The Respiratory System: Structure, Function, and Disorders

The Respiratory System

Organs of the Respiratory System

The respiratory system consists of several organs that work together to facilitate gas exchange and maintain homeostasis. Each organ has a specific role in the process of breathing and oxygen delivery.

• Nose: The only externally visible part; filters, moistens, and warms incoming air.

• Pharynx: Muscular passageway (throat) connecting nasal cavity to larynx; divided into nasopharynx, oropharynx, and laryngopharynx.

• Larynx: Voice box; routes air and food into proper channels; contains the epiglottis.

• Trachea: Windpipe; passageway from neck to lungs.

• Bronchi: Branches from trachea into lungs; right bronchus is wider, shorter, and straighter.

• Lungs: Main organs of respiration; contain alveoli for gas exchange.

Example: The nose contains olfactory epithelium for smell and respiratory mucosa to trap and destroy foreign particles.

Functions of the Respiratory System

The primary functions are to supply oxygen to the body and remove carbon dioxide. Passageways also purify, humidify, and warm incoming air.

• Gas Exchange: Occurs only in the alveoli.

• Air Conditioning: Passageways purify, humidify, and warm air.

• Oxygen Supply: Delivers oxygen to tissues.

• Carbon Dioxide Disposal: Removes waste gas from the body.

Anatomy of the Nose and Sinuses

The nose is the entry point for air and contains structures to filter and condition it. Sinuses lighten the skull and aid in speech.

• Olfactory Epithelium: Responsible for the sense of smell.

• Respiratory Mucosa: Moistens air, traps particles, destroys bacteria (via lysozyme), and moves mucus to the throat.

• Conchae: Projections that increase trapping of inhaled particles.

• Sinuses: Lighten skull, act as resonance chambers, and produce mucus.

The Pharynx

The pharynx is a muscular passageway divided into three regions, serving as a common route for air and food.

• Nasopharynx: Superior region behind nasal cavity.

• Oropharynx: Middle region behind mouth.

• Laryngopharynx: Inferior region attached to larynx.

• Epiglottis: Routes food to esophagus and air to trachea.

• Pharyngotympanic Tubes: Drain middle ear into nasopharynx.

• Tonsils: Lymphatic tissue clusters; include pharyngeal (adenoid), palatine, lingual, and tubal tonsils.

The Larynx

The larynx, or voice box, is made of eight rigid hyaline cartilages and routes air and food appropriately.

• Epiglottis: Directs food to esophagus and air to trachea.

The Trachea and Bronchi

The trachea (windpipe) leads to the main bronchi, which branch into the lungs. The right bronchus is more likely to receive aspirated material.

• Trachea: Reinforced with cartilage.

• Main Bronchi: Right is wider, shorter, straighter.

The Lungs

The lungs are divided into lobes and covered by serous membranes. The pleural fluid reduces friction during breathing.

• Apex: Superior portion near clavicle.

• Base: Rests on diaphragm.

• Lobes: Left lung has two; right lung has three.

• Pleura: Pulmonary (visceral) pleura covers lung; parietal pleura lines thoracic cavity.

• Pleural Fluid: Fills space between pleurae; decreases friction.

Bronchial (Respiratory) Tree

The bronchial tree is a network of branching passageways, ending in alveoli where gas exchange occurs.

• Main Bronchi: Subdivide into smaller branches and bronchioles.

• 23 Branches: Trachea is the trunk; branches decrease in size.

• Terminal Bronchioles: Lead to respiratory zone structures.

• Respiratory Zone: Includes respiratory bronchioles, alveolar ducts, sacs, and alveoli.

• Conducting Zone: All other passageways except terminal bronchioles.

Alveoli and Gas Exchange

Alveoli are the primary site of gas exchange, covered by pulmonary capillaries. The respiratory membrane separates air from blood.

• Respiratory Membrane: Air on one side, blood on the other.

• Gas Exchange: Oxygen enters blood; carbon dioxide enters alveoli.

• Alveolar Macrophages: Remove debris and bacteria.

• Surfactant: Lipid molecule that decreases surface tension and prevents alveolar collapse.

Events of Respiration

Respiration involves four main events, each essential for oxygen delivery and carbon dioxide removal.

1. Pulmonary Ventilation: Moving air into and out of lungs (breathing).

2. External Respiration: Gas exchange between pulmonary blood and alveoli.

3. Respiratory Gas Transport: Transport of gases via bloodstream.

4. Internal Respiration: Gas exchange between blood and tissue cells.

Pulmonary Ventilation: Inspiration and Expiration

Pulmonary ventilation consists of two phases: inspiration and expiration, driven by muscle contraction and lung elasticity.

• Inspiration: Diaphragm and external intercostal muscles contract; intrapulmonary volume increases; gas pressure decreases.

• Expiration: Passive process; depends on lung elasticity.

Pressure and Volume Relationships

Intrapleural pressure is always negative, preventing lung collapse. If it equals atmospheric pressure, lungs collapse.

• Intrapleural Pressure: Maintains lung inflation.

Respiratory Volumes and Capacities

Different volumes of air are moved during breathing, measured to assess lung function.

Volume/Capacity	Description	Typical Value (ml)
Tidal Volume (TV)	Normal quiet breathing	500
Inspiratory Reserve Volume (IRV)	Air forcibly inhaled above TV	3,100
Expiratory Reserve Volume (ERV)	Air forcibly exhaled beyond TV	1,200
Residual Volume	Air remaining after expiration	1,200
Vital Capacity	Total exchangeable air	4,800 (men), 3,100 (women)
Dead Space Volume	Air in conducting zone	150
Functional Volume	Air reaching respiratory zone	350

Formula:

$\text{Vital Capacity} = \text{TV} + \text{IRV} + \text{ERV}$

Control of Respiration

Breathing is regulated by neural and non-neural factors, primarily in the medulla and pons.

• Medulla: Sets basic rhythm; contains central respiratory group (VRG).

• Pons: Smoothes out respiratory rate.

• Normal Rate: 12-15 breaths per minute.

• Hyperpnea: Increased rate due to extra oxygen needs.

Factors Influencing Respiratory Rate

Respiratory rate is affected by physical, emotional, and chemical factors.

• Physical: Increased temperature, exercise, talking, coughing.

• Emotional: Fear, anger, excitement.

• Chemical: Oxygen and carbon dioxide levels; information sent to medulla.

• Hypoventilation: Allows CO2 to accumulate.

• Hyperventilation: Rising CO2 (acidosis) causes faster, deeper breathing; exhaling more CO2 elevates blood pH.

Respiratory Disorders

Several disorders affect the respiratory system, often linked to smoking and chronic inflammation.

• Chronic Obstructive Pulmonary Disease (COPD): Includes chronic bronchitis and emphysema; characterized by labored breathing, frequent infections, hypoxia, CO2 retention, respiratory acidosis, and eventual failure.

• Chronic Bronchitis: Inflammation and excessive mucus impair ventilation; patients become cyanotic ("blue bloaters").

• Emphysema: Alveolar walls destroyed, lungs lose elasticity; patients use more energy to exhale, develop barrel chest, and are called "pink puffers." Cyanosis appears late.

• Lung Cancer: Leading cause of cancer deaths; 90% linked to smoking; aggressive and rapidly metastasizing. Types include adenocarcinoma, squamous cell carcinoma, and small cell carcinoma.

Example: COPD patients often have a history of smoking and suffer from chronic hypoxia and respiratory acidosis.

Additional info: The respiratory system is essential for maintaining acid-base balance and homeostasis. Disorders can severely impact oxygen delivery and overall health.