Respiratory System Anatomy: Route of Air Flow

Respiratory System Anatomy

Route of Air Flow

• Inspiratory and expiratory pathways pass through: nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and alveoli located in the lungs.
• Nasal cavity: warms, humidifies, and filters air.
• Pharynx: has three areas (nasopharynx, oropharynx, and laryngopharynx) and serves as a passage for air and food/liquid.

Functions of Organs

• Larynx: contains cartilage and other connective tissue, involved in breathing, producing sound (vocal cords), and protects the trachea against food and liquid aspiration.
• Trachea: contains C-shaped cartilage rings and a small area of smooth muscle (dorsal side).
• Bronchi and bronchioles: conduct air to and from the respiratory zone structures.
• Respiratory zone structures: respiratory bronchioles, alveoli involved in gas exchange (external respiration).
• Lungs: composed of alveoli, elastic tissue, and airways.

Alveolus and Respiratory Membrane

• Alveolus: site of external respiration.
• Alveolar epithelium: mostly simple squamous for gas exchange, also has simple cuboidal cells that secrete lung surfactant.
• Macrophages (innate immune system) are present in alveoli.
• Respiratory membrane: consists of alveolar epithelium, capillary epithelium (endothelium), and fused basement membranes.

Changes in Airway Structure

• As you progress closer to the alveoli:
  • Mucociliary escalator (presence of mucous and cilia) is present.
  • Cartilage is present in larynx to small bronchi (not in bronchioles).
  • Smooth muscle is present in pharynx, trachea (dorsal side), and bronchioles, becoming more prominent in smaller airways.

Protective Mechanisms of the Respiratory System

• Mucous production: traps and kills bacteria.
• Cilia: works with mucous to remove debris (mucociliary escalator).
• Tonsils: trap and remove pathogens.
• Epiglottis: prevents food and liquid from entering the trachea.
• Cartilage: keeps airways open.
• Lung surfactant: reduces surface tension in the alveoli.
• Macrophages: part of the innate immune system.

Pulmonary Ventilation

Volume Changes and Pressure Changes

• As volume increases, pressure decreases; as volume decreases, pressure increases.
• Total pressure is the sum of all partial pressures (e.g., pO2 and pN2).

Sequence of Events in Pulmonary Ventilation

• Brainstem: sends signals to spinal nerves.
• Spinal nerves: stimulate diaphragm and intercostal muscles.
• Diaphragm and intercostal muscles: contract and relax, causing changes in air pressure.
• Pressure gradients: develop between the thoracic cavity and the atmosphere.
• Airflow: occurs due to pressure gradients.

Respiratory Muscles and Lung Elasticity

• Diaphragm and intercostal muscles: primary muscles involved in inspiration and expiration.
• Additional muscles (e.g., sternocleidomastoid, scalenes, internal intercostals, and abdominal-wall muscles) are recruited for forced inspiration and expiration.
• Lung elasticity: plays a crucial role in producing volume changes that cause air to flow into and out of the lungs.