NCLEX Review Guide: Adult Health - Respiratory Anatomy and Physiology

Upper Respiratory Tract

• Nose and nasal cavity filter, warm, and humidify incoming air while the pharynx serves as a shared pathway for respiratory and digestive systems.
• The larynx contains the vocal cords and epiglottis, which prevents aspiration by covering the trachea during swallowing.
• Trachea is a 10-12 cm tube reinforced with C-shaped cartilage rings that bifurcates at the carina into right and left main bronchi.

Lower Respiratory Tract

• The right main bronchus is shorter, wider, and more vertical than the left, making it more prone to aspiration of foreign objects.
• Bronchi progressively divide into smaller bronchioles, with terminal bronchioles being the smallest airways without alveoli.
• Alveoli are microscopic air sacs where gas exchange occurs, surrounded by pulmonary capillaries and lined with surfactant to prevent collapse.

Ventilation Process

1. Inspiration: Diaphragm contracts and moves downward, creating negative pressure that draws air into lungs
2. Expiration: Diaphragm relaxes and moves upward, creating positive pressure that pushes air out of lungs
3. Accessory muscles (intercostals, scalenes) assist during increased respiratory demand or respiratory distress

Gas Exchange

• External respiration occurs at the alveolar-capillary membrane where oxygen diffuses into blood and carbon dioxide diffuses into alveoli.
• Internal respiration happens at the tissue level where oxygen moves from blood to cells and carbon dioxide moves from cells to blood.
• Normal oxygen saturation is 95-100% and partial pressure of oxygen (PaO2) should be 80-100 mmHg in arterial blood.

Neural Control

• The medulla oblongata contains the respiratory center that automatically controls breathing rate and depth based on chemical stimuli.
• Primary drive is hypercapnic (increased CO2 levels), while hypoxic drive (low oxygen) is secondary in healthy individuals.
• Patients with COPD may develop hypoxic drive dependency, requiring careful oxygen administration to prevent respiratory depression.