Study Guide: The Respiratory System (Anatomy & Physiology)

Ch. 22: The Respiratory System

I. Introduction

The respiratory system supplies the body with oxygen and removes carbon dioxide, a process known as respiration. Respiration involves several distinct processes that ensure efficient gas exchange between the body and the environment.

• Primary Function: Exchange of gases (O2 and CO2) between the atmosphere and body cells.

• Respiration: Includes ventilation, external respiration, transport of gases, and internal respiration.

II. Events of Respiration

• Pulmonary Ventilation: Movement of air into and out of the lungs (breathing).

• External Respiration: Exchange of O2 and CO2 between lungs and blood.

• Transport of Respiratory Gases: Movement of O2 and CO2 in the blood.

• Internal Respiration: Exchange of gases between blood and tissue cells.

III. Functional Anatomy of the Respiratory System

A. Nose and Paranasal Sinuses

• Warms, moistens, and filters air; houses olfactory receptors.

B. Pharynx

• Passageway for air and food; connects nasal cavity to larynx and esophagus.

C. Larynx

• Routes air and food; houses vocal cords.

D. Trachea

• Windpipe; conducts air to bronchi.

E. Bronchi and Subdivisions: The Bronchial Tree

• Branching system of airways: primary bronchi → secondary bronchi → tertiary bronchi → bronchioles → terminal bronchioles.

• Respiratory Zone: Includes respiratory bronchioles, alveolar ducts, and alveoli (site of gas exchange).

F. Lungs

• Paired organs containing bronchial tree and alveoli; surrounded by pleurae.

G. Pleurae

• Double-layered serous membranes (parietal and visceral) surrounding each lung; reduce friction.

IV. Mechanics of Breathing

A. Pressure Relationships in the Thoracic Cavity

• Atmospheric Pressure (Patm): Pressure exerted by air surrounding the body (at sea level, 760 mm Hg).

• Intrapulmonary Pressure (Ppul): Pressure in alveoli; fluctuates with breathing but always equalizes with atmospheric pressure.

• Intrapleural Pressure (Pip): Pressure in pleural cavity; always negative relative to Ppul (about -4 mm Hg).

B. Factors Holding the Lungs to the Thorax Wall

• Surface tension of pleural fluid, negative pressure in pleural cavity, and elasticity of lungs.

• Opposing forces: lung recoil (collapses lungs) vs. chest wall elasticity (expands thorax).

C. Pulmonary Ventilation: Inspiration and Expiration

• Boyle's Law: At constant temperature, pressure of a gas varies inversely with its volume: $P_1V_1 = P_2V_2$

• Inspiration: Diaphragm and external intercostals contract, increasing thoracic volume and decreasing pressure, drawing air in.

• Expiration: Usually passive; diaphragm and intercostals relax, thoracic volume decreases, pressure increases, air flows out.

V. Physical Factors Influencing Pulmonary Ventilation

• Airway Resistance: Determined by airway diameter; greatest in medium-sized bronchi.

• Alveolar Surface Tension: Surfactant reduces surface tension, preventing alveolar collapse.

• Lung Compliance: Measure of lung expandability; decreased by fibrosis, reduced surfactant, or decreased thoracic flexibility.

VI. Respiratory Volumes and Capacities

• Tidal Volume (TV): Air moved in/out during normal breathing (~500 mL).

• Inspiratory Reserve Volume (IRV): Air forcibly inhaled after normal inspiration.

• Expiratory Reserve Volume (ERV): Air forcibly exhaled after normal expiration.

• Residual Volume (RV): Air remaining in lungs after forced expiration.

• Dead Space: Volume of air not involved in gas exchange (anatomic + alveolar dead space).

VII. Gas Exchange in the Body

A. Basic Properties of Gases

• Dalton's Law of Partial Pressures: Total pressure of a gas mixture is the sum of the pressures exerted by each gas independently.

• Henry's Law: Amount of gas dissolved in a liquid is proportional to its partial pressure and solubility.

B. Composition of Alveolar Gas

• Alveolar air differs from atmospheric air due to gas exchange, humidification, and mixing of inspired/expired air.

C. Gas Exchange

• External Respiration: O2 enters, CO2 leaves blood at alveoli.

• Internal Respiration: O2 leaves, CO2 enters blood at tissues.

• Driven by partial pressure gradients and diffusion.

D. Ventilation-Perfusion Coupling

• Efficient gas exchange requires matching of alveolar ventilation and pulmonary blood flow.

• Local autoregulatory mechanisms adjust airflow and blood flow to optimize exchange.

E. Surface Area and Thickness of Respiratory Membrane

• Large surface area and thin membrane (0.5–1 μm) facilitate rapid gas exchange.

VIII. Transport of Respiratory Gases by Blood

A. Oxygen Transport

• 98.5% of O2 is carried bound to hemoglobin (Hb) in red blood cells; 1.5% dissolved in plasma.

• O2 binds reversibly to iron in Hb: $\text{Hb} + \text{O}_2 \leftrightarrow \text{HbO}_2$

• Oxygen-hemoglobin dissociation curve shows relationship between O2 partial pressure and Hb saturation.

B. Carbon Dioxide Transport

• CO2 is transported in three forms:

  1. Dissolved in plasma (7–10%)

  2. Chemically bound to Hb as carbaminohemoglobin (20%)

  3. As bicarbonate ion (HCO3-) in plasma (70%)

• CO2 conversion to bicarbonate: $\text{CO}_2 + \text{H}_2\text{O} \leftrightarrow \text{H}_2\text{CO}_3 \leftrightarrow \text{H}^+ + \text{HCO}_3^-$

C. Haldane and Bohr Effects

• Haldane Effect: Deoxygenated blood can carry more CO2.

• Bohr Effect: Increased CO2 or H+ decreases Hb's affinity for O2, enhancing O2 release in tissues.

IX. Control of Respiration

A. Neural Control

• Medullary Respiratory Centers: Ventral and dorsal respiratory groups set basic rhythm.

• Pontine Respiratory Centers: Modify and fine-tune breathing rhythms.

B. Influence of Higher Brain Centers

• Hypothalamus and cortical controls can modify respiratory rate and depth (e.g., emotions, voluntary breath holding).

C. Chemical Factors

• Central and peripheral chemoreceptors monitor CO2, O2, and H+ levels.

• Rising CO2 (hypercapnia) is the most powerful respiratory stimulant.

Table: Forms of Carbon Dioxide Transport in Blood

Form	Percentage	Description
Dissolved in plasma	7–10%	CO2 directly dissolved in blood plasma
Carbaminohemoglobin	20%	CO2 bound to hemoglobin (HbCO2)
Bicarbonate ion (HCO3-)	70%	CO2 converted to bicarbonate in plasma

Key Equations

• Boyle's Law: $P_1V_1 = P_2V_2$

• CO2 to Bicarbonate: $\text{CO}_2 + \text{H}_2\text{O} \leftrightarrow \text{H}_2\text{CO}_3 \leftrightarrow \text{H}^+ + \text{HCO}_3^-$

Summary Table: Respiratory Volumes

Volume	Definition	Typical Value (mL)
Tidal Volume (TV)	Normal breath in/out	500
Inspiratory Reserve Volume (IRV)	Extra air inhaled after normal inspiration	3100
Expiratory Reserve Volume (ERV)	Extra air exhaled after normal expiration	1200
Residual Volume (RV)	Air remaining after forced expiration	1200

Example: If a person increases the volume of their thoracic cavity during inspiration, the pressure inside the lungs drops below atmospheric pressure, causing air to flow in.

Additional info: Some explanations and values were expanded for clarity and completeness based on standard Anatomy & Physiology textbooks.