Chapter 22 – The Respiratory System

Overview of the Respiratory System

The respiratory system is responsible for gas exchange, supplying oxygen to the blood and removing carbon dioxide. It consists of anatomical structures organized into conducting and respiratory divisions, each with distinct functions.

• Functions: Gas exchange, regulation of blood pH, voice production, olfaction, and protection against pathogens.

• Process of Respiration: Includes ventilation (breathing), external respiration (gas exchange between air and blood), internal respiration (gas exchange between blood and tissues), and cellular respiration.

Divisions of the Respiratory System

The respiratory system is divided into the conducting and respiratory portions, each with specific roles in air movement and gas exchange.

• Conducting Division: Consists of structures that transport air but do not participate in gas exchange (e.g., nose, pharynx, larynx, trachea, bronchi, bronchioles).

• Respiratory Division: Includes structures where gas exchange occurs (e.g., respiratory bronchioles, alveolar ducts, alveoli).

• Function Comparison: Conducting division filters, warms, and moistens air; respiratory division facilitates gas exchange.

Anatomy of the Upper Respiratory Tract

The upper respiratory tract includes the nasal and oral cavities, pharynx, and larynx, each with unique features and functions.

• Nasal Cavity: Contains conchae (bony projections) and meatuses (passageways) that increase surface area and turbulence for air filtration.

• Palate: Separates the nasal and oral cavities; the hard palate is bony, the soft palate is muscular.

• Tongue: Assists in swallowing and speech.

• Pharynx: Divided into nasopharynx, oropharynx, and laryngopharynx; serves as a passage for air and food.

• Entrances: Air enters via the nasal cavity; food enters via the oral cavity.

Swallowing and Airway Protection

Swallowing involves coordinated movements to prevent food and liquids from entering the trachea.

• Epiglottis: A flap that covers the glottis during swallowing, preventing aspiration.

• Process: The soft palate rises to close off the nasopharynx; the larynx elevates, and the epiglottis folds over the glottis.

Larynx Structure and Function

The larynx is composed of cartilages and houses the vocal folds, which are essential for sound production.

• Cartilages: Includes thyroid, cricoid, arytenoid, and others.

• Vocal Folds (Cords): Vibrate to produce sound; tension determines pitch.

• Glottis: The opening between the vocal folds.

• Tightening Vocal Ligaments: Increases pitch; Loosening: Decreases pitch.

Trachea and Bronchial Tree

The trachea and bronchi conduct air to the lungs and undergo structural changes as they branch.

• Trachea: Located anterior to the esophagus; reinforced by C-shaped cartilage rings for patency and flexibility.

• Bronchi: Primary bronchi enter each lung; secondary bronchi supply lobes; tertiary bronchi supply segments.

• Structural Changes: Cartilage decreases, smooth muscle increases from primary bronchi to terminal bronchioles.

Gross Anatomy of the Lungs

The lungs are paired organs with distinct lobes, roots, and hilus, surrounded by pleural membranes.

• Lobes: Right lung has three lobes; left lung has two.

• Root: Contains pulmonary vessels, bronchi, nerves.

• Hilus: The entry/exit point for structures at the lung root.

• Pleural Membranes: Visceral pleura covers lungs; parietal pleura lines thoracic cavity; pleural cavity contains lubricating fluid.

Alveolar Structure and Gas Exchange

Alveoli are the primary sites of gas exchange, with structural adaptations to maximize efficiency.

• Alveolus: Thin-walled sac surrounded by capillaries; lined by simple squamous epithelium.

• Type I Cells: Form the alveolar wall.

• Type II Cells: Produce surfactant to reduce surface tension.

• Surface Area: Increased by numerous alveoli and branching; essential for efficient gas exchange.

• Gas Exchange: Occurs across the respiratory membrane; thinness and large surface area facilitate diffusion.

Principles of Ventilation

Air movement is governed by pressure-volume relationships and physical laws.

• Boyle’s Law: ; pressure and volume are inversely related.

• Dalton’s Law: ; total pressure is the sum of partial pressures.

• Henry’s Law: ; gas solubility in liquid is proportional to partial pressure.

• Pressure Gradients: Air flows from high to low pressure; inspiration increases thoracic volume, decreasing pressure.

• Resistance: ; flow is proportional to pressure difference and inversely proportional to resistance.

Mechanics of Breathing

Breathing involves changes in thoracic cavity volume, driven by muscle activity.

• Rest: Diaphragm contracts (increases volume), relaxes (decreases volume).

• Activity: Intercostal and accessory muscles further increase volume.

• Pneumothorax: Air in pleural cavity disrupts pressure, causing lung collapse.

Factors Affecting Gas Exchange

Gas exchange efficiency depends on membrane thickness, surface area, and partial pressure gradients.

• Membrane Thickness: Increased thickness reduces diffusion rate.

• Surface Area: Greater area enhances exchange.

• Partial Pressure: Higher gradients drive faster diffusion.

Respiratory Cycle and Airflow

The respiratory cycle includes inspiration and expiration, influenced by pressure differentials and resistance.

• Airflow: Determined by .

• Resistance: Affected by airway diameter, smooth muscle tone, and mucus.

• Regulation: Bronchodilation decreases resistance; bronchoconstriction increases resistance.

Muscles of Ventilation

Several muscles contribute to breathing movements.

• Primary: Diaphragm, external intercostals.

• Accessory: Sternocleidomastoid, scalenes, abdominal muscles (during forced breathing).

Lung Compliance and Elasticity

Compliance and elasticity are critical for normal lung function.

• Compliance: Ease of lung expansion; decreased in fibrosis.

• Elasticity: Ability to return to original shape; decreased in emphysema.

Transport of Oxygen and Carbon Dioxide

Oxygen and carbon dioxide are transported in the blood by different mechanisms.

• Oxygen: Mostly bound to hemoglobin; some dissolved in plasma.

• Carbon Dioxide: Transported as bicarbonate ion, bound to hemoglobin, or dissolved in plasma.

• Haldane Effect: Deoxygenated hemoglobin increases CO2 carrying capacity.

• Blood pH: CO2 increases acidity; excess leads to respiratory acidosis.

Hypoxia

Hypoxia is a deficiency of oxygen in tissues, with various causes and effects.

• Causes: Low oxygen, poor circulation, anemia, carbon monoxide poisoning.

• Effects: Fatigue, cyanosis, organ dysfunction.

Control of Respiration

Respiratory rate and depth are regulated by neural and chemical mechanisms.

• Medullary Centers: Control basic rhythm.

• Chemoreceptors: Respond to CO2, O2, and pH.

• Hering-Breuer Reflex: Prevents over-inflation of lungs via stretch receptors.

Lung Diseases

Lung diseases are classified as restrictive or obstructive, each with distinct characteristics.

• Restrictive Diseases: Decrease lung compliance (e.g., pulmonary fibrosis).

• Obstructive Diseases: Increase airway resistance (e.g., asthma, chronic bronchitis, emphysema).

Lung Surfactant and Infant Respiratory Distress Syndrome

Surfactant is a substance produced by type II alveolar cells, essential for reducing surface tension and preventing alveolar collapse.

• Role: Maintains alveolar stability during breathing.

• Infant Respiratory Distress Syndrome: Caused by insufficient surfactant in premature infants, leading to difficulty breathing.

Summary Table: Conducting vs Respiratory Division

Summary Table: Restrictive vs Obstructive Lung Diseases

Example: In asthma (an obstructive disease), airway smooth muscle constricts, increasing resistance and reducing airflow, which can be alleviated by bronchodilators.

Additional info: Academic context was added to expand brief points into full explanations, including definitions, examples, and tables for comparison.