Respiratory System Overview

Anatomy and Histology

The respiratory system is responsible for gas exchange, supplying oxygen to the body and removing carbon dioxide. Its anatomy includes the nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and alveoli. Histologically, the respiratory tract transitions from pseudostratified ciliated columnar epithelium in the upper airways to simple squamous epithelium in the alveoli, facilitating efficient gas exchange.

• Key Structures: Nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, alveoli

• Histology: Epithelium type changes along the tract for protection and gas exchange

• Example: Alveoli are lined with simple squamous epithelium to allow rapid diffusion of gases

Functional Anatomy

Tonsils of the Pharynx

Tonsils are lymphatic tissues located in the pharynx that help protect against inhaled or ingested pathogens.

• Pharyngeal Tonsil (Adenoid): Located in the nasopharynx

• Palatine Tonsil: Located in the oropharynx

• Lingual Tonsil: Located at the base of the tongue in the oropharynx

• Example: The palatine tonsil is commonly inflamed in tonsillitis

Bronchopulmonary Segments

Each lung is divided into bronchopulmonary segments, each supplied by a tertiary (segmental) bronchus.

• Tertiary Bronchus: Forms the bronchopulmonary segments

• Example: The right lung has 10 segments, each ventilated by its own tertiary bronchus

Respiratory Physiology

Forces Keeping the Lungs Inflated

The lungs remain inflated due to the negative pressure in the pleural cavity between the parietal and visceral pleura.

• Negative Intrapleural Pressure: Prevents lung collapse

• Additional info: Elastic recoil and surface tension also play roles, but negative pressure is primary

Consequences of Equal Pulmonary and Intrapleural Pressure

If pulmonary and intrapleural pressures become equal, the lungs will collapse due to loss of the negative pressure gradient.

• Lung Collapse (Atelectasis): Occurs when the pressure gradient is lost

• Example: Pneumothorax can cause equalization of pressures and lung collapse

Pressure-Volume Relationship: Boyle's Law

Boyle's Law explains the inverse relationship between pressure and volume in the lungs during breathing.

• Boyle's Law:

• Application: As lung volume increases, pressure decreases, allowing air to flow in

Airway Resistance and Asthma

During an asthma attack, airway resistance increases due to bronchoconstriction, leading to decreased airflow.

• Resistance Increases: Airflow decreases ()

• Example: Asthma causes constriction of bronchioles, increasing resistance

Role of Surfactant in Alveoli

Surfactant decreases surface tension in the alveoli, preventing collapse and aiding in lung compliance.

• Surface Tension: Surfactant reduces it, making breathing easier

• Example: Premature infants may lack surfactant, leading to respiratory distress syndrome

Factors Influencing External Respiration

External respiration is affected by pressure gradients, ventilation-perfusion coupling, and the structure of the respiratory membrane. Gas solubility is not a primary factor.

• Pressure Gradients

• Ventilation-Perfusion Coupling

• Respiratory Membrane Structure

• Not a Factor: Gas solubility

Flow Equation in Respiratory Physiology

Airflow (F) is determined by the pressure gradient (ΔP) divided by resistance (R):

• Equation:

• Key Point: If resistance increases, flow decreases

Respiratory Volumes and Capacities

Respiratory volumes measure the amount of air moved during breathing. Tidal volume (TV) is the amount of air inhaled or exhaled per breath.

• Tidal Volume (TV): Normal value is about 500 mL

• Minute Ventilation:

• Example: If TV = 487 mL and rate = 12/min, minute ventilation = mL/min

Forced Expiratory Volume (FEV1)

FEV1 is the volume of air exhaled in the first second of a forced breath. It is useful in diagnosing obstructive diseases like asthma.

• Low FEV1: Indicates airway obstruction

• Example: Asthma patients have reduced FEV1 due to bronchoconstriction

Gas Transport and Exchange

Partial Pressure of Gases

Each gas in a mixture exerts a partial pressure, which is proportional to its concentration.

• Partial Pressure: Pressure exerted by a single gas in a mixture

• Example: and are important in respiratory physiology

Carbon Dioxide Transport

CO2 is transported in the blood mainly as bicarbonate ions, with smaller amounts bound to hemoglobin and dissolved in plasma.

• Bicarbonate Ions: Majority of CO2 transport

• Other Forms: Carbaminohemoglobin, dissolved CO2

Chloride Shift

The chloride shift refers to the movement of chloride ions into or out of red blood cells to maintain electrical neutrality during CO2 transport.

• Mechanism: Chloride ions exchange with bicarbonate ions

• Example: Occurs in systemic and pulmonary capillaries

Control of Breathing

Respiratory Centers

The medullary respiratory centers control the rhythm and depth of breathing. Damage to these centers can result in cessation of breathing.

• Ventral Respiratory Group (VRG): Essential for generating respiratory rhythm

• Dorsal Respiratory Group (DRG): Integrates sensory input

• Example: Damage to VRG can cause apnea

Factors Affecting Depth and Rate of Respiration

Respiratory depth and rate are influenced by neural controls, chemoreceptors, and stretch receptors in the lungs and airways.

• Neural Controls: Medullary and pontine centers

• Chemoreceptors: Detect changes in CO2, O2, and pH

• Stretch Receptors: Prevent over-inflation of lungs

Clinical Scenarios

Chest Trauma and Pneumothorax

Chest trauma can lead to pneumothorax, where air enters the pleural space, causing lung collapse and impaired gas exchange.

• Pneumothorax: Air in pleural space equalizes pressure, leading to collapse

• Symptoms: Cyanosis, apnea, decreased breath sounds

• Example: Fractured ribs may puncture lung tissue

Blood Gas Changes in Trauma

Trauma affecting breathing can alter blood gases, leading to decreased O2 and increased CO2, resulting in acidosis (decreased pH).

• Decreased O2: Hypoxemia

• Increased CO2: Hypercapnia

• Decreased pH: Respiratory acidosis

Drug Therapy in Asthma

Asthma is treated with bronchodilators and anti-inflammatory drugs. Cough suppressants are not appropriate as they do not address airway constriction.

• Bronchodilators: Enhance sympathetic input to bronchioles

• Anti-inflammatory Drugs: Reduce immune response

• Not Appropriate: Cough suppressants (e.g., dextromethorphan)

Key Equations and Tables

Important Equations

• Boyle's Law:

• Flow Equation:

• Minute Ventilation:

Table: Forms of Carbon Dioxide Transport

Table: Factors Affecting Oxygen-Hemoglobin Affinity

Additional info: Some explanations and tables have been expanded for academic completeness and clarity.