Final answer:
The claim regarding interstitial fluid colloid osmotic pressure increasing with a decrease in sodium concentration is false; colloid osmotic pressure is affected by plasma proteins, not sodium concentration.
Step-by-step explanation:
The statement that a decrease in interstitial fluid sodium concentration will cause an immediate increase in interstitial fluid colloid osmotic pressure is false. Colloid osmotic pressure (also known as oncotic pressure) is primarily due to the plasma proteins that are suspended in blood and are unable to cross the semipermeable capillary cell membrane.
Since these proteins remain in the plasma, they create an osmotic gradient that attracts water from the interstitial fluid back into the capillaries. If the sodium concentration in the interstitial fluid decreases, this does not directly increase the colloid osmotic pressure; instead, it could lead to a movement of water back into cells, trying to balance the osmotic gradient created by the diluted extracellular fluid (ECF).
Furthermore, when discussing fluid balance and blood sodium levels, it's important to note that conditions such as hypernatremia—which is an abnormal increase in blood sodium levels—can disturb the balance of fluids. In such cases, the body maintains osmotic pressure by osmosis at the cellular level, where hyponatremia can result in increased water entry into the cells and potentially cause cell swelling or other serious cellular damage. The body's natural mechanisms strive to balance solute concentrations to prevent such damage.