Final answer:
The circular region of tightly stretched skin refers to the dermis layer, specifically the papillary and reticular layers, and is also exhibited in the circular nature of orbicularis muscles like the orbicularis oris and orbicularis oculi.
Step-by-step explanation:
The circular region of tightly stretched skin is known as the dermis. This layer of skin has two distinct parts; the upper is the papillary layer which contains papillae that extend into the epidermis, and the lower is the reticular layer composed of denser connective tissues. The term 'orb' (meaning circular) in the orbicularis muscles, such as orbicularis oris and orbicularis oculi, indicates their circular nature. These muscles function as sphincters, creating openings when they relax and closing them when they contract.