7.2 Respiratory System Anatomy

7.2 Respiratory System Anatomy

Quick Answer: The respiratory system moves air between the atmosphere and alveoli, where gas exchange occurs. Know upper vs lower airway, the sequence nasal cavity → pharynx → larynx → trachea → bronchi → bronchioles → alveoli, right 3 / left 2 lung lobes, visceral vs parietal pleura, diaphragm as the primary inspiratory muscle, and the alveolar-capillary membrane as the exchange surface. Breathing mechanics and gas transport physiology come later—this section is structure and location for NEX Human Anatomy.

Airways warm, humidify, filter, and conduct air; alveoli provide the huge moist surface for O₂/CO₂ exchange with pulmonary capillary blood. Nursing assessments (breath sounds, airway patency, chest tubes, oxygen delivery) all rest on knowing what sits where in the thorax and neck.

Divisions of the Respiratory System

For NEX, being able to sort a named structure into upper/lower and conducting/respiratory zones is high-yield.

Upper Airway Structures

Nose and Nasal Cavity

Inspired air is filtered by hairs and mucus, warmed by rich vascular plexuses, and humidified before reaching lower airways—anatomy that protects delicate alveoli.

Pharynx (Throat)

A muscular tube shared by respiratory and digestive systems, divided into three regions:

Larynx (Voice Box)

The larynx connects pharynx to trachea and houses the vocal folds.

Epiglottis anatomy is critical for aspiration prevention: during swallowing it helps divert food toward the esophagus. Clinical airway management (intubation) uses laryngeal landmarks—useful nursing context tied to structure names.

Lower Airway: Trachea to Alveoli

Trachea

The trachea is a tube of C-shaped hyaline cartilage rings (open posteriorly against the esophagus) lined with ciliated mucosa. It descends in the neck into the mediastinum and bifurcates at the carina into primary bronchi.

Bronchial Tree

Cartilage decreases and smooth muscle relative importance increases as airways narrow—explains why small-airway constriction dramatically affects airflow (physiology later; structure now).

Alveoli and the Gas-Exchange Surface

Alveoli are thin-walled air sacs—about 300 million in adult lungs—creating an enormous surface area (~70 m²).

Alveolar-capillary (respiratory) membrane — the structural interface for gas exchange:

1. Alveolar epithelium (mainly type I)
2. Fused basement membranes
3. Capillary endothelium

This barrier is extremely thin (~0.5 µm). Pathology that thickens it (edema, fibrosis) impairs exchange—clinical hooks that start from knowing the layered anatomy.

Lungs: Lobes, Surfaces, and Hilum

Each lung has:

• Apex — superior tip above the clavicle region
• Base — rests on diaphragm
• Costal surface — against ribs
• Medial (mediastinal) surface — faces mediastinum
• Hilum — medial doorway where primary bronchus, pulmonary arteries/veins, lymphatics, and nerves enter/leave

Bronchopulmonary segments are pyramid-shaped subunits each with its own segmental bronchus and arterial supply—important surgically; intro exams mainly want lobe counts and hilum contents awareness.

Pleura and Pleural Cavity

Pleural fluid lubricates and creates surface tension that helps keep lungs expanded against the chest wall. Pneumothorax introduces air into the pleural cavity and can collapse the lung—anatomy of the space explains the clinical event. Chest tubes drain air/fluid from this cavity, not from lung parenchyma itself.

Diaphragm, Accessory Muscles, and Thoracic Context

Diaphragm

The diaphragm is a dome-shaped sheet of skeletal muscle forming the floor of the thoracic cavity and roof of the abdomen. It is the primary muscle of inspiration. When it contracts, the dome flattens, increasing thoracic vertical dimension. It is innervated by the phrenic nerves (C3–C5). Openings transmit the IVC, esophagus, and aorta (hiatal anatomy at intro awareness level).

Accessory and Supporting Muscles (Structures)

Quiet expiration is largely passive elastic recoil; forced breathing recruits these named muscles—know them as anatomical players.

Mediastinum

The mediastinum is the central thoracic compartment between the lungs, containing the heart and pericardium, great vessels, trachea, esophagus, thymus (especially in youth), lymph nodes, and phrenic/vagus nerves. Respiratory and cardiovascular anatomy meet here: tracheal bifurcation, pulmonary trunk, and aortic arch relationships matter for imaging and trauma context.

Pathway Summary: Inspired Air to Blood

1. Nares → nasal cavity (or mouth → oral cavity)
2. Pharynx (naso-/oro-/laryngopharynx)
3. Larynx (past epiglottis/glottis)
4. Trachea → primary bronchi → lobar → segmental bronchi
5. Bronchioles → terminal → respiratory bronchioles
6. Alveolar ducts/sacs → alveoli
7. Across alveolar-capillary membrane ↔ pulmonary capillary blood

Pulmonary arteries bring oxygen-poor blood to alveolar capillaries; pulmonary veins return oxygen-rich blood to the left atrium—linking this section to cardiovascular anatomy.

Clinical and Nursing Anchors

• Right mainstem intubation or aspiration: right bronchus anatomy (wider, more vertical).
• Lobar pneumonia / auscultation: map findings to right middle lobe vs left lower lobe, etc.
• Pleural effusion / pneumothorax / chest tube: pleural cavity anatomy.
• Airway obstruction: upper (tongue, larynx, foreign body) vs lower (bronchospasm).
• Surfactant deficiency (neonatal RDS): type II cell product—structure name connects to clinical syndrome.
• Diaphragm paralysis: phrenic nerve injury impairs primary inspiratory muscle.

Exam Traps

• Lobe count: right 3, left 2—not the reverse.
• Visceral vs parietal pleura: visceral on organ; parietal on wall (same logic as pericardium/peritoneum).
• Epiglottis: routes food away from larynx—not a lung structure.
• Alveoli vs bronchi: alveoli exchange; most bronchi only conduct.
• Diaphragm tissue type: skeletal muscle, even though breathing can be automatic.
• Carina: bifurcation landmark—sensitive cough reflex zone.
• Left lung cardiac notch: space for the heart, explaining fewer lobes.

Study Map for NEX

1. Recite the air pathway from nares to alveoli without skipping larynx or carina.
2. Draw right vs left lung lobes and mark the cardiac notch.
3. Define visceral pleura, parietal pleura, and pleural cavity in one sentence each.
4. Name the diaphragm as primary inspiratory muscle and list three accessory inspiratory muscles.
5. List the three layers of the alveolar-capillary membrane.

With airway tree, lobes, pleura, and exchange-surface anatomy locked in, you are ready for respiratory physiology (ventilation, partial pressures, transport) and Health topics such as smoking, infection control, and oxygen safety that appear elsewhere on NEX Science.