The document summarizes the body's three lines of defense against pathogens. The first line of defense consists of physical and chemical barriers like the skin, mucus, and sweat. The second line of defense involves defensive cells and proteins that attack pathogens that breach the first line, such as mast cells, neutrophils, and the complement system. The third line of defense comprises lymphoid cells that develop in primary organs like the bone marrow and thymus and secondary organs including the spleen, lymph nodes, and MALT tissues. Together, these layered defenses protect the body from infection.

1. DEFENCE MECHANISM
MAN BAHADUR RANA
BPH
ACAS,NEPAL

2. Body’s Defence
Mechanism
1st Line of
Defence
3rd Line of
Defence
2nd Line of
Defence

3. The First Line of Defense:
physical + chemical barriers
Physical Barriers
• Skin
• Mucous membrane
• Hair in nose

4. The First Line of Defense:
Chemical Barriers
• Sweat
• Sebum
• mucous
• Saliva and tears
• Cerumen (ear wax)

6. The Second Line of Defense:
Defensive Cells
• pathogen penetrates the first line of defense Defensive
cells and proteins Second line of defense

7. Mast
Cell

8. The Second Line of Defense: Defensive Cells
Myeloid cells
• polymorphonuclear leukocytes (PMNs).
Neutrophils
Eosinophils
Basophils

9. The Second Line of Defense: Defensive Cells

10. The Second Line of Defense: Defensive Cells
• Mast Cells

11. The Second Line of Defense: Defensive Cells
• Monocytes and Macrophages
•

12. DENDRITIC CELLS
The Second Line of Defense: Defensive Cells

13. The Second Line of Defense:
Defensive Proteins
Interferon Protein
-

14. The Second Line of Defense:
Defensive Proteins
Complement System

15. The Second Line of Defense:
Fever
A mild or moderate fever fight bacterial infections

16. The Second Line of Defense: Defensive Cells

17. The third Line of Defense: Defensive Cells
Lymphoid cells
site of differentiation and on receptors:

18. Organs Of Immune System
• Primary Lymphoid
Organs
– Bone Marrow and
Thymus
Maturation Site
• Secondary Lymphoid
Organs
– Spleen, lymph nodes,
– MALT (mucosal associated
lymph tissue)

19. THYMUS

20. SPLEEN

22. MALT
• throat (NALT) respiratory (BALT), digestive (GALT),
and lymphoid tissue associated with genitourinary