Components of the ﬁRst Line of Defense Include All of the Following

Question

Components of the ﬁrst line of defense include all of the following, except _______.
A) the ﬂushing action of urine
B) phagocytic white blood cells
C) the tough cell sheet of the upper epidermis of the skin
D) the ﬂushing action of tears and blinking
E) nasal hairs

Accepted Answer

Phagocytic white blood cells are part of the body's second line of defense, not the first. The first line of defense includes physical and chemical barriers that prevent pathogens from entering the body, such as skin, tears, and nasal hairs. Phagocytosis by white blood cells is a cellular response that occurs after pathogens have breached these initial barriers.