Final answer:
Albumin is the main protein responsible for fluid balance in the body, maintaining osmotic pressure and fluid distribution, complemented by hormones.
Step-by-step explanation:
The main protein involved in regulating fluid balance in the body is albumin. Albumin, which is produced by the liver, plays a crucial role in maintaining osmotic pressure, which keeps water within the blood vessels, thus regulating blood volume and blood pressure.
This protein, being large, does not easily pass through plasma membranes, making it instrumental in controlling the movement of fluids in the body. It accounts for about 54 percent of the total plasma protein content and has a concentration in clinical levels of 3.5-5.0 g/dL of blood.
Moreover, unrelated to albumin, hormones like ADH (antidiuretic hormone) are also key in preserving water balance by promoting water reabsorption in the kidneys. This tight regulation is vital for homeostasis, ensuring that water intake and output are balanced.