Fluid & Electrolyte Balance Quiz

Fluid & Electrolyte Balance

• Body fluids make up 50-70% of an adult's weight
• Intracellular fluid (ICF) is inside cells (cytosol)
• Extracellular fluid (ECF) is outside cells
  • Interstitial fluid surrounds cells
  • Intravascular fluid is in blood vessels (blood/lymph)

Fluid Composition Varies

• Leaner tissue has more fluid (muscle ~70%, adipose ~10-20%)
• Males typically have more lean muscle, females more fat (influenced by reproductive hormones)
• As we age, lean muscle tissue decreases.

Body Fluid Composition

• Water (H₂O) is essential for life but cells can't survive water alone
• Solutes (dissolved substances) are crucial
  • Sodium, potassium, chloride, phosphorus, calcium, & magnesium are essential

Electrolytes

• Water is a universal solvent, dissolving various substances like sugars, amino acids, vitamins, and minerals. Water's polarity attracts different parts of molecules, pulling them apart.
• Mineral salts (e.g., NaCl, KCl) dissolve in water, dissociating into charged particles called ions. These ions are electrolytes.
  • Examples of electrolytes include sodium (Na+), chloride (Cl-), and potassium (K+).

Contributions of Water & Electrolytes to Human Functioning

• Water transportation: Blood (plasma ~55% whole blood) carries nutrients (glucose), gases (oxygen), waste, and hormones. Fat-soluble vitamins are attached to water-soluble proteins.
• Blood volume & blood pressure
  • Blood volume is plasma + red blood cells (RBC) + white blood cells (WBC). Increased volume raises blood pressure. Decreased volume leads to low blood pressure (lethargy, confusion).
• Body temperature regulation
  • Water has a high specific heat capacity, helping maintain stable body temperature. Blood vessel dilation increases blood circulation to dissipate heat, and sweat evaporation cools the body.
• Water lubrication & protection
  • Water lubricates joints (synovial fluid). Mucin from saliva protects the brain and spinal cord. Amniotic fluid protects a fetus, while pleural fluid surrounds the lungs.

Electrolytes Support Body Functions

• Electrolytes (substances that carry a charge) conduct electrical impulses in the body. Na⁺, Ca²⁺, Cl⁻, K⁺, and HPO₄²⁻ carry these charges.
• Electrolyte balance regulation: Electrolytes attract water molecules, and osmosis moves water towards high solute concentrations.
• Nerve impulse conduction
  • Depolarization: Influx of sodium (Na⁺) into the cell reduces its negative charge. If enough sodium enters, an action potential triggers.
  • Repolarization: Outflow of potassium (K⁺) to the outside of the cell restores the cell to a resting state.
• Muscle contraction
  • Action potentials trigger the release of calcium ions (Ca²⁺) from the endoplasmic reticulum to activate the proteins necessary for muscle contraction.

How the Body Maintains Fluid Balance

• Hypothalamus regulates thirst. Neurons in the hypothalamus sense changes in fluid and solute concentrations, triggering thirst/fluid intake. The ideal fluid/solute ratio is ~9g of sodium (Na⁺) per Liter of water.
• Thirst mechanism triggers:
  • Tissue dryness stimulates less saliva production, lowering the fluid in blood stream which is sensed by the body via the hypothalamus
  • Osmoreceptors respond to changes in extracellular fluid tonicity
    • Physical search for water.
    • Release of antidiuretic hormone (ADH) to trigger kidneys to retain water.
  • Baroreceptors sense decreased extracellular fluid caused by factors such as bleeding or vomiting. This stimulates the hypothalamus to create a message for the kidneys to release renin (enzyme). Renin converts angiotensinogen (liver molecule) into Angiotensin (hormone) to better regulate blood pressure through constricting blood vessels and increasing water/salt absorption.

Fluid Gain vs Loss

• Fluid Gain:
  • Food(30%): fruits/vegetables (high in water content)
  • Metabolic water (10%): produced through chemical reactions when breaking down carbohydrates, fats, and proteins.
  • Beverages (60%): water, juices, soda, tea.
• Fluid Loss:
  • Urine (~60%), sweat (5%), feces (5%), and insensible water loss (30%).
  • Insensible water loss: evaporation through skin/lungs; 1 litre of water per day at rest; 2 Liters + per hour when exercising or in hot conditions.
• Dietary Reference Intakes (DRIs) for water: Male (19-50): ~3.7 Liters; Female (19-50): ~2.7 Liters (These are averages and may vary depending on circumstances).

Factors Increasing Fluid Requirements

• Increased physical activity
• Hot/Cold climate
• Altitude
• Alcohol consumption
• High protein/fiber diets
• Certain medical conditions (e.g. diarrhea, diabetes insipidus).

Minerals (Electrolytes)

• Sodium (Na⁺): major extracellular electrolyte; essential to maintaining blood pressure, fluid balance, nerve & muscle function.
• Potassium (K⁺): major intracellular electrolyte; essential to maintaining fluid balance, nerve & muscle function, blood pressure, electrical impulses.
• Chloride (Cl⁻): consumed as sodium chloride (NaCl), important for maintaining fluid balance, aids WBC response aiding in digestion, and CO2 removal from the blood.
• Phosphorus: major intracellular electrolyte, critical for bone formation, crucial for energy production (ATP), and cell component (phospholipids)