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The Urinary System
Chapter 15
1
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Outline
Functions of the Urinary System
Overview of the Urinary System
Kidney Structure
Urine Formation
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Glomerular Filtration
Tubular Reabsorption
Tubular Secretion
Maintaining Water-Salt Balance
Maintaining Blood pH
Homeostasis
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Functions of the Urinary System
Carry out excretion of metabolic wastes.
–
–
•
Excretion is the removal of metabolic waste
products- Elimination is the removal of un-used
or un-usable material from the body
Urea is the primary nitrogenous end product,
but ammonium, creatinine, and uric acid are
also excreted.
Maintains salt-water balance of blood and
thus regulates blood volume and blood
pressure.
+
– Ions regulated include sodium (Na ),
potassium (K+), and calcium (Ca2+).
3
Functions of the Urinary System (Con’t)
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•
•
•
Maintains acid-base balance of the blood.
– Regulates bicarbonate ions (HCO3 ) and
hydrogen ions (H+).
Performs these functions by producing urine
and conducting it outside the body.
Has a hormonal function.
– Produces erythropoietin.
– Produces renin for the renin-angiotensinaldosterone system.
Activates inactive form of Vitamin D
4
Overview of the Urinary System
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•
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Kidneys are primary organs of the urinary
system.
– The concave side of a kidney has
depression called the hilum where the
renal artery enters and the renal vein and
ureters exit the kidney.
Urinary bladder gradually expands as urine
enters.
Urethra extends from the urinary bladder to
an exterior opening.
5
Figure 15.1a Organs of the urinary system.
Overview of the Urinary System
Hepatic veins (cut)
Inferior vena cava
Adrenal gland
Aorta
Renal artery
Renal hilum
Renal vein
Kidney
Iliac crest
Ureter
Rectum (cut)
Uterus (part
of female
reproductive
system)
(a)
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Urinary
bladder
Urethra
Figure 15.1b Organs of the urinary system.
12th rib
(b)
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Kidney Structure
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The kidney contains three major regions:
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Additional structures of importance
–
–
–
–
•
Renal cortex.
Renal medulla.
Renal pelvis.
Renal columns
Renal papilla
Renal pyramids
Minor & major calyces
Microscopically, the kidney is composed of
over one-million nephrons that produce urine.
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PATH OF URINE DRAINAGE:
Nephron
Collecting duct
Renal
hilum
Minor calyx
Renal cortex
Renal artery
Renal medulla
Renal vein
Major calyx
Renal pelvis
Renal column
Renal pyramid
in renal medulla
Renal papilla
Ureter
Renal capsule
Urinary bladder
(a) Anterior view of dissection of right kidney
Blood Supply to
the Kidney
Glomerulus
Frontal plane
Afferent
arteriole
Peritubular
capillary
Efferent
arteriole
Interlobular
vein
Vasa recta
Blood supply of nephron
Interlobular artery
Renal capsule
Arcuate artery
Interlobar artery
Segmental artery
Renal cortex
Renal artery
Renal vein
Interlobar vein
Renal pyramid
in renal medulla
Arcuate vein
Interlobular vein
(a) Frontal section of right kidney
Kidney Structure: The Nephron
•
Nephron is functional unit of the kidney.
–
•
Two types of nephrons
 Coritcal: 80-85%, normal renal function
 Juxtamedullary: 15-20%, involved with generation of
very dilute or very concentrated urine
Each nephron has its own blood supply.
–
–
From the renal artery, afferent arteriole leads to the
glomerulus, then to the efferent arteriole and then to the
peritubular capillary network (or vasa recta of
juxtamedullary nephrons) which surrounds the nephron.
From there blood goes into a venule that joins the renal
vein.
12
Figure 15.3a Structure of the nephron.
Cortical nephron
Collecting
duct
Renal
cortex
Renal
medulla
Fibrous capsule
Proximal
convoluted
tubule
Glomerulus
Renal
cortex
Renal
pelvis
Distal
convoluted
tubule
Ureter
Nephron loop
Renal
medulla
(a)
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Juxtamedullary
nephron
Kidney Structure: The Nephron (Con’t)
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Kidney Structure: The Nephron (Con’t)
•
Each nephron is composed of several parts.
– Glomerular capsule (Bowman’s capsule).

–
Proximal convoluted tubule.

–
Tubular reabsorption and secretion
Distal convoluted tubule.

–
Tubular reabsorption
Loop of the nephron (loop of Henle).

–
Filtration
Tubular reabsorption and secretion
Collecting duct.

Tubular reabsorption
15
16
Glomerular
capsule
Glomerular
space
Glomerulus
Blood flow
Movement of glomerular filtrate
Afferent arteriole
Efferent arteriole
a) The outer surface of
several glomerular
capillaries.
Podocyte
Filtrate
Proximal tubule
Capillary wall
b) A highly magnified view of the inner surface
of a single glomerular capillary, revealing its
porous sievelike structure.
© 2012 Pearson Education, Inc.
Figure 15.7
Renal corpuscle
Afferent
arteriole
Glomerular filtration (filtration
of blood plasma by glomerulus)
Glomerular
capsule
Renal tubule and collecting duct
Glomerulus
Glomerular filtrate
in renal tubule
1
2 Tubular reabsorption
from glomerular
filtrate into blood
Efferent
arteriole
Peritubular capillaries
3 Tubular secretion
Urine
(contains
excreted
substances)
from blood into
glomerular filtrate
Blood
(contains
reabsorbed
substances)
•
Urine Formation
Urine formation is divided into three steps.
1.
Glomerular filtration.

Filterable blood components

water

nitrogenous wastes

nutrients

salts (ions)

Nonfilterable blood components

white and red blood cell, platelets

plasma proteins
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2.
Urine Formation (Con’t)
Tubular reabsorption.

Reabsorbed filtrate components

most water

nutrients

required salts (ions)

Nonreabsorbed filtrate components

some water

much nitrogenous waste

excess salts (ions)
20
Urine Formation (Con’t)
3.
Tubular secretion.

Active removal from the blood of
some compounds, such as drugs,
with secretion into the distal
convoluted tubule
21
Filtration and Reabsorption
22
Maintaining Salt-Water Balance
•
Reabsorption of Water- Water Balance
–
–
–
Very dilute or very concentrated urine
 Dependent upon reabsorption of water from the
descending limb of loops of Henle and collecting
ducts
 Mostly juxtamedullary nephrons
Osmotic gradient exists within the tissues of the renal
medulla.
Antidiuretic hormone (ADH) released by the posterior
lobe of the pituitary (due to osmolarity of plasma)
causes more water to be reabsorbed in collecting ducts
and less urine to form
 Diuretics increase urine flow


Alcohol- inhibits ADH release from posterior
pituitary
Caffeine- inhibits reabsorption of Na+
23
Maintaining Salt-Water Balance
•
Reabsorption of Water- Water Balance
– Osmotic gradient exists within the tissues of the
renal medulla
 Creation of osmotic gradient
 Countercurrent multiplication- nephron
tubules
 Maintenance of osmotic gradient
 Countercurrent exchange- vasa recta
blood vessels
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Creation of Osmotic Gradient
Vasa
recta
Maintenance of Osmotic Gradient
Loop of
Henle
Juxtamedullary
nephron and its blood
supply together
Glomerular (Bowman’s) capsule
Afferent
arteriole
Distal convoluted
tubule
Efferent
arteriole
300
400
600
Osmotic
gradient
800
1000
Proximal
convoluted
tubule
Interstitial fluid
in renal medulla
200
HO
H2O 2
300
H2O
Interstitial
fluid in
renal cortex
Flow of tubular fluid
320
300
Collecting duct
300
H2O
300
320
100
Na+Cl–
380
H2O
200
1
580
Symporters in thick
ascending limb
cause buildup of
Na+ and Cl– in
780
renal medulla
H2O
2
Countercurrent flow
1200 through loop of
Henle establishes
osmotic gradient
H2O
Na+Cl–
Blood flow
Presence of Na+–K+–2Cl–
symporters
Glomerulus
400
H2O
400
H2O
H2O
3 Principal cells in
collecting duct
reabsorb more
water when ADH
is present
400
500
Na+Cl–
600
H2O
Na+Cl–
600
H 2O
600
Urea 800
1000
800
980
H2O
1200
Loop of Henle
(a) Reabsorption of Na+, Cl–, and water in
long-loop juxtamedullary nephron
1200
1200
4 Urea recycling
700
800
causes buildup of
urea in renal
medulla
H2O 900
H2O
Na+Cl–
1000
Na+Cl–
1100
Papillary duct
1200
Concentrated urine
(b) Recycling of salts and urea in vasa recta
Maintaining Salt-Water Balance
•
Reabsorption of Water- Water Balance
–
–
Very dilute or very concentrated urine
 Dependent upon reabsorption of water from the
descending limb of loops of Henle and collecting
ducts
 Mostly juxtamedullary nephrons
Antidiuretic hormone (ADH) released by the posterior
lobe of the pituitary (due to osmolarity of plasma)
causes more water to be reabsorbed in collecting ducts
and less urine to form
 Diuretics increase urine flow
 Alcohol- inhibits ADH release from posterior
pituitary
+
 Caffeine- inhibits reabsorption of Na
26
ADH &
Making
Dilute Urine
Afferent
arteriole
Glomerular (Bowman's) capsule
Glomerulus
Distal convoluted
tubule
Efferent
arteriole
100
300
Proximal
convoluted
tubule
90
300 300
350 350
150
Interstitial
fluid in
renal
cortex
350
Collecting
duct
550 550
750 750
350
550
550
80
Interstitial
fluid in
renal
medulla
750
70
900
Loop of
Henle
65
65
Papillary
duct
Dilute
urine
ADH & Making
Concentrated Urine
Vasa
recta
Loop of
Henle
Juxtamedullary
nephron and its blood
supply together
Glomerular (Bowman’s) capsule
Afferent
arteriole
Distal convoluted
tubule
Efferent
arteriole
300
400
600
Osmotic
gradient
800
1000
Proximal
convoluted
tubule
Interstitial fluid
in renal medulla
200
HO
H2O 2
300
H2O
Interstitial
fluid in
renal cortex
Flow of tubular fluid
320
300
Collecting duct
300
H2O
300
320
100
Na+Cl–
380
H2O
200
1
580
Symporters in thick
ascending limb
cause buildup of
Na+ and Cl– in
780
renal medulla
H2O
2
Countercurrent flow
1200 through loop of
Henle establishes
osmotic gradient
H2O
Na+Cl–
Blood flow
Presence of Na+–K+–2Cl–
symporters
Glomerulus
400
H2O
400
H2O
H2O
3 Principal cells in
collecting duct
reabsorb more
water when ADH
is present
400
500
Na+Cl–
600
H2O
Na+Cl–
600
H 2O
600
Urea 800
1000
800
980
H2O
1200
Loop of Henle
(a) Reabsorption of Na+, Cl–, and water in
long-loop juxtamedullary nephron
1200
1200
4 Urea recycling
700
800
causes buildup of
urea in renal
medulla
H2O 900
H2O
Na+Cl–
1000
Na+Cl–
1100
Papillary duct
1200
Concentrated urine
(b) Recycling of salts and urea in vasa recta
•
Maintaining Salt-Water Balance
Fluid Compartments & Fluid Balance
–
–
Intracellular fluid (ICF)- inside cells
Extracellular fluid (ECF)- outside cells
Interstitial fluid- microscopic space outside every
cell of the body
 Plasma

–
Renal processes of filtration, reabsorption,
diffusion, and osmosis promote continuous
exchange between the fluid compartments
 Thus fluid balance is directly related to
electrolyte (ions) balance
 “Wherever salt goes water follows”
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Total body
mass (female)
Total body
mass (male)
45%
Solids
40%
Solids
Renal effects
on salt
distribution
will affect
fluid
distribution
Total body
fluid
2/3
Intracellular
fluid (ICF)
55%
Fluids
60%
Fluids
Tissue
cells
Extracellular
fluid
1/3
Extracellular
fluid (ECF)
80%
Interstitial
fluid
20% Plasma
(a) Distribution of body solids and fluids in average lean, adult female and male
Blood capillary
(b) Exchange of water among body
fluid compartments
•
Maintaining Salt-Water Balance
Reabsorption of Salt.
–
Kidneys regulate blood’s salt balance by
controlling excretion and reabsorption of
various ions, most important one being Na+

–
Usually more than 99% of sodium filtered at the
glomerulus is returned to the blood
Hormonal control of salt reabsorption
Starts at juxtaglomerular apparatus (JGA)
 Decrease in blood volume/pressure-renin from the
JGA is released into blood-enzymatically cleaves
angiotensinogen to angiotensin-I, angiotensin-I
converted to angiotensin-II in lungs, angiotensin-II
stimulates release of aldosterone from adrenal
cortex, aldosterone stimulates Na+ reabsorption

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Juxtaglomerular Apparatus
32
Figure 15.3b Structure of the nephron.
Peritubular
capillaries
Proximal convoluted
tubule (PCT)
Glomerular
capillaries
Distal
convoluted
tubule
(DCT)
Glomerular
(Bowman’s)
capsule
Efferent arteriole
Afferent arteriole
Cells of the
juxtaglomerular
apparatus
Cortical radiate
artery
Arcuate artery
Arcuate
Cortical radiate
vein
vein
Collecting duct
(b)
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Nephron loop
•
Maintaining Salt-Water Balance
Reabsorption of Salt.
–
Hormonal control of salt reabsorption (Cont.)
Wherever salt goes water follows, thus increase
reabsorption of water
 Causes of decrease blood volume- blood loss
(hemorrhage), profuse sweating (includes loss of
blood water/salt), profuse vomiting, profuse diarrhea
 Reabsorption of water increases blood volume
 Decreased blood volume means decreased blood
pressure- hence increase in blood volume- increase
in blood pressure
 Thus direct link between salt regulation and blood
pressure regulation
 ADH increases to increase water reabsorption

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ADH
Blood volume
Increase
Set point
Save water
Kidneys
Decrease
Save
salt
Kidneys
Adrenal
cortex
Angiotensinconverting
enzyme
Lungs
Angiotensinogen
Vasoconstriction,
blood pressure
Liver
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Figure 15.15
36
•
Maintaining Salt-Water Balance
Reabsorption of Salt.
–
Hormonal control of salt reabsorption (Cont.)
Starts at atria of heart
+
 Increase in Na concentration in plasma- huge salt
filled meal
+
 99% of Na reabsorbed- wherever salt goes water
follow
 Water enters blood from fluid compartmentsintracellular space, then interstitial space, then into
plasma
 Increase in blood volume
 Increase stretch of atria of heart- release atrial
natriuretic peptide
+
 Causes increased salt excretion (decrease Na
reabsorption)

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•
Maintaining Salt-Water Balance
Reabsorption of Salt.
–
Hormonal control of salt reabsorption (Cont.)
Wherever salt goes water follows
 Increase removal of water from blood- decrease in
blood volume- decrease in blood pressure
 Hypertension- may be a defect in atrial
natriuretic peptide system
 What is happening to ADH during this situation?
 Increased osmolarity of blood should stimulate ADH
release but that can’t happen because that would
increase blood volume when you want to decrease
it
 Thus ADH is mostly involved when you have
changes in water affecting osmolarity not salt
affecting osmolarity

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39
40
•
•
•
Fate of Some Compounds,
Normal Amount of Urine
Nutrients- amino acids, glucose / all filtered
from blood into urine in glomerulus / all
reabsorbed in proximal / none in urine
Water and salts / most filtered from blood
into urine in glomerulus / most reabsorbed in
proximal and collecting duct / concentration
in urine dependent on need and hormones
Metabolic wastes- urea, uric acid/ all filtered
from blood into urine in glomerulus / none
reabsorbed / concentration in urine higher
than blood
41
Fate of Some Compounds,
Low Amount of Urine- After Sleeping
•
•
•
Nutrients- amino acids, glucose / all filtered from
blood into urine in glomerulus / all reabsorbed in
proximal / none in urine
Water / most filtered from blood into urine in
glomerulus / even more reabsorbed in proximal
and collecting duct due to prevention of loss
during sleep / ADH increases reabsorption in
collecting duct
Metabolic wastes- urea, uric acid/ all filtered from
blood into urine in glomerulus / none reabsorbed /
concentration in urine much higher than under
normal condition due to less water
42
© 2012 Pearson Education, Inc.
Table 15.1
Fate of Some Compounds,
High Amount of Urine- After McDonalds Meal
•
•
•
Nutrients- amino acids, glucose / all filtered from
blood into urine in glomerulus / all reabsorbed in
proximal / none in urine
Salt and water / most filtered from blood into urine
in glomerulus / most reabsorbed in proximal and
collecting duct / high salt in food, goes into blood,
water follows, increase volume, increase pressure,
ANH released, salt reabsorption decreased, ADH
turned off, water follows salt into urine
Metabolic wastes- urea, uric acid/ all filtered from
blood into urine in glomerulus / none reabsorbed /
concentration in urine lower than normal due to
large amount of water in urine
44
Maintaining Blood pH
•
Reabsorption of bicarbonate ions and
secretion of hydrogen ions
•
Exhalation of Carbon Dioxide
45
Maintaining Blood pH
46
•
•
•
•
•
Homeostasis
In conjunction with the lungs, maintenance
of acid-base balance.
Maintenance of water-salt balance of blood
and the overall osmolarity.
Helps regulate blood volume and pressure.
– Releases-erythropoietin; increases
number of red blood cells
Regulates the concentration of important
ions such as calcium (Ca2+) and potassium
(K+).
In conjunction with the liver, excretion of
metabolic wastes.
47
Need to Know
1.
2.
Functions of the urinary system
A.
Metabolic waste excretion
B.
Salt-Water balance
C.
Blood pressure regulation
D.
Acid-base balance
E.
Red blood cell quantity regulation
F.
Activation of inactive Vitamin D
Kidney Structure: The Nephron
A.
Afferent and efferent arterioles
B.
Glomerulus
C.
Peritubular capillary network
48
Need to Know (Cont.)
2.
3.
Kidney Structure: The Nephron (Cont.)
D.
Glomerular capsule
E.
Proximal convoluted tubule
F.
Loop of the nephron
G.
Distal convoluted tubule
H.
Collecting duct
Urine formation
A.
Glomerular filtration concept
B.
Tubular reabsorption concept
C.
Tubular secretion concept
D.
Must know what’s filtered and not filtered,
what’s reabsorbed and not reabsorbed and
what’s secreted
49
Need to Know (Cont.)
4.
5.
Reabsorption of salt
A.
Juxtaglomerular apparatus
B.
Renin-angiotensin-aldosterone system
C.
Atria natriuretic hormone
D.
Blood pressure regulation
Acid-Base balance
A.
Reabsorption of bicarbonate ion
B.
Excretion of hydrogen ion
50
Need to Know (Cont.)
6.
7.
Kidney Structure: Gross anatomy
A.
Renal cortex
B.
Renal medulla
C.
Renal pelvis
Urinary system: General
A.
Kidney
B.
Ureters
C.
Urinary bladder
D.
Urethra
51