Essentials of Human Anatomy & Physiology

Twelfth Edition

Chapter 15
The Urinary System

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Functions of the Urinary System
•  Kidneys dispose of waste products in urine
–  Nitrogenous wastes
–  Toxins
–  Drugs
–  Excess ions
•  Kidneys’ regulatory functions include:
–  Production of renin to maintain blood pressure
–  Production of erythropoietin to stimulate red blood cell
production
–  Conversion of vitamin D to its active form

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Organs of the Urinary System
•  Kidneys
•  Ureters
•  Urinary bladder
•  Urethra

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.1a Organs of the Urinary
System (1 of 2)

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Kidneys (1 of 7)
•  Location and structure
–  The kidneys are situated against the dorsal body wall in
a retroperitoneal position (behind the parietal
peritoneum)
–  The kidneys are situated at the level of the T12 to L3
vertebrae
–  The right kidney is slightly lower than the left (because
of position of the liver)

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.1b Organs of the Urinary
System

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Kidneys (2 of 7)
•  Kidney structure
–  An adult kidney is about 12 c m (5 in ) long and 6 c m
enti eters ches enti eters

(2.5 in ) wide
ches

–  Renal hilum
▪  A medial indentation where several structures
enter or exit the kidney (ureters, renal blood
vessels, and nerves)
–  An adrenal gland sits atop each kidney

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Kidneys (3 of 7)
•  Kidney structure
–  Three protective layers enclose the kidney
▪  Fibrous capsule encloses each kidney
▪  Perirenal fat capsule surrounds the kidney and
cushions against blows
▪  Renal fascia is the most superficial layer that
anchors the kidney and adrenal gland to
surrounding structures

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Kidneys (4 of 7)
•  Kidney structure
–  Three regions revealed in a longitudinal section
1.  Renal cortex—outer region
2.  Renal medulla—deeper region
– Renal (medullary) pyramids—triangular regions
of tissue in the medulla
– Renal columns—extensions of cortexlike
material that separate the pyramids

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Kidneys (5 of 7)
•  Kidney structure
–  Three regions
3.  Renal pelvis—medial region that is a flat, funnel-
shaped tube
– Calyces form cup-shaped “drains” that enclose
the renal pyramids
– Calyces collect urine and send it to the renal
pelvis, on to the ureter, and to the urinary
bladder for storage

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.2a Internal Anatomy of
the Kidney

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.2b Internal Anatomy of the
Kidney (1 of 2)

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Kidneys (6 of 7)
•  Blood supply
–  One-quarter of the total blood supply of the body
passes through the kidneys each minute
–  Renal artery provides each kidney with arterial blood
supply
–  Renal artery divides into segmental arteries →
interlobar arteries → arcuate arteries → cortical
radiate arteries

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Kidneys (7 of 7)
•  Venous blood flow
–  Cortical radiate veins → arcuate veins → interlobar
veins → renal vein
–  There are no segmental veins
–  Renal vein returns blood to the inferior vena cava

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.2b Internal Anatomy of the
Kidney (2 of 2)

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.2c Internal Anatomy of
the Kidney

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Nephrons (1 of 7)
•  Structural and functional units of the kidneys
•  Each kidney contains over a million nephrons
•  Each nephron consists of two main structures

1.  Renal corpuscle

2.  Renal tubule

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.3a Structure of the Nephron (1 of 3)

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Nephrons (2 of 7)
•  Renal corpuscle consists of:
1.  Glomerulus, a knot of capillaries made of podocytes
▪  Podocytes make up the inner (visceral) layer of the
glomerular capsule
– Foot processes cling to the glomerulus
– Filtration slits create a porous membrane—ideal
for filtration
2.  Glomerular (Bowman’s) capsule is a cup-shaped
structure that surrounds the glomerulus
▪  First part of the renal tubule

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.3c Structure of the Nephron (1 of 2)

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.3d Structure of the Nephron

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Nephrons (3 of 7)
•  Renal tubule
–  Extends from glomerular capsule and ends when it
empties into the collecting duct
–  From the glomerular (Bowman’s) capsule, the
subdivisions of the renal tubule are:
1.  Proximal convoluted tubule (PCT)
2.  Nephron loop (loop of Henle)
3.  Distal convoluted tubule (DCT)

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.3a Structure of the Nephron (2 of 3)

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.3b Structure of the Nephron (1 of 2)

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Nephrons (4 of 7)
•  Cortical nephrons
–  Located entirely in the cortex
–  Include most nephrons
•  Juxtamedullary nephrons
–  Found at the cortex-medulla junction
–  Nephron loop dips deep into the medulla
–  Collecting ducts collect urine from both types of
nephrons, through the renal pyramids, to the calyces,
and then to the renal pelvis

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.3a Structure of the Nephron (3 of 3)

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Nephrons (5 of 7)
•  Two capillary beds associated with each nephron
1.  Glomerulus
2.  Peritubular capillary bed

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Nephrons (6 of 7)
•  Glomerulus
–  Fed and drained by arterioles
▪  Afferent arteriole—arises from a cortical radiate
artery and feeds the glomerulus
▪  Efferent arteriole—receives blood that has passed
through the glomerulus
–  Specialized for filtration
–  High pressure forces fluid and solutes out of blood
and into the glomerular capsule

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.3c Structure of the Nephron (2 of 2)

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Nephrons (7 of 7)
•  Peritubular capillary beds
–  Arise from the efferent arteriole of the glomerulus
–  Low-pressure, porous capillaries
–  Adapted for absorption instead of filtration
–  Cling close to the renal tubule to receive solutes and
water from tubule cells
–  Drain into the interlobar veins

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.3b Structure of the Nephron (2 of 2)

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Urine Formation and Characteristics (1 of 11)
•  Urine formation is the result of three processes
1.  Glomerular filtration
2.  Tubular reabsorption
3.  Tubular secretion

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.4 The Kidney Depicted Schematically
as a Single Large, Uncoiled Nephron

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Concept Link 1
Recall that filtration, as a passive process, requires a
pressure gradient (Chapter 3, p. 78). The capillaries of the
glomerulus are under higher pressure compared to the
glomerular capsule; as a result, fluids move down the
pressure gradient, from the blood into the glomerular
capsule.

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Urine Formation and Characteristics (2 of 11)
•  Glomerular filtration
–  The glomerulus is a filter
–  Filtration is a nonselective passive process
▪  Water and solutes smaller than proteins are forced
through glomerular capillary walls
▪  Proteins and blood cells are normally too large to
pass through the filtration membrane
▪  Once in the capsule, fluid is called filtrate
▪  Filtrate leaves via the renal tubule

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Urine Formation and Characteristics (3 of 11)
•  Glomerular filtration
–  Filtrate will be formed as long as systemic blood
pressure is normal
▪  If arterial blood pressure is too low, filtrate
formation stops because glomerular pressure will
be too low to form filtrate

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Urine Formation and Characteristics (4 of 11)
•  Tubular reabsorption
–  The peritubular capillaries reabsorb useful substances
from the renal tubule cells, such as:
▪  Water
▪  Glucose
▪  Amino acids
▪  Ions
–  Some reabsorption is passive; most is active (ATP)
–  Most reabsorption occurs in the proximal convoluted
tubule

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.5 Sites of Filtration, Reabsorption,
and Secretion in a Nephron (1 of 2)

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Urine Formation and Characteristics (5 of 11)
•  Tubular secretion
–  Reabsorption in reverse
–  Some materials move from the blood of the
peritubular capillaries into the renal tubules to be
eliminated in filtrate
▪  Hydrogen and potassium ions
▪  Creatinine

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Urine Formation and Characteristics (6 of 11)
•  Tubular secretion
–  Secretion is important for:
▪  Getting rid of substances not already in the filtrate
▪  Removing drugs and excess ions
▪  Maintaining acid-base balance of blood
–  Materials left in the renal tubule move toward the ureter

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Concept Link 2
Recall that pH is a measure of hydrogen ion (H+)
concentration (see Chapter 2, p. 41 ). When the body
experiences a high level of hydrogen ions, which can lower
pH, the kidneys help by eliminating excess hydrogen ions
from the body via the urine.

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Urine Formation and Characteristics (7 of 11)
•  Nitrogenous wastes
–  Nitrogenous waste products are poorly reabsorbed, if
at all
–  Tend to remain in the filtrate and are excreted from
the body in the urine
▪  Urea—end product of protein breakdown
▪  Uric acid—results from nucleic acid metabolism
▪  Creatinine—associated with creatine metabolism in
muscles

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.5 Sites of Filtration, Reabsorption,
and Secretion in a Nephron (2 of 2)

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Urine Formation and Characteristics (8 of 11)
•  In 24 hours, about 1.0 to 1.8 liters of urine are produced
•  Urine and filtrate are different
–  Filtrate contains everything that blood plasma does
(except proteins)
–  Urine is what remains after the filtrate has lost most of
its water, nutrients, and necessary ions through
reabsorption
–  Urine contains nitrogenous wastes and substances that
are not needed

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Urine Formation and Characteristics (9 of 11)
•  Urine characteristics
–  Clear and pale to deep yellow in color
–  Yellow color is normal and due to the pigment
urochrome (from the destruction of hemoglobin) and
solutes
▪  Dilute urine is a pale, straw color
–  Sterile at the time of formation
–  Slightly aromatic, but smells like ammonia with time
–  Slightly acidic (pH of 6)
–  Specific gravity of 1.001 to 1.035

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Urine Formation and Characteristics (10 of 11)
•  Solutes normally found in urine
–  Sodium and potassium ions
–  Urea, uric acid, creatinine
–  Ammonia
–  Bicarbonate ions

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Urine Formation and Characteristics (11 of 11)
•  Solutes Not normally found in urine
–  Glucose
–  Blood proteins
–  Red blood cells
–  Hemoglobin
–  WBCs (pus)
–  Bile

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Table 15.1 Abnormal Urinary
Constituents
Substance Name of condition Possible causes

Glucose Glycosuria (gli”ko-su’re-ah) Nonpathological: Excessive intake

of sugary foods
Pathological: Diabetes mellitus
Proteins Proteinuria (pro”te-˘ı-nu’re-ah) (also Nonpathological: Physical exertion,
called albuminuria) pregnancy
Pathological: Glomerulonephritis,
hypertension
Pus (WBCs and bacteria) Pyuria (pi-u’re-ah) Urinary tract infection

RBCs Hematuria (he”mah-tu’re-ah) Bleeding in the urinary tract (due to

trauma, kidney stones, infection)

Hemoglobin Hemoglobinuria Various: Transfusion reaction,

(he”mo-glo-b˘ı-nu’re-ah) hemolytic anemia

Bile pigment Bilirubinuria (bil″˘ı-roo-b˘ı-nu′re-ah) Liver disease (hepatitis)

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Ureters
•  Slender tubes 25–30 c m (10–12 inches) attaching the
enti eters

kidney to the urinary bladder

–  Continuous with the renal pelvis
–  Enter the posterior aspect of the urinary bladder
–  Run behind the peritoneum
•  Peristalsis aids gravity in urine transport

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.1a Organs of the Urinary
System (2 of 2)

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.6 Basic Structure of the Female
Urinary Bladder and Urethra (1 of 4)

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Urinary Bladder (1 of 3)
•  Smooth, collapsible, muscular sac situated posterior to
the pubic symphysis
•  Stores urine temporarily
•  Trigone—triangular region of the urinary bladder base
based on three openings
–  Two openings from the ureters (ureteral orifices)
–  One opening to the urethra (internal urethral orifice)
•  In males, the prostate surrounds the neck of the urinary
bladder

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.6 Basic Structure of the Female
Urinary Bladder and Urethra (2 of 4)

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Urinary Bladder (2 of 3)
•  Wall of the urinary bladder
–  Three layers of smooth muscle collectively called the
detrusor muscle
–  Mucosa made of transitional epithelium
–  Walls are thick and folded in an empty urinary bladder
–  Urinary bladder can expand significantly without
increasing internal pressure

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Urinary Bladder (3 of 3)
•  Capacity of the urinary bladder
–  A moderately full bladder is about 5 inches long and
holds about 500 m l of urine
illi iters

–  Capable of holding twice that amount of urine

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.7 Position and Shape of a Distended
and an Empty Urinary Bladder in an Adult Male

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Urethra (1 of 3)
•  Thin-walled tube that carries urine from the urinary
bladder to the outside of the body by peristalsis
•  Function
–  Females—carries only urine
–  Males—carries urine and sperm

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Urethra (2 of 3)
•  Release of urine is controlled by two sphincters
1.  Internal urethral sphincter
▪  Involuntary and made of smooth muscle
2.  External urethral sphincter
▪  Voluntary and made of skeletal muscle

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.6 Basic Structure of the Female
Urinary Bladder and Urethra (3 of 4)

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Urethra (3 of 3)
•  Length
–  In females: 3 to 4 c m (1.5 inches long)
enti eters

–  In males: 20 c m (8 inches long)

enti eters

•  Location
–  Females—anterior to the vaginal opening
–  Males—travels through the prostate and penis
▪  Prostatic urethra
▪  Membranous urethra
▪  Spongy urethra

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.6 Basic Structure of the Female
Urinary Bladder and Urethra (4 of 4)

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Micturition (1 of 2)
•  Micturition
–  Voiding, or emptying of the urinary bladder
–  Two sphincters control the release of urine, the
internal urethral sphincter and external urethral
sphincter
•  Bladder collects urine to 200 m l illi iters

•  Stretch receptors transmit impulses to the sacral region

of the spinal cord
•  Impulses travel back to the bladder via the pelvic
splanchnic nerves to cause bladder contractions

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Micturition (2 of 2)
•  When contractions become stronger, urine is forced past
the involuntary internal sphincter into the upper urethra
•  Urge to void is felt
•  The external sphincter is voluntarily controlled, so
micturition can usually be delayed

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Fluid, Electrolyte, and Acid-Base
Balance (1 of 2)
•  Blood composition depends on three factors
1.  Diet
2.  Cellular metabolism
3.  Urine output

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Fluid, Electrolyte, and Acid-Base
Balance (2 of 2)
•  Kidneys have four roles in maintaining blood composition

1.  Excreting nitrogen-containing wastes (previously

discussed)
2.  Maintaining water balance of the blood
3.  Maintaining electrolyte balance of the blood
4.  Ensuring proper blood pH

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Maintaining Water Balance of the
Blood (1 of 7)
•  Normal amount of water in the human body
–  Young adult females = 50%
–  Young adult males = 60%
–  Babies = 75%
–  The elderly = 45%
•  Water is necessary for many body functions, and levels
must be maintained

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Maintaining Water Balance of the
Blood (2 of 7)
•  Water occupies three main fluid compartments
1.  Intracellular fluid (ICF)
▪  Fluid inside cells
▪  Accounts for two-thirds of body fluid
2.  Extracellular fluid (ECF)
▪  Fluids outside cells; includes blood plasma,
interstitial fluid (IF), lymph, and transcellular fluid
3.  Plasma (blood) is ECF, but accounts for 3L of total iters

body water.
▪  Links external and internal environments
(Figure 15.9)
Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.8 The Major Fluid Compartments
of the Body

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.9 The Continuous Mixing of
Body Fluids

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Maintaining Water Balance of the
Blood (3 of 7)
•  The link between water and electrolytes
–  Electrolytes are charged particles (ions) that conduct
electrical current in an aqueous solution
–  Sodium, potassium, and calcium ions are electrolytes

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Maintaining Water Balance of the
Blood (4 of 7)
•  Regulation of water intake and output
–  Water intake must equal water output if the body is to
remain properly hydrated
–  Sources for water intake
▪  Ingested foods and fluids
▪  Water produced from metabolic processes (10%)
–  Thirst mechanism is the driving force for water intake

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.10 Water Intake and Output

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Maintaining Water Balance of the
Blood (5 of 7)
•  Thirst mechanism
–  Osmoreceptors are sensitive cells in the
hypothalamus that become more active in reaction to
small changes in plasma solute concentration
–  When activated, the thirst center in the hypothalamus
is notified
–  A dry mouth due to decreased saliva also promotes
the thirst mechanism
–  Both reinforce the drive to drink

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.11 The Thirst Mechanism for
Regulating Water Intake

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Maintaining Water Balance of the
Blood (6 of 7)
•  Sources of water output
–  Lungs (insensible since we cannot sense the
water leaving)
–  Perspiration
–  Feces
–  Urine

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Maintaining Water Balance of the
Blood (7 of 7)
•  Hormones are primarily responsible for reabsorption of
water and electrolytes by the kidneys
–  Antidiuretic hormone (ADH) prevents excessive water
loss in the urine and increases water reabsorption
–  ADH targets the kidney’s collecting ducts

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Concept Link 3
Remember the concept of interrelationships among organ
systems (see Figure 1.3, p. 8), and notice that the
interdependent events regulating sodium ion and water
balance (see Figure 15.12, p. 528) involve four body
systems: urinary, nervous, endocrine, and cardiovascular.

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Maintaining Electrolyte Balance
•  Small changes in electrolyte concentrations cause
water to move from one fluid compartment to another
•  A second hormone, aldosterone, helps regulate blood
composition and blood volume by acting on the kidney
–  For each sodium ion reabsorbed, a chloride ion
follows, and a potassium ion is secreted into the
filtrate
–  Water follows salt: when sodium is reabsorbed,
water follows it passively back into the blood

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Electrolyte Balance (1 of 2)
•  Renin-angiotensin mechanism
–  Most important trigger for aldosterone release
–  Mediated by the juxtaglomerular (JG) apparatus of the
renal tubules
–  When cells of the JG apparatus are stimulated by low
blood pressure, the enzyme renin is released into blood

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Electrolyte Balance (2 of 2)
•  Renin-angiotensin mechanism
–  Renin catalyzes reactions that produce angiotensin II
–  Angiotensin II causes vasoconstriction and
aldosterone release
–  Result is increase in blood volume and blood pressure

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.12 Flowchart of Mechanisms Regulating
Sodium Ion and Water Balance to Help Maintain
Blood Pressure Homeostasis

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Maintaining Acid-Base Balance of
Blood (1 of 8)
•  Blood pH must remain between 7.35 and 7.45 to maintain
homeostasis
–  Alkalosis—pH above 7.45
–  Acidosis—pH below 7.35
–  Physiological acidosis—pH between 7.0 and 7.35

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Maintaining Acid-Base Balance of
Blood (2 of 8)
•  Kidneys play greatest role in maintaining acid-base
balance
•  Other acid-base controlling systems
–  Blood buffers
–  Respiration

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Maintaining Acid-Base Balance of
Blood (3 of 8)
•  Blood buffers
–  Acids are proton (H+) donors
▪  Strong acids dissociate completely and liberate all of
their H+ in water
▪  Weak acids, such as carbonic acid, dissociate only
partially
–  Bases are proton (H+) acceptors
▪  Strong bases dissociate easily in water and tie up H+
▪  Weak bases, such as bicarbonate ion and ammonia,
are slower to accept H+

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Figure 15.13 Dissociation of Strong and
Weak Acids in Water

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Maintaining Acid-Base Balance of
Blood (4 of 8)
•  Molecules react to prevent dramatic changes in hydrogen
ion (H+) concentrations
–  Bind to H+ when pH drops
–  Release H+ when pH rises
•  Three major chemical buffer systems
1.  Bicarbonate buffer system
2.  Phosphate buffer system
3.  Protein buffer system

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Maintaining Acid-Base Balance of
Blood (5 of 8)
•  The bicarbonate buffer system
–  Mixture of carbonic acid (H2CO3) and sodium
bicarbonate (NaHCO3)
▪  Carbonic acid is a weak acid that does not
dissociate much in neutral or acid solutions
▪  Bicarbonate ions (HCO3−) react with strong acids
to change them to weak acids

HCL + NaHCO3 → H2CO3 + NaCl

strong acid weak base weak acid salt

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Maintaining Acid-Base Balance of
Blood (6 of 8)
•  The bicarbonate buffer system
–  Carbonic acid dissociates in the presence of a strong
base to form a weak base and water

NaOH + H2CO3 → NaHCO3 + H2O

strong base weak acid weak base water

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Maintaining Acid-Base Balance of
Blood (7 of 8)
•  Respiratory mechanisms
–  Respiratory rate can rise and fall depending on
changing blood pH to retain CO2 (decreasing the
blood pH) or remove CO2 (increasing the blood pH)

CO2 + H2O Ä H2CO3 Ä H+ + HCO3 −

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Maintaining Acid-Base Balance of
Blood (8 of 8)
•  Renal mechanisms
–  When blood pH rises:
▪  Bicarbonate ions are excreted
▪  Hydrogen ions are retained by kidney tubules
–  When blood pH falls:
▪  Bicarbonate ions are reabsorbed
▪  Hydrogen ions are secreted
–  Urine pH varies from 4.5 to 8.0

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Developmental Aspects of the Urinary
System (1 of 4)
•  The kidneys begin to develop in the first few weeks of
embryonic life and are excreting urine by the third month
of fetal life
•  Common congenital abnormalities include polycystic
kidney and hypospadias
•  Common urinary system problems in children and young
to middle-aged adults include infections caused by fecal
microorganisms, microorganisms causing sexually
transmitted infections, and Streptococcus

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Developmental Aspects of the Urinary
System (2 of 4)
•  Control of the voluntary urethral sphincter does not start
until age 18 months
•  Complete nighttime control may not occur until the child is
4 years old
•  Urinary tract infections (UTIs) are the only common
problems before old age
–  Escherichia coli (E. coli), a bacterium, accounts for
80 percent of UTIs

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Developmental Aspects of the Urinary
System (3 of 4)
•  Renal failure is an uncommon but serious problem in
which the kidneys are unable to concentrate urine, and
dialysis must be done to maintain chemical homeostasis
of blood
•  With age, filtration rate decreases and tubule cells
become less efficient at concentrating urine, leading to
urgency, frequency, and incontinence
•  In men, urinary retention is another common problem

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Developmental Aspects of the Urinary
System (4 of 4)
•  Problems associated with aging
–  Urgency—feeling that it is necessary to void
–  Frequency—frequent voiding of small amounts of
urine
–  Nocturia—need to get up during the night to urinate
–  Incontinence—loss of control
–  Urinary retention—common in males, often the result
of hypertrophy of the prostate gland

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved
Copyright

This work is protected by United States copyright laws and is

provided solely for the use of instructors in teaching their
courses and assessing student learning. Dissemination or sale of
any part of this work (including on the World Wide Web) will
destroy the integrity of the work and is not permitted. The work
and materials from it should never be made available to students
except by instructors using the accompanying text in their
classes. All recipients of this work are expected to abide by these
restrictions and to honor the intended pedagogical purposes and
the needs of other instructors who rely on these materials.

Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved