Immune System System

The immune system is crucial for protecting the body against invading pathogens including bacteria, viruses, fungi, and protists.

Lymphatic System: Includes lymph, lymph capillaries, lymph vessels, and lymph nodes.
Bone Marrow: Red bone marrow is responsible for the production of leukocytes (white blood cells).
Leukocytes: Various types of white blood cells play different roles in immune defense.

Lymph Capillaries: Tissue fluid enters these capillaries and combines to form lymph vessels.
Skeletal Muscle Contraction: Moves lymph one way through the lymphatic system to lymphatic ducts, which eventually return lymph to the venous blood supply.
Lymph Nodes: Located along lymph vessels; they filter lymph of pathogens and matter, concentrated in areas like the neck, armpits, and groin.
Lymphatic Tissue: Includes tonsils, adenoids, thymus, spleen, and Peyer's patches.
- Tonsils: Located in the pharynx, protect against pathogens entering through the mouth and throat.
- Thymus: Maturation chamber for immature T cells formed in the bone marrow.
- Spleen: Cleans blood of dead cells and pathogens.
- Peyer's Patches: Located in the small intestine, protect the digestive system from pathogens.

Skin: Intact epidermis and dermis serve as barriers against bacteria.
Ciliated Mucous Membranes: Cilia sweep pathogens out of the respiratory tract.
Glandular Secretions: Secretions from exocrine glands help destroy bacteria.
Gastric Secretions: Gastric acid aids in destroying pathogens.
Normal Bacterial Populations: Compete with pathogens in the gut and vagina.

Phagocytes and the inflammatory response mobilize white blood cells and chemical reactions to halt infection:
- Responses include: localized redness, tissue repair, and fluid seepage filled with healing agents.
- Plasma Proteins: Act as the complement system to repel bacteria and pathogens.

Macrophages: Long-living phagocytes that alert T cells to foreign substances.
T Lymphocytes: Directly attack cells infected by viruses and bacteria.
B Lymphocytes: Target specific bacteria for destruction.

Memory Cells: Contribute to long-term immunity.
Suppressor T Cells: Suppress other T cells when an infection has been resolved.
Helper T Cells: Assist in the production of antibodies and other chemical responses.

Antibody-Mediated Response: Occurs in response to an antigen.
Cell-Mediated Response: Targets already infected cells.
The immune response recedes after foreign agents are destroyed, with memory lymphocytes remaining vigilant for future attacks.

Antigens: Substances that stimulate the immune system, typically proteins on the surfaces of pathogens.
- Can also include drugs, toxins, and foreign particles.
The immune system recognizes antigens of its own cells and attacks those that are unfamiliar.
Upon pathogen entry:
- Macrophage Action: Engulfs the pathogen and presents antigen fragments on its surface.
- Helper T Cells: Activate further immune response by stimulating killer T cells and B cells.
- Killer T Cells: Seek and destroy infected cells.
- B Cells: Differentiate into plasma cells (produce specific antibodies) and memory cells.

Innate Immune System: Present at birth, provides immediate but short-term protection.
Adaptive Immunity: Develops when exposed to infection or through immunization; includes:
- Naturally Acquired Active Immunity: Gained through natural exposure to pathogens.
- Artificially Acquired Active Immunity: Gained through vaccinations.
- Naturally Acquired Passive Immunity: Antibodies transferred from mother to fetus during pregnancy or through breastfeeding, providing temporary protection to the infant.
- Artificially Acquired Passive Immunity: Provides quick but short-lived immunity through inoculation with antibodies sourced from other individuals or animals during emergencies.