Fluid, Electrolyte and pH Balance

Fluid, Electrolyte and pH Balance Biology 2122 Chapter 26

Introduction – Body Fluids 1. Males (60%); Females (50%) Water 2. Fluidcompartments • ICF vs ECF • Electrolytes 3. FluidMovement • Moves through IF and plasma • Figure 26.3

Electrolyte Comparison ECF vs. ICF Figure 26.2

Water Intake and Output 1. Intake • 2500 ml/day 2. Output • Insensible Water Loss • Osmolarity Changes • Thirst • ADH released from posterior pituitary 3. Hypothalamus – ThirstCenter • Osmoreceptors – lose water • Figure 26.5 4. SensibleWaterLoss

Thirst Mechanism

Water Balance Problems 1. Dehydration • Hypovolemic Shock 2. HypotonicHydration • Overhydration – ECF dilution 3. Hyponatremia • Low Na+ concentration; high water concentration 4. Edema • Interstitial space around tissue • Volume increase – IF only! 5. Hypoproteinemia

Electrolyte Balance – Importance of Sodium 1. Level – 142 mEq/L • Sodium bicarbonate and sodium chloride 2. ECFstability 3. Changes in plasmaNa+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)

Regulation of Sodium

Regulating Potassium 1. Main ICF ion 2. ECFbalance 3. Buffer 4. Regulation • PCT (reabsorb 60-80%) • Loop of Henle (10-20%) • Collecting ducts (primary secretion) 5. BloodPlasmaConcentration • Diets 6. Aldosterone • Enhances K+ secretion

Acid – Base Balance 1. ArterialBlood = 7.4 • IF = 7.35 • ICF = 7.0 2. Alkalosis or Alkalemia 3. Acidosis or acidemia 4. Where do the Hydrogenions come from? • Protein catabolism; lactic acid; lipid metabolism; carbon dioxide transport 5. Regulation of pH • Chemical buffering; brain stem; kidneys

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

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

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!

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

Reabsorption of filtered bicarbonate – H+ secretion

New bicarbonate via excretion of H+ by HPO42-

Abnormalities • 1. RespiratoryAcidosis • CO2 in blood; pH • 2. Respiratoryalkalosis • CO2; pH • 3. Metabolicacidosis • HCO3- ; pH • 4. Metabolicalkalosis • HCO3- ; pH

Fluid, Electrolyte and pH Balance