1. D. C. Mikulecky Faculty Mentoring Program Virginia Commonwealth Univ.
Renal Physiology
D. C. Mikulecky
Faculty Mentoring Program
Virginia Commonwealth Univ.
11/12/2018

2. FUNCTIONS OF THE KIDNEY
Water balance
Electrolyte balance
Plasma volume
Acid-base balance
Osmolarity balance
Excretion
Hormone secretion
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3. THE URINARY SYSTEM Kidneys Blood supply: Renal arteries and veins
Ureter
Urinary bladder
Urethra
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4. THE NEPHRON IS THE FUNCTIONAL UNIT OF THE KIDNEY
Bowman’s
Capsule
Proximal
Convoluted
Tubule
Distal
Convoluted
Tubule
Peritubular Capillaries
Cortex
Glomerulus
Artery
Medulla
Collecting
Duct
Loop of Henle
Vein
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5. 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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6. BASIC RENAL PROCESSES GF TR TA Urine Excreted Efferent Arteriole
Afferent
Arteriole
Glomerulus GF TR
Kidney
Tubule
Peritubular Capillary TA
Urine Excreted
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7. Glomerular Filtration
First step in urine formation
180 liters/day filtered
Entire plasma volume filtered 65 times/day
Proteins not filtered
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8. Forces Involved in Glomerular Filtration
Glomerular Capillary
Blood Pressure + 55 -
Plasma Colloid
Osmotic Pressure 30 -
Bowman’s Capsule
Hydrostatic Pressure 15
Net Filtration Pressure + 10
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9. Tubular Reabsorption Water: 99% reabsorbed Sodium: 99.5% reabsorbed
Urea: 50% reabsobed
Phenol: 0% reabsorbed
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10. Tubular Reabsorption By passive diffusion
By primary active transport: Sodium
By secondary active transport: Sugars and Amino Acids
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11. Tubular Reabsorption is a Function of the Epithelial Cells Making up the Tubule
Plasma
Lumen
Cells
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12. Sodium Reabsorption PUMP: Na/K ATPase Sodium Lumen Cells Plasma
Potassium
Chloride
Water
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13. Rennin-Angiotensin-Aldosterone System
Stimulates Sodium Reabsorption in distal and collecting tubules
Naturetic peptide inhibits
In absence of Aldosterone, 20mg of sodium/day may be excreted
Aldosterone can cause 99.5% retention
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14. Rennin-Angiotensin-Aldosterone System
Fall in NaCl, extracellular fluid volume, arterial blood pressure
Helps
Correct
Adrenal
Cortex
Juxtaglomerular
Apparatus
Liver
Renin
Lungs +
Converting
Enzyme
Angiotensin
Angiotensin
Angiotensin
Aldosterone
Increased
Sodium
Reabsorption
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15. 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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16. 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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17. GLUCOSE REABSORPTION HAS A TUBULAR MAXIMUM
Reabsorbed
mg/min
Excreted
Filtered
Reabsorbed
Renal threshold (300mg/100 ml)
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Plasma Concentration of Glucose

18. Tubular Secretion Protons (acid/base balance) Potassium Organic ions
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19. Potassium Secretion PUMP: Na/K ATPase Sodium Lumen Cells Plasma
Chloride
Water
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20. DUAL CONTROL OF ALDOSTERONE SECRETION
Fall in sodium
ECF Volume
Blood Pressure
Increased
Plasma
Potassium
Increased Aldosterone secretion
Increased Tubular
Potassium Secretion
Increased Tubular
Sodium Reabsorption
Increased Urinary
Potassium Secretion
Fall in Urinary
Sodium Excretion
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21. Reabsorption in Proximal Tubule (Summary)
Glucose and Amino Acids
67% of Filtered Sodium
Other Electrolytes
65% of Filtered Water
50% of Filtered Urea
All Filtered Potassium
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22. Secretion in Proximal Tubule (Summary)
Variable Proton secretion for acid/base regulation
Organic Ion secretion
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23. Reabsorption in Distal Tubule (Summary)
Variable Sodium controlled by Aldosterone
Chloride follows passively
Variable water controlled by vasopressin
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24. Secretion in Distal Tubule (Summary)
Variable Proton for acid/base regulation
Variable Potassium controlled by aldosterone
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25. Collecting Duct (Summary)
Variable water reabsorption controlled by vasopressin
Variable Proton secretion for acid/base balance
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26. REGULATION OF URINE CONCENTRATION
Medullary countercurrent system
Vasopressin
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27. Medullary countercurrent system
Osmotic gradient established by long loops of Henle
Descending limb
Ascending limb
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28. Descending limb Highly permeable to water No active sodium transport
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29. Ascending limb
Actively pumps sodium out of tubule to surrounding interstitial fluid
Impermeable to water
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30. COUNTERCURRENT MAKES THE OSMOTIC GRADIENT
From
Proximal
Tubule
To Distal
Tubule
Cortex
Medulla
300
450
600
750
900
1050
1200
100
250
400
550
700
850
1000
300
450
600
750
900
1050
1200
Active
Sodium
Transport
Passive
Water
Transport
Long Loop
of Henle
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31. THE OSMOTIC GRADIENT CONCENTRATES THE URINE WHEN VASOPRESSIN (ANTI DIURETIC HORMONE [ADH]) IS PRESENT
Interstitial Fluid
From
Distal
Tubule
Cortex
Medulla
300
400
550
700
850
1000
1100
1200
300
450
600
750
900
1050
1200
Collecting
Duct
Pores
Open
Passive Water Flow
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32. WHEN VASOPRESSIN (ANTI DIURETIC HORMONE [ADH]) IS ABSENT A DILUTE URINE IS PRODUCE
Interstitial Fluid
From
Distal
Tubule
Cortex
Medulla
100
300
450
600
750
900
1050
1200
Collecting
Duct
Pores
Closed
No Water Flow
Out of Duct
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33. 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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34. 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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35. 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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