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04/09/23
THREE BASIC RENAL PROCESSES
Glomerular Filtration: Filtering of blood into tubule forming the primitive urine
Tubular Reabsorption: Absorption of substances needed by body from tubule to blood
Tubular Secretion: Secretion of substances to be eliminated from the body into the tubule from the blood
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BASIC RENAL PROCESSES
GF
TR
TA
Urine Excreted
Efferent ArterioleAfferentArteriole
Glomerulus
KidneyTubule
Peritubular Capillary
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Glomerular Filtration
First step in urine formation180 liters/day filteredEntire plasma volume filtered 65
times/dayProteins not filtered
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Forces Involved inGlomerular Filtration
Glomerular CapillaryBlood Pressure + 55
Plasma Colloid Osmotic Pressure
-30
15
10
Bowman’s CapsuleHydrostatic Pressure
-
Net Filtration Pressure +
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Tubular Reabsorption
Water: 99% reabsorbed
Sodium: 99.5% reabsorbed
Urea: 50% reabsobed
Phenol: 0% reabsorbed
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Tubular Reabsorption
By passive diffusion
By primary active transport: Sodium
By secondary active transport: Sugars and Amino Acids
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Tubular Reabsorption is a Function of the Epithelial Cells Making up the Tubule
Lumen
Plasma
Cells
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Sodium Reabsorption
Lumen
Plasma
Cells
PUMP: Na/K ATPase
Sodium
Potassium
Chloride
Water
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Rennin-Angiotensin-Aldosterone System
Stimulates Sodium Reabsorption in distal and collecting tubules
Naturetic peptide inhibitsIn absence of Aldosterone, 20mg of
sodium/day may be excretedAldosterone can cause 99.5%
retention
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Rennin-Angiotensin-Aldosterone System
Fall in NaCl, extracellular fluid volume, arterial blood pressure
JuxtaglomerularApparatus
ReninLiver
Angiotensin
+
Angiotensin Angiotensin Aldosterone
Lungs
ConvertingEnzyme
AdrenalCortex
IncreasedSodiumReabsorption
HelpsCorrect
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DIURETICS
ACE Inhibitors (Angiotensin Converting Enzyme): Cause loss of salt---> water follows
Atrial Naturetic Peptide (ANP) also inhibits sodium reabsorption
Osmotic diuretics: Are not reabsorbed
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Glucose and Amino Acids are reabsorbed by secondary active transport
They are actively transported across the apical cell membranes of the epithelial cells
Their active transport depends on the sodium gradient across this membrane
All other steps are passive
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GLUCOSE REABSORPTION HAS A TUBULAR MAXIMUM
Renal threshold (300mg/100 ml)
Plasma Concentration of Glucose
GlucoseReabsorbedmg/min
Filtered Excreted
Reabsorbed
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Tubular Secretion
Protons (acid/base balance)
Potassium
Organic ions
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Potassium Secretion
Lumen
Plasma
Cells
PUMP: Na/K ATPase
Sodium
Potassium
Chloride
Water
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DUAL CONTROL OF ALDOSTERONE SECRETION
Fall in sodium
ECF Volume
Blood Pressure
Increased PlasmaPotassium
Increased Aldosterone secretion
Increased TubularPotassium Secretion
Increased UrinaryPotassium Secretion
Increased TubularSodium Reabsorption
Fall in Urinary
Sodium Excretion
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Reabsorption in Proximal Tubule (Summary)
Glucose and Amino Acids67% of Filtered SodiumOther Electrolytes65% of Filtered Water50% of Filtered UreaAll Filtered Potassium
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Secretion in Proximal Tubule (Summary)
Variable Proton secretion for acid/base regulation
Organic Ion secretion
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Reabsorption in Distal Tubule (Summary)
Variable Sodium controlled by Aldosterone
Chloride follows passively
Variable water controlled by vasopressin
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Secretion in Distal Tubule (Summary)
Variable Proton for acid/base regulation
Variable Potassium controlled by aldosterone
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Collecting Duct (Summary)
Variable water reabsorption controlled by vasopressin
Variable Proton secretion for acid/base balance
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REGULATION OF URINE CONCENTRATION
Medullary countercurrent system
Vasopressin
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Medullary countercurrent system
Osmotic gradient established by long loops of Henle
Descending limb
Ascending limb
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Descending limb
Highly permeable to water
No active sodium transport
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Ascending limb
Actively pumps sodium out of tubule to surrounding interstitial fluid
Impermeable to water
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COUNTERCURRENT MAKESTHE OSMOTIC GRADIENT
300
450
600
750
900
1050
1200
1200
From ProximalTubule
To DistalTubule
Cortex
Medulla300
450
600
750
900
1050
1200
1200
100
250
400
550
700
850
1000
1000
ActiveSodiumTransport
PassiveWaterTransport
Long Loopof Henle
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THE OSMOTIC GRADIENT CONCENTRATES THE URINE WHEN VASOPRESSIN (ANTI DIURETIC HORMONE [ADH]) IS PRESENT
From DistalTubule
Cortex
Medulla300
450
600
750
900
1050
1200
1200
300
400
550
700
850
1000
1100
1200
Interstitial Fluid
CollectingDuct
PoresOpen
Passive Water Flow
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WHEN VASOPRESSIN (ANTI DIURETIC HORMONE [ADH]) IS ABSENT A DILUTE URINE IS PRODUCE
From DistalTubule
Cortex
Medulla300
450
600
750
900
1050
1200
1200
100
100
100
100
100
100
100
100
Interstitial Fluid
CollectingDuct
PoresClosed
No Water FlowOut of Duct
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Renal Failure
Acute: Sudden onset, rapid reduction in urine output - usually reversible
Chronic: Progressive, not reversible
Up to 75% function can be lost before it is noticeable
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THE URINARY BLADDER STORES THE URINE
Gravity and peristaltic contractions propel the urine along the ureter
Parasympathetic stimulation contracts the bladder and micturition results if the sphincters (internal and external urethral sphincters) relax
The external sphincter is under voluntary control
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Reflex and Voluntary Control of Micturition
Bladder filling reflexively contracts the bladder
Internal Sphincter mechanically opens
Stretch receptors in bladder send inhibitory impulses to external sphincter
Voluntary signals from cortex can override the reflex or allow it to take place
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