Respiratory System Overview

Respiratory System

• The respiratory system exchanges gases between the atmosphere and blood.
• The system is divided into two parts
  • Upper respiratory system
    • Nose
    • Throat (Pharynx)
    • Associated structures
  • Lower respiratory system
    • The remainder of the system
      • Conducting portion
        • Nose
        • Pharynx
        • Larynx
        • Trachea
        • Bronchus
        • Bronchioles
        • Terminal bronchioles
      • Respiratory portion
        • Tissues where gas exchange occurs
          • Respiratory bronchioles
          • Alveolar ducts
          • Alveolar sacs
          • Alveoli
• The bony framework of the respiratory system includes
  • Frontal bone
  • Nasal bones
  • Maxillae

Nose

• The external nose is made up of two nasal bones.
• The internal nose has a large cavity in the skull.
• It merges with the external nose anteriorly.
• Posteriorly, it is connected to the pharynx through internal nares (choanae).
• Four paranasal sinuses (frontal, sphenoidal, maxillary, and ethmoidal) and the nasolacrimal ducts also open into the internal nose.
• Cartilaginous framework includes lateral nasal cartilages, septal cartilage, and alar cartilages.

Laryngeal Cartilages

• Paired laryngeal cartilages include arytenoid cartilages, corniculate cartilages, and cuneiform cartilages.
• The arytenoid cartilages are pyramidal, located at the superior border of the cricoid cartilage.
• They attach to vocal cords and pharyngeal muscles, affecting vocal cord movement.
• Other cartilages (corniculate and cuneiform) are cone-shaped and rod-shaped, respectively, and contribute to the structure.

Trachea

• A tubular structure about 12 cm in length and 2.5 cm in diameter.
• Located anterior to the esophagus.
• Divides into right and left primary bronchi at the 5th thoracic vertebra.
• The tracheal epithelium is pseudostratified columnar epithelium.
• Consists of ciliated columnar cells, goblet cells, and basal cells.
• Seromucous glands and their ducts are present in the submucosa.

Bronchi

• Bifurcate into right and left primary bronchi at the sternal angle.
• The right primary bronchus is more vertical, shorter, and wider than the left.
• The left primary bronchus gives rise to superior and inferior secondary (lobar) bronchi.
• The primary bronchi contain incomplete rings of cartilage and are lined with pseudostratified ciliated epithelium.

Lungs

• Paired, cone-shaped organs, separated by the heart
• Extend from the diaphragm to a point about 1.5–2.5 cm superior to the clavicles, situated against the ribs anteriorly and posteriorly.

Lung Compliance

• This is the ease with which lungs and the thoracic wall expand.
• High compliance means easy expansion.
• Factors affecting compliance include elasticity and surface tension.
• Surfactant reduces surface tension and increases lung compliance.

Pulmonary Surfactant

• Alveolar fluid coats the inner surface of alveoli.
• Surfactant is phospholipid that reduces surface tension of alveolar fluid.
• Maintaining low surface tension in alveoli prevents collapse and facilitates lung expansion.

Airway Resistance

• Airflow resistance is dependent on airway wall resistance and the pressure gradient.
• The volume of airflow is directly proportional to the pressure gradient and is inversely proportional to the resistance.
• Airway diameter influences resistance.
• Reduced airway diameter increases resistance.

Lung Volumes and Capacities

• Lung volumes are the amounts of air moved into or out of the lung during specific respiratory events.
• Lung capacities are the combination of two or more lung volumes.

Pulmonary Ventilation

• The process of breathing involves air flowing between the atmosphere and the lungs due to pressure gradients.
• Inspiration involves expanding the thoracic cavity and decreasing the intrapulmonic pressure.
• Expiration involves decreasing the thoracic cavity volume and increasing intrapulmonic pressure.

Fate of Oxygen in the Blood

• Oxygen delivery depends on factors including pulmonary gas exchange, blood flow to tissues, and the blood's capacity to carry oxygen.
• Blood flow depends on vascular bed constriction/dilation and cardiac output.

Fate of Carbon Dioxide in the Blood

• Carbon dioxide is transported in the plasma as dissolved gas, carbamino compounds, and bicarbonate ions (HCO3-).
• A portion of carbon dioxide is transported in red blood cells as carbamino compounds.
• The majority of carbon dioxide is transported as bicarbonate ions and is hydrated to form carbonic acid (H2CO3).