Fluid, Electrolyte and Acids

• Changes in water content can jeopardize cellular activities, leading to protein denaturation, enzyme dysfunction, and cell death
• Body fluids are distributed between the intracellular fluid (ICF) and extracellular fluid (ECF) compartments
• The ICF compartment contains approximately two-thirds of the body water in healthy adults
• The ECF compartment contains large amounts of sodium and chloride, moderate amounts of bicarbonate, but only small quantities of potassium, magnesium, calcium, and phosphate
• Electrolytes in body fluids dissociate in solution to form charged particles or ions
• Nonelectrolytes like glucose and urea do not dissociate into ions
• Diffusion is the movement of particles along a concentration gradient, while osmosis is the movement of water across a semi-permeable membrane
• Tonicity refers to the effect of osmotic pressure on cell size due to water movement across the cell membrane
• Fluid balance involves regulating the content and distribution of body water in the ECF and ICF
• Electrolyte balance primarily involves balancing absorption rates across the digestive tract with loss rates at the kidneys
• Acid-base balance occurs when the production of hydrogen ions is precisely offset by their loss
• Capillary-Interstitial fluid exchange is governed by Starling forces, including capillary filtration, capillary colloidal osmotic pressure, interstitial fluid pressure, and tissue colloidal osmotic pressure
• Capillary filtration is the movement of water through capillary pores due to mechanical forces
• Capillary colloidal osmotic pressure is generated by plasma proteins that are too large to pass through capillary pores, pulling fluids back into the capillary
• Interstitial fluid pressure opposes the outward movement of water from the capillary into the interstitial spaces
• Interstitial spaces:

  • TCOP pulls water out of the capillary into the tissue spaces, reflecting the small amount of plasma proteins that escape from the capillary to enter the interstitial spaces
• Edema is defined as palpable swelling produced by expansion of the interstitial fluid volume
• Causes of edema include increased capillary pressure, decreased colloidal osmotic pressure, increased capillary permeability, and obstruction of lymphatic flow
• Increased capillary pressure leads to the movement of vascular fluid into the interstitial spaces, causing edema that can be localized or generalized
• Decreased sodium and water excretion by the kidneys leads to an increase in extracellular volume, resulting in edema
• Edema due to decreased capillary colloidal osmotic pressure is usually the result of inadequate production or abnormal loss of plasma proteins
• Increased capillary permeability occurs when capillary pores become enlarged or the integrity of the capillary wall is damaged, leading to plasma proteins leaking into the interstitial spaces
• Obstruction of lymph flow can cause conditions like lymphedema, where osmotically active plasma proteins and other large particles rely on the lymphatic system for movement back into circulation
• Major factors involved in fluid balance include water losses and water gains
• Dehydration develops when water losses outpace water gains, leading to a rise in osmotic concentration of the extracellular fluid (ECF)
• Overhydration can be caused by ingestion of a large volume of fresh water or inability to eliminate excess water in urine, leading to abnormally low sodium ion concentration (hyponatremia)
• Electrolyte balance is crucial as total electrolyte concentration directly affects water balance and the concentrations of individual electrolytes can impact cell functions
• Approximately 98% of the potassium content of the human body is in the intracellular fluid (ICF), with cells expending energy to recover potassium ions as they diffuse out of the cytoplasm and into the extracellular fluid (ECF)
• Potassium loss in urine is regulated by controlling the activities of ion pumps along the distal portions of the nephron and collecting system
• Athletes experiencing salt loss through sweat should drink liquids at regular intervals to prevent volume depletion, as water loss is the primary issue
• Research has shown no basis for the rumor that cramps will result if you drink while exercising, and salt pills and sports beverages claiming faster absorption and better electrolyte balance have no apparent benefits despite their high cost
• increase in Na+ concentrate in ECF lead to thirst and fluids being retained

  
• Intracellular fluid volume

  • 25 L, 40% body weight
• Plasma volume

  • 3 L, 20% of ECF
• Interstitial fluid volume

  • 12 L, 80% of ECF
• Total body water volume

  • 40 L, 60% body weight
• Extracellular fluid volume

  • 15 L, 20% body weight