One person or group designs a system leaving all its internal parts to be designed by others. The part designers receive requirements from the system designer. So requirements and designs are dependent on the scope of the component you are looking at.
You could hand off a requirements document to a general contractor who would ship part of the document to a subcontractor responsible for a part of a system who would immediately begin requirements analysis of his part then partition its parts to his developers for design. Depending on the scope of a product this could repeat several times. In general it is a naturally recursive process where the design at an outer level is the requirements for the next level.