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Essentials of Anatomy & Physiology, 4th Edition
Martini / Bartholomew
18
The Urinary
System
PowerPoint® Lecture Outlines
prepared by Alan Magid, Duke University
Slides 1 to 91
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Urinary System Organization
Functions of the Urinary System
• Eliminate organic wastes
• Regulate plasma ion levels
• Regulate blood volume and blood pressure
• Adjust water loss
• Release cardiovascular hormones
• Stabilize blood pH
• Conserve nutrients
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Urinary System Organization
Components of the Urinary System
• Kidneys
• Produce urine, a fluid made of water,
ions, soluble compounds
• Ureters
• Urinary bladder
• Urethra
• During urination, conducts urine out of
the body
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Urinary System Organization
The Components of the Urinary System
Figure 18-1
The Kidneys
Anatomy of the Kidney
• Kidneys are retroperitoneal
• Left kidney superior to right
• Fibrous capsule surrounds the kidney
• Renal artery and renal nerve enter at
hilum
• Renal vein and ureter exit at hilum
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Kidneys
An Overview of Kidney Anatomy
Figure 18-2a
The Kidneys
An Overview of Kidney Anatomy
Figure 18-2(b)
The Kidneys
Internal Anatomy of the Kidney
• Nephrons
• Urine produced by nephrons
• About a million nephrons per kidney
• Renal pelvis
• Urine collects here from calyces
• Input from two major calyces
• Each major calyx is fed by four to
five minor calyces
• Urine leaves pelvis to ureter
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Kidneys
The Structure of
the Kidney
Figure 18-3(a)
The Kidneys
The Structure of
the Kidney
Figure 18-3(b)
The Kidneys
The Structure of the Kidney
Figure 18-3(c)
The Kidneys
Kidney Blood Supply
• Renal artery
• Interlobar arteries
• Arcuate arteries
• Interlobular arteries
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Kidneys
Kidney Blood Supply
• Nephron level
• Afferent arteriole
• Branch of interlobular artery
• Glomerulus
• Efferent arteriole
• Peritubular capillaries
• Vasa recta
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Kidneys
The Blood Supply to the Kidneys
Figure 18-4(a)
The Kidneys
The Blood Supply to the Kidneys
Figure 18-4(b)
The Kidneys
The Blood Supply to the Kidneys
Figure 18-4(c)
The Kidneys
The Blood
Supply to
the Kidneys
Figure 18-4(d)
The Kidneys
The Nephron
• Basic functional unit of the
kidney
• Two parts to the nephron
• Renal corpuscle
• Renal tubule
• Feeds into collecting system
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Kidneys
Pathway of Urine through the Nephron
• First, filtered in the renal corpuscle
• Urine begins as filtrate
• Next, filtrate flows into renal tubule
• First, into the proximal convoluted tubule
(PCT)
• Next, the loop of Henle
• Finally, the distal convoluted tubule (DCT)
• Last, exits to collecting duct
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Kidneys
A Representative Nephron and the
Collecting System
Figure 18-5
The Kidneys
Key Note
The kidneys remove waste products
from the blood; they also assist in the
regulation of blood volume and blood
pressure, ion levels, and blood pH.
Nephrons are the primary functional
units of the kidneys.
PLAY
Kidney Function: Urinary System Structure
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Kidneys
Functions of the Nephron
• Production of filtrate
• Glomerulus
• Reabsorption of nutrients
• PCT
• Reabsorption of water and ions
• DCT, collecting duct
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Kidneys
Parts of the Renal Corpuscle
• Glomerulus
• Knot of interconnected capillaries
with a spherical shape
• Bowman’s capsule
• Encloses glomerulus with
squamous epithelium
• Afferent arteriole
• Blood supply to glomerulus
• Efferent arteriole
• Blood drainage from glomerulus
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Kidneys
The Renal
Corpuscle
Figure 18-6(a)
The Kidneys
The Renal
Corpuscle
Figure 18-6(b)
The Kidneys
Glomerulus Anatomy
• Glomerular capillaries covered by
podocytes
• Narrow slits separate foot processes
of podocytes
• Capsular space surrounds glomerulus
• Filtrate accumulates here
• Bounded by Bowman’s capsule
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Kidneys
Proximal Convoluted Tubule
• Reabsorbs critical substances from filtrate
• Nutrients (e.g., glucose, amino acids)
• Ions
• Proteins
• Releases them into surrounding interstitial
fluid
• Enter peritubular capillaries and return to
blood stream
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Kidneys
Loop of Henle
• Descending limb
• Permeable to water
• Ascending limb
• Impermeable to water
and solutes
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Kidneys
Distal Convoluted Tubule (DCT)
• Transport activities
• Actively secretes substances into urine
• Actively reabsorbs sodium from urine
• Juxtaglomerular apparatus
• Releases renin, erythropoietin
• Located at start of DCT
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Kidneys
Collecting Ducts
• Receive urine from nephrons
• Merge into papillary ducts
• Delivers urine to minor calyx
• Adjust final osmotic pressure of urine
• By reabsorbing water
• By transporting ions
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Principles of Urine Production
Primary Purpose of Urine Production
• Excretion of dissolved solutes
• Metabolic wastes
• Urea
• Creatinine
• Uric acid
• Excess ions
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Principles of Urine Production
Processes in Urine Formation
• Filtration
• Reabsorption
• Secretion
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Principles of Urine Production
Filtration at the Glomerulus
• Blood pressure forces fluid and
dissolved substances across the
endothelial wall of glomerular
capillaries into the capsular space
• Glomerular filtration rate (GFR)
depends on blood pressure
• Any change in blood pressure
affects filtration
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Principles of Urine Production
Renin Release
• Decline in filtration pressure (blood
pressure) triggers renin release
• Released by juxtaglomerular apparatus
• Renin leads to increased blood volume
and blood pressure
• GFR returns toward normal
• Restores homeostasis
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Principles of Urine Production
Key Note
Roughly 180 liters of filtrate is
produced at the glomeruli each day.
That represents 70 times the total
plasma volume. Almost all of that fluid
volume must be reabsorbed to avoid
fatal dehydration.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Principles of Urine Production
Tubular Reabsorption/Secretion
• PCT reabsorbs 60–70% of filtrate
• Nutrients
• Sodium, other ions
• Water
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Principles of Urine Production
Tubular Reabsorption/Secretion (cont’d)
• Releases them into venous drainage for
return to the blood stream
• Also, PCT secretes substances into
tubular fluid
PLAY
Kidney Function: Urine Formation
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Principles of Urine Production
Tubular Reabsorption/Secretion (cont’d)
• Loop of Henle
• Reclaims water, ions from filtrate
• Ascending limb pumps out sodium and
chloride ions
• Descending limb absorbs water
• Interstitial osmotic pressure pulls water
from tubular fluid
• Urea concentration rises as fluid is lost
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Principles of Urine Production
Tubular Reabsorption/Secretion (cont’d)
• Distal Convoluted Tubule (DCT)
• Performs final adjustment
• Secretes or reabsorbs ions
• Reabsorbs sodium in exchange for
secreted potassium and hydrogen
ions
• Aldosterone increases sodium
reabsorption and potassium loss
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Principles of Urine Production
Control by Antidiuretic Hormone (ADH)
• Regulates water loss
• DCT, collecting tubule, collecting duct made
permeable to water by ADH
• Water then exits to interstitial fluid and
remains in the body
• Urine becomes concentrated (low in water,
high in solute)
• The higher the ADH level, the more
concentrated the urine
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Principles of Urine Production
The Effects of ADH
on the DCT and
Collecting Duct
Figure 18-7(a)
Principles of Urine Production
The Effects of ADH
on the DCT and
Collecting Duct
Figure 18-7(b)
Principles of Urine Production
Water Balance in the Kidney
• More than 99% of water is
reabsorbed from the filtrate
by the renal tubules
• Water content of normal
urine ranges from 93% to
97%
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Principles of Urine Production
Principles of Urine Production
A Summary of
Kidney Function
and Urine
Formation
Figure 18-8
Principles of Urine Production
Key Note
Reabsorption depends on diffusion,
osmosis, and active transport. The
mechanism of water reabsorption is
“water follows salt.” Many of these
processes are regulated by local or
hormonal mechanisms. Secretion is
a selective, carrier-mediated
process.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Principles of Urine Production
Vascular Control of Kidney Function
• Automatic regulation of filtration pressure
by changes in diameter of afferent and
efferent arterioles
• Autonomic regulation by sympathetic
activation
• Powerful vasoconstriction of afferent
arterioles
• Decreases GFR
• Also, redirects blood flow to other organs
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Principles of Urine Production
Hormonal Control of Kidney Function
•
•
•
•
Angiotensin II
Aldosterone
ADH
Atrial natriuretic peptide (ANP)
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Principles of Urine Production
Roles of the
Renin-Angiotensin
System in the
Regulation of
GFR
Figure 18-9
Transport, Storage, & Excretion
Transport and Storage of Urine
• Urine modification ends when
fluid enters the renal pelvis
• Ureters, urinary bladder, urethra
specialized for transport, storage,
and excretion of urine
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Transport, Storage, & Excretion
Ureters
• Ureters extend from renal pelvis
to urinary bladder
• Smooth muscle in walls contract
peristaltically
• Push urine toward bladder
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Transport, Storage, & Excretion
Urinary Bladder
• Distensible muscular sac for
urine storage
• Internal features include
• Trigone
• Neck
• Internal urethral sphincter
• Detrussor muscle
• Contraction forces urine
into urethra
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Transport, Storage, & Excretion
Organs for the Conduction and Storage
of Urine
Figure 18-10(a)
Transport, Storage, & Excretion
Organs for the Conduction and Storage
of Urine
Figure 18-10(b)
Transport, Storage, & Excretion
Organs for
the
Conduction
and Storage
of Urine
Figure 18-10(c)
Transport, Storage, & Excretion
The Urethra
• Longer in males than females
• External urethral sphincter
formed by a circular band of
skeletal muscle of pelvic floor
• Under voluntary control
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Transport, Storage, & Excretion
Micturition Reflex and Urination
• Urination coordinated by micturition reflex
• Initiated by stretch receptors in the bladder
wall
• Voluntary urination couples reflex with
relaxation of external urinary sphincter
• Permits internal urinary sphincter to open
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Transport, Storage, & Excretion
The Micturition Reflex
Figure 18-11
Fluid, Electrolyte, & Acid-Base
Homeostasis of Fluids
• Maintenance of normal volume and
composition is crucial to life
• Three types of homestasis required
• Fluid balance
• Electrolyte balance
• Acid-base balance
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Fluid, Electrolyte, & Acid-Base
Fluid and Electrolyte Balance
• Two fluid “compartments”
• Intracellular fluid (ICF)
• About 60% of total body water
• Extracellular fluid (ECF)
• About 40% of total body water
• Water moves freely within the ECF
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Fluid, Electrolyte, & Acid-Base
Body Fluid
Compartments
Figure 18-12
Fluid, Electrolyte, & Acid-Base
Ions in Body Fluids
Figure 18-13
Fluid, Electrolyte, & Acid-Base
Fluid, Electrolyte, & Acid-Base
Water Balance
• Water intake normally
equals water loss
• Water is gained from
• Eating
• Drinking
• Aerobic metabolism
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Fluid, Electrolyte, & Acid-Base
Fluid Shift—Water movement
between the ECF and the ICF
• Water moves to establish osmotic
equilibrium
• Hypertonic ECF pulls water out of cells
• Hypotonic ECF push water into cells
• Causes cellular swelling
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Fluid, Electrolyte, & Acid-Base
Electrolyte Balance
• Total electrolyte concentration affects water
balance
• Individual concentrations affect a range of
cellular functions
• Problems commonly result from a
mismatch of sodium ion gain/loss
• Potassium ion imbalance can be
dangerous or deadly
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Fluid, Electrolyte, & Acid-Base
Sodium Ion Balance
• Sodium uptake from the gut parallels
dietary intake
• Sodium loss occurs mainly in urine and
sweat
• Sodium reabsorption along DCT stimulated
by aldosterone
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Fluid, Electrolyte, & Acid-Base
Potassium Ion Balance
• Concentration of K+ in ECF normally
very low
• Urinary excretion increases when
sodium levels are low or when
potassium levels are high
• Aldosterone stimulates potassium ion
excretion
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Fluid, Electrolyte, & Acid-Base
Key Note
Fluid balance and electrolyte balance
are interrelated. The impact of water
gains or losses is reduced by fluid shifts
between the ECF and ICF and by
hormonal control of intake and
excretion. Electrolyte gains or losses
are opposed by fluid shifts, adjustments
in ion absorption and secretion, and to
water gain and loss.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Fluid, Electrolyte, & Acid-Base
Acid-Base Balance
• Normal pH of body fluids range from
pH 7.35 to pH 7.45
• pH > 7.45 is alkalosis (too alkaline)
• pH < 7.35 is acidosis (too acidic)
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Fluid, Electrolyte, & Acid-Base
Carbonic Acid and pH
• Carbonic acid most important factor on pH
• CO2 reacts with H2O to form carbonic acid
• Carbonic acid releases H+ when it
dissociates
• As CO2 levels go up, pH goes down
• As CO2 levels go down, pH goes up
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Fluid, Electrolyte, & Acid-Base
The Basic Relationship Between Carbon
Dioxide and Plasma pH
Figure 18-14
Fluid, Electrolyte, & Acid-Base
Metabolic Acids
• Acids produced by metabolism
• Lactic acid
• Produced by glycolysis
• Ketone bodies
• Produced in starvation
(dieting), diabetes
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Fluid, Electrolyte, & Acid-Base
Buffer Systems
• Resist changes in pH
• Consist of a weak acid and it anion
dissociation product
• Three major buffer systems in the body
• Protein buffer system (in ECF and ICF)
• Carbonic acid-bicarbonate buffer system (in
ECF)
• Phosphate buffer system (in ICF)
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Fluid, Electrolyte, & Acid-Base
Protein Buffer Systems
• Amino acid subunits respond to
H+ changes
• Important proteins for buffering
• Plasma proteins
• Hemoglobin within RBCs
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Fluid, Electrolyte, & Acid-Base
• Carbonic Acid-Bicarbonate
Buffer System
• Resists pH changes in ECF
caused by metabolic (organic)
acids
• Phosphate Buffer System
• Resists pH changes within cells
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Fluid, Electrolyte, & Acid-Base
Compensations for pH Disturbances
• Respiratory compensation—Changes in
ventilation lead to changes in pH by
raising or lowering CO2 levels
• Renal compensation—Kidney varies H+
secretion and bicarbonate reabsorption
depending on pH of ECF
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Fluid, Electrolyte, & Acid-Base
Two Classes of Acid-Base Disorders
• Respiratory acid-base disorder—Caused
by abnormal respiratory function leading to
large changes in CO2 levels
• Metabolic acid-base disorder—Caused by
formation of organic acids or conditions
which disturb the level of bicarbonate ion
such as diarrhea or vomiting
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Fluid, Electrolyte, & Acid-Base
Key Note
The most common and acute
acid-base disorder is respiratory
acidosis, which develops when
respiratory activity cannot keep
pace with the rate of carbon
dioxide generation in peripheral
tissues.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Aging and the Urinary System
Age-Related Changes in Urinary System
•
•
•
•
Loss of functional nephrons
Reduced GFR
Reduced response to ADH
Urinary retention in men with prostate
enlargement
• Drop in body water and mineral content
• Disorders of fluid, electrolyte, or acid-base
balance
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Urinary System
in Perspective
FIGURE 18-15
Functional Relationships Between
the Urinary System and Other Systems
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 18-15
1 of 11
The Integumentary System
• Sweat glands assist in
elimination of water and
solutes, especially sodium and
chloride ions; keratinized
epidermis prevents excessive
fluid loss through skin surface;
epidermis produces vitamin
D3, important for the renal
production of calcitriol
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 18-15
2 of 11
The Skeletal System
• Axial skeleton provides some
protection for kidneys and
ureters; pelvis protects
urinary bladder and proximal
portion of urethra
• Conserves calcium and
phosphate needed for bone
growth
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Figure 18-15
3 of 11
The Muscular System
• Sphincter controls urination
by closing urethral opening;
muscle layers of trunk
provide some protection for
urinary organs
• Removes waste products of
protein metabolism; assists in
regulation of calcium and
phosphate concentrations
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Figure 18-15
4 of 11
The Nervous System
• Adjusts renal blood pressure;
monitors distension of urinary
bladder and controls urination
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Figure 18-15
5 of 11
The Endocrine System
• Aldosterone and ADH adjust
rates of fluid and electrolyte
reabsorption in kidneys
• Kidney cells release renin
when local blood pressure
declines and erythropoietin
(EPO) when renal oxygen
levels decline
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 18-15
6 of 11
The Cardiovascular System
• Delivers blood to capillaries,
where filtration occurs;
accepts fluids and solutes
reabsorbed during urine
production
• Releases renin to elevate
blood pressure and
erythropoietin to accelerate
red blood cell production
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Figure 18-15
7 of 11
The Lymphatic System
• Provides specific defenses
against urinary tract infections
• Eliminates toxins and wastes
generated by cellular
activities; acid pH of urine
provides nonspecific defense
against urinary tract infections
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 18-15
8 of 11
The Respiratory System
• Assists in the regulation of pH
by eliminating carbon dioxide
• Assists in the elimination of
carbon dioxide; provides
bicarbonate buffers that
assist in pH regulation
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Figure 18-15
9 of 11
The Digestive System
• Absorbs water needed to
excrete wastes at kidneys;
absorbs ions needed to
maintain normal body fluid
concentrations; liver removes
bilirubin
• Excretes toxins absorbed by
the digestive epithelium;
excretes bilirubin and
nitrogenous wastes produced
by the liver; calcitrol production
by kidneys aids calcium and
phosphate absorption along
digestive tract
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Figure 18-15
10 of 11
The Reproductive System
• Accessory organ secretions
may have antibacterial
action that helps prevent
urethral infections in males
• Urethra in males carries
semen to the exterior
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Figure 18-15
11 of 11