Recording-2025-02-18T18_41_01.530Z

Immune System Overview

• The immune system comprises various cells and processes to defend the body against pathogens.

Digestive Secretions and Mucus

• Digestive secretions play a role in defending against pathogens.

• Mucus acts as a protective barrier in the respiratory and digestive tracts.

White Blood Cells (Leukocytes)

• Phagocytes: engulf and digest pathogens and damaged tissue.

  • Monocytes: inactive form, become macrophages.

  • Macrophages: active phagocytic cells found in tissues; derived from monocytes.

• Neutrophils: also phagocytic; important in response to infection; contribute to pus formation.

• Eosinophils: play a role in combating multicellular parasites and certain infections.

• Antigen-Presenting Cells: Macrophages and other professional antigen-presenting cells display antigens to T cells, activating adaptive immunity.

Natural Killer Cells (NK Cells)

• Derived from lymphoid stem cells, provide immunological surveillance; recognize and destroy abnormal cells (including cancerous cells).

• Utilize perforin, a protein that forms pores in the target cell membrane, leading to cell lysis.

• Natural killer cells check for abnormal markers on cells and respond by attacking those with tumor-specific markers.

Inflammation

• A non-specific defensive response to tissue damage or infection.

• Prostaglandins are released by damaged cells, triggering nearby mast cells.

• Mast Cells: release histamine and heparin in response to prostaglandins.

• Histamine promotes vasodilation, increasing blood flow to the area, which enhances the delivery of immune cells.

• Symptoms of inflammation include redness, swelling, heat, and pain.

Fever

• A systemic response that often accompanies infection, typically raising body temperature above normal (98.6°F).

• Caused by release of pyrogens (such as interleukin-1) that signal the hypothalamus to increase body temperature.

• High temperatures can inhibit the growth of some pathogens and boost immune cell activity.

• Caution: Extremely high fevers can be harmful and may denature the body’s own proteins.

Complement System

• A group of inactive proteins in the blood that become activated during an immune response, particularly against bacteria.

• Activated complement proteins form the Membrane Attack Complex (MAC), which creates pores in bacterial membranes, leading to cell lysis.

• Composed of 11 proteins that work together in response to pathogens.

Major Histocompatibility Complex (MHC)

• Proteins that present antigens on the cell surface; play a crucial role in immune system recognition.

  • Class I MHC: Present on all nucleated cells; interacts with cytotoxic T cells (CD8+ T cells).

  • Class II MHC: Present primarily on professional antigen-presenting cells; interacts with helper T cells (CD4+ T cells).

• Importance of MHC in the identification of abnormal cells needing immune response.

Conclusion

• The immune system employs various cells and mechanisms to detect and eliminate pathogens and abnormal cells. Phagocytes, natural killer cells, inflammatory responses, fever, the complement system, and MHC complexes form a coordinated defense strategy against infections and diseases.