The first line of defense against external injury and infection contains several thin layers of cells undergoing different stages of maturation.This first line of defense is known as the _______.

First Line Defense

The body's initial response to prevent infection or damage through barriers like skin and mucous membranes, and physiological processes like acidity and enzymatic activity.

Maturation

The process of becoming mature or fully developed, either in a biological context or referring to the development of concepts and skills.