1. Chapter 21 The Urinary System
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Urinary System
Two kidneys and two ureters
Urinary bladder & urethra
Effector organ for
Regulation of Plasma ion composition
Regulation of Body water Volume (BP)
Regulation of blood pH (with lung)
Production of Hormones
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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14. 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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16. Glomerular Filtration Rate
= GFR 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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17. 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
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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21. 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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25. 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 ( 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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28. 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
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