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Copyright 2010, John Wiley & Sons, Inc.
Chapter 21
The Urinary System
Copyright 2010, John Wiley & Sons, Inc.
End of Chapter 21
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Urinary System
Two kidneys and two ureters
Urinary bladder & urethra
Effector organ for
1. Regulation of Plasma ion composition
2. Regulation of Body water Volume (BP)
3. Regulation of blood pH (with lung)
4. Production of Hormones
5. Excretion of waste
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Urinary System
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Kidney
Divided into cortex –outer portion
Medulla- inner portion
Contain renal pyramids & renal columns
Urine goes into renal pelvis
Edges are made of major & minor calyces
Then out ureter
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Kidney
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Renal Blood Supply
20-25% resting CO goes through kidneys
L. & R. renal arteries then
Segmental interlobar arcuate interlobular
afferent arterioles
glomerulus (capillary network)
efferent arterioles
peritubular capillaries veins
renal vein
Capillaris Units –nephrons grouped at pyramids
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Renal
Blood
Supply
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Renal Blood Supply
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Nephron
Unit of renal function: corpuscle & tubule
Corpuscle: forms filtrate
Glomerulus & Glomerular capsule (cortex)
Proximal convoluted tubule (cortex)
Descending Loop of Henle (into medulla)
ascending Loop of Henle (into medulla)
Distal convoluted tubule (cortex)
Collecting duct minor calyx
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Nephron
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Basic Operation
Glomerular filtration-filter plasma
Tubular reabsorption Reabsorb needed compounds & water from
filtrate
Tubular Secretion Secrete some materials into filtrate
Let rest go out as a solution called urine–see
Table 21.1
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Basic Operation
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Glomerular Filtration
Two layers of capsule surround glomerulus
Between is capsular space
Podocytes support capillary epithelium
Form filtration membrane
Permeable to water & solute
but not most proteins & blood cells
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Filtration Pressure
Blood pressure for filtration
Opposed by colloid osmotic pressure and
capsular pressure
Efferent and afferent arteriole diameters
adjust to maintain a net filtration pressure
Even with small changes in blood pressure
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Glomerular Filtration Rate
= GFR 105-125 ml/min
Determines net reabsorption because it determines filtrate flow
ANP increases GFR
Responds to increased blood volume
Sympathetic stimulation vasoconstriction decreased GFR
Urine production
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Glomerular Filtration
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Tubular Reabsorption
Proximal tubule
~65% Na+ & H2O
Normally 100% nutrients
~100% HCO3- (depends on blood pH)
Active transport of solutes
Osmosis moves water
Cells distal to proximal tubule fine tune reabsorption under control
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Tubular Secretion
Takes place all along tubule
Major substances : H+, K+, ammonia, urea,
creatine, drugs like penicillin
Helps regulate plasma pH 7.35-7.45
Diet is acid urine is typically acidic
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Urine Route
Collecting ducts to calyces
Calyces to ureter
Ureter to bladder
Bladder to urethra
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Filtration, Reabsorption,
Secretion
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Hormonal Regulation
Angiotensin II & aldosterone
Angiotensin II- stimulates NaCl in proximal tube
Aldosterone- increases Na+ reabsorption & K+
secretion in DCT & CD
More ions reabsorbed more water
ANP-increases GFR & inhibits aldosterone
action less Na+ reabsorbed
ADH- responds to increased concentration of
solute in blood + fall in BP
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Hormonal Regulation
ADH: important to body water balance
Increased concentration of solute in blood + fall in BP ADH
With no ADH: DCT & CD walls are impermeable to water dilute urine
With ADH: water reabsorption occurs concentrated urine
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Components of Urine
Urine = 1-2 l /day
95% water
+ urea, creatine, K+, ammonia, uric acid, Na+,
Cl-, Mg2+, sulfate, phosphate & Ca2+
Depends on diet and state of health
See table 21.3
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Regulation of
Water
Reabsorption
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Urine Route Collecting ducts calyces
Ureter Lined with mucus & transitional epithelium
Pass under bladder
Full bladder prevents backflow
Bladder- directly in front of rectum Can stretch (700-800 ml)
Smaller in females because of uterus
Three layers of detrussor muscle
Urethra- internal urethral sphincter
External urethral sphincter (voluntary)
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Urine Route
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Micturition = Urination
Autonomic reflex- internal sphincter
Responds to stretch like rectum
Parasympathetic detrusor muscle
contraction
Conscious control-external sphincter
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Aging
Kidneys shrink- decrease in capacity
Thirst decreases dehydration
urinary tract infections
Males: prostate enlargement frequent urination & slow flow
Females: more prone to leakage of external sphincter (incontinence)
Both: nocturia