During a sprint, daily scrum meetings or short project status meetings are held with product owner and developers. In these meetings, each developer shares what he had done on the previous day, what they plan to do for the current day, and impediments encountered, if any.
A sprint deadline is never extended. If a requirement cannot be completed, it gets moved back to the product backlog. Also, during a sprint, requirements are never changed. Thus, developers are shielded from requirement changes allowing them to work uninterruptedly.