Osmolality and Passive Transport
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Passive transport depends on the concentration of fluids. Two examples of passive transportation are diffusion and osmosis. Both types of passive transportation and a comparison of osmolality and osmolarity are explained in this chapter.
 Figure 3-1 Osmolality and passive transport. |
Frequently, the terms osmolarity, the osmolar concentration of 1 L of solution, and osmolality, the osmolar concentration in 1 kg of water, are used interchangeably. This switching of terms is accepted because 1 L of water is equal to 1 kg in weight. However, osmolarity is used most often when referring to solutions and fluids outside the body and osmolality when referring to fluids inside the body.
OSMOLALITYThe semipermeable membrane of the cell allows a constant movement of some solutes, whereas others remain confined within their boundaries. Whether confined or free to move, a solution’s osmotic concentration is determined by the amount of dissolved particles. The normal
range for serum osmolality is 275-295 mOsm/kg (milliosmols per kilogram). Blood values that fall below this range indicate a hypoosmolar state and those that are greater than 295 mOsm/kg are considered a hyperosmolar state. The following formula is used to determine serum osmolality:
range for serum osmolality is 275-295 mOsm/kg (milliosmols per kilogram). Blood values that fall below this range indicate a hypoosmolar state and those that are greater than 295 mOsm/kg are considered a hyperosmolar state. The following formula is used to determine serum osmolality:
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