Irene Montgomery Chap 25 Fluid, Electrolyte, and Acid-Base Balance - Student Notes

Module 25: Fluid, Electrolyte, and Acid-Base Balance

Overview of Homeostasis

• Chapter 25 focuses on mechanisms regulating body fluids and their homeostasis.

Module 25.1: Body Composition

• Composition Overview: Body composition can be divided into solids and two main fluid compartments:

  • Extracellular Fluid (ECF):

  • Definition: Fluid found outside of cells.

  • Subtypes Include:

    • Interstitial Fluid: The fluid between cells.

    • Other Fluids: Includes cerebrospinal fluid (CSF), lymph, aqueous humor.

  • Total percentage in adults: 21.5%.

  • Intracellular Fluid (ICF):

  • Definition: Fluid contained within cells, primarily in the cytosol.

  • Total percentage in adults: 60%.

• Water Composition:

  • Adult Male Body Water Composition:

  • Total Water: 50% of total body weight.

    • ICF: 27%.

    • ECF: 18%.

    • Plasma: 4.5%.

    • Other Body Fluids: ≤1%.

  • Adult Female Body Water Composition:

  • Total Water: 40% of total body weight. (due to higher adipose tissue, making up 10% more solids)

    • ICF: 33%.

    • ECF: 21.5%.

    • Plasma: 4.5%.

    • Other Body Fluids: ≤1%.

• Comparison of Solids:

  • Solids represent 40% of body weight in males (composed of organic and inorganic materials).

  • Women tend to have more solids and less water due to a higher proportion of fat (lipids).

• Solid Components Include:

  • Carbohydrates

  • Proteins

  • Lipids

Mechanisms of Fluid Shift

• Water Movement:

  • Water can shift between extracellular and intracellular compartments due to plasma membrane properties.

  • Plasma membranes contain a high density of aquaporins (water channels) leading to selective permeability.

  • Example: Osmosis allows water to move in response to concentration gradients in body fluids.

Module 25.2: Fluid Balance

• Fluid Balance: Occurs when water gain equals water loss

  • Major Sources of Water Gain:

  • Ingestion of liquids.

  • Water content of food.

  • Metabolic water production during catabolism (e.g., electron transport system).

  • Major Sources of Water Loss:

  • Urination.

  • Evaporation through skin and lungs.

  • Loss in feces.

• Daily Input and Output Calculation:

  • Daily Water Input (in mL):

  • Water absorbed across the digestive epithelium: 2200 mL.

  • Metabolic Water: 300 mL.

  • Total Daily Input: 2500 mL.

  • Daily Water Output (in mL):

  • Water lost in urine: 1200 mL.

  • Water lost by evaporation (skin and lungs): 1150 mL.

  • Water lost in feces: 150 mL.

  • Total Daily Output: 2500 mL.

• Dehydration Consequences:

  • When dehydrated, fluid levels are imbalanced:

  • Increased osmotic concentration in the ECF due to water loss.

  • Osmosis causes water to move from ICF to ECF to maintain an isotonic state.

  • Symptoms may include thirst, changes in blood pressure, concentrated urine, skin wrinkling, and headaches.

Module 25.3: Mineral Balance

• Definition: Involves balancing electrolyte gain and loss across the body.

  • Minerals: Inorganic compounds acting as electrolytes, dissociating in solution into ions.

  • Example of Dissociation:

    • Ca3(PO4)2 ightarrow 3Ca^{2+} + 2PO4^{3-}

• Ion Absorption and Excretion:

  • Ion absorption occurs mainly across the epithelial lining of the small intestine and colon.

  • Primary site of ion loss: kidneys.

  • Secondary site of ion loss: sweat glands.

• Daily Intake versus Loss:

  • Daily mineral loss must equal daily intake for maintaining balance.

Major Minerals and Their Functions

• Potassium (K):

  • Major cation in cytosol.

  • Essential for normal membrane function.

  • Total body content in adults: 140 g, excreted primarily via urine.

  • Recommended Dietary Allowance: 4700 mg.

• Sodium (Na):

  • Major cation in body fluids with a total body content of 110 g.

  • Important for normal membrane function.

  • Recommended Dietary Allowance: 1500 mg, primarily excreted in urine, sweat, and feces.

• Chloride (Cl):

  • Major anion in body fluids, functions in forming hydrochloric acid (HCl).

  • Total body content: 89 g, primarily excreted in urine and sweat.

• Calcium (Ca):

  • Total body content: 1.36 kg, primarily in skeleton.

  • Functions in muscle contraction and nerve transmission.

  • Recommended Dietary Allowance: 1000-1200 mg, excreted in urine and feces.

• Phosphorus (P):

  • Essential for high-energy compounds and nucleic acids.

  • Total body content: 29 g, primarily in skeleton and excreted in urine.

  • Recommended Dietary Allowance: 700 mg.

• Magnesium (Mg):

  • Total body content: approximately 29 g (skeleton and body fluids).

  • Essential for normal membrane functions.

  • Recommended Dietary Allowance: 310-400 mg, excreted via urine.

Trace Minerals

• Iron (Fe):

  • Component of hemoglobin and myoglobin.

  • Total body content: 3.9 g, excreted in traces via urine.

  • Recommended Dietary Allowance: 8-18 mg.

• Zinc (Zn):

  • Cofactor of enzyme systems, notably carbonic anhydrase.

  • Total body content: 2 g, excreted in urine and hair.

  • Recommended Dietary Allowance: 8-11 mg.

• Copper (Cu):

  • Required as a cofactor for hemoglobin synthesis.

  • Total body content: 127 mg, excreted in urine and feces.

  • Recommended Dietary Allowance: 0.9 mg.

• Manganese (Mn):

  • Total body content: 11 mg, serves as a cofactor for some enzymes.

  • Recommended Dietary Allowance: 1.8-2.3 mg.

• Cobalt (Co):

  • Total body content: 0.0001 g, serves as a mineral in vitamin B12 (cobalamin).