The Human Defence System Part 1

The Human Defence System

Introduction

• Building immunity is the main goal of the human defense system.

• Immunity is defined as the body's ability to resist infection.

• Pathogens are disease-causing organisms (e.g., bacteria, fungi, viruses).

General vs. Specific Defense Systems

• The human defense system consists of two main parts:

  • General Defense System: Prevents entry of all pathogens, deals with all pathogens similarly.

  • Specific Defense System: Tailored response to specific pathogens, involves antibody production. This video focuses on the General Defense System.

General Defense System

• Not specific; similar response regardless of the pathogen.

• Primarily prevents pathogen entry, but also uses:

  • Inflammation

  • White blood cells (monocytes/macrophages)

  • Specialized defense proteins

Barriers to Entry (First Line of Defense)

Skin

• Physical barrier preventing pathogen entry.

• Integrity is crucial (no cracks or breaks).

Sebum

• Oil secreted by sebaceous glands.

• Functions:

  • Lubricates skin preventing dryness and cracking.

  • Contains chemicals inhibiting bacteria and fungi growth.

Mucus

• Sticky substance trapping pathogens.

• Produced by mucous membranes lining various tracts (respiratory, digestive, reproductive).

• Contains lysozyme, an enzyme that breaks down bacterial cell walls.

Ciliated Cells

• Line airways, possess cilia (hair-like projections).

• Cilia waft mucus and trapped pathogens upwards to the pharynx (throat) to be swallowed.

• Swallowed mucus is then subjected to hydrochloric acid in the stomach.

Lysozyme

• Enzyme breaking down bacterial cell walls.

• Found in mucus, tears, sweat, and saliva.

Hydrochloric Acid

• Kills many microorganisms in the stomach.

Beneficial Bacteria

• Mutualistic relationship (both benefit).

• Examples:

  • Bacteria in the vagina producing lactic acid, creating an acidic environment inhibiting pathogens.

  • Bacteria in the large intestine suppressing the growth of pathogenic bacteria.

What Happens When Barriers are Breached? (Second Line of Defense)

• If pathogens or toxins enter the blood or tissues, the general defense system relies on:

White Blood Cells (Monocytes/Macrophages)

• Monocytes are phagocytes: engulf and destroy other cells.

• Large phagocytes are called macrophages.

• Macrophages reside in tissues and patrol for invaders.

• High numbers found in lymphatic tissues (spleen, tonsils).

• Phagocytosis: Macrophages engulf bacteria and secrete enzymes to destroy them.

Inflammation

• Signified by: Swelling, redness, heat, and pain.

• Generalized inflammation is fever.

• Vasodilation brings more blood (and white blood cells) to the area, especially macrophages.

Complement System

• System of proteins that, when activated:

  • Clump together and burst bacterial cells.

  • Attract macrophages.

Interferon

• Released by virus-infected cells.

• Travels to uninfected cells, warning them to produce chemicals that prevent viral replication.

• Interferon interferes with viral replication.

Summary of Defenses

First Line of Defense (Barrier System)

• Skin

• Sebum

• Mucus

• Cilia

• Hydrochloric acid

• Lysozyme

• Lactic acid-producing bacteria in vagina

• Beneficial bacteria in large intestine

Second Line of Defense

• White blood cells (monocytes/phagocytes/macrophages) perform phagocytosis.

• Inflammation (hot, sore, swollen due to increased blood flow and white blood cells).

• Interferon (viral-infected cells signal non-infected cells to prepare).

• Complement system (proteins destroy bacteria and mark pathogens for macrophage destruction).

Key Definitions to Remember

• Define immunity.

• Define pathogen.

• Outline the components of general defense system.