What is considered the first line of defense against infection in the human body?

The first line of defense against infection in the human body is indeed intact skin. The skin serves as a physical barrier that prevents pathogens, such as bacteria and viruses, from entering the body. It is equipped with multiple layers, which provide structural support and protection. The outermost layer, the epidermis, consists of tightly packed cells that create a formidable barrier, while the dermis contains additional protective features such as sweat and oil glands that produce substances that can kill or inhibit the growth of pathogens.

In addition to its physical presence, skin also plays a vital role in the immune response. It contains immune cells, such as Langerhans cells, which can detect foreign invaders and signal other immune responses. Overall, intact skin not only acts as a primary barrier but also initiates immune activity, making it an essential first line of defense in maintaining the body’s overall health against infections.

Other options like immune cells, gastric secretions, and antibodies represent later components of the immune response, which engage once pathogens have breached the initial barrier of skin and mucous membranes.