Anatomy 1352: Unit Nine Part Two - Fluid and Electrolyte Balance

Overview of Body Fluids

• Fluid Composition: Water comprises more than half of the body.
  • Adult males: ~55%
  • Newborns: ~80%
• Fluid Movement:
  • Processes: Diffusion, Osmosis, Filtration, Reabsorption
  • Intracellular Fluid (Inside cells): 2/3 of total body fluid
  • Extracellular Fluid (Outside cells): Remaining 1/3
    • Includes interstitial fluid (between cells), intravascular (inside vessels), and other compartments like lymph, cerebrospinal fluid, etc.

Fluid Intake and Loss

• Average Intake: 2+ liters/day
• Metabolic Water: ~200 mL produced daily
• Fluid Loss:
  • Fecal matter: ~100 mL/day
  • Exhalation: ~300 mL/day
  • Skin evaporation: ~500 mL/day
• Kidneys' Role: Adjust fluid balance based on intake; less intake leads to concentrated urine.

Dehydration and Fluid Balance

• Dehydration Factors:
  • Elderly and infants are more susceptible.
  • Thirst may not correspond to dehydration rate.
  • Consequences include confusion and decreased mental status.
• Dehydration Causes:
  • Dry mouth, increased blood osmolarity, decreased blood pressure
  • Detected by osmoreceptors, renin production (kidneys), and angiotensin II levels
  • Stimulates thirst center in hypothalamus

Hormonal Regulation of Fluids

• Key Hormones:
  • Angiotensin, Aldosterone: Increase sodium and water reabsorption
  • Atrial Natriuretic Peptide (ANP): Promotes excretion of sodium and water
  • Antidiuretic Hormone (ADH/Vasopressin): Retains water, reduces urine output

Water Intoxication

• Occurs when water intake exceeds kidney excretion capacity (~15 mL/min)
• Symptoms: Confusion, convulsions, coma, can be fatal
• Treatment: Administer salt (oral or IV)

Electrolytes and Their Functions

• Importance: Affect osmosis, acid-base balance, and neural/muscle function
• Major Electrolytes:
  • Sodium (Na): Dominant extracellular ion, regulated by aldosterone
    • Hyponatremia: Low sodium
    • Hypernatremia: High sodium, linked to hypertension
  • Chloride (Cl): Follows sodium, part of gastric juices
  • Potassium (K): Intracellular, crucial for action potentials
    • Hyperkalemia: High potassium, can cause cardiac issues
  • Bicarbonate (HCO₃⁻): CO₂ balance, affects pH
  • Calcium (Ca): Bone health, neurotransmitter release
  • Phosphate (PO₄³⁻): Bone health, part of ATP
  • Magnesium (Mg): Enzyme co-factor, affects heart function

pH and Buffer Systems

• Normal Blood pH: 7.35 - 7.45
• Buffers:
  • Proteins, Carbonic Acid-Bicarbonate system, Phosphate buffers

Acid-Base Imbalances

• Acidosis: Low pH
  • Respiratory: Due to low ventilation (e.g., pulmonary edema)
  • Metabolic: Due to excessive acid production (e.g., diabetic ketoacidosis)
• Alkalosis: High pH
  • Respiratory: Due to hyperventilation
  • Metabolic: Due to excessive vomiting or antacid intake

Key Points

• Balance of fluids and electrolytes is crucial for homeostasis.
• Hormones and kidneys play a major role in regulating fluid balance.
• Electrolyte imbalances can impact heart, muscle, and nerve function.
• Maintaining pH within the normal range is vital for overall health.

Remember to review this material thoroughly and bring any questions to class for further discussion.