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The immune system is the body’s defense network that protects against harmful pathogens such as bacteria, viruses, fungi, and parasites. Its main functions are to recognize foreign invaders (antigens), respond to eliminate them, and remember past infections for faster future responses (immunity). It helps maintain overall health by preventing infections and destroying damaged or abnormal cells.
The immune system is the body’s defense network that protects against harmful pathogens such as bacteria, viruses, fungi, and parasites. Its main functions are to recognize foreign invaders (antigens), respond to eliminate them, and remember past infections for faster future responses (immunity). It helps maintain overall health by preventing infections and destroying damaged or abnormal cells.
The Three Lines of Defense:
The Three Lines of Defense:
1. First Line of Defense (Physical & Chemical Barriers)
1. First Line of Defense (Physical & Chemical Barriers)
This is the body’s external protection, preventing pathogens from entering. Skin acts as a barrier. Mucous membranes traps microbes. And Secretions creates tears, saliva, stomach acid kill pathogens and keep them out.
This is the body’s external protection, preventing pathogens from entering. Skin acts as a barrier. Mucous membranes traps microbes. And Secretions creates tears, saliva, stomach acid kill pathogens and keep them out.
2. Second Line of Defense (Innate Immunity)
2. Second Line of Defense (Innate Immunity)
This is a non-specific internal defense activated if pathogens get inside:
This is a non-specific internal defense activated if pathogens get inside:
White blood cells (phagocytes) engulf pathogens
White blood cells (phagocytes) engulf pathogens
Inflammation (redness, swelling, heat, pain)
Inflammation (redness, swelling, heat, pain)
Fever (slows pathogen growth)
Fever (slows pathogen growth)
3. Third Line of Defense (Adaptive Immunity)
3. Third Line of Defense (Adaptive Immunity)
This is a specific and targeted response:
This is a specific and targeted response:
Lymphocytes (B cells and T cells)
Lymphocytes (B cells and T cells)
Antibodies produced to target specific pathogens
Antibodies produced to target specific pathogens
Memory cells allow faster response in future infections
Memory cells allow faster response in future infections
The Role of the 9 Leukocytes (White Blood Cells):
The Role of the 9 Leukocytes (White Blood Cells):
1. Neutrophils
1. Neutrophils
First responders to infection
First responders to infection
Engulf and destroy bacteria (phagocytosis)
Engulf and destroy bacteria (phagocytosis)
2. Eosinophils
2. Eosinophils
Fight parasitic infections
Fight parasitic infections
Involved in allergic reactions
Involved in allergic reactions
3. Basophils
3. Basophils
Release histamine
Release histamine
Trigger inflammation and allergic responses
Trigger inflammation and allergic responses
4. Monocytes
4. Monocytes
Circulate in blood and become macrophages or dendritic cells
Circulate in blood and become macrophages or dendritic cells
Engulf pathogens
Engulf pathogens
5. Macrophages
5. Macrophages
“Big eaters” that destroy pathogens
“Big eaters” that destroy pathogens
Activate other immune cells
Activate other immune cells
6. Dendritic Cells
6. Dendritic Cells
Capture antigens and present them to T cells
Capture antigens and present them to T cells
Bridge innate and adaptive immunity
Bridge innate and adaptive immunity
7. B Lymphocytes (B Cells)
7. B Lymphocytes (B Cells)
Produce antibodies
Produce antibodies
Form memory cells for long-term immunity
Form memory cells for long-term immunity
8. Helper T Cells (CD4 T Cells)
8. Helper T Cells (CD4 T Cells)
Coordinate immune response
Coordinate immune response
Activate B cells and other T cells
Activate B cells and other T cells
9. Cytotoxic T Cells (CD8 T Cells)
9. Cytotoxic T Cells (CD8 T Cells)
Kill infected or abnormal cells (like virus-infected cells)
Kill infected or abnormal cells (like virus-infected cells)
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