Final answer:
The two compartments where fluid levels must be tightly regulated are the intracellular fluid (ICF) and extracellular fluid (ECF) compartments, which include plasma and interstitial fluid, essential for maintaining osmotic pressure and electrolyte balances affecting blood pressure.
Step-by-step explanation:
The fluid levels in two compartments that must be tightly regulated are the intracellular fluid (ICF) compartment and the extracellular fluid (ECF) compartment. Mammalian systems have evolved to tightly regulate the osmotic pressure and the concentrations of important electrolytes in these two major fluid compartments. The ICF is the fluid contained within cells, enclosed by their plasma membranes, while the ECF is the fluid that surrounds all cells, consisting of two primary components: the plasma, which is the fluid part of the blood, and the interstitial fluid (IF), which bathes the cells not in the blood.
Moreover, osmotic pressure influences how water moves across cell membranes, affecting the volume of these fluid compartments and thereby having an impact on blood pressure. The movement of water and the transport of electrolytes such as sodium, potassium, and chloride are crucial for maintaining the balance of fluid in these compartments.