1. Intravascular versus Interstitial Fluid
    • Intravascular: blood plasma
    • Interstitial: fluid outside of the cells and vascular system
  2. Extracellular Fluid (ECF)
    made up of the Intravascular and Interstitial Fluid
  3. Electrolytes
    Substances that dissociate into charged particles known as ions. e.g. Na⁺
  4. Cations versus Anions
    • Cations: positively charges ions (e.g. Na⁺, K⁺, Ca⁺⁺, Mg⁺⁺)
    • Anions: negatively charges ions (Cl⁻, HCO₃⁻, HPO₄⁻)
  5. Na⁺
    • Sodium Cation: most common cation in the ECF.
    • Maintains osmolarity in ECF.
    • Involved in water movement and
    • nerve impulses.
  6. Relative increases/decreases in sodium are called:
    Hypernatremia / Hyponatremia
  7. K⁺
    • Potassium Cation: most common cation in the ICF.
    • Maintains osmolarity in ICF.
    • Involved in nerve impulses.
  8. Relative increases/decreases in potassium are called:
    Hyperkalemia / Hypokalemia
  9. Ca⁺⁺
    • Calcium Cation:
    • Involved in nerve impulses and
    • muscle contraction.
  10. Relative increases/decreases are called:
    Hypercalcemia / Hypocalcemia
  11. Mg⁺⁺
    • Magnesium Cation: several biochemical processes and closely associated to phosphates.
    • Relative increases/decreases are called: Hypermagnesemia / Hypomagnesemia
  12. Cl⁻
    Chloride Anion: involved in fluid balance and renal function.
  13. HCO₃⁻
    Bicarbonate Anion: principle buffer of the body, neutralising highly acidic hydrogen ions (H⁺)
  14. HPO₄⁻
    • Phosphate Anion: used in ATP.
    • Closely associated with Mg⁺⁺ in renal function.
    • Acts as a buffer primarily in the ICF.
  15. Acidosis versus Alkalosis
    • Acidosis: pH below 7.35
    • Alkalosis: pH above 7.45
    • The body is constantly creating hydrogen ions (H⁺) through metabolism, creating acidity.
    • A variation of around 0.4 pH can be fatal
  16. Osmosis
    Passage of a solvent (usually water) through a membrane
  17. Diffusion
    Passage of molecules through a membrane from an area of greater concentration to an area of lesser concentration.
  18. Isotonic
    Equal concentration of solute molecules on either side of a membrane
  19. Hypotonic
    less concentrated
  20. Hypertonic
    more concentrated
  21. Osmotic gradient
    water moves to saltier enviro
  22. Active transport
    • Movement of a substance against Osmotic gradient
    • Is faster than diffusion but requires energy.
  23. Facilitated Diffusion
    • Diffusion of a substance, such as glucose, through a cell membrane with the assistance of a "helper" or carrier protein.
    • It may or may not require energy.
  24. Osmolarity / Osmolality
    • Osmolarity: concentration of solute/kg of water
    • Osmolality: concentration of solute/litre of water
  25. Osmotic pressure
    Pressure exerted by the concentration of solutes. Is a pull, not a push force.
  26. Oncotic force
    Colloid osmotic pressure
  27. Net filtration
    • Total loss of water from plasma to interstitial space.
    • Value is usually zero, because of Starling's Hypothesis
  28. Hydrostatic pressure
    • BP. It tends to force water out of the capillaries into the interstitial space, by a process called:
    • Filtration
  29. Starling's Hypothesis
    Net filtration = (Forces favouring filtration) - (Forces opposing filtration)
  30. Bicarbonate buffer system
    • Fastest of the three mechanisms
    • H⁺ + HCO₃⁻ ↔ H₂CO₃
    • Hydrogen ion + bicarbonate ion ↔ carbonic acid
  31. Healthy ratio of bicarbonate ions to molecules of carbonic acid.
  32. Acid-Base 20:1 ratios and its relation to Respiratory/Metabolic acidosis
    • 20:1 is normal pH [bicarbonate ions : molecules of carbonic acid]
    • 20:4 is an excess of carbonic acid and is Respiratory acidosis
    • 15:1 is a deficit of bicarbonate and is Metabolic acidosis
  33. Respiratory Acidosis versus Metabolic Acidosis
    • RA: 20:4
    • MA: 15:1
  34. Carbonic anhydrase
    • Erythrocytes contain the enzyme carbonic anhydrase which rapidly converts carbonic acid to CO₂ and water. This process can go in both directions:
    • H₂CO₃ ↔ H₂O + CO₂
  35. Acidosis in relation to kidney function
    • pH can be lowered (made more acidic) by excretion of bicarbonate ions, because there is less bicarbonate available to bind with the H⁺ ions:
    • ↓ HCO₃⁻ → ↑ H⁺
  36. 3 mechanisms of H⁺ removal
    • 1. Bicarbonate buffer system
    • 2. Respiration
    • 3. Kidney function
  37. Acidosis in relation to CO₂ stress
    • Hypoventilation leads to a build up of CO₂ which creates a 'stress' that shifts the following equation to the left, thus leading to an excess of H⁺ and Respiratory acidosis:
    • H⁺ + HCO₃⁻ ↔ H₂CO₃ ↔ H₂O + CO₂
    • So an increase of CO₂ leads to an increase of H⁺ and a drop in pH (acidosis):
    • ↑ CO₂ ↔ ↑ H⁺
    • So you can see that an increase in respiration will lower CO₂ levels and thus lower the excess of H⁺, resolving the acidosis:
    • ↑ Respiration → ↓ CO₂ → ↓ H⁺
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