water leaves in urine.
d The blood
volume rises.
Stepped Art
Fig. 12.8, p. 219
How Kidneys Help Manage Fluid Balance
and Blood Pressure

Decreases in the volume of extracellular fluid is
sensed by cells in the efferent arterioles; these
cells, part of the juxtaglomerular apparatus,
release renin.
•
•

Renin stimulates production of angiotensin I, which is
converted to angiotensin II.
Angiotensin II stimulates the adrenal cortex of the
kidney to make aldosterone, which causes cells of
the distal tubules and collecting ducts to increase
reabsorption of salts.
Caffeine and alcohol are diuretics, substances
that promote loss of water.
Fig. 12.9, p. 219
(efferent
renin-secreting cells
arteriole
in juxtaglomerular
leaving the
apparatus
glomerus)
distal
tubule
© 2005
Bowman’s capsule
(afferent
arteriole leading
into glomerus)
proximal tubule
Fig. 12.9a, p. 219
Receptors in kidneys,
elsewhere detect falling
sodium level
Renin released from cells in the JGA
Angiotensinogen converts to angiotensin I
Angiotensin II
Aldosterone secreted (from adrenal glands)
Aldosterone acts on distal tubules
Sodium (and water) reabsorbed
Fig. 12.9b, p. 219
How Kidneys Help Manage Fluid Balance
and Blood Pressure
A thirst center monitors sodium.



When solute concentration in the extracellular
fluid rises, the amount of saliva produced by the
salivary glands drops; a dry mouth stimulates
the thirst center of the brain.
Stimulation of the thirst center and release of
ADH cause liquid-seeking behavior.
Useful References for Section 4
The latest references for topics covered in this section can be found at
the book companion website. Log in to the book’s e-resources page at
www.thomsonedu.com to access InfoTrac articles.
 InfoTrac:
Urinary Concentration and Dilution.
Nephrology Nursing Journal, May–June
2004.
Section 5
Removing Excess Acids
and Other Substances in
Urine
Removing Excess Acids and Other
Substances in Urine


The body’s acid-base balance, the relative
amounts of acidic and basic substances in
extracellular fluid, is maintained in part by
the kidneys.
Kidneys maintain acid-base balance by
controlling the levels of bicarbonate in the
blood.
Removing Excess Acids and Other
Substances in Urine

When the blood is too acid, water and carbon
dioxide combine in cells in the wall of the
nephron tubules to give rise to bicarbonate and
H+.
•
•

The bicarbonate enters the peritubular capillaries
and from there it enters the blood to neutralize acid.
The H+ in the tubules enters the filtrate to combine
with phosphate, ammonia, or bicarbonate to be
excreted.
When the blood is too alkaline, less bicarbonate
is reabsorbed into the blood.
cells of
tubule wall
tubule interior
H2O
peritubular
capillary
CO2
enzyme action
(carbonic
acid)
H2CO3
tissue fluid
H
H ammonia
HCO 3
bicarbonate
enters
bloodstream
H phosphate
excreted in
urine
Fig. 12.10, p. 220
Removing Excess Acids and Other
Substances in Urine

Many other substances end up in urine
once filtered from the blood: traces of drugs;
excess glucose, which is a sign of diabetes;
pus, a sign of infection; and even blood, a
sign of infection, cancer, or injury.
Useful References for Section 5
The latest references for topics covered in this section can be found at
the book companion website. Log in to the book’s e-resources page at
www.thomsonedu.com to access InfoTrac articles.
 InfoTrac:
Urine Albumin Considered
Independent Marker for Kidney,
Cardiovascular Disease. Heart Disease
Weekly, July 4, 2004.
Section 6
Kidney Disorders
Kidney Disorders
Kidney stones are deposits of uric acid,
calcium salts, and other substances that
have settled out of urine and collected in the
renal pelvis.



Small stones can pass out during urination, but
larger stones can inhibit urination.
Lithotripsy uses sound waves to fragment the
stones so they can pass out in the urine.
Kidney Disorders



Inflammation of the bladder (cystitis) or
kidneys (pyelonephritis) is the result of
infections to the urinary tract; nephritis is
general inflammation of the kidneys and can
be severe enough to limit function.
Polycystic kidney disease is an inherited
disorder in which cysts form in the kidneys
and gradually destroy normal tissue.
Glomerulonephritis describes a variety of
disorders that disrupt the flow of blood
through the glomeruli of the kidneys.
Kidney Disorders

Dialysis refers to the exchange of
substances across a membrane between
solutions of differing compositions; in
hemodialysis, a machine is connected to
an artery or vein, blood enters the tubes of
the machine, and
materials are removed
from the blood before
it is returned to the body.
Figure 12.11
Useful References for Section 6
The latest references for topics covered in this section can be found at
the book companion website. Log in to the book’s e-resources page at
www.thomsonedu.com to access InfoTrac articles.
 National
Institute of Diabetes and Digestive
and Kidney Disease: National Kidney and
Urologic Diseases Information Clearinghouse
 InfoTrac: Filter Fault Is Kidney Failure. The
Economic Times, April 24, 2006.
 InfoTrac: Battle Well Fought: Miami Herald,
July 13, 2006.