Immune & Respiratory Systems: Study Guide for Anatomy & Physiology

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Immune System

Lines of Immune Defense

The immune system protects the body from pathogens through multiple layers of defense, classified as first, second, and third lines.

First Line: Physical and chemical barriers such as skin, mucous membranes, and secretions (e.g., saliva, tears).
Second Line: Non-specific responses including inflammation, fever, and phagocytic cells (e.g., neutrophils, macrophages).
Third Line: Specific (adaptive) immunity involving lymphocytes and the production of antibodies.

Additional info: The first line prevents entry, the second line responds to breaches, and the third line targets specific pathogens.

Innate vs. Adaptive Immunity

Immunity is divided into innate (non-specific) and adaptive (specific) types, each with distinct mechanisms and components.

Innate Immunity: Present from birth, includes barriers and general responses (e.g., inflammation, phagocytosis).
Adaptive Immunity: Develops after exposure, involves lymphocytes (T cells and B cells) and the production of antibodies.

Comparison Table:

Feature	Innate Immunity	Adaptive Immunity
Specificity	Non-specific	Highly specific
Memory	No	Yes
Cells involved	Phagocytes, NK cells	T cells, B cells
Response time	Immediate	Delayed (days)

Types of Lymphocytes and Immune Cells

Lymphocytes are central to adaptive immunity, while other immune cells contribute to both innate and adaptive responses.

T cells: Mediate cellular immunity; include helper, cytotoxic, and regulatory subtypes.
B cells: Produce antibodies for humoral immunity.
NK cells: Destroy infected or abnormal cells without prior sensitization.
Macrophages: Engulf pathogens and present antigens to lymphocytes.

Types of Immunity

Immunity can be classified by how it is acquired and its duration.

Natural Active: Exposure to pathogens leads to immunity (e.g., infection).
Artificial Active: Immunization via vaccines.
Natural Passive: Transfer of antibodies (e.g., maternal antibodies to fetus).
Artificial Passive: Injection of antibodies (e.g., antivenom).

MHC Proteins and Antigen Presentation

Major Histocompatibility Complex (MHC) proteins are essential for presenting antigens to T cells.

MHC I: Present on all nucleated cells; present endogenous antigens to cytotoxic T cells.
MHC II: Present on antigen-presenting cells (APCs); present exogenous antigens to helper T cells.

Antibodies and Immunoglobulin Classes

Antibodies are proteins produced by B cells that bind specific antigens. There are several classes, each with unique functions.

IgA: Found in mucosal areas, protects body surfaces.
IgG: Most abundant, provides long-term immunity.
IgM: First antibody produced during primary response.
IgE: Involved in allergic reactions.
IgD: Functions mainly as a B cell receptor.

Example: IgM is the first antibody detected after initial exposure to an antigen.

Respiratory System

Anatomy of the Respiratory System

The respiratory system consists of structures that conduct air and facilitate gas exchange.

Conducting Zone: Includes nose, pharynx, larynx, trachea, bronchi, and bronchioles; transports air to lungs.
Respiratory Zone: Includes respiratory bronchioles, alveolar ducts, and alveoli; site of gas exchange.

Pathway of Air: Nasal cavity → pharynx → larynx → trachea → bronchi → bronchioles → alveoli

Mechanics of Breathing

Breathing involves inspiration and expiration, driven by pressure changes in the thoracic cavity.

Inspiration: Diaphragm contracts, thoracic volume increases, pressure decreases, air flows in.
Expiration: Diaphragm relaxes, thoracic volume decreases, pressure increases, air flows out.

Equation:

(Boyle's Law: pressure and volume are inversely related)

Respiratory Volumes and Capacities

Respiratory volumes measure the amount of air in the lungs during different phases of breathing.

Tidal Volume (TV): Volume of air inhaled or exhaled in a normal breath.
Inspiratory Reserve Volume (IRV): Additional air inhaled after a normal inspiration.
Expiratory Reserve Volume (ERV): Additional air exhaled after a normal expiration.
Residual Volume (RV): Air remaining in lungs after maximal exhalation.
Vital Capacity (VC): Maximum air exhaled after maximal inhalation ().

Example: If TV = 500 mL, IRV = 3000 mL, ERV = 1200 mL, then mL.

Gas Exchange and Transport

Oxygen and carbon dioxide are exchanged between alveoli and blood, and transported by hemoglobin.

Oxygen Transport: Most oxygen binds to hemoglobin in red blood cells.
CO2 Transport: Carried as bicarbonate ions, dissolved in plasma, or bound to hemoglobin.

Equation:

Factors Affecting Hemoglobin Affinity for Oxygen

Hemoglobin's ability to bind and release oxygen is influenced by several factors.

pH: Lower pH (acidic) decreases affinity, promoting oxygen release.
Temperature: Higher temperature decreases affinity.
pCO2: Increased CO2 decreases affinity.
2,3-BPG: Increases oxygen unloading.

Example: During exercise, increased CO2 and temperature favor oxygen release to tissues.

Inflammation and Immune Responses

Cardinal Signs of Inflammation

Inflammation is a protective response to injury or infection, characterized by four cardinal signs:

Redness (rubor)
Heat (calor)
Swelling (tumor)
Pain (dolor)

Cause: Increased blood flow, vascular permeability, and migration of immune cells.

Cytotoxic T Cells

Cytotoxic T cells (CD8+) destroy infected or abnormal cells by inducing apoptosis.

Mechanism: Release perforin and granzymes to kill target cells.
Difference from NK Cells: Cytotoxic T cells require antigen presentation via MHC I; NK cells do not.

Practice Questions

Which antibody class is first released during a primary immune response? Answer: IgM
What is the role of surfactant in the alveoli? Answer: Surfactant reduces surface tension, preventing alveolar collapse.
What causes air to move into the lungs during inhalation? Answer: Decreased intrapulmonary pressure relative to atmospheric pressure.
What conditions favor oxygen unloading from hemoglobin into tissues? Answer: Low pH, high temperature, high CO2, and increased 2,3-BPG.