What is considered the body’s first line of defense against infection?

The skin is considered the body's first line of defense against infection because it serves as a physical barrier that protects the internal organs and systems from pathogens such as bacteria, viruses, and fungi. This protective layer not only acts as a shield against infectious agents entering the body but also plays a crucial role in regulating body temperature and preventing fluid loss.

The skin is made up of multiple layers, including the epidermis and dermis, which are structured to withstand various types of damage. Additionally, the skin produces antimicrobial substances and has an acidic pH, which further deters the growth of harmful microorganisms.

While other options listed, such as the lungs, digestive system, and immune system, do contribute to the body’s overall defense mechanisms, they are not the primary barrier against initial exposure to infections. For example, the lungs serve to filter and warm the air we breathe, while the digestive system has its own means of combating pathogens through digestive enzymes and a healthy gut microbiota. The immune system, while vital for identifying and fighting off infections, responds after the pathogen has breached other barriers like the skin. Thus, the skin is best recognized as the first line of defense in preventing infections.