Unit 3: 1: Respiratory System: Structure, Function, and Physiology Study Guide

Major Events in Respiration

Pulmonary Ventilation

Pulmonary ventilation refers to the movement of air into and out of the lungs, enabling gas exchange with the external environment.

• Definition: The process of breathing, including inhalation and exhalation.

• Mechanism: Driven by bulk flow, which is the movement of air due to pressure gradients.

• Example: Air moves from the atmosphere into the lungs when alveolar pressure drops below atmospheric pressure.

External Respiration

External respiration is the exchange of gases (O2 and CO2) between alveoli and pulmonary capillaries.

• Definition: Gas exchange between the air in the alveoli and the blood in the pulmonary capillaries.

• Mechanism: Occurs via diffusion, driven by concentration gradients of gases.

• Example: Oxygen diffuses from alveoli (high O2) to blood (low O2).

Cardiovascular Transport

This process involves the movement of gases through the bloodstream to and from tissues.

• Definition: Bulk flow of blood carrying dissolved gases throughout the body.

• Mechanism: Bulk flow, driven by pressure gradients generated by the heart.

• Example: Oxygen-rich blood is pumped from the lungs to tissues.

Internal Respiration

Internal respiration is the exchange of gases between systemic capillaries and tissue cells.

• Definition: Diffusion of O2 from blood to tissues and CO2 from tissues to blood.

• Mechanism: Occurs via diffusion, driven by local concentration gradients.

• Example: Oxygen diffuses from capillaries (high O2) to cells (low O2).

Comparison of Mechanisms

• Bulk Flow: Pulmonary ventilation, cardiovascular transport

• Diffusion: External respiration, internal respiration

Bulk Flow and Diffusion: Gradients and Resistance

Flux and Gradients

Both bulk flow and diffusion describe the movement (flux) of substances, but they are driven by different types of gradients.

• Bulk Flow: Movement due to pressure gradients (e.g., air or blood flow).

• Diffusion: Movement due to concentration gradients (e.g., O2 and CO2 across membranes).

Resistance

Resistance is any factor that opposes the movement of air or blood.

• Definition: The opposition to flow, often due to friction or narrow passages.

• Formula: $\text{Flow} = \frac{\Delta P}{R}$, where $\Delta P$ is the pressure difference and $R$ is resistance.

• Example: Narrow airways increase resistance, reducing airflow.

Pathway of Airflow and Airway Structure

Airflow Pathway

During inhalation, air travels through a series of anatomical structures:

• Nasal cavity

• Pharynx

• Larynx

• Trachea

• Bronchi

• Bronchioles

• Alveoli

Trachea vs. Bronchus: Structure and Function

The trachea and bronchi are both major airways, but they differ in design and function.

Feature	Trachea	Bronchus
Diameter	Larger	Smaller
Wall Structure	C-shaped cartilage rings	Cartilage plates
Ability to Change Diameter	Limited (rigid)	Somewhat flexible
Function	Main airway	Branching to lungs

Similarity: Both have cartilage for support and are lined with mucosa. Difference: Trachea is more rigid; bronchi can change diameter more due to less cartilage.

Additional info: Bronchioles lack cartilage and have smooth muscle, allowing significant diameter changes.

Vocal Folds and Hormonal Influence

Shape Changes During Vocalization

Vocal folds (true vocal cords) alter their shape to produce sound.

• During speech: Folds are brought together and vibrate as air passes through.

• During breathing: Folds are apart, allowing free airflow.

Hormonal Effects

• Testosterone: Thickens and lengthens vocal folds, resulting in a deeper voice.

• Estrogen: Maintains thinner, shorter vocal folds, resulting in a higher pitch.

Airway Cell Types and Mucous Production

Ciliated Cells

Ciliated cells line the airways and help move mucus and trapped particles out of the lungs.

• Function: Propel mucus toward the pharynx for removal.

• Inhibition: Toxins (e.g., cigarette smoke, pollutants) can damage or kill ciliated cells.

Goblet (Mucous) Cells

Goblet cells produce mucus to trap dust, microbes, and other particles.

• Factors Increasing Production: Allergens, infections, irritants.

• Factors Decreasing Production: Dehydration, certain medications.

Airway Dilation and Constriction

Dilation (Bronchodilation)

• Events/Substances: Sympathetic stimulation (e.g., adrenaline), bronchodilator drugs (e.g., albuterol).

Constriction (Bronchoconstriction)

• Events/Substances: Parasympathetic stimulation, allergens, irritants, cold air.

Airway Resistance: Key Regions

Resistance to airflow is greatest in medium-sized bronchi due to their diameter and branching.

• Biggest Effect: Bronchioles, due to their small diameter and ability to constrict or dilate.

• Clinical Relevance: Asthma and other obstructive diseases primarily affect bronchioles.

Radius and Airway Resistance

The radius of an airway is the most important factor controlling resistance to airflow.

• Relationship: Resistance is inversely proportional to the fourth power of the radius.

• Formula: $R \propto \frac{1}{r^4}$

• Graph: As radius increases (X-axis), relative airflow (Y-axis) increases sharply.

Additional info: Small changes in airway radius cause large changes in resistance and airflow.

Effects of Vaping on Lung Structure and Ventilation

Vaping introduces chemicals and particulates into the lungs, affecting their structure and function.

• Structural Effects: Damage to alveolar walls, inflammation, and impaired ciliated cell function.

• Ventilation Effects: Increased airway resistance, reduced gas exchange efficiency.

• Clinical Consequences: Higher risk of respiratory infections, chronic bronchitis, and decreased lung capacity.

Additional info: Some vaping substances may cause acute lung injury (EVALI).