The Human Defense System - Part 1: General Defense System

Overview

Immunity: The body's ability to resist infection.
Pathogens: Disease-causing organisms such as bacteria, fungi, and viruses.
Defense System: Comprises the general and specific defense systems.
- General Defense System: Non-specific, same response to all pathogens.
- Specific Defense System: Tailored response involving antibodies.

Skin: Acts as a physical barrier to prevent pathogen entry.
- Sebum: Oil produced by sebaceous glands that lubricates the skin and has antibacterial and antifungal properties.
Mucus: Sticky substance trapping pathogens.
- Mucous Membranes: Thin cell layers lining many body tracts (respiratory, digestive, reproductive).
- Lysozyme: Enzyme found in mucus, tears, sweat, and saliva that breaks down bacterial cell walls.
Cilia: Hairlike structures in airways that waft mucus towards the pharynx for swallowing.
Hydrochloric Acid (HCl): In the stomach, kills many microorganisms.
Beneficial Bacteria: Exist in the vagina (produce lactic acid) and large intestine (suppress growth of pathogenic bacteria).

White Blood Cells
- Monocytes: Phagocytes that engulf and destroy pathogens (process called phagocytosis).
- Macrophages: Large phagocytes found in tissues, lymphatic system (e.g., spleen, tonsils).
Inflammation: Areas become swollen, red, hot, and painful due to increased blood flow and white blood cell activity.
Complement System: Proteins that burst bacterial cells and attract macrophages.
Interferon: Protein released by virus-infected cells that prevents viral replication in uninfected cells.

First Line of Defense: Barriers like skin, sebum, mucus, cilia, HCl, lysozyme, and beneficial bacteria.
Second Line of Defense: Monocytes (phagocytosis), inflammation, interferon, and complement system.