Immunity

Overview of Immune Lines of Defense

The immune system protects the body from pathogens through multiple lines of defense, each with distinct mechanisms and components.

• First Line: Non-specific barriers that protect against all pathogens (e.g., skin, mucous membranes).

• Second Line: Non-specific internal defenses such as phagocytes, inflammation, and fever.

• Third Line (Adaptive Immunity): Specific defense mechanisms involving lymphocytes and the production of antibodies.

Adaptive Immunity

Adaptive immunity is a specific immune response that develops after exposure to antigens. It is characterized by memory and specificity.

• Antigens: Substances that provoke an immune response by being recognized as foreign by the body.

• Epitopes (Antigenic Determinants): Specific regions on antigens that are recognized by antibodies or lymphocyte receptors.

• Antibodies: Y-shaped proteins produced by B cells that bind to specific antigens. There are five classes of antibodies (IgG, IgA, IgM, IgE, IgD), each with unique functions and structures. Additional info: For example, IgG is the most abundant and can cross the placenta, while IgE is involved in allergic responses.

• Antibody Titer: The concentration of antibodies in the blood, indicating the strength of an immune response.

• B Cells and T Cells: Lymphocytes that play central roles in adaptive immunity.

  • B Cells: Mature in the bone marrow and are responsible for humoral immunity (antibody production).

  • T Cells: Mature in the thymus and are responsible for cell-mediated immunity. Subtypes include helper T cells (CD4+) and cytotoxic T cells (CD8+).

Antigen-Presenting Cells (APCs)

APCs are cells that process and present antigens to T cells, initiating the adaptive immune response.

• MHC Class I: Present on all nucleated cells; present antigens to CD8+ cytotoxic T cells.

• MHC Class II: Present on professional APCs (e.g., dendritic cells, macrophages, B cells); present antigens to CD4+ helper T cells.

Immune Tolerance

Tolerance is the immune system's ability to distinguish self from non-self, preventing autoimmune reactions.

Cytokines

Cytokines are signaling proteins released by cells that mediate and regulate immunity, inflammation, and hematopoiesis.

Types of Acquired Immunity

Acquired immunity can be classified based on how it is obtained:

• Active Naturally Acquired Immunity: Immunity developed after natural exposure to an antigen (e.g., infection).

• Active Artificially Acquired Immunity: Immunity developed after exposure to an antigen via vaccination.

• Passive Naturally Acquired Immunity: Immunity acquired by the transfer of antibodies from mother to fetus through the placenta or breast milk.

• Passive Artificially Acquired Immunity: Immunity acquired by the injection of antibodies (e.g., antiserum).

Autoimmune Diseases

Autoimmune diseases occur when the immune system attacks the body's own tissues.

Immunodeficiency Diseases/Syndromes

Immunodeficiency diseases are conditions in which the immune system's ability to fight infectious disease is compromised or entirely absent.

• Congenital: Present at birth (e.g., Severe Combined Immunodeficiency, SCID).

• Acquired: Develops later in life (e.g., AIDS caused by HIV infection).

Hypersensitivity

Hypersensitivity refers to exaggerated or inappropriate immune responses to antigens, leading to tissue damage (e.g., allergies, autoimmune reactions).

Respiratory System (Chapter 22)

Pulmonary Ventilation

Pulmonary ventilation, or breathing, is the process of moving air into and out of the lungs to facilitate gas exchange.

• External Respiration: Exchange of gases between the lungs and the blood.

• Internal Respiration: Exchange of gases between the blood and body tissues.

Upper & Lower Respiratory Structures and Functions

The respiratory system is divided into upper and lower tracts, each with specialized structures and functions.

• Upper Respiratory Tract: Includes the nose, nasal cavity, pharynx, and larynx; functions in filtering, warming, and humidifying air.

• Lower Respiratory Tract: Includes the trachea, bronchi, bronchioles, and lungs; functions in conducting air and gas exchange.

Voice/Speech

Voice production occurs in the larynx, where the vocal cords vibrate as air passes through, producing sound.

Respiratory Pressures

Several pressures are involved in breathing:

• Intrapulmonary Pressure: Pressure within the alveoli.

• Intrapleural Pressure: Pressure within the pleural cavity.

• Transpulmonary Pressure: Difference between intrapulmonary and intrapleural pressures.

• Atmospheric Pressure: Pressure exerted by the air surrounding the body.

Vital Capacity

Vital capacity is the maximum amount of air a person can expel from the lungs after a maximum inhalation.

• Formula:

Partial Pressure Gradients

Gas exchange in the lungs and tissues is driven by differences in partial pressures of oxygen and carbon dioxide.

Surfactant

Surfactant is a substance produced by type II alveolar cells that reduces surface tension, preventing alveolar collapse.

Ventilation-Perfusion Coupling

This mechanism matches the amount of air reaching the alveoli (ventilation) with the blood flow in pulmonary capillaries (perfusion) for efficient gas exchange.

Hemoglobin Saturation & Dissociation

Hemoglobin binds oxygen in the lungs and releases it in the tissues. The oxygen-hemoglobin dissociation curve describes this relationship.

• High Saturation: Occurs in the lungs where oxygen pressure is high.

• Dissociation: Occurs in tissues where oxygen pressure is low.

Oxygen Loading & Unloading

Oxygen loading occurs in the lungs, while unloading occurs in the tissues, facilitated by changes in partial pressures and hemoglobin affinity.

Carbonic Anhydrase Equation

Carbonic anhydrase catalyzes the conversion of carbon dioxide and water to carbonic acid, which dissociates into bicarbonate and hydrogen ions.

• Equation:

• Function: Helps transport CO2 in the blood and maintain acid-base balance.

Hypoxia

Hypoxia is a condition in which tissues are deprived of adequate oxygen supply.

Respiratory Control Centers

Respiratory centers in the brainstem (medulla oblongata and pons) regulate the rate and depth of breathing.

Homeostatic Imbalances

Disorders that disrupt normal respiratory function, such as asthma, chronic obstructive pulmonary disease (COPD), and pneumonia.

Lung Cancers

Lung cancer is a malignant tumor of the lungs, often associated with smoking and exposure to carcinogens.

Table: Types of Acquired Immunity