Said another way, osmosis is the movement of water from an area of lower solute concentration to and area of higher solute concentration.
Starling Forces
Starling Forces govern the passive exchange of water between the capillary microcirculation and the interstitial fluid. These forces not only determine the direction of net water movement between the capillary and interstitial fluid but also determines the rate at which water exchange occurs. This rate is dependant on the permeability of the capillary wall. Osmotic pressure : the pressure exerted by the concentration of solutes that cannot cross the membrane. The higher the solute concentration, the higher the osmotic pressure. The actual pressure required to restore starting conditions is referred to as the Osmotic Pressure. Osmotic pressure prevents osmosis . Oncotic Pressure (colloidal osmotic pressure) refers to osmotic pressure generated by proteins in the blood. These proteins are unable to leave the blood and therefore create a higher pressure within the capillary. It acts to draw fluid into the capillary. Hydrostatic Pressure refers to the pressure exerted by the fluid against its barrier walls. The more confined the space, the higher the hydrostatic pressure. This pressure acts to push fluid out of the capillary. In cells, the osmotic pressure in the cytosol is equal to the osmotic pressure of the interstitial fluid outside of the cells. Because of this, the volume of the cell remains relatively constant. However, if we place cells in an environment (solution) that has a different osmotic pressure than the cytosol, water moves by osmosis into or out of the cells and thus their volume either increases or decreases. Tonicity : is the measure of a solutions ability to change the volume of cells by altering their water content. If a solution causes the cell to maintain its shape, the solution is said to be Isotonic . The concentrations of the solutes unable to pass through the membrane are equal on both sides. If cells are placed in a solution that has a lower concentration of impermeable solutes than the cytosol of the cell, the solution is called Hypotonic . In this case, water enters the cell faster than water leaves and the cells eventually swell and rupture, referred to as lysis. In a Hypertonic solution, the solution has a higher impermeable solute concentration than the cytosol. Therefore, water will move out of the cell faster than water will move into the cell. This causes the cell to shrink, referred to a crenation.
Real example: most sport drinks are hypotonic for rehydration of your body cells.
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