A Level Biology Practice Exam

What does oncotic pressure refer to?

1. The pressure caused by the movement of blood

2. The pressure created by osmotic effects of solutes

3. The pressure within the arteries

4. The pressure in the lungs during respiration

The correct answer is: The pressure created by osmotic effects of solutes

Oncotic pressure specifically refers to the pressure exerted by proteins, particularly albumin, in a blood vessel's plasma that tends to pull water into the circulatory system. This effect is a type of osmotic pressure and is crucial in maintaining fluid balance between the blood and surrounding tissues. In this context, oncotic pressure helps prevent excess fluid from leaking out of blood vessels into the tissues, which could lead to edema. The presence of solutes, particularly proteins, draws water toward them, so the higher the concentration of these solutes, the higher the oncotic pressure. This mechanism is essential for proper fluid distribution and is a key factor in the overall homeostasis of body fluids. Understanding how oncotic pressure works is fundamental in areas such as kidney function, fluid therapy, and conditions like heart failure, where fluid shifts within the body are significant.