Final answer:
The liver secretes most of the plasma proteins, including albumin, alpha and beta globulins, and gamma globulins (antibodies or immunoglobulins).
Step-by-step explanation:
The organ that secretes most of the plasma proteins is the liver.
The liver produces albumin, which is the most abundant plasma protein and contributes to the osmotic pressure of blood.
In addition to albumin, the liver also produces the alpha and beta globulins, which transport iron, lipids, and fat-soluble vitamins, and the gamma globulins, also known as antibodies or immunoglobulins, which are involved in immunity.