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Renal Physiology _ Acid Base Disorders

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					Renal Physiology & Acid Base
         Disorders
      Andres Mascaro PGY II
                Overview
• Water Balance

• Na+ Balance

• Acid Base Balance

• K+ Balance
      Steady State Balance
• Input=Output
            Water Balance
Changes in water balance will lead to:
• Hyponatremia

• Hypernatremia

• SET POINT: BODY FLUID OSMOLALITY
    Water Balance-physiology
• Systems involved:
• ADH, Thirst, Kidneys
• Purpose:
• Maintain body fluid osmolality constant(275-
  298mosm/kg H20)
• How Assesed: Changes in serum Na+
• Hyponatremia:+ water balance(Overhydration)
• Hypernatremia: - water balance(Dehydration)
    Water Balance-physiology
• 60% of our body weight is water

• Ditributed between ICF and ECF

• Water moves freely from ICF and ECF
             Water Balance
•   Intake: 1,5lt per day
•   Excretion: 1,5 Lt per day
•   Unregulated-Non Constant
•   Lungs(hyperventilation)
•   Sweat(fever)
•   GI(diarrhea)
•   Regulated
•   Kidney
            Water Balance
• Effector systems:
• Osmotic Control:
• ADH(posterior pituitary, supraventricular
  nucleii)
• THIRST
• Non Osmotic Control:
• Barroreceptors
  Water Balance (Osmotic control)
• Osmotic
  Control
• Sensor:
• Hypothalamus
• Effector systems:
• ADH
• THIRST
(Very sensitive to minimal
  changes in serum
  osmolality)
Water Balance-ADH&Thirst
      Water Balance -Non osmotic
                control
•   Sensors:
•   High pressurebarorceptors(carotid sinus)
•   Low pressure receptors(lung, atria)
•   They sense ECV
•   Efectors: The Same as in Osmotic Control
•   ADH
•   Thirst

• Less sensitive than changes in osmolality (you need
  greater changes in ECV than you would need in
  osmolality to get same release of ADH)
Water Balance-Non osmotic control
           Water Balance
• Both Osmotic and Non Osmotic water
  balance systems work together
    Water Balance(Effect of Non
          osmotic control)
• Non Osmotic system can override the
  Osmotic system

• “The Kidney prefers to have dilute fluid
  circulating than NOT enough fluid
  circulating”
Water Balance(Effect of Non
      osmotic control)
Water Balance-ADH effect on
          Kidneys
Water transport by Nephron
             • Proximal tubule and
               descending loop of henle:
               ISOSMOTIC
               ABSORPTION
             • Ascending loop of Henle
               only Nacl are asborbed:
               DILUTION OF URINE
             • Collecting duct: ADH
               action which regulates
               water absorption and
               finally urine concentration
       Hyponatremia
(Water Intake>Water Output)
       Hypernatremia
(Water Intake<Water Output)
  Physiology of NA+ Balance
• Changes in the volume of ECF

• Volume Contraction
• Volume Expansion(Edema)


• SET POINT: ECV(Effective Circulating
  Volume)
    Physiology of NA+ Balance
• Purpose: Maintain a Effective circulating volume
   constant
• Systems Involved: Volume sensors, Renin-Angiotensin-
   Aldosterone system, Kidneys, Natriuretic Peptides
• Setpoint: Effective circulating volume
• Assesment: Changes in Extracelular fluid/Body weight
-(+)Na balance:volume expansion- WEIGHT GAIN
-(-)Na balance :volume contraction- WEIGHT LOSS
TOTAL AMOUNT OF Na+ IN THE BODY, NOT
   CONCENTRATION
Physiology of NA+ Balance
             • Most Na+ is
               Extracelluar
             • If 150mEq intake daily
             • Excretion should be
               the same:
               150mEq/day
• Why do Changes in Na balance lead to
  changes in body weight(ECV/ECF) and
  Not to changes in serum Na
  concentration??
Physiology of NA+ Balance
             • Extra Na intake- will lead
               to Intake>Excretion
             • Transient Hypernatremia
               that leads to ADH
               secretion and kidneys
               retain water to maintain
               constant osmolality -and
               there is increase in ECF
               and body weight
                  ECV
    (Effective Circulating Volume)
• Related to adequate tissue perfusion
-Cardiac Output
-Arterial pressure
-ECF and vascular volume
• In Normal individual changes in ECF are related
  to changes in ECV
• NOT always like that—CHF
• Renal Excretion of Na+ are in response to ECV
                  Sensors
• Vascular- respond to pressure or stretch
• Low pressure
-Cardiac Atria
-PulmonaryVasculature
• High Pressure
-Carotid Sinus and Aortic Arch
-Yuxtaglomerular Apparatus-Afferent artery

• Nervous system- symapathetic nerves
• Hepatic
ECV Signals
ECV Signals
Renin-Angiotensin-Aldosterone
Sympathetic Nerves
ADH/ANP
     Decreased ECV:Summary
• SIGNALS
-Increase in Renin-Angio-Aldosterone
-Increase in Sympathetic nerve
-Increase In ADH secretion
• RESPONSE OF KIDNEYS
-Decrease in filtered Load of Na
-Increase in Reabsorption of proximal and distal Na
-Increase in Collecting duct H20 absortion
• HOMEOSTATIC RESULT
-Na and Water retention By the kidney
-ECV and ECF expansion
 ACID-BASE Balance Physiology
• Purpose: Maintain Body fluid Ph Constant
• Systems Involved: Kidneys, Lung and
   Liver
• Assesment: Body Ph
-(+) H+ Balance: Acidosis
-(-) H+ Balance: Alkalosis
Overview
         Role of the Kidney
• Reabsorb Filtered Load of Hco3

• Excrete Acid equal to the amount of Non
  volatile acid generated by the metabolism

• Generate Hco3 That was lost during the
  titration of Non volatile acid
Bicarbonate Reabsorption
Generation of new Hc03
Generation of new
Hc03(ammonium)
Generation of new
Hc03(ammonium)
         Net Acid Excretion



• Excretion of Ammonium
• Excretion of Titrable Acid
• Minus Excretion Hc03 (prevents loss of
  Hc03)
         Net Acid Excretion


• Reflects the amount of Acid excreted with
  Urinary Buffers(UTA)
• Very important Factor is the amount of
  Ammonium Excretion, because the kidney
  regulates excretion of ammonium in
  response to Acid-Base Balance and it
  does Not do that for Titrable Acid
    Regulation of H+ Secretion




• Changes in Cell pH lead to changes in the
  expression of H and Hc03 transportes in the
  Nephron
• Changes acid-Base staus are the primary
  regulators of proton excretion by the kidney
     Renal Response to Acidosis
•   Stimulation H+ Secretion
•   Decrease in Hc03 excretion
•   Decrease in Urine pH
•   Increase in Titration of urine Buffers
•   Stimulation NH4 production and Excretion




• Net Effect is Increase in NAE
    Renal Response to Alkalosis
•   Increase in Hc03 Filtered load
•   Decreased H+ Secretion
•   Increase in Hc03 Excretion
•   Increase in Urine pH
•   Decrease in Titration of urine Buffers
•   Decrease NH4 production and
    Excretion
Causes of Acid-Base Disorders
• Alterations in Metabolism and/or input or
  output of Acid or Alkali

• Alterations in respiratory function(CO2
  Excretion)

• Alterations In Renal Function(H+ excretion
  and new generation of HcO3)
    Alterations in Metabolism
• Lactic Acid
• Ketoacids
• Ingestion of:
Ethylene glucol
Methanol
Hyperalimentation
• Diarrhea
• Pancreatic Hypersecretion
 Alterations in respiratory function
• ACIDOSIS             • ALKALOSIS
• Decrease In          • Increase in
  Respiratory Rate       respiratory Rate
• Decrease in          • Increase in
  Respiratory muscle     respiratory muscle
  function               function
• Airway Obstruction   • Increase in Gas
• Decrease in Gas        Exchange
  Exchange
  Alterations In Renal Function
• ACIDOSIS            • ALKALOSIS
• Renal Failure       • Hyperaldosteronism
• RTA                 • Decreased Hc03
-Decreased H+           excretion
  secretion           -Decreased ECV
-Decreased NH4        -Diuretics
  production and
  secretion
• Hypoaldosteronism
               Anion Gap



• Quantitates Unmeasured anions

• It measures if the Acid added to the body
  is HCL or not
Anion Gap
      K+ Physiology Balance
• Purpose: Maintain constant K
  concentration(3,5-5,0 mEq\lt)

• Systems Involved: Kidneys, Insulin,
  Aldosterone, Epinephrine

• Assesment: K+ serum Concentration
      K+ Physiology Balance
• Most of K+ located intracellular fluid(ICF)
• 90% of ingested K+ excreted by kidneys
• 10% of ingested K+ excreted by GI tract

• Balance maintained by:
• Renal System
• Extrarenal system
         Extrarenal Balance
• Physiological:Maintain constant [K+]




• Pathological:Alter [K+]
 Extrarenal Balance(Acid-Base)
• There will changes in [K+] resulting from Acid-
  Base changes in plasma if these changes are:
• 1-Metabolic(Acidosis-Alkalosis)
• 2-Acidosis is mineral(HCL)
• There will NOT be changes in [K+] if:
• 1-Respiratory A-B disorder
• 2-Acidosis is mineral(Lactate, ketoacid)
• THIS ONLY APLLIES TO ACUTE CHANGES
          Renal BALANCE
• With low K diet 99% of K+ is reabsorbed in
  proximal tubule and loop of Henle
• With Normal -High K+ diet 99% is
  reabsorbed in proximal tubule and loop of
  Henle, but there is Secretion of K+in the
  Distal part of the Nephron
• It is this Secretion that determines how
  much K+ is excreted in the Urine
   Renal BALANCE(secretion)
• Principal Cells are responsible for K+
  secretion in the distal Nephron
• The main Regulators Are:
• Plasma [K+]
• Aldosterone
• Secondary regulators are:
• Acid-Base balance
• Urine flow rate
Renal BALANCE(secretion)
            • 1-High Plasma [K+]
            • Increase in K uptake by
              principal cells
            • Increase in apical Mb
              permeability
            • Increase in Aldosterone
              secretion
            • 2-Increase in
              Aldosterone
            • Stimulate Na-K ATPase
            • Increase in apical Mb
              permeability
Renal BALANCE(secretion)
            • 1-Increase in Urine
              Flow Rate
            • Increase in Luminal
              Na in distal Nephron
            • Increase
              Reabsorption of Na in
              Exchange for K
            • Increase in K
              secretion
Renal BALANCE(secretion)
            • Acute Acidosis:
            • Inhibits Na-K-ATPase
              activity
            • Inhibits apical Mb
              permeability
            • Decreases K+ Secretion
            • Acute Alkalosis:
            • Stimulate Na-K ATPase
              Activity
            • Increase in apical Mb
              permeability
            • Increases K+ Secretion
     Renal BALANCE(secretion)
• Chronic Acidosis:




• Net Effect is Increase in K+ Excretion
     Renal BALANCE(secretion
• Chronic Alkalosis




• Net Effect is Hypokalemia
  Renal BALANCE
Summary (Acid-Base)
                  Hypokalemia
•   Decreased Intake
•   Increased GI Loss(Diarrhea)
•   Shift in to cells
•   Alkalosis
•   Insulin, B-adrenergic,Hyperaldosteronism
•   Hypoosmolality
•   Increased Renal Loss
•   Thiazide and loop diuretics
•   Chronic metabolic and Chronic Metabolic Alkalosis
•   Hyperaldosteronism
                  HyperKalemia
• Increased Intake
• Shift Out of Cell
•   Cell Lysis
•   Metabolic Acidosis(Mineral HCL)
•   Insulin deficiency
•   Hyperosmolality
• Decreased Renal Excretion
•   Renal Failure
•   K+ sparing diuretics
•   Hypoaldosteronism
•   ECV contraction

				
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posted:2/29/2012
language:English
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