MICR290_Chapter 15_AFernando_part 2 LECTURE AUDIO

Innate Immunity Overview

• Innate immunity is the natural defense system we are born with to resist infections.

• It is the body's first line of defense against pathogens encountered from birth.

First Line of Defense

• Skin and mucous membranes serve as entry portals for microbes.

• Mucous membranes line body cavities and are made up of epithelial cells that help block pathogen entry.

• The skin consists of two layers: the epidermis (outer) and dermis (inner).

Skin Defense Mechanisms

• Sweat (Perspiration)

  • Contains salt which inhibits microbial growth.

  • Contains antimicrobial peptides (e.g., leukocidins) that help eliminate microbes.

• Sebum

  • Secreted by oil glands, moistens skin and lowers pH to deter bacterial growth.

Mucous Membranes

• Mucous membranes line body cavities (e.g., digestive and respiratory systems).

• Epithelial cells provide a tight barrier to prevent microbial invasion.

• They regenerate continuously, shedding dead cells and trapping foreign materials.

Protective Secretions

• Lacrimal Apparatus

  • Produces tears that wash away foreign particles and contain lysozymes to break down bacterial cell walls.

Normal Microflora and Antagonism

• Normal microflora competes with pathogenic microorganisms, reducing infection risk.

• Antagonism

  • Normal flora inhibit the overgrowth of pathogens, enhancing the body's innate immunity.

Second Line of Defense

• Activated when pathogens breach the skin or mucous barriers.

• Involves various blood cells, receptors, and cytokines to combat pathogens.

Blood Components

• Blood consists of plasma, cells, and clotting factors:

  • Plasma: Contains water, electrolytes, proteins, and nutrients.

  • Cells: Include red blood cells (erythrocytes), white blood cells (leukocytes), and platelets.

Types of White Blood Cells (Leukocytes)

• Granulocytes:

  • Neutrophils: First responders, capable of phagocytosis and non-phagocytic methods of killing.

  • Eosinophils: Target helminthic infections, release toxic mediators but are not primarily phagocytic.

  • Basophils: Release histamines, involved in inflammatory responses.

• Agranulocytes:

  • Lymphocytes: Support adaptive immunity (B and T cells).

  • Monocytes: Differentiate into macrophages upon entering tissues, potent phagocytes.

Hematopoiesis

• The formation of blood cells from stem cells in the bone marrow.

• Stem cells differentiate into specific types of blood cells based on body needs.

Phagocytosis and Chemotaxis

• Phagocytosis: The process by which certain white blood cells engulf and destroy pathogens:

  • Stages: chemotaxis, adherence, ingestion, killing, and elimination of waste.

• Chemotaxis: Movement of cells toward the site of infection in response to chemical signals.

• Diapedesis: Movement of white blood cells through the blood vessel wall into tissues.

Inflammatory Response

• Inflammation is a non-specific response to injury or infection characterized by redness, heat, swelling, and pain.

• Driven by dilation of blood vessels, increased permeability, and movement of immune cells to the site of damage.

  • Can be acute or chronic.

Fever and Pyrogens

• Fever is a systemic response to inflammation, regulated by the hypothalamus.

• Pyrogens are substances that induce fever, often resulting from pathogen invasion.

Chemical Defenses

• Interferons: Proteins released by infected cells that inhibit viral replication in neighboring cells.

• Complement System: A series of serum proteins that enhance the body's ability to clear pathogens through opsonization and lysis.

Complement Activation

• Three pathways: classical, alternative, and lectin pathways, leading to the formation of a membrane attack complex that lyses pathogens.

Summary of Key Points

• Understand differences between serum and plasma, the role of leukocytes in immunity (especially granulocytes and agranulocytes), and the processes of phagocytosis, inflammation, and the complement system.

• Recognize the importance of the innate immune system as the body's first line of defense against pathogens and how it interacts with the adaptive immune response.