Which plasma protein maintains oncotic pressure in vivo?

Which plasma protein maintains oncotic pressure in vivo?

• A. Albumin
• B. Hemoglobin
• C. Fibrinogen
• D. α2-macroglobulin

Answer: (A)

Oncotic pressure in the blood is the pulling force that keeps water inside the vessels, and it is driven mainly by plasma proteins that stay within the vascular space. The dominant contributor is albumin, the most abundant and relatively large plasma protein produced by the liver. Its high concentration makes it highly effective at generating colloid osmotic pressure, helping to counterbalance the hydrostatic pressure pushing fluid out of capillaries. Hemoglobin sits inside red blood cells, not in plasma, so it doesn’t contribute to plasma oncotic pressure. Fibrinogen is a plasma protein involved in clotting, but its osmotic effect is small compared with albumin due to its lower concentration and different role. α2-macroglobulin is a large protease inhibitor present at lower levels and thus also contributes minimally to oncotic pressure. Thus, albumin maintains oncotic pressure in vivo, and reductions in albumin lead to decreased intravascular fluid retention and potential edema.

Oncotic pressure in the blood is the pulling force that keeps water inside the vessels, and it is driven mainly by plasma proteins that stay within the vascular space. The dominant contributor is albumin, the most abundant and relatively large plasma protein produced by the liver. Its high concentration makes it highly effective at generating colloid osmotic pressure, helping to counterbalance the hydrostatic pressure pushing fluid out of capillaries.

Hemoglobin sits inside red blood cells, not in plasma, so it doesn’t contribute to plasma oncotic pressure. Fibrinogen is a plasma protein involved in clotting, but its osmotic effect is small compared with albumin due to its lower concentration and different role. α2-macroglobulin is a large protease inhibitor present at lower levels and thus also contributes minimally to oncotic pressure.

Thus, albumin maintains oncotic pressure in vivo, and reductions in albumin lead to decreased intravascular fluid retention and potential edema.