If an opening, gap, or something hollow closes up, or if you close it up, it becomes closed or covered. Don't use cold water as it shocks the blood vessels into closing up
If someone closes up a building, they shut it completely and securely, often because they are going away. Just close up the shop The summer house had been closed up all year. = shut up, lock up
The camera is placed close to an object or person so that our attention is focusede on a particular detail These may serve as an in-point to a new scene, depicting a new fact or location in the story Close ups of a person have a number of different functions
A larger-than-normal image that is formed on a negative by focusing the subject closer than normal to the lens with the use of supplementary lenses, extension tubes or bellows