Fluid, Electrolyte and pH Balance

Biology 2122 Chapter 26

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

Electrolyte Comparison ECF vs. ICFFigure 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 – Thirst Center – Osmoreceptors – lose water

– Figure 26.5

4. Sensible Water Loss

Thirst Mechanism

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

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)

Regulation of Sodium

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

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

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. Respiratory Acidosis

– CO2 in blood; pH

• 2. Respiratory alkalosis

– CO2; pH

• 3. Metabolic acidosis

– HCO3- ; pH

• 4. Metabolic alkalosis

– HCO3- ; pH