Week 13: Respiratory Pathophysiology

Immunoglobulins and Allergic Response

Antibodies (like IgE) that protect the body. IgE binds to allergens and triggers mast cells/basophils to release chemical mediators (e.g., histamine), causing allergic reactions.

Primary Chemical Mediators

Substances like Histamine (causes vasodilation, bronchoconstriction), Eosinophil Chemotactic Factor, Platelet Activating Factor, and Prostaglandins, released immediately by mast cells.

Secondary Chemical Mediators

Substances like Leukotrienes, Bradykinin, and Serotonin, which cause prolonged smooth muscle contraction, bronchospasm, and increased vascular permeability.

Hypersensitivity

An excessive or atypical immune response. Sensitization initiates the buildup of antibodies, typically not occurring on the first exposure.

Type I Hypersensitivity

Anaphylactic; IgE-mediated; rapid onset; examples include hives, allergic rhinitis, and systemic anaphylaxis from bee stings.

Type II Hypersensitivity

Cytotoxic; reaction against "self" antigens; involves opsonization and lysis of cells; examples include Myasthenia Gravis and transfusion reactions.

Type III Hypersensitivity

Immune Complex; antigens bind to antibodies and deposit in tissues, causing injury; examples include Systemic Lupus Erythematosus and Rheumatoid Arthritis.

Type IV Hypersensitivity

Delayed-Type; T-Cell mediated; inflammation occurs 1-3 days after exposure; examples include PPD skin test and contact dermatitis.

Anaphylaxis

A life-threatening Type I hypersensitivity reaction. Major mediators are histamine, prostaglandins, and leukotrienes, causing bronchoconstriction, hypotension, and edema.

Allergic Rhinitis

A common Type I respiratory allergy with histamine as the major mediator. Symptoms include sneezing, nasal congestion, and itchy, watery eyes.

Respiratory System Basics

Respiratory System Function

Delivers oxygen, expels carbon dioxide, warms and filters air. Protective mechanisms include cough, goblet cells (secrete mucus), and cilia.

Ventilation

The process of air moving in and out of the lungs. Inspiration involves diaphragm contraction (lowers pressure), and expiration involves diaphragm relaxation (increases pressure).

Perfusion (Oxygen Transport)

Oxygen crosses the alveolar-capillary membrane by diffusion and binds to hemoglobin in red blood cells to form oxyhemoglobin (HgbO₂) for transport.

Perfusion (Carbon Dioxide Transport)

CO₂, a metabolic waste product, diffuses from venous blood into the alveoli. It crosses the alveolar-capillary membrane more easily than oxygen.

V/Q Ratio (Ventilation-Perfusion Ratio)

The balance between ventilation (airflow) and perfusion (blood flow) in the lungs. Crucial for adequate gas exchange.

Normal V/Q Ratio

Approximately 1:1 or 0.8:0.9, meaning ventilation matches or is slightly less than perfusion.

Low V/Q Ratio (Shunt)

Perfusion is greater than ventilation; blood bypasses alveoli without gas exchange. Caused by airway obstruction, pneumonia, or atelectasis.

High V/Q Ratio (Dead Space)

Ventilation is greater than perfusion; not enough blood flow for gas exchange. Caused by pulmonary embolism or cardiogenic shock.

Hypoxia

A decrease in oxygen delivery to the body's tissues or cells.

Hypoxemia

A state of low arterial oxygen supply. Symptoms include tachypnea, tachycardia, restlessness, and cyanosis.

Hypercapnia

A condition arising from too much carbon dioxide in the blood. Acute symptoms include rapid breathing, headache, confusion, and flushed skin.

Pathologies (COPD, Pneumonia, Cold)

COPD (Chronic Obstructive Pulmonary Disease)

A preventable, treatable, slowly progressive disease with airflow obstruction that is not fully reversible. Includes chronic bronchitis and emphysema.

Chronic Bronchitis

Defined by a chronic cough and sputum production for at least 3 months in 2 consecutive years. Pathophysiology includes airway inflammation, cilia destruction, and mucus gland hyperplasia.

Emphysema

Characterized by the destruction of alveoli due to overdistention. Caused by smoking or alpha1-antitrypsin deficiency. Leads to loss of elastic recoil and barrel chest.

Pneumonia

A lower respiratory tract infection causing inflammation of the lung parenchyma. Can be caused by bacteria, viruses, fungi, or aspiration.

Common Cold (Viral Rhinitis)

An acute upper respiratory infection (URI) caused by a virus (e.g., Rhinovirus). Symptoms include rhinorrhea, congestion, cough, and sore throat. It is self-limiting.