What is the first line of defense in the immune system?

The first line of defense in the immune system consists of the skin and mucous membranes. These physical barriers are crucial in preventing pathogens from entering the body. The skin acts as a tough, impermeable barrier, making it difficult for bacteria and viruses to penetrate. Similarly, mucous membranes line various body cavities and secrete mucus, which traps pathogens and other foreign particles. Additionally, these membranes often secrete other protective substances, such as lysozymes, which can break down bacterial cell walls.

Other components of the immune system, such as inflammation and adaptive immunity, play significant roles but come into action after the initial barriers are breached. Clotting factors are important for wound healing and preventing blood loss but are not directly involved in the immune defense against pathogens. Therefore, the combination of skin and mucous membranes provides the essential first line of defense in protecting the body from infections.