Tonicity And Osmolarity PDF

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Osmolarity: Just based on total solute concentration of the solution Tonicity: effect the solution has on cell volume Depends on 2 things: - the solute concentration of the concentration - permeability of cell membrane TONICITY ALWAYS DESCRIBES A SOLUTION RELATIVE TO THE EFFECT IT HAS ON CELLS, IT HAS NO UNITS

: Needed for patients who have: Lost blood Had diarrhoea Not been able to drink

Lots of different fluids available depending on need, commonly contain either Saline (NaCl) and/or Dextrose (glucose)

Move freely through cell membranes: PENETRATING or PERMEANT Not be able to freely cross cell membranes: NON PENETRATING or IMPERMEANT

. if blood loss has occurred-mostly from ECF not cells Use isotonic solution QUESTIONS: E.g. if sever dehydration has caused water loss from cells A cell contains only Use hypotonic solution ‘Lactated Ringer’ solution impermeant solute at Used in lab in experiments 300mOsM. It is placed in a Mimics tissue fluid solution that contains 400mOsM Sodium 130mM impermeant solute. What Chloride 109mM Tonicity is determined by the concentration of happens to the cell? Lactate 28mM The cell will shrink as water T solute in a solution, this is Potassium 4mM leaves. The solution is because the shrinkage or swelling of cells is Calcium 1.5mM hypertonic and hyperosmotic. caused by water movement pH 7.4 Cell intracellular concentration = 300mOsM Total osmolarity 273mOsM impermeant solute. What would happen if a cell was placeld in a solution of

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N - 300mOsM impermeant H - less than 300 mOsM impermeant solute HYPERTONIC SOLUTION - greater than 300 mOsM impermeant solute. How to know if solute is permeant or impermeant? Mostly ions, amino acids etc. are impermeant Small organic molecules are permeant (urea) Permeant solutes do not affect water movement into or out of cells Only impermeant solute can make water move Permeant solutes contribute to osmolarity of a solution, but not tonicity

In case of osmolarity (relative to the cell cytoplasm), a solution is described as:

ISOSMOTIC: if it contains 300 mOsM permeant and impermeant solute. HYPO-OSMOTIC: if it contains less than 300mOsM permeant and impermeant solute HYPEROSMOTIC: if it contains greater than 300 mOsM permeant and impermeant solute

permeant solute at 400mOsM? Impermeant solution is 0mOsM < 300mOsM The cell will swell (hypotonic) and hyperosmotic If a cell was placed in a solution of 200mM NaCl (which is impermeant) will the cell swell, shrink or be unchanged? 200mM x 2 = 400mOsM/impermeant Cell shrinks as it loses water. If a cell, was placed in a solution of 100mM NaCl (which is impermeant) and 100mM urea (which is permeant) will the cell swell, shrink or be unchanged? 100mM x 2 = 200OsM NaCl, cell swells up as it gains water. Cell 300mOsM, hypotonic solution...