lecture 20 physiology

Lecture Overview

• Course: BIO 1220 - Human Physiology

• Lecture Topic: Immunity

• Instructor: Dr. Suzanne Gray, UPEI

• Term: Winter 2025

Introduction to Immunity

• Definition: Ability to protect the body against disease-causing organisms and nonliving substances.

• Functions of the Immune System:

  • Recognizing pathogenic agents.

  • Disposal of aging cells and cellular debris.

  • Participation in wound healing.

  • Recognizing mutant cells that can become cancerous.

• Types of Immune Responses:

  • Innate Immunity

  • Adaptive Immunity

Innate Immunity

• Definition: Defenses present at birth; immediate and non-specific.

• Pathogen Definition: Any harmful microorganism.

Surface Barriers

• Skin and Mucosae:

  • Act as the body's first line of defense.

  • Skin offers nonspecific protection against foreign matter.

  • Skin is home to millions of microorganisms, rich in microbial fauna.

• Microbial Entry Points:

  • Microorganisms rarely penetrate the epidermis due to keratin.

  • Sebum and sweat contain chemicals that are toxic to bacteria.

  • Entry points: skin breaches allow pathogens to enter and initiate an inflammatory response.

Internal Defenses

• Cells Involved:

  • Neutrophils, macrophages, natural killer (NK) cells.

  • Functions of Phagocytes:

    1. Ingest pathogen.

    2. Enclose pathogen in vesicle.

    3. Fusion with lysosome.

    4. Breakdown and killing of pathogen.

    5. Release of waste.

• Natural Killer (NK) Cells:

  • Unique lymphocytes that destroy infected or cancerous cells.

  • Respond quickly within hours to viral infections.

  • Release perforins that create holes in membranes of target cells.

Inflammatory Response

• Definition: Response to tissue damage (heat, chemicals, infection).

• Symptoms: Redness, heat, swelling, pain.

• Functions of Inflammation:

  1. Prevent spread of damaging agents.

  2. Disposes of debris and pathogens.

  3. Alerts the adaptive immune system.

  4. Prepares tissue for repair.

• Stages of Inflammation:

  1. Mast cells release histamine, causing vasodilation and increased permeability of capillaries.

  2. Phagocytes (neutrophils, then macrophages) flood the area to clear debris.

Adaptive Immunity

• Protects against specific pathogens and abnormal cells (e.g., cancer).

• Learning Aspect: Must learn to recognize specific pathogens, allowing quicker responses on re-exposure.

Characteristics of Adaptive Immunity

• Specificity.

• Systemic nature.

• Memory formation.

Antigens and their Role

• Definition: Substances that provoke an immune response (not normally found in the body).

• Types of Antigens:

  • Bacteria, fungi, viruses, and large foreign proteins.

  • Incomplete antigens may combine with body proteins to provoke a response.

Immune Cells of Adaptive Responses

• B Lymphocytes (B Cells):

  • Produce antibodies targeting specific pathogens.

  • Differentiate into plasma cells (produce antibodies) and memory cells (provide faster immune response).

• T Lymphocytes (T Cells):

  • Help regulate immune response; include helper T cells (activate B cells) and cytotoxic T cells (attack infected or cancerous cells).

  • Activation occurs via antigen-presenting cells (APCs).

Antigen-Presenting Cells (APCs)

• Examples: Dendritic cells and macrophages.

  • Capture and present antigens to T cells to elicit an immune response.

Cellular Immune Response

• Activation involves:

  1. MHC protein presenting antigen on infected cells.

  2. Killer T cells binding to these complexes and releasing chemicals to kill the target cells.

Problems with the Immune System

Organ Transplants

• Rejection can occur; success depends on tissue similarity and MHC antigen matching.

• Immunosuppressant drugs are necessary but can lower overall immune effectiveness.

Immunodeficiencies

• Conditions impairing immune function (e.g., AIDS, Hodgkin’s Lymphoma).

Autoimmune Diseases

• Immune system mistakenly attacks self-tissues (e.g., rheumatoid arthritis, multiple sclerosis).

Hypersensitivities

• Overreactions to harmless substances can lead to severe allergic reactions (e.g., anaphylactic shock).

Conclusion

• Key Topics to Remember:

  1. Different types of innate defenses.

  2. Understanding adaptive defenses.

  3. Issues and problems with the immune system.

Next Lecture

• Topic: Respiration