Final answer:
Albumin is the major plasma protein that maintains blood osmotic pressure. It is the most abundant plasma protein, accounting for a significant portion of blood serum protein. Albumin holds water inside blood vessels and contributes to blood volume and pressure.
Step-by-step explanation:
The major plasma protein that maintains the blood osmotic pressure is albumin. Albumin is the most abundant plasma protein, constituting about half of the blood serum protein. It is produced by the liver and serves as a transport vehicle for fatty acids and steroid hormones. Additionally, albumin plays a significant role in maintaining both blood volume and blood pressure by holding water inside the blood vessels and drawing water from the tissues, across blood vessel walls, and into the bloodstream.