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Chapter 23
Lecture
Outline
See PowerPoint Image Slides
for all figures and tables pre-inserted intoPowerPoint without notes.
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The Urinary System
Functions of urinary system
Anatomy of kidney
Urine formation glomerular filtration - podocytes
tubular reabsorption
tubular secretion
Urine and renal function tests
Urine storage and elimination
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Urinary System
Two kidneys
Two ureters
Urethra
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Kidney Location
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Kidney Functions
Filters blood plasma returns useful substances to blood
eliminates waste
Regulates osmolarity of body fluids, blood volume, BP
acid base balance
Secretes renin and erythropoietin
Detoxifies free radicals and drugs
Gluconeogenesis
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Nitrogenous Wastes
Urea proteinsamino acids NH2
removed forms ammonia, liverconverts to urea
Uric acid nucleic acid catabolism
Creatinine creatine phosphate catabolism
Renal failure azotemia: BUN, nitrogenous
wastes in blood
uremia: toxic effects as wastes
accumulate
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Excretion
Separation of wastes from body fluids andeliminating them; by four systems
respiratory: CO2
integumentary: water, salts, lactic acid, urea
digestive: water, salts, CO2, lipids, bile
pigments, cholesterol
urinary: many metabolic wastes, toxins,drugs, hormones, salts, H+and water
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Anatomy of Kidney
Position, weight and size retroperitoneal, level of T12 to L3
about 160 g each
about size of a bar of soap (12x6x3 cm) Shape
lateral surface - convex; medial - concave
CT coverings renal fascia: binds to abdominal wall
adipose capsule: cushions kidney
renal capsule: encloses kidney like cellophane
wrap
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Anatomy of Kidney
Renal cortex: outer 1 cm
Renal medulla: renal columns, pyramids - papilla
Lobe of kidney: pyramid and it
s overlying
cortex
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Lobe of Kidney
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Renal Corpuscle
Glomerular filtrate collects in capsular space, flows into renal tubule
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Renal (Uriniferous) Tubule Proximal convoluted
tubule (PCT) longest, most coiled,
simple cuboidal withbrush border
Nephron loop - Ushaped; descendingand ascending limbs thick segment
(simple cuboidal)initial part ofdescending limb andpart or all ofascending limb,active transport of
salts thin segment (simple
squamous) verywater permeable
Distal convolutedtubule (DCT)
cuboidal, minimalmicrovilli
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Renal (Uriniferous) Tubule 2
Collecting duct several DCT
s join
Flow of glomerular
filtrate: glomerular capsule
PCT nephronloop DCTcollecting duct
papillary ductminor calyxmajor calyx renalpelvis ureterurinary bladderurethra
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Nephrons
True proportions of nephronloops to convoluted tubules
shown
Cortical nephrons (85%)
short nephron loops
efferent arterioles branch off
peritubular capillaries
Juxtamedullary nephrons
(15%)
very long nephron loops,
maintain salt gradient, helps
conserve water
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Nephron Diagram
Peritubular capillaries shown only on right
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Path of Blood Through Kidney
Renal artery
interlobararteries(up renal columns, between lobes)
arcuatearteries(over pyramids)
interlobulararteries(up into cortex)afferentarterioles
glomerulus(cluster of capillaries)
efferentarterioles(near medulla vasa recta)
peritubular capillaries
interlobular veins arcuate veins interlobar veins
Renal vein
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Blood Supply Diagram
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Urine Formation Preview
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Filtration Membrane Diagram
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Filtration Membrane
Fenestrated endothelium 70-90nm pores exclude blood
cells
Basement membrane proteoglycan gel, negative
charge excludes molecules >8nm
blood plasma 7% protein,
glomerular filtrate 0.03% Filtration slits
podocyte arms have pedicelswith negatively charged filtrationslits, allow particles < 3nm topass
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Filtration Pressure
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Glomerular Filtration Rate (GFR)
Filtrate formed per minute
GFR = NFP x Kf 125 ml/min or 180 L/day, male
GFR = NFP x Kf
105 ml/min or 150 L/day, female filtration coefficient (Kf) depends on permeability and
surface area of filtration barrier
99% of filtrate reabsorbed, 1 to 2 L urine
excreted
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Effects of GFR Abnormalities
GFR, urine output rises dehydration,electrolyte depletion
GFR wastes reabsorbed (azotemia
possible)
GFR controlled by adjusting glomerular
blood pressure
autoregulation
sympathetic control
hormonal mechanism: renin and angiotensin
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Juxtaglomerular Apparatus
- vasomotion
- monitor salinity
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Renal Autoregulation of GFR
BP constrictafferent arteriole, dilateefferent
BP dilate afferentarteriole, constrictefferent
Stable for BP range of
80 to 170 mmHg(systolic)
Cannot compensate for
extreme BP
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Renal Autoregulation of GFR
Myogenic mechanismBP stretches afferent arteriole afferent
arteriole constricts restores GFR
Tubuloglomerular feedback Macula densa on DCT monitors tubular fluid
and signals juxtaglomerular cells (smooth muscle,
surrounds afferent arteriole)
to constrict afferentarteriole to GFR
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Negative Feedback Control of GFR
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Sympathetic Control of GFR
Strenuous exercise or acute conditions(circulatory shock) stimulate afferent
arterioles to constrict
GFR and urine production, redirectingblood flow to heart, brain and skeletal
muscles
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Renin-Angiotensin-Aldosterone
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Effects of Angiotensin II
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Tubular Reabsorption and Secretion
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Peritubular Capillaries
Blood has unusually high COP here, andBHP 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)
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Proximal Convoluted Tubules (PCT)
Reabsorbs 65% of GF to peritubular capillaries
Great length, prominent microvilli and abundant
mitochondria for active transport
Reabsorbs greater variety of chemicals thanother parts of nephron
transcellular route - through epithelial cells of PCT
paracellular route - between epithelial cells of PCT
Transport maximum: when transport proteins of cell
membrane are saturated; bloodglucose > 220 mg/dLsome remains in urine (glycosuria); glucose Tm = 320
mg/min
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Mechanisms of Reabsorption in the Proximal Convoluted Tubule
T b l S ti f PCT
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Tubular Secretion of PCT
and Nephron Loop
Waste removal
urea, uric acid, bile salts, ammonia,catecholamines, many drugs
Acid-base balance secretion of hydrogen and bicarbonate ions
regulates pH of body fluids
Primary function of nephron loop water conservation
generates salinity gradient, allows CD to conc.urine
also involved in electrolyte reabsorption
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DCT and Collecting Duct
Principal cells
receptors for hormones;involved in salt/water balance
Intercalated cells involved in acid/base
balance Function
fluid reabsorption here is variable, regulated
by hormonal action
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DCT and Collecting Duct
Aldosterone effectsBP renin release angiotensin II
formation
angiotensin II stimulates adrenal cortex
adrenal cortex secretes aldosterone
promotes Na+reabsorption promotes water
reabsorption urine volume maintains BP
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DCT and Collecting Duct
Effect of ADH dehydration stimulates hypothalamus
hypothalamus stimulates posterior pituitary
posterior pituitary releases ADH
ADH water reabsorption
urine volume
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DCT and Collecting Duct
Atrial natriuretic peptide (ANP) atria secrete ANPin response to BP
has four actions:
1. dilates afferent arteriole, constricts efferent
arteriole - GFR
2. inhibits renin/angiotensin/aldosterone
pathway
3. inhibits secretion and action of ADH4. inhibits NaCl reabsorption
Promotes Na+and water excretion,
urine volume,
blood volume and BP
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DCT and Collecting Duct
Effect of PTHcalcium reabsorption in DCT - blood Ca2+
phosphate excretion in PCT, new boneformation
stimulates kidney production of calcitriol
Collecting Duct Concentrates
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Collecting Duct Concentrates
Urine
Osmolarity 4x as concentrated
deep in medulla
Medullary portion of CD is more
permeable to water than to NaCl
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Control of Water Loss
Producing hypotonic urine NaCl reabsorbed by cortical CD
water remains in urine
Producing hypertonic urine dehydration ADH aquaporin
channels, CD
s water permeability
more water is reabsorbed
urine is more concentrated
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Countercurrent Multiplier
Recaptures NaCl and returns it to renal medulla
Descending limb
reabsorbs water but not salt
concentrates tubular fluid
Ascending limb reabsorbs Na+, K+, and Cl-
maintains high osmolarity of renal medulla
impermeable to water tubular fluid becomes hypotonic
Recycling of urea: collecting duct-medulla urea accounts for 40% of high osmolarity of medulla
Countercurrent Multiplier
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Countercurrent Multiplier
of Nephron Loop Diagram
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Countercurrent Exchange System
Formed by vasa recta provide blood supply to medulla
do not remove NaCl from medulla
Descending capillaries water diffuses out of blood
NaCl diffuses into blood
Ascending capillaries water diffuses into blood
NaCl diffuses out of blood
Maintenance of Osmolarity
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Maintenance of Osmolarity
in Renal Medulla
Summary of Tubular
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Summary of Tubular
Reabsorption and Secretion
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Composition and Properties of Urine
Appearance
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
Specific gravity density of urine ranges from 1.001 -1.028
Osmolarity - (blood - 300 mOsm/L) ranges from50 mOsm/L to 1,200 mOsm/L in dehydrated person
pH - range: 4.5 - 8.2, usually 6.0 Chemical composition: 95% water, 5% solutes
urea, NaCl, KCl, creatinine, uric acid
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Urine Volume
Normal volume - 1 to 2 L/day Polyuria > 2L/day
Oliguria < 500 mL/day
Anuria - 0 to 100 mL/day
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Diabetes
Chronic polyuria of metabolic origin With hyperglycemia and glycosuria
diabetes mellitus I and II, insulin
hyposecretion/insensitivity gestational diabetes, 1 to 3% of pregnancies
ADH hyposecretion
diabetes insipidus; CD
water reabsorption
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Diuretics
Effectsurine output
blood volume
Uses hypertension and congestive heart failure
Mechanisms of action
GFR
tubular reabsorption
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Renal Function Tests
Renal clearance: volume of plasma cleared of awaste 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)
Determine GFR: inulin is neither reabsorbed orsecreted so its GFR = renal clearance GFR =
UV/P
Clinical GFR estimated from creatinine excretion
S
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Urine Storage and Elimination
Ureters (about 25 cm long) from renal pelvis passes dorsal to bladder and
enters it from below, with a small flap ofmucosa 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
lumen very narrow, easily obstructed
Urinary Bladder and Urethra -
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Urinary Bladder and Urethra
Female
U i Bl dd
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Urinary Bladder
Located in pelvic cavity, posterior to pubicsymphysis
3 layers parietal peritoneum, superiorly; fibrous adventitia rest
muscularis: detrusor muscle, 3 layers of smoothmuscle
mucosa: transitional epithelium
trigone: openings of ureters and urethra,
triangular rugae: relaxed bladder wrinkled, highly
distensible
capacity: moderately full - 500 ml, max. - 800 ml
F l U th
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Female Urethra
3 to 4 cm long External urethral orifice
between vaginal orifice and
clitoris
Internal urethral sphincter
detrusor muscle thickened,
smooth muscle, involuntary
control
External urethral sphincterskeletal muscle, voluntary
control
M l Bl dd d U th
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Male Bladder and Urethra
18 cm long
Internal urethral sphincter
External urethral sphincter
3 regionsprostatic urethra
during orgasm receives semen
membranous urethra
passes through pelvic cavity
spongy urethra
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N l C t l f Mi t iti
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Neural Control of Micturition
Hemodialysis
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Hemodialysis
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