Human Physiology · MU Plovdiv

70. Water-electrolyte balance of the organism. Body fluids and electrolytes. Dynamics of body fluids volume and osmolality. Control of Water-Salts homeostasis. Thirst – physiologic mechanisms.

Inside: 16 sections · 11 labelled pictures · 32 flashcards · 9 min

Topic 70 of 80 in the MU Plovdiv syllabus for Human Physiology (Medicine, Year 2). The free AceMed note covers it in 16 sections, about 1,093 words (9 min of reading), with 32 flashcards.

In this note

  1. Volume and composition of body fluids. Water and electrolyte balance in the body.
  2. Body Fluid Compartments
  3. Composition of Body Fluid Compartments
  4. Units for Measuring Solute Concentrations
  5. Water and Electrolyte Balance
  6. Water Intake
  7. Water Losses
  8. Regulation of Water and Electrolyte Balance
  9. Body Fluid Volume and Osmolality Dynamics. Regulation of Fluid and Electrolyte Balance
  10. Osmolality vs. Osmolarity
  11. Normal Osmolality Values (Clinical Reference)
  12. Electrolytes and Osmolality
  13. Water Balance – Intake and Loss
  14. Regulation of Fluid and Electrolyte Balance
  15. Fluid Output Regulation (Urinary)
  16. Recap Questions

Body Fluid Compartments

  • Water is a major component of the body, distributed among two major compartments: intracellular fluid (ICF) and extracellular fluid (ECF).
  • ICF is contained within cells and comprises two-thirds of total body water.
  • ECF is outside the cells and comprises one-third of total body water.
  • ECF is further divided into two subcompartments: plasma and interstitial fluid.
  • Plasma is the fluid circulating in blood vessels.
  • Interstitial fluid bathes the cells.
  • Total body water correlates inversely with body fat.
  • Individuals with lower body fat have a higher percentage of total body water.
  • Females, having a higher percentage of adipose tissue, tend to have less body water than males.
  • The transcellular compartment, minor compartment, includes cerebrospinal, pleural, peritoneal, and digestive fluids.

Composition of Body Fluid Compartments

  • ICF and ECF have vastly different concentrations of various solutes.
  • The major cation in ECF is sodium (Na+), with chloride (Cl-) and bicarbonate (HCO3-) as the balancing anions.
  • The major cations in ICF are potassium (K+) and magnesium (Mg2+), balanced by proteins and organic phosphates as anions.
  • Plasma and interstitial fluid also differ in solute concentrations due to the exclusion of proteins from interstitial fluid.

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