B3 - Infection and Response

• What is the first line of defense against pathogens?


  The **skin** and **mucous membranes** act as the first line of defense, providing a physical barrier against pathogens.
• How does the skin prevent infection?


  The skin prevents infection through:

  • **Intact epidermis**: A tough, outer layer that prevents pathogens from entering.
  • **Sebum**: An oily secretion that inhibits microbial growth.
  • Sweat: Has a low pH, making it difficult for many pathogens to survive.
• How do mucous membranes prevent infection?


  Mucous membranes prevent infection through:

  • **Physical barrier**: Traps pathogens.
  • Mucus: A sticky substance that traps pathogens, preventing them from entering the body.
  • **Cilia**: Tiny hair-like structures that move mucus and trapped pathogens out of the body.
• What is the role of cilia in the respiratory tract?


  Cilia in the respiratory tract move **mucus** and trapped pathogens upwards towards the **pharynx**, where they can be **swallowed** or **coughed out**.
• How does tears and saliva contribute to non-specific defense?


  Tears and saliva contribute to non-specific defense through:

  • **Lysozyme**: An enzyme that breaks down bacterial cell walls.
  • **Washing action**: Helps to remove pathogens from the eyes and mouth.
• What is the role of stomach acid in non-specific defense?


  Stomach acid, with its low pH ($pH \approx 1.5-3.5$), creates an **environment** that is **unfavorable** for many pathogens to survive, helping to kill ingested microorganisms.