First and Second line of Defence

Overview: The first line of defence comprises mechanisms that prevent pathogens from entering the body. This involves both physical and chemical barriers.

Skin: Provides a protective barrier by blocking pathogens from entering the body.
Mucus: Serves to trap pathogens, preventing them from reaching deeper respiratory pathways.
Cilia: Microscopic hair-like structures that move mucus out of the airways, helping to clear trapped pathogens.
Nose Hairs: Act as filters to trap larger particles and pathogens from inhaled air.

Stomach Acid: The acidic environment in the stomach kills most pathogens that are ingested with food and drink.
Tears and Saliva: Both contain enzymes that can break down bacterial cell walls, offering protection against pathogens.
Sweat: Contains substances that inhibit bacterial growth, providing a chemical defense.
Nature of Defences: The first line of defence operates non-specifically and is always active.

Overview: This line of defence is activated when pathogens breach the first line and enter the body. It involves a rapid, non-specific immune response.

White Blood Cells (Phagocytes): Specialized cells that engulf and destroy pathogens through a process called phagocytosis.
- Function: Phagocytes recognize, engulf, and kill pathogens that have invaded the body.
Inflammation: An immune response characterized by increased blood flow to the site of infection, which facilitates the delivery of immune cells to the affected area.
- Outcome: Leads to localized swelling, redness, heat, and pain.
Fever: An increase in body temperature that occurs as a systemic immune response, which can slow down the growth of pathogens and enhance immune function.
Nature of Defences: The second line of defence is also non-specific, but it provides a rapid response to infections, making it crucial for initial pathogen control.