Hyoid boneIt sits above the larynx and anchors the tongue.
Thyroid cartilageIts front is the Adam’s apple.
Cricoid cartilageThe only complete ring of cartilage in the airway.
TracheaIt carries air from the larynx to the bronchi.
Tracheal cartilages16 to 20 C-shaped pieces of hyaline cartilage hold the trachea open.
The bronchial tree 6
CarinaIt is very sensitive: anything touching it sets off a cough.
Right primary bronchusShorter, wider and steeper than the left. So swallowed objects more often lodge here.
Left primary bronchusLonger and more level than the right, passing under the aortic arch.
Tertiary bronchiAlso called segmental bronchi; each serves one segment of a lung.
BronchiolesAbout a millimetre across; they branch on until they become terminal bronchioles.
Terminal bronchiolesThey lead on to the air sacs where gas exchange happens. Each lung has more than 1,000.
How this list was compiled: Every name and detail checked on 2026-09-29 against OpenStax Anatomy and Physiology 2e, section 22.1 Organs and Structures of the Respiratory System (hyoid bone, thyroid and cricoid cartilages, trachea of 16 to 20 C-shaped hyaline cartilages, carina and the cough reflex, right and left primary bronchi, tertiary bronchi, bronchioles about 1 mm across, more than 1000 terminal bronchioles in each lung), https://openstax.org/books/anatomy-and-physiology-2e/pages/22-1-organs-and-structures-of-the-respiratory-system, and against Wikipedia, text only: Bronchus, Carina of trachea, Larynx and Trachea. Licence: own work
The drawing: Drawn for this site on 2026-09-29 from plain geometry; nothing traced. Licence: own work
How it works
The lower respiratory tract from the front, the body's right on the viewer's left. Air passes the larynx, runs down the trachea, splits at the carina and branches smaller and smaller inside the lungs.
Read the full guide
Top to bottom, then out along the tree
Numbers 1 to 5 are the larynx and trachea: the hyoid bone, the thyroid and cricoid cartilages, the trachea and its C-shaped rings. Numbers 6 to 8 are where it divides: the carina and the two primary bronchi. Numbers 9 to 11 follow the tree out: the tertiary bronchi, the bronchioles and the terminal bronchioles.
Right is short, wide and steep: that is why inhaled objects usually end up in the right primary bronchus.
Questions and answers
What are the parts of the lower respiratory tract?
The trachea, which divides at the carina into the right and left primary bronchi, and the bronchial tree that branches from them inside the lungs: smaller bronchi, bronchioles and terminal bronchioles. Many books also count the larynx.
What is the carina?
The ridge at the bottom of the trachea where it divides into the two primary bronchi. It is very sensitive, and anything touching it sets off a strong cough.
Why is the trachea made of C-shaped rings?
The rings of hyaline cartilage hold the trachea open. The open back of each C is closed by muscle and connective tissue, so the esophagus behind it can bulge when you swallow.