Overview
This lecture covers how electrolytes regulate fluid balance in the body, the mechanisms involved (including osmosis and hormonal regulation), and their roles in maintaining blood pressure and nutrient absorption.
Electrolyte Roles in Fluid Balance
- Electrolytes are charged particles (ions) that help manage fluid movement in and out of cells.
- Water follows solutes down the concentration gradient, meaning water moves toward areas with higher electrolyte concentration.
- Sodium (Na⁺) and potassium (K⁺) are the main cations; chloride (Cl⁻) and phosphate (PO₄³⁻) are key anions.
- Any shift in electrolyte concentrations leads to water movement across cell membranes, maintaining balance.
- Osmosis is the movement of water from areas of low to high solute (electrolyte) concentration.
Sodium-Potassium Pump and Its Functions
- The sodium-potassium pump is a protein that actively moves sodium out of and potassium into cells.
- Sodium leaks into cells, and water follows; the pump then expels sodium and water to prevent cell swelling.
- The sodium-potassium pump also helps generate electrical charges for muscle contractions and supports nutrient absorption (e.g., for glucose and amino acids).
Albumin and Blood Fluid Balance
- Albumin is a protein in the blood essential for maintaining fluid balance in the bloodstream.
- Low albumin causes fluid to move out of blood vessels and into tissues, leading to swelling (edema).
- Severe protein malnutrition (e.g., kwashiorkor) reduces albumin, causing abdominal swelling in affected individuals.
Hormonal Regulation of Fluid and Blood Pressure
- Two key hormones regulate blood volume and pressure: antidiuretic hormone (ADH) and aldosterone.
- ADH is released when sodium is high or water is low; it signals kidneys to retain water and increases thirst, reducing urine output.
- Aldosterone is released via the renin-angiotensin pathway if blood volume is low; it prompts kidneys to retain sodium, increasing water retention and blood pressure.
- Both hormones help restore and maintain appropriate blood volume and pressure.
Key Terms & Definitions
- Electrolyte — a charged particle (ion) key for fluid and electrolyte balance.
- Osmosis — movement of water toward higher solute concentration across a membrane.
- Sodium-potassium pump — a cell membrane protein that moves sodium out and potassium into cells.
- Albumin — a plasma protein maintaining blood fluid balance.
- Antidiuretic hormone (ADH) — hormone prompting kidneys to retain water.
- Aldosterone — hormone causing sodium and thus water retention by kidneys.
- Renin-angiotensin system — hormone cascade that regulates blood pressure via blood vessel constriction and aldosterone release.
- Edema — swelling caused by excess fluid in tissues.
Action Items / Next Steps
- Review Figure 11.7 for a visual of the sodium-potassium pump.
- Read the related textbook section on electrolyte and fluid balance mechanisms.
- Prepare for next lecture on water needs, dehydration, and overhydration effects.