Respiratory passage - radiology anatomy flowchart

Nose / Mouth
     ↓
Nasal cavity / Oral cavity
     ↓
Pharynx
  ├─ Nasopharynx
  ├─ Oropharynx
  └─ Laryngopharynx
     ↓
Larynx
     ↓
Trachea
     ↓
Carina (normally around T4-T5 level)
     ↓
┌───────────────────────────────────┐
│ Right main bronchus               │ Left main bronchus
│ - Shorter, wider, more vertical   │ - Longer, narrower, more horizontal
└───────────────────────────────────┘
     ↓                                      ↓
Right upper-lobe bronchus                Left upper-lobe bronchus
     ↓                                      ↓
Bronchus intermedius                     Lingular bronchus
     ↓                                      ↓
├─ Right middle-lobe bronchus            Left lower-lobe bronchus
└─ Right lower-lobe bronchus
     ↓
Segmental (tertiary) bronchi
     ↓
Subsegmental bronchi
     ↓
Bronchioles
     ↓
Terminal bronchioles
     ↓
Respiratory bronchioles
     ↓
Alveolar ducts
     ↓
Alveolar sacs
     ↓
Alveoli

Lobar bronchial anatomy for CT and chest radiograph correlation

RIGHT MAIN BRONCHUS
 ├─ Right upper-lobe bronchus
 │   ├─ Apical segment (S1)
 │   ├─ Posterior segment (S2)
 │   └─ Anterior segment (S3)
 │
 └─ Bronchus intermedius
     ├─ Right middle-lobe bronchus
     │   ├─ Lateral segment (S4)
     │   └─ Medial segment (S5)
     │
     └─ Right lower-lobe bronchus
         ├─ Superior segment (S6)
         ├─ Medial basal segment (S7)
         ├─ Anterior basal segment (S8)
         ├─ Lateral basal segment (S9)
         └─ Posterior basal segment (S10)


LEFT MAIN BRONCHUS
 ├─ Left upper-lobe bronchus
 │   ├─ Apicoposterior segment (S1+S2)
 │   ├─ Anterior segment (S3)
 │   └─ Lingula
 │       ├─ Superior lingular segment (S4)
 │       └─ Inferior lingular segment (S5)
 │
 └─ Left lower-lobe bronchus
     ├─ Superior segment (S6)
     ├─ Anteromedial basal segment (S7+S8)
     ├─ Lateral basal segment (S9)
     └─ Posterior basal segment (S10)

Radiology points

• The carina is the tracheal bifurcation and is a key landmark on chest radiography and CT.
• The right main bronchus is more vertical, so aspirated material more often enters the right lung, commonly the right lower lobe in an upright patient.
• The bronchus intermedius supplies the right middle and lower lobes. Obstruction here can collapse both lobes.
• Bronchopulmonary segments correspond to segmental bronchi, which is why bronchial anatomy helps localize atelectasis, consolidation, bronchiectasis, and endobronchial obstruction on CT. The Radiology Assistant lung-segment guide describes this trachea-to-main-to-lobar-to-segmental branching pattern.