Respiratory System: Structure, Function, and Physiology Study Guide

Respiratory System

Overview of the Respiratory System

The respiratory system is essential for gas exchange, supplying oxygen to the body and removing carbon dioxide. It consists of a series of organs and tissues that facilitate breathing and maintain homeostasis.

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

• Secondary Functions: Regulation of blood pH, voice production, olfaction, and protection against pathogens.

Main Tissue Types in Respiratory Structures

Different regions of the respiratory tract are lined with specific tissue types adapted to their functions.

• Nasal cavity: Pseudostratified ciliated columnar epithelium with goblet cells.

• Nasopharynx: Pseudostratified ciliated columnar epithelium.

• Oropharynx: Stratified squamous epithelium.

• Laryngopharynx: Stratified squamous epithelium.

• Trachea: Pseudostratified ciliated columnar epithelium with goblet cells.

Functions of Respiratory Tissue Types

Each tissue type serves a specific protective or functional role in the respiratory tract.

• Pseudostratified ciliated columnar epithelium: Traps and moves particles out of the airway via cilia and mucus.

• Stratified squamous epithelium: Provides protection against abrasion in areas exposed to food and air.

Flow of Air from Nose to Alveolar Sacs

Air travels through a series of structures before reaching the alveoli for gas exchange.

1. Nose/Nasal cavity

2. Nasopharynx

3. Oropharynx

4. Laryngopharynx

5. Larynx

6. Trachea

7. Bronchi (primary, secondary, tertiary)

8. Bronchioles

9. Alveolar ducts

10. Alveolar sacs

Functions of Key Respiratory Structures

Each structure in the respiratory system has a specialized function.

• Nose and nasal cavity: Filters, warms, and moistens incoming air; houses olfactory receptors.

• Paranasal sinuses: Lighten skull, produce mucus, and contribute to voice resonance.

• Nasopharynx: Passageway for air; contains pharyngeal tonsils for immune defense.

• Oropharynx: Passageway for food and air; contains palatine and lingual tonsils.

• Laryngopharynx: Directs food to esophagus and air to larynx.

• Larynx: Produces sound; routes air and food into proper channels.

• Trachea: Conducts air to bronchi; lined with cilia and mucus for protection.

Respiratory vs. Conducting Zones

The respiratory tract is divided into zones based on function.

• Conducting zone: Includes all structures that transport air but do not participate in gas exchange (nose to terminal bronchioles).

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

Components of the Bronchial Tree

The bronchial tree consists of branching airways that conduct air to the lungs.

• Primary bronchi

• Secondary (lobar) bronchi

• Tertiary (segmental) bronchi

• Bronchioles

• Terminal bronchioles

• Respiratory bronchioles

Type I and Type II Alveolar Cells

Alveoli contain two main cell types with distinct functions.

• Type I alveolar cells: Simple squamous cells; form the structure of the alveolar wall and facilitate gas exchange.

• Type II alveolar cells: Secrete pulmonary surfactant to reduce surface tension and prevent alveolar collapse.

Structure of the Lungs

The lungs are paired organs composed of lobes, bronchi, bronchioles, and alveoli, surrounded by pleural membranes.

• Right lung: Three lobes (superior, middle, inferior)

• Left lung: Two lobes (superior, inferior)

• Pleura: Double-layered membrane (visceral and parietal)

First Process of Respiration

Respiration involves several processes; the first is pulmonary ventilation.

• Pulmonary ventilation: Movement of air into and out of the lungs (inspiration and expiration).

Pressure Gradients Influencing Pulmonary Ventilation

Three main pressure gradients drive air movement during breathing.

• Atmospheric pressure: Pressure of air outside the body.

• Intrapulmonary (alveolar) pressure: Pressure within the alveoli.

• Intrapleural pressure: Pressure within the pleural cavity; always lower than alveolar pressure to keep lungs inflated.

Factors Affecting Pulmonary Ventilation

Several physical factors influence the efficiency of ventilation.

• Airway diameter: Wider airways reduce resistance and increase airflow.

• Airway resistance: Opposition to airflow; increased by constriction or obstruction.

• Alveolar surface tension: Tendency of alveolar fluid to contract; surfactant reduces tension.

• Pulmonary surfactant: Lipoprotein that lowers surface tension, preventing alveolar collapse.

• Pulmonary compliance: Measure of lung expandability; affected by surface tension, elasticity, and chest wall flexibility.

Relevant equation:

$\text{Compliance} = \frac{\Delta V}{\Delta P}$

where $\Delta V$ is change in lung volume and $\Delta P$ is change in transpulmonary pressure.

Lung Volumes

Lung volumes are measurements of air during different phases of breathing.

• Tidal volume (TV): Volume of air inhaled or exhaled in a normal breath.

• Minute volume: Total volume of air inhaled/exhaled per minute.

• Inspiratory reserve volume (IRV): Maximum volume of air that can be inhaled after a normal inspiration.

• Expiratory reserve volume (ERV): Maximum volume of air that can be exhaled after a normal expiration.

Relevant equation:

$\text{Minute Volume} = \text{Tidal Volume} \times \text{Respiratory Rate}$

Processes Involved in Gas Exchange

Gas exchange occurs in the lungs and tissues via two main processes.

• External respiration: Exchange of gases between alveoli and blood.

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

Factors Affecting Pulmonary Gas Exchange

Three factors influence the rate and efficiency of gas exchange in the lungs.

Factor	Effect on Gas Exchange
Surface area of respiratory membrane	Greater surface area increases gas exchange efficiency.
Thickness of respiratory membrane	Thicker membrane decreases rate of gas exchange.
Ventilation-perfusion matching	Optimal matching of airflow and blood flow maximizes gas exchange.

Loading and Unloading of Oxygen

Oxygen binds to hemoglobin in the lungs (loading) and is released in tissues (unloading).

• Loading: Occurs in alveoli where PO2 is high.

• Unloading: Occurs in tissues where PO2 is low.

Effects of PO2, Temperature, and pH on Hemoglobin Saturation

Hemoglobin's affinity for oxygen is influenced by several factors.

• PO2: Higher partial pressure increases saturation.

• Temperature: Higher temperature decreases affinity, promoting oxygen release.

• pH: Lower pH (more acidic) decreases affinity (Bohr effect), promoting oxygen release.

Transport of Carbon Dioxide and Role of Bicarbonate

Carbon dioxide is transported in the blood by three main mechanisms.

• Dissolved in plasma: About 7% of CO2 is transported this way.

• Bound to hemoglobin: About 20% binds to globin portion of hemoglobin (carbaminohemoglobin).

• As bicarbonate ions: About 70% is converted to bicarbonate (HCO3-) via the following reaction:

$\text{CO}_2 + \text{H}_2\text{O} \leftrightarrow \text{H}_2\text{CO}_3 \leftrightarrow \text{H}^+ + \text{HCO}_3^-$

• Importance of bicarbonate: Maintains blood pH and serves as a buffer system.