Function & Purpose of the Immune System

The immune system protects the body from harmful invaders like bacteria, viruses, fungi, and parasites.

Main functions:

Defense: Detects and destroys pathogens

Surveillance: Identifies abnormal cells like cancer cells

Memory: Remembers past infections for faster future responses

Regulation: Controls the intensity of immune responses to avoid damage

Three Lines of Defense

 First Line of Defense Physical & Chemical Barriers

Prevents pathogens from entering the body.

Examples:

Skin physical barrier

Mucus and cilia in airways

Tears, saliva contain enzymes

Stomach acid

 Goal: Keep pathogens out

 Second Line of Defense Innate Immunity

Acts quickly if pathogens get inside; non-specific.

Components:

Inflammation

Fever

Phagocytic white blood cells

Natural killer NK cells

Antimicrobial proteins

 Goal: Slow down and destroy invaders

Third Line of Defense Adaptive Immunity

Specific, targeted response to pathogens.

Components:

B cells  produce antibodies

T cells kill infected cells or help coordinate response

Goal: Eliminate specific pathogens and create memory

 Roles of the 9 Leukocytes White Blood Cells

 1. Neutrophils

First responders to infection

Engulf and digest bacteria phagocytosis

 2. Eosinophils

Attack parasites especially worms

Involved in allergic reactions

 3. Basophils

Release histamine

Trigger inflammation and allergic responses

 4. Monocytes

Circulate in blood, then become macrophages or dendritic cells in tissues

Phagocytosis and antigen presentation

5. Macrophages

Big eaters that engulf pathogens and debris

Activate other immune cells by presenting antigens