Download chapter 23

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Functions of urinary system
Anatomy of kidney
Urine formation
glomerular filtration
 tubular reabsorption
 tubular secretion
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Urine and renal function tests
Urine storage and elimination
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Is the passive transport of WATER across a
selectively permeable membrane
Two kidneys
Two ureters
One urethra
23-3
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Filters blood plasma
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returns useful substances to blood
eliminates waste
Regulates
osmolarity of body fluids, blood volume, BP
 acid base balance
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Secretes
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renin and erythropoietin
Detoxifies free radicals and drugs
Gluconeogenesis
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Urea (most abundant)
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Uric acid
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nucleic acid catabolism
Creatinine
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proteinsamino acids NH2
removed forms ammonia
liver converts to urea
creatine phosphate catabolism
Renal failure
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azotemia is defined as BUN,
nitrogenous wastes in blood
uremia is a term used more loosely =
toxic effects of  nitrogenous wastes
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Separation of wastes from body fluids and
eliminating them; by four systems
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Lungs: CO2
Skin: water, salts, lactic acid, urea
Digestive: water, salts, CO2, lipids, bile pigments,
cholesterol
Urinary: many metabolic wastes, toxins, drugs,
hormones, salts, H+ and water
23-6
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Position, weight and size
retroperitoneal, level of T12 to L3
 about 160 g each
 about size of a bar of soap (12x6x3 cm)
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Shape
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lateral surface - convex; medial - concave
Connective tissue coverings
renal fascia: binds to abdominal wall
 adipose capsule: cushions kidney
 renal capsule: encloses kidney like cellophane
wrap
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23-7
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Renal cortex: outer 1 cm
Renal medulla: renal columns, pyramids - papilla
Lobe of kidney: pyramid and it’s overlying cortex
23-8
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Notice where the nephron sits
Where is the glomerulus?
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Nephrons connect to
collecting ducts
- Glomerulus (vascular)
- Bowman’s Capsule (collecting)
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Renal artery
 interlobar arteries (up renal columns, between lobes)
 arcuate arteries (over pyramids)
 interlobular arteries (up into cortex)
 afferent arterioles
 glomerulus (cluster of capillaries)
 efferent arterioles (near medulla  vasa recta)
 peritubular capillaries
 interlobular veins  arcuate veins  interlobar veins
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Renal vein
23-11
The glomerulus is a portal system
no segmental
veins
23-12
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Proximal convoluted tubule
(PCT)
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Nephron loop - U shaped;
descending and ascending
limbs
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longest, most coiled, simple
cuboidal with brush border
thick segment (simple
cuboidal) initial part of
descending limb and part or
all of ascending limb, active
transport of salts
thin segment (simple
squamous) very water
permeable
Distal convoluted tubule
(DCT) – typo on pg 901
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cuboidal, minimal microvilli
Arcuate artery
and vein
Interlobular
artery and vein
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Collecting duct
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several DCT’s join
Flow of glomerular
filtrate:
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glomerular capsule  PCT
 nephron loop  DCT 
collecting duct  papillary
duct  minor calyx 
major calyx  renal pelvis
 ureter  urinary
bladder  urethra
Arcuate
Arcuate artery
artery
and
and vein
vein
Interlobar
artery
Interlobular
andand
veinvein
artery
23-14
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True proportions of nephron loops to
convoluted tubules shown
Cortical nephrons (85%)
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short nephron loops
efferent arterioles branch off peritubular
capillaries
Juxtamedullary nephrons (15%)
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very long nephron loops, maintain salt
gradient, helps conserve water
Arcuate artery
and vein
Interlobular
artery and23-15
vein
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Peritubular
capillaries
shown only on
right
23-16
23-18
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Fenestrated endothelium
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70-90nm pores exclude blood cells
Basement membrane
proteoglycan gel, negative charge
excludes molecules > 8nm
 blood plasma 7% protein, glomerular
filtrate 0.03%
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Filtration slits
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podocyte arms have pedicels with
negatively charged filtration slits,
allow particles < 3nm to pass
23-19
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GFR = mls of filtrate
formed per minute
filtration coefficient (Kf)
depends on permeability
and surface area of
filtration barrier
Blood hydrostatic
pressure is higher than
usual capillaries
99% of filtrate reabsorbed, 1 to 2 L urine excreted
23-20
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GFR = mls of filtrate
formed per minute
filtration coefficient (Kf)
depends on
permeability and
surface area of filtration
barrier
Blood hydrostatic
pressure is higher than
usual capillaries
99% of filtrate reabsorbed, 1 to 2 L urine excreted
23-21
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Hypertension ruptures glomerular capillaries
Leads to scarring of glomeruli
Scarred glomeruli have decreased permeability
thus decreased GFR
Nitrogenous wastes accumulate
Kidney failure
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Inappropriate increase in GFR, urine output rises
can result in dehydration and electrolyte depletion
If disease GFR  wastes are not efficiently
excreted (azotemia possible)
If MAP rose from 100 to 125 mmHg then, in the
absence of control mechanisms, urine output
would rise to 45 liters/day
GFR controlled by adjusting glomerular blood
pressure
1.
2.
3.
Autoregulation
Sympathetic control
Hormonal mechanisms: renin and angiotensin
23-23
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Juxtaglomerular Cells
 dilate or constrict
arterioles
 secrete renin
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Mesangial Cells
 Mysterious function
 Gap junctions
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Macula Densa Cells
 monitors salinity
 inhibit renin release
23-24
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Myogenic mechanism
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 BP  stretches afferent arteriole  afferent
arteriole constricts  restores GFR
Tubuloglomerular feedback
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Macula densa on DCT monitors tubular fluid for
high salt and signals juxtaglomerular cells (smooth
muscle, surrounds afferent arteriole) to constrict
afferent arteriole to  GFR
23-25
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If BP  constrict
afferent arteriole and
dilate efferent to bring
GFR back to normal
If BP   dilate
afferent arteriole and
constrict efferent
Stable for BP range of
80 to 170 mmHg
(systolic)
Cannot compensate for
extreme hypertension
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Strenuous exercise or acute conditions (circulatory
shock) stimulate afferent arterioles to constrict
through both innervation and epinephrine effect
This results in  GFR and  urine production,
redirecting blood flow to heart, brain and skeletal
muscles
23-27
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JG cells secrete renin when
blood pressure drops
Renin is an enzyme that acts
in the production of
angiotensin II
23-29
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Azotemia
Uremia
Glycosuria
Pyuria
Glomerulonephritis
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Urinary incontinence
Renal failure
Oliguria
Proteinuria
UTI - cystitis
23-31
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There is about 180 liters
of glomerular filtrate
each day!
The renal tubules act to
maximize retention of
water and Na+ while
maximizing elimination
of wastes
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Blood has unusually high
COP here, and BHP is
only 8 mm Hg (or lower
when constricted by
angiotensin II); this
favors reabsorption
Water absorbed by
osmosis and carries
other solutes with it
(solvent drag)
23-33
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Reabsorbs 65% of GF to
peritubular capillaries
Great length, prominent microvilli
and abundant mitochondria for
active transport
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Reabsorbs greater variety of
chemicals than other parts of
nephron
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transcellular route - through
epithelial cells of PCT
paracellular route - between
epithelial cells of PCT
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Transport maximum
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when transport proteins of cell
membrane are saturated
blood glucose > 220 mg/dL some
remains in urine (glycosuria)
Solvent drag
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Waste removal
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Acid-base balance
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urea, uric acid, bile salts,
ammonia, catecholamines,
many drugs
secretion of hydrogen and
bicarbonate ions regulates
pH of body fluids
Primary function of nephron loop
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Arcuate artery
and vein
Interlobar artery
Arcuate artery
and vein
and vein
water conservation
generates salinity gradient, allows DCT to concentrate urine
also involved in electrolyte reabsorption
23-37
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Principal cells (more abundant) –
receptors for hormones
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involved in salt/water balance
Intercalated cells (lots of mitochondria)
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involved in acid/base balance
K+ in, H+ out
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Action affected by hormones
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ADH
Atrial Natriuretic Peptide
Aldosterone
Parathyroid
Effect of ADH
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dehydration stimulates hypothalamus
hypothalamus stimulates posterior pituitary
posterior pituitary releases ADH
ADH  water reabsorption
 urine volume
Atrial natriuretic peptide (ANP)
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atria secrete ANP in response to high blood pressure
has four actions:
1. dilates afferent arteriole, constricts efferent arteriole -  GFR
2. inhibits renin/angiotensin/aldosterone pathway
3. inhibits secretion and action of ADH
4. inhibits NaCl reabsorption
Promotes Na+ and water excretion,  urine volume, 
blood volume and BP
23-40
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Aldosterone effects
 BP  renin release  angiotensin II
formation
 angiotensin II stimulates adrenal cortex
 adrenal cortex secretes aldosterone
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 promotes Na+ reabsorption  promotes
water reabsorption   urine volume 
maintains BP
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Effect of PTH
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 calcium reabsorption in DCT -  blood Ca2+
 phosphate excretion in PCT,  new bone formation
stimulates kidney production of calcitriol
23-42
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Osmolarity is 4x as
concentrated deep in
medulla
Medullary portion of CD
is more permeable to
water than to NaCl
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Producing hypotonic urine
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NaCl reabsorbed by cortical collecting ducts (CD’s)
water remains in urine
Producing hypertonic urine
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dehydration   ADH   aquaporin channels,
 CD’s water permeability
more water is reabsorbed
urine is more concentrated
is possible only because of the countercurrent
multiplier
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Recaptures NaCl and returns it to renal medulla
Descending limb
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The thick segment of the ascending limb
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reabsorbs water but not salt
concentrates tubular fluid
reabsorbs Na+, K+, and Clmaintains high osmolarity of renal medulla
impermeable to water
tubular fluid becomes hypotonic
Recycling of urea: collecting duct-medulla
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urea accounts for 40% of high osmolarity of medulla
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Descending capillaries
water diffuses out of blood
 NaCl diffuses into blood
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Formed by vasa recta
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provide blood supply to medulla
do not remove NaCl from medulla
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Ascending capillaries
water diffuses into blood
 NaCl diffuses out of blood
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Some species of E. coli live harmlessly in your GI tract
A few types of bacteria, usually E. coli strain O157:H7,
cause food poisoning and are nephrotoxic
Shiga toxin enters the bloodstream, attaches to renal
endothelium and initiates an inflammatory reaction
leading to acute renal failure (ARF)
The toxin also initiates destruction of RBCs and platelets
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Appearance
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almost colorless to deep amber; yellow color due to
urochrome, from breakdown of hemoglobin (RBC’s)
Odor - as it stands bacteria degrade urea to ammonia
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Specific gravity
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density of urine ranges from 1.001 -1.028
Osmolarity - (blood - 300 mOsm/L) ranges from
50 mOsm/L to 1,200 mOsm/L in dehydrated person
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pH - range: 4.5 - 8.2, usually 6.0
Chemical composition: 95% water, 5% solutes
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urea, NaCl, KCl, creatinine, uric acid
Normal urine does
not contain glucose
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Normal volume - 1 to 2 L/day
Polyuria > 2L/day
Oliguria < 500 mL/day
Anuria - 0 to 100 mL/day
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Chronic polyuria of metabolic origin
With hyperglycemia and glycosuria
diabetes mellitus I and II, insulin
hyposecretion/insensitivity
 gestational diabetes, 1 to 3% of pregnancies
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ADH hyposecretion
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diabetes insipidus; CD  water reabsorption
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Effects
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Uses
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 urine output
 blood volume
hypertension and congestive heart failure
Mechanisms of action
 GFR
  tubular reabsorption
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Renal clearance: volume of plasma cleared of a waste
in 1 minute
Determine renal clearance (C) by assessing blood and
urine samples: C = UV/P
U (waste concentration in urine)
 V (rate of urine output)
 P (waste concentration in plasma)
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Determine GFR: inulin is neither reabsorbed or
secreted so its GFR = renal clearance GFR = UV/P
Clinical GFR estimated from creatinine excretion
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Ureters (about 25 cm or 10 inches long)
 from renal pelvis passes dorsal to bladder and
enters it from below, with a small flap of mucosa
that acts as a valve into bladder
 3 layers
 adventitia - CT
 muscularis - 2 layers of smooth muscle with 3rd
layer in lower ureter
 urine enters, it stretches and contracts in peristaltic
wave
 mucosa - transitional epithelium
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lumen very narrow, easily obstructed
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Located in pelvic cavity, posterior to pubic symphysis
3 layers
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parietal peritoneum, superiorly; fibrous adventitia rest
muscularis: detrusor muscle, 3 layers of smooth muscle
mucosa: transitional epithelium
Trigone: openings of ureters and urethra, triangular
rugae: relaxed bladder wrinkled, highly distensible
capacity: moderately full - 500 ml, max. - 800 ml
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3 to 4 cm long
External urethral orifice
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between vaginal orifice and
clitoris
Internal urethral sphincter
detrusor muscle thickened,
smooth muscle
 involuntary control
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External urethral sphincter
skeletal muscle
 voluntary control
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much longer than the
female urethra
Internal urethral sphincter
External urethral sphincter
3 regions
prostatic urethra
during orgasm receives semen
membranous urethra
passes through pelvic cavity
spongy (penile) urethra
200 ml urine in bladder, stretch receptors send signal
to sacral spinal cord
Signals ascend to
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Signals descend to
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further inhibit sympathetic neurons
stimulate parasympathetic neurons
Result
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urinary bladder contraction
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relaxation of internal urethral sphincter
External urethral sphincter - corticospinal tracts to sacral
spinal cord inhibit somatic neurons - relaxes
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inhibitory synapses on sympathetic neurons
micturition center (integrates info from amygdala, cortex)