In the body, water moves constantly into and out of fluid compartments as conditions change in different parts of the body.įor example, if you are sweating, you will lose water through your skin. In the body, water moves by osmosis from plasma to the IF (and the reverse) and from the IF to the ICF (and the reverse). Water will move by osmosis from the side where its concentration is high (and the concentration of solute is low) to the side of the membrane where its concentration is low (and the concentration of solute is high). The magnitude of the osmotic gradient is proportional to the difference in the concentration of solutes on one side of the cell membrane to that on the other side.
Recall that an osmotic gradient is produced by the difference in concentration of all solutes on either side of a semi-permeable membrane. Extreme dehydration can result in kidney failure.įluid also moves between compartments along an osmotic gradient. If hydrostatic pressure in the kidneys drops too low, as can happen in dehydration, the functions of the kidneys will be impaired, and less nitrogenous wastes will be removed from the bloodstream. As hydrostatic pressure in the kidneys increases, the amount of water leaving the capillaries also increases, and more urine filtrate is formed. Hydrostatic pressure is especially important in governing the movement of water in the nephrons of the kidneys to ensure proper filtering of the blood to form urine. What happens in the tissue when capillary blood pressure is less than osmotic pressure? Watch this video to see an explanation of the dynamics of fluid in the body’s compartments. The surplus fluid in the interstitial space that is not returned directly back to the capillaries is drained from tissues by the lymphatic system, and then re-enters the vascular system at the subclavian veins. Filtration pressure squeezes fluid from the plasma in the blood to the IF surrounding the tissue cells. Fluid and the cellular wastes in the tissues enter the capillaries at the venule end, where the hydrostatic pressure is less than the osmotic pressure in the vessel. This pressure forces plasma and nutrients out of the capillaries and into surrounding tissues.
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