Bio40C schedule
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Chapter 26:
The Urinary System
Lecture exam 1
AVG = 74
Scores posted by DeAnza 4 digit ID#
Look at your scantrons in lab
Extra credit


Critical thinking questions at end of
chapters (5 pts/chapter)
Due anytime before Mar 11
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Kidney functions
The nephron: know its parts

Excretion of metabolic wastes

Urea and other nitrogenous wastes
Maintenance of salt and water balance

Maintenance of acid-base balance

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Blood volume, blood pressure
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Blood pH = 7.4
Production of hormones
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Renal corpuscle – filters
blood plasma
Renal tubule – processes
the filtered fluid
1.
2.
Calcitriol (active form of vitamin D)
Erythropoietin (stimulates RBC production)
3.

Glomerulus – capillary
network
Glomerular (Bowman’s)
capsule – double-walled cup
surrounding glomerulus
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
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Urine formation:
excretion of metabolic wastes

Renal tubule and collecting duct
Renal corpuscle
Afferent
arteriole
carbon
backbone
Glomerular
capsule
1 Filtration of
plasma
Efferent
arteriole
What causes
high filtration
pressure?
Urine
Fluid in
renal tubule
Water
Glucose
Amino acids
Salts
Urea, etc.
Urea – a metabolic waste
2
3

Water
Salts
Urea, etc

Water
Glucose
Amino acids
NaCl (65%)
H+ ions
Creatinine
Drug metabolites
Selective active
transport
glom. Filtration 1:10
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Sons, Inc.

Amino acid catabolism: the
amino group is removed and
converted to ammonia
NH3 is a toxic substance, and
can damage the brain and
cause coma.
Usually, the ammonia is
converted into urea in the liver
and the urea transported
through the blood to the
kidneys
Urea is excreted in the urine
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1
Test your understanding

Glucose and protein are both normally
absent in urine, but for different
reasons.

Explain why glucose is absent

Explain why protein is absent
Kidney functions

Excretion of metabolic wastes

Maintenance of salt and water balance

 Blood volume, blood pressure
Maintenance of acid-base balance
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Production of hormones
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It’s reabsorbed in the renal tubule

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It isn’t filtered through the glomerulus
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Homeostasis of body fluid volume
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Fluid intake is highly variable, but total
volume of fluid in the body is stable
Kidneys regulate rate of water loss in
urine
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High fluid intake → lots of dilute urine
Low fluid intake → a little concentrated
urine
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Forming an osmotic gradient
in the medulla
cortex
The descending and
ascending limbs of the loop of
Henle have different
permeability characteristics
medulla
Descending limb:
permeable to water
Ascending limb:
impermeable to water;
active transport of NaCl
out of filtrate
Called countercurrent flow
because the fluids are moving in
opposite directions
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Urea and other nitrogenous wastes
Blood pH = 7.4
Calcitriol (active form of vitamin D)
Erythropoietin (stimulates RBC production)
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How do kidneys produce dilute or
concentrated urine?

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Kidneys can change the osmotic
concentration of the urine
Osmotic concentration of a solution =
total number of dissolved particles/liter
Osmolarity
plasma
300 mOsm
sea water
1000 mOsm
fresh water
5 mOsm
conc’d urine
1400 mOsm
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Generating an osmotic
gradient in the medulla
The ability to concentrate
urine depends on generating
an osmotic gradient in the
medulla.
 The loops of Henle are set
up to concentrate osmolarity
in the deepest part of the
medulla.
 This occurs because the
ascending and descending
limbs have different
permeabilities to salt and
water.
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Generating an osmotic
gradient in the medulla
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In the ascending limb, Na+ and
Cl- are pumped out of the
filtrate into the ECF
This increases the osmotic
concentration in the fluid
around the loop of Henle
Result: water leaves the filtrate
in the descending limb and the
filtrate becomes more
concentrated
Generating an osmotic
gradient in the medulla

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Countercurrent flow in the loop of
Henle causes the osmolarity
differences to multiply as the renal
tubule descends into the medulla
The filtrate inside the descending
limb becomes progressively more
concentrated.
But in ascending limb, active
reabsorption of ions causes the
filtrate to become less
concentrated.
The result is that osmolarity
becomes trapped in the medulla.
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Blood flow in the medulla
maintains the osmotic gradient
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The vasa recta are capillaries that
flow in parallel to the loops of
Henle.
The osmolarity of the plasma
inside the vasa recta increases
as it descends into the medulla,
and then decreases again on the
ascending side.
This allows blood to flow to the
medulla, without eliminating the
osmotic gradient.
Copyright 2009, John Wiley &
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How do the kidneys vary their
urine concentrating ability?
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vasa recta
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They regulate water reabsorption in
the collecting ducts
The permeability of cell membranes to
water depends upon the presence of
water channels known as aquaporins
When ADH binds to its receptor on
the collecting duct cells, it stimulates
the insertion of aquaporins into the
membrane
Increases reabsorption of water,
makes urine more concentrated and
increase blood volume
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ADH controls blood (and
urine) volume

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Antidiuretic hormone
In the absence of
ADH, urine is dilute
(water is excreted)
A high level of ADH
stimulates
reabsorption of
water into the blood,
producing a
concentrated urine
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YouTube

Function of the nephron 2:32

http://www.youtube.com/watch?v=glu0dzK4dbU&f
eature=related
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3
Recap: Production of dilute &
concentrated urine
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In the absence of ADH, kidneys produce dilute urine
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Aldosterone
Renal tubules absorb less water
↑ reabsorption of water & salts
↑ blood volume
↓ urine volume
In the presence of ADH, kidneys produce a
concentrated urine
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Homeostasis of body fluid volume
Large amts of water are reabsorbed from the fluid in the
tubules
ADH
↑ reabsorption of water
↑ blood volume
↓ urine volume
The countercurrent multiplier establishes an osmotic
gradient in the renal medulla that enables production
of concentrated urine when ADH is present
Urine volume
1. Osmotic gradient in renal medulla
2. ADH
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Diabetes insipidus
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Defect in the ability to concentrate urine
Causes:
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lack of ADH
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genetic mutation where ADH is missing or defective
defect in the ability of the kidney to respond to ADH
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defect in ADH receptors
defect in the gene for AQP2. This prevents the proper
localization of AQP2 proteins on the apical membrane of
collecting duct cells
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Natural diuretics
Caffeine – inhibits
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reabsorption
(water follows Na+)
Alcohol – inhibits secretion of ADH
Most act by promoting loss of NaCl in the
urine
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Substances that slow renal reabsorption
of water → increases urine volume
This in turn reduces blood volume
Diuretic drugs are prescribed to treat
hypertension

Lowering blood volume usually reduces
blood pressure
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
Na+
Diuretic drugs
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Diuretics
Urine transport, storage and
elimination
Diuretics
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Urine drains into the renal
pelvis
Ureters transport urine to the
bladder
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Inhibit transport proteins responsible for Na+
reabsorption
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Primarily by peristalsis
hydrostatic pressure and
gravity contribute
No anatomical valve at the
opening of the ureter into
bladder – when bladder fills
it compresses the opening
and prevents backflow
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4
Micturition reflex
Urinary bladder
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Hollow, muscular organ
Capacity 700-800 mL
In the floor of the urinary
bladder is a small, smooth
triangular area, the trigone.
The ureters enter the urinary
bladder near two posterior
points in the triangle; the
urethra drains the urinary
bladder from the anterior point
of the triangle
Two sphincters
 external urethral sphincter
is composed of skeletal
(voluntary) muscle
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discharge of urine from bladder
Combination of voluntary and
involuntary muscle contractions
When urine volume increases,
stretch receptors in the urinary
bladder wall transmit impulses
that initiate a spinal micturition
reflex
In early childhood we learn to
initiate and stop it voluntarily
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Urinary incontinence
Urethra

Micturition = urination
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The urethra is a tube
leading from the floor of
the urinary bladder to
the exterior
The function of the
urethra is to discharge
urine from the body
The male urethra
serves as a duct for
semen as well as urine
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A lack of voluntary control over
urination
In children under 2-3 years old
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Incontinence in adults

Overflow incontinence
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Stress incontinence
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If the urethra is blocked, the
bladder overfills and the pressure
causes small amts of urine to leak
out
Evaluation of kidney function

Due to weak muscles of pelvic floor
Coughing and other stresses that
increase abdominal pressure cause
urine leakage
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common in older people
Abrupt urge to urinate
Causes: irritation of bladder by
infection, neurologic disorders
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Blood composition depends on 3 major
factors
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Diet, cellular metabolism, urinary output
In 24 hours
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Urge incontinence
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Incontinence is normal
Neurons to the external urethral
sphincter muscle are not
completely developed
Voiding occurs when the bladder
is sufficiently distended to
stimulate the micturition reflex
the nephrons filter 150-180 L of plasma
selectively process the filtrate in the renal tubules
Urinary output is 1-1.8 L of urine which contains
by-products of metabolism and excess ions
Certain pathological conditions change urine
composition dramatically
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5
Evaluation of kidney function
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Urinalysis
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Analysis of the volume and physical, chemical and microscopic
properties of urine
Water accounts for 95% of total urine volume
Typical solutes in urine:

Evaluation of kidney function
Electrolytes that are not reabsorbed
Urea (from breakdown of protein)
Creatinine (from breakdown of creatine phosphate in muscle)
Uric acid (from breakdown of nucleic acids)
Blood tests

Blood urea nitrogen (BUN) – measures blood nitrogen that is
part of the urea
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Plasma creatinine – results from catabolism of creatine
phosphate in skeletal muscle
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Normal urine is protein-free
A valuable diagnostic tool
High BUN indicates abnormally low GFR
May indicate renal disease or obstruction of urinary tract
An elevated creatinine level indicates poor renal function
If disease alters metabolism or kidney function, traces if substances
normally not present or normal constituents in abnormal amounts may
appear

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Evaluation of kidney function
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Renal plasma clearance
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Measures how effectively the kidneys remove (clear) a
substance from blood plasma
More useful in diagnosis of kidney problems than above
The clearance of inulin gives the glomerular filtration rate
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Disorders of the urinary tract
Inulin is filtered but not reabsorbed or secreted
The clearance of PAH (para-aminohippuric acid) measures
renal plasma flow

PAH is is filtered and secreted in a single pass through the
kidneys
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Urinary tract infection
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Urinary tract infection (UTI)
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an infection of a part of the urinary system or
the presence of large numbers of microbes in
urine.
More common in females due to shorter
length of the urethra
UTIs include

Kidney stones (renal calculi)
urethritis (inflammation of the urethra)
cystitis (inflammation of the urinary bladder)
pyelonephritis (inflammation of the kidneys)
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Crystals of salts present in urine can
precipitate and solidify into insoluble stones
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crystals commonly contain calcium
When a stone lodges in a ureter, the pain can
be intense
Rx: shock wave lithotripsy (litho =stone),
surgery

High-energy shock waves disintegrate the stone
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6
Renal failure
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Renal failure
Kidney failure can be caused by injury, illness, or
many other factors
Chronic renal failure – a progressive and generally
irreversible decline in glomerular filtration rate
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Stage 1: Many nephrons are destroyed, but no symptoms
Stage 2: Renal insufficiency: 75% of nephrons are lost,
decreased GFR, increase in BUN
Stage 3: End-stage renal failure: 90% of nephrons are lost,
further increase in plasma urea and createnine

Patient needs dialysis therapy or kidney transplant
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Dialysis
Artificial cleansing of the blood
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Hemodialysis directly filters the patient’s blood by
removing wastes and excess electrolytes and
returning the cleansed blood to the patient
Dialysis for kidney disease 1:29

http://www.youtube.com/watch?v=JXQb-0aDSrc
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Case study 1

Jacob Rollins, 69 year old male, presents in his physician's
office for a post-surgery check up. He was diagnosed with
benign prostate hypertrophy several years ago and had surgery
6 weeks ago. His catheter was removed 4 weeks ago. He
reports that he hasn't felt well the past week. He has had some
back, side and groin pain and noticed an increased urgency and
burning with urination. He noticed that his urine has a pink tinge
yesterday. His vital signs reveal fever and an increased heart
rate. His urine test reveals bacteria. What do you suspect?


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Prostate cancer
UTI related to recent indwelling catheter
Kidney stone
Nothing, this is normal in the pos-operative period
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Figure 21.18
Case Study 2

A 23 year old male presents to the emergency room
complaining of severe sharp, rhythmic pain in the left
side and back. The pain was of sudden onset. He
reports that he also feels nauseated. His urine is
positive for blood. Based upon his history and
symptoms you would suspect:
 Glomerulonephritis (inflamed glomeruli)
 A kidney stone
 A urinary tract infection
 Early renal failure
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7
Case study 3
Case study 3 (cont)
J.S. is a 39-year-old male truck driver who presented
to the ER on a Friday night complaining of polyuria
(excessive urination), excessive thirst, and fatigue of
2 weeks' duration. He also reported a 15- to 20-lb
weight loss over the past 1-2 months.
He was taking no medications. There was no family
history of diabetes, hypertension, or heart disease.
His physical exam was remarkable only for signs of
mild dehydration. His BMI is 32.
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Urinalysis results:
Urine glucose >1000 mg/dl
Urine ketones >40 mg/dl
Based upon his history and symptoms you
would suspect __?__

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Diabetes mellitus
Type 1 or Type 2?
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Kidney functions

Excretion of metabolic wastes

 Urea and other nitrogenous wastes
Maintenance of salt and water balance

Maintenance of acid-base balance

Production of hormones



Blood pH = 7.4



Calcitriol (active form of vitamin D)
Erythropoietin (stimulates RBC production)
Calcitriol (active form of
vitamin D)
Vitamin D metabolism

Blood volume, blood pressure


Production of calcitriol

Precursor formed in skin
Metabolized in liver
Converted to active form in
the proximal tubule of kidney
Calcitriol increases blood
calcium levels by


increasing absorption of
calcium from the GI tract
increasing reabsorption of
calcium in renal tubule.
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Production of erythropoietin

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Erythropoietin – stimulates RBC
production
Specific sensors in the kidney monitor
O2 content of blood.
If blood O 2 is low, the kidneys
increase production of erythropoietin
(EPO).
EPO stimulates proliferation of RBC
progenitor cells in the bone marrow
The number of RBCs increases,
correcting tissue hypoxia.
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Calcitriol =
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Homework

Look over Ch 27

Fluid, electrolyte and acid-base
homeostasis
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8