📝 STANDARD DESCRIPTION:
Structure: Tube of C-shaped cartilage rings, open dorsally; gap closed by Trachealis muscle + fibrous membrane.
Number of rings (Ox): About 48-60.
Course: Larynx → through neck (cervical part) → enters thorax → bifurcates at 5th-6th intercostal space (T5) → Right & Left Principal Bronchi.
Special in OX & PIG: An extra TRACHEAL BRONCHUS (Bronchus trachealis / eparterial bronchus) leaves the RIGHT side of trachea BEFORE the bifurcation, supplying the cranial (apical) lobe of the right lung.
Lining: Pseudostratified ciliated columnar epithelium with goblet cells (mucociliary escalator).
📚 DETAILED DESCRIPTION:
THE WINDPIPE — TRACHEA
The trachea is a flexible tube that carries air between the larynx and the lungs. It must stay open at all times, so its wall is supported by a series of cartilage rings.
SHAPE OF THE RINGS: Each ring is shaped like the letter 'C', open on the dorsal (back) side. The open part faces the oesophagus and is closed by:
• A smooth muscle band — the trachealis muscle.
• A fibroelastic membrane.
This soft dorsal wall lets the oesophagus expand into the trachea when a food bolus passes — a clever space-saving design.
COURSE & DIVISIONS:
• Cervical part: Runs down the neck, just below the oesophagus, easily palpable.
• Thoracic part: Enters chest at the thoracic inlet, runs in the cranial mediastinum.
• Bifurcation (Carina): At about the level of the 5th-6th rib (T5 vertebra) in ox, the trachea splits into the right and left principal bronchi, which go to the lungs.
SPECIAL — THE TRACHEAL BRONCHUS:
In ox, sheep and pig there is an EXTRA bronchus that leaves the trachea on the right side BEFORE the main bifurcation. It is called the tracheal bronchus (also eparterial bronchus) and it goes to the cranial (apical) lobe of the right lung. This is a unique ruminant/pig feature — horse and dog do NOT have it; in them all bronchi come off the bifurcation.
WALL STRUCTURE (microscopic, brief): Inside lined by pseudostratified ciliated columnar epithelium with mucus-producing goblet cells. Together they form the 'mucociliary escalator' that constantly moves dust and germs upward to be swallowed or coughed out.
BLOOD/NERVE SUPPLY: Bronchial arteries; vagal (parasympathetic — constricts) and sympathetic (dilates) nerves.
// COMPARATIVE ANALYSIS
| HORSE |
About 48-60 rings; NO tracheal bronchus. Bifurcation at 5th-6th rib. |
| DOG |
About 35-45 rings; rounded shape. NO tracheal bronchus. |
| PIG |
Has TRACHEAL BRONCHUS (like ox). Rings tend to overlap. |
| FOWL |
Rings are COMPLETE (closed circles) — not C-shaped. Trachea ends in SYRINX (voice organ) at bifurcation, not larynx. |
CLINICAL RELEVANCE
Tracheotomy: Emergency airway opening — usually performed in the upper third of the cervical trachea (between rings 3-5), avoiding the thyroid gland.
Tracheal collapse (small dogs): The dorsal trachealis becomes lax; rings flatten → severe cough.
