Fluid, Electrolyte and pH Balance
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Fluid, Electrolyte and pH Balance
Biology 2122 Chapter 26
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Introduction – Body Fluids
1. Males (60%); Females (50%) Water
2. Fluid compartments – ICF vs ECF – Electrolytes
3. Fluid Movement – Moves through IF and plasma – Figure 26.3
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Electrolyte Comparison ECF vs. ICFFigure 26.2
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Water Intake and Output 1. Intake – 2500 ml/day
2. Output – Insensible Water Loss
– Osmolarity Changes • Thirst
• ADH released from posterior pituitary
3. Hypothalamus – Thirst Center – Osmoreceptors – lose water
– Figure 26.5
4. Sensible Water Loss
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Thirst Mechanism
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Water Balance Problems 1. Dehydration – Hypovolemic Shock
2. Hypotonic Hydration – Overhydration – ECF dilution
3. Hyponatremia – Low Na+ concentration; high water concentration
4. Edema – Interstitial space around tissue
– Volume increase – IF only!
5. Hypoproteinemia
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Electrolyte Balance – Importance of Sodium
1. Level – 142 mEq/L – Sodium bicarbonate and sodium chloride
2. ECF stability 3. Changes in plasma Na+ levels – Plasma volume; BP; ICF and IF
4. Regulation of Na+ balance – No specific sodium receptors
– Aldosterone
– Angiotensin II
– ANP
– Sex Hormones (Estrogen; progesterone; glucocorticoids)
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Regulation of Sodium
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Regulating Potassium 1. Main ICF ion
2. ECF balance
3. Buffer
4. Regulation – PCT (reabsorb 60-80%)
– Loop of Henle (10-20%)
– Collecting ducts (primary secretion)
5. Blood Plasma Concentration – Diets
6. Aldosterone – Enhances K+ secretion
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Acid – Base Balance 1. Arterial Blood = 7.4– IF = 7.35
– ICF = 7.0
2. Alkalosis or Alkalemia
3. Acidosis or acidemia
4. Where do the Hydrogen ions come from?– Protein catabolism; lactic acid; lipid metabolism; carbon dioxide
transport
5. Regulation of pH– Chemical buffering; brain stem; kidneys
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Bicarbonate Buffering System • (1). Only important buffer in the ECF
• (2). Composed of:– Carbonic acid (H2CO3) and (NaHCO3) in solution – buffering substances
• (3). Reaction – HCl + NaHCO3 ------------ H2CO3 + NaCl
(SA) (WB) (WA) (SALT)– NaOH + H2CO3 ----------- NaHCO3 + H2O
(SB) (WA) (WB)
• (4). Alkaline reserve – Bicarbonate = 25 mE/L and carbonic acid = 1 mE/L
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Phosphate Buffering System • (1). Components
– Sodium hihydrogen phosphate and hydrogen phosphate ion
• (2). Reactions – HCl + NaHPO4 -------------- NaH2PO4 + NaCl
(SA) (WB) (WA) (Salt)
– NaOH + NaH2PO4 ------------ Na2HPO4 + H2O
(SB) (WA) (WB)
• (3). Low concentrations phosphate – ECF – Blood plasma buffer – not as important; Important in urine and ICF
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Respiratory Regulation [H+]• (1). General Characteristics – 2x buffering power compared to chemical buffering systems – Slower
• (2). During cell respiration – carbon dioxide and transport – CO2 + H2O ----------- H2CO3 ----------- H+ + HCO3 –
----------- ----------
During carbon dioxide unloading: reaction shifts left and H+ produced from carbonic acid is reincorporated into water!
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Renal Mechanisms • (1). Lungs can dispose of CO2 , chemical buffers do not
dispose of excess acids and bases. – Acids generated by metabolism – metabolic ‘fixed’ acids
• (2). Kidneys can eliminate excess acids and bases
• (3). Renal mechanisms – regulating acid-base blood balance – Conservation- reabsorption of bicarbonate– Excretion of bicarbonate
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Reabsorption of filtered bicarbonate – H+ secretion
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New bicarbonate via excretion of H+ by HPO42-
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Abnormalities • 1. Respiratory Acidosis
– CO2 in blood; pH
• 2. Respiratory alkalosis
– CO2; pH
• 3. Metabolic acidosis
– HCO3- ; pH
• 4. Metabolic alkalosis
– HCO3- ; pH