Respiratory System and Acid-Base Balance: Study Guide for Anatomy & Physiology II (Chapters 22 & 25)

Chapter 22: The Respiratory System

Overview and Functions of the Respiratory System

The respiratory system is essential for gas exchange, supplying oxygen to the body and removing carbon dioxide. It works closely with the circulatory system to transport gases throughout the body.

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

• Relationship with Circulatory System: Oxygen from inhaled air diffuses into blood, while carbon dioxide from blood diffuses into alveoli to be exhaled.

Processes of Respiration

Respiration involves four main processes, each utilizing different organ systems:

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

• External Respiration: Gas exchange between alveoli and blood (respiratory and circulatory systems).

• Transport of Respiratory Gases: Movement of gases in the blood (circulatory system).

• Internal Respiration: Gas exchange between blood and tissues (circulatory system).

Pathway of Air Through the Respiratory System

Air follows a specific route as it enters and exits the body:

1. Nasal cavity

2. Pharynx

3. Larynx

4. Trachea

5. Bronchi (primary, secondary, tertiary)

6. Bronchioles

7. Alveolar ducts

8. Alveoli

Divisions of the Respiratory System

• Upper Respiratory Tract: Nose, nasal cavity, pharynx, and larynx.

• Lower Respiratory Tract: Trachea, bronchi, bronchioles, alveolar ducts, and alveoli.

• Conducting Division: Passages that transport air (nose to terminal bronchioles).

• Respiratory Division: Sites of gas exchange (respiratory bronchioles, alveolar ducts, alveoli).

Functions and Locations of Respiratory Organs

• Nose/Nasal Cavity: Filters, warms, and moistens air; olfaction.

• Pharynx: Passageway for air and food.

• Larynx: Voice production; routes air and food.

• Trachea: Air passage to bronchi; contains cilia and mucus to trap debris.

• Bronchi/Bronchioles: Conduct air; regulate airflow via smooth muscle.

• Alveoli: Site of gas exchange.

Nasal Cavity Conditioning of Air

• Warming: Rich blood supply warms incoming air.

• Humidifying: Mucous membranes add moisture.

• Filtering: Hairs and mucus trap particles.

Laryngeal Cartilages

• Major Cartilages: Thyroid, cricoid, arytenoid, corniculate, cuneiform, and epiglottis.

• Composition: Mostly hyaline cartilage; epiglottis is elastic cartilage.

Linings of the Respiratory Tract

• Olfactory Mucosa: Located in superior nasal cavity; contains olfactory receptors.

• Respiratory Mucosa: Pseudostratified ciliated columnar epithelium with goblet cells; lines most of nasal cavity and trachea.

• Stratified Squamous Epithelium: Lines oropharynx and laryngopharynx; protects against abrasion.

• Simple Squamous Epithelium: Lines alveoli; facilitates gas exchange.

• Simple Cuboidal Epithelium: Found in smaller bronchioles.

Compositional Changes Along the Respiratory Tract

• Cartilage: Decreases from trachea to bronchioles; absent in bronchioles.

• Smooth Muscle: Increases in bronchioles, allowing regulation of airflow.

• Epithelium: Changes from ciliated pseudostratified columnar (with goblet cells) to simple cuboidal and then to simple squamous in alveoli.

• Cilia and Goblet Cells: Present in upper tract; absent in alveoli.

Alveolar Wall Cells and Functions

• Type I Alveolar Cells: Simple squamous cells; form the structure of the alveolar wall.

• Type II Alveolar Cells: Secrete surfactant to reduce surface tension.

• Alveolar Macrophages: Remove debris and pathogens.

• Alveolar Pores: Allow air pressure equalization and alternate air routes.

Structure of the Alveolar Wall and Respiratory Membrane

• Alveolar Wall: Composed of Type I and Type II cells, and macrophages.

• Respiratory Membrane: Consists of alveolar epithelium, capillary endothelium, and fused basement membranes; site of gas exchange.

Bronchopulmonary Segments

• Definition: Subdivisions of the lung, each supplied by its own bronchus and blood vessels.

• Significance: Allows for localized disease treatment and surgical removal.

Lung Stroma

• Main Component: Elastic connective tissue, providing recoil and flexibility.

Pulmonary vs. Bronchial Circulation

• Pulmonary Circulation: Carries deoxygenated blood to lungs for oxygenation.

• Bronchial Circulation: Supplies oxygenated blood to lung tissue.

Innervation of the Lungs

• Parasympathetic: Constricts airways.

• Sympathetic: Dilates airways.

Pleura and Its Significance

• Visceral Pleura: Covers lung surface.

• Parietal Pleura: Lines thoracic cavity.

• Pleural Fluid: Reduces friction, allows smooth expansion and recoil.

Pressure Relationships in the Thoracic Cavity

• Intrapulmonary Pressure (Ppul): Pressure within alveoli; fluctuates with breathing.

• Intrapleural Pressure (Pip): Pressure within pleural cavity; always negative relative to Ppul.

• Transpulmonary Pressure: Difference between Ppul and Pip; keeps lungs inflated.

Forces Acting on the Lungs

• Inward Forces: Elastic recoil of lung tissue and surface tension of alveolar fluid.

• Outward Force: Elasticity of chest wall pulling outward.

Transpulmonary Pressure Equalization

• If transpulmonary pressure equals intrapulmonary or atmospheric pressure, lungs collapse (no pressure gradient to keep lungs inflated).

Pulmonary Ventilation: Mechanics and Boyle's Law

Pulmonary ventilation is driven by mechanical changes in thoracic volume, which alter pressure and cause airflow.

• Boyle's Law: Pressure and volume are inversely related: $P_1V_1 = P_2V_2$

• Increasing thoracic volume decreases pressure, causing air to flow in; decreasing volume increases pressure, causing air to flow out.

Muscles of Breathing

• Inspiration (Restful): Diaphragm and external intercostals.

• Inspiration (Forced): Sternocleidomastoid, scalenes, pectoralis minor.

• Expiration (Passive): Relaxation of inspiratory muscles.

• Expiration (Forced): Internal intercostals, abdominal muscles.

Physical Factors Influencing Pulmonary Ventilation

• Airway Resistance: Friction in airways; major source is medium-sized bronchi. Inverse relationship: higher resistance, lower airflow. Usually insignificant due to large total cross-sectional area of small airways; resistance greatest in bronchi.

• Alveolar Surface Tension: Attraction between liquid molecules at alveolar surface; tends to collapse alveoli. Surfactant reduces surface tension.

• Lung Compliance: Measure of lung expandability; normally high due to elastic tissue and surfactant. Diminished by fibrosis, reduced surfactant, or increased thoracic resistance.

Alveolar Ventilation Rate (AVR)

• Definition: Volume of air reaching alveoli per minute.

• Importance: Better indicator of effective ventilation than respiratory rate alone.

• Increasing AVR: Increasing breathing depth is more effective than increasing rate.

Gas Laws in Respiration

• Dalton’s Law: Total pressure of a gas mixture equals the sum of partial pressures of individual gases.

• Partial Pressure Calculation: $P_{gas} = F_{gas} \times P_{total}$

• Altitude Effects: Partial pressures decrease at high altitudes, increase at low altitudes.

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

• Solubility: Carbon dioxide is more soluble in plasma than oxygen.

Alveolar Air vs. Atmospheric Air

• Alveolar Air: Contains more carbon dioxide and water vapor, less oxygen than atmospheric air.

• Causes: Gas exchange, humidification, and mixing of old and new air.

External Respiration Influences

• Partial Pressure Gradients and Gas Solubilities: Drive diffusion of gases.

• Thickness and Surface Area of Respiratory Membrane: Thicker membrane or reduced area impairs gas exchange.

• Ventilation-Perfusion Coupling: Matching of airflow and blood flow for optimal gas exchange.

Example Table: Comparison of Respiratory Tract Linings

Region	Epithelium Type	Special Features
Nasal Cavity (Respiratory)	Pseudostratified ciliated columnar	Goblet cells, cilia
Oropharynx/Laryngopharynx	Stratified squamous	Protection from abrasion
Trachea/Bronchi	Pseudostratified ciliated columnar	Goblet cells, cilia
Bronchioles	Simple cuboidal	No cartilage, some cilia
Alveoli	Simple squamous	Type I and II cells, macrophages

Additional info: Some explanations and examples have been expanded for clarity and completeness, including the table comparing respiratory tract linings and the summary of gas laws.