Physiology Study Notes: Infection Resistance

Physiology Study Notes

• Physiology Overview: This document discusses the body's resistance to infection, focusing on leukocytes (white blood cells), granulocytes, monocytes, macrophages, and the inflammatory response. It also covers various white blood cell types, and their roles in infection defense. Further, the text explains the life cycle of white blood cells, their development in different parts of the body like bone marrow and lymphoid organs, and their lifespan. Finally, there is a discussion of the methods of killing bacteria and the process of phagocytosis.

Resistance to Infection

• Leukocytes: White blood cells; crucial in defending against infection. There are different types such as neutrophils, eosinophils, basophils, monocytes, and lymphocytes, each with specific roles in defending against infection.
  • These cells circulate in the bloodstream and can enter tissues when needed.
  • They are key in inflammation and phagocytosis.
• Granulocytes: A type of leukocyte, including neutrophils, eosinophils, and basophils. They are critical in the initial stages of defense against infection..
  • Neutrophils are the most abundant granulocyte, arriving at infection sites quickly and engulfing pathogens.
  • Eosinophils and basophils play roles in allergic reactions or parasitic infections.
• Monocytes/Macrophages: A type of leukocyte, crucial for engulfing and breaking down pathogens and cellular debris, also play an essential role in the inflammatory process.
  • Macrophages, developed from monocytes, are usually at the site of infection for longer periods, compared to neutrophils.
• Inflammation: A complex biological response to harmful stimuli, characterized by redness, swelling, heat, and pain. White blood cells play a significant role.

White Blood Cell Types and Counts

• Types: Numerous types of white blood cells (leukocytes) exist, each crucial for different aspects of the body's defense mechanisms.
  • Including Neutrophils, Eosinophils, Basophils, Monocytes/Macrophages, and Lymphocytes are all essential components of the immune response.
• Counts: Total white blood cell count (WBC) in a healthy adult is approximately 7,000 cells per cubic millimeter of blood.
  • The proportions of each type of white blood cell vary.
  • Neutrophils compose roughly 62%, while lymphocytes account for about 30%.
  • Counts can change based on infection presence or inflammation.

Leukopoiesis

• Leukopoiesis: Production of white blood cells in the bone marrow. Stem cells in the bone marrow are the starting point. The process includes several stages and specific types of cells.
• Myelopoiesis: Formation of myeloid cells (neutrophils, eosinophils, basophils, monocytes, etc).
• Lymphopoiesis: Development of lymphoid cells (T lymphocytes, B lymphocytes). This process occurs in lymphoid tissue and is vital to cell-mediated immunity and antibody-mediated immunity.

Phagocytosis

• Mechanism: Phagocytes (like neutrophils and macrophages) ingest and destroy foreign particles.
• Foreign Particle Discrimination: Phagocytes distinguish between foreign invaders and the body's own cells.
• Opsonization: An important part of phagocytosis. Antibodies that bind to the foreign organism increase its likelihood of being engulfed.

White Blood Cell Function

• Neutrophils: Crucial in bacterial infections, arrive rapidly to infection sites.
  • Responsible for engulfing pathogens, destroying them, and participate in early inflammatory response.
• Macrophages: Key in tissue inflammation and participate in cleaning up debris and pathogens.
  • They phagocytize pathogens and other foreign particles by engulfing and destroying them.
• Monocytes: Precursors of macrophages, contribute significantly to the inflammatory process.

Defense Against Infection - Other Mechanisms

• Other White Cells (Lymphocytes): These cells, including B and T cells, are part of acquired immunity and crucial for targeting specific microorganisms.

Inflammation Response

• Chemical Mediators: A complex cascade initiated by several chemical factors, inducing the inflammatory response (ex. histamine, bradykinin, serotonin etc.).
• Cellular Responses to Chemicals: Chemical mediators in turn stimulate the release of other chemical signals.
• Fluid Leakage: Capillaries become more permeable, allowing fluids and proteins to leak into tissues causing swelling.

Immune Cell Activity & Life Span

• Granulocytes: Short lifespan. The timing depends on infections, but they usually circulate in the blood for a relatively short period (4-8 hours), then move into tissues.
• Macrophages: Long lifespan. They can remain in tissues for months and continue to phagocytize pathogens and clean up debris.
• Lymphocytes: Can survive for extended periods. Their function depends on the presence or absence of a stimulus or infection.

Phagocytosis of particles

• Specialized Macrophages: Macrophages can reside in specific tissues throughout the body. Different tissues have specialized macrophages, including alveolar macrophages, Kupffer cells in the liver and macrophages in lymph nodes, spleen, and bone marrow.
• Mechanisms: These specialized macrophages are crucial for immune responses in their specific tissues. They phagocytize pathogens, cellular debris, and participate in clearing up the site of inflammation within tissues.
• Immune responses: This ensures that the immune response is targeted toward the sites where they are most needed.

Other Clinical Aspects

• Leukopenia: A low white blood cell count. Reduced white blood cell production can be due to various factors; such as radiation, chemical toxins, and certain medications.
• Leukemias: Uncontrolled production of abnormal white blood cells due to genetic mutations. Characterized by different types that vary in their clinical aspects.
• Allergic Reactions: The immune system's response to harmless substances, characterized by various symptoms.
• Autoimmune Diseases: When the immune system improperly attacks the body's own tissues. These conditions can result in several problems and symptoms.