Which of the following is a physical barrier against pathogens in the first-line defenses of the skin?

• A. Mucous membranes
• B. Lymphocytes
• C. Sebaceous glands
• D. Epidermis

Answer: (D)

Verified step by step guidance

1. Understand the concept of the body's first line of defense: The first line of defense includes physical and chemical barriers that are always ready and prepared to defend the body from infection. These barriers include the skin, mucous membranes, and secretions.
2. Identify the role of the epidermis: The epidermis is the outermost layer of the skin, which acts as a physical barrier to protect the body from pathogens, such as bacteria and viruses.
3. Differentiate between physical and chemical barriers: Physical barriers, like the epidermis, provide a tough outer layer that prevents pathogens from entering the body. Chemical barriers, such as secretions from sebaceous glands, can also protect by creating an environment hostile to pathogens.
4. Evaluate the options given: Mucous membranes are also a physical barrier but are not part of the skin. Lymphocytes are part of the immune response, not a physical barrier. Sebaceous glands produce sebum, which is a chemical barrier.
5. Conclude that the epidermis is the correct answer: Since the epidermis is the outermost layer of the skin and serves as a physical barrier, it is the correct answer to the question.