Student or Learner
Would you be kind to explain in plain English the meaning of the expression in bold in the following excerpt from a NYT’s article?
The boy had a shunt in his brain to drain fluid, but he was vomiting and had an extreme headache, two signs that the shunt was blocked and fluid was building up.
I know at least two meanings of the phrasal verb build up but I couldn’t catch the meaning of the expression in question in full.
build up (v) = 1. enlarge, develop, or increase by degrees or in stages; 2. form or accumulate steadily
What condition results in Cholesterol building up in the wall of blood vessels?
Thank you for your efforts.