Question

because the brain is inside the skull, the brain can only swell a small amount.
what will happen to the pressure in the brain if water moves into it from the blood?
increase decrease stay the same

Explanation:

Step1: Understand the principle of pressure

Pressure is related to the volume of a confined space. When the volume of a substance (here, the brain) in a confined space (the skull) increases, and the space cannot expand much (as the brain can only swell a small amount), the pressure will change according to the relationship \(P=\frac{F}{A}\) (where \(F\) is the force exerted and \(A\) is the area). In a more intuitive sense for this biological context, if the amount of matter (water moving into the brain) increases in a relatively fixed - volume space (skull), the pressure will be affected.

Step2: Analyze the situation

Since water is moving into the brain (increasing the volume of the brain tissue) and the skull limits the expansion of the brain (brain can only swell a small amount), the pressure inside the brain will increase. This is similar to the concept in physics where for a gas in a rigid container (\(V\) is constant), if more gas molecules (analogous to water molecules here) are added (assuming ideal - gas - like behavior in terms of pressure - volume - amount relationship, \(\frac{P_1}{n_1}=\frac{P_2}{n_2}\) for constant \(V\) and \(T\)), the pressure increases. In the brain - skull system, with the "container" (skull) having limited expandability, adding more "content" (water into the brain) leads to higher pressure.

Answer:

Increase