我估你係想問點解會有concentration既difference掛--係villi既出面同入面 villi既入面有好多blood vessel 佢地可以出吸返黎既 nutrient好快咁運走 同埋食物係同水一齊吸入去嫁 吸水既速度快過吸食物..so..you know what i have said?
the 'food' 'go' to villi via concentration gradient AND it go to all part of our body via bloodstream! So, the concentration of 'food' in villi can then be kept at a low level.