The trachea, or windpipe, is a hollow tube about 10 to 13 centimeters long that runs from the base of your throat down into your chest, where it splits into two branches leading to each lung. It looks something like a ridged vacuum hose or a corrugated shower drain pipe, with visible rings running horizontally along its length. Those rings give the trachea its most recognizable feature: a bumpy, segmented outer surface that distinguishes it from the smooth esophagus sitting directly behind it.
Size and Shape
In adults, the trachea measures roughly 10 to 13 cm from top to bottom, with an average length of about 11.8 cm. Its diameter is surprisingly small. In men, the internal airway ranges from about 13 to 25 mm side to side. In women, it ranges from about 10 to 21 mm. That puts it in the ballpark of a nickel to a quarter, depending on the person. Interestingly, tracheal size has no meaningful correlation with body height or weight, so a tall person doesn’t necessarily have a wider windpipe than a short one.
The cross-sectional shape isn’t a perfect circle. It’s more of a flattened oval, wider from side to side than from front to back, because the back wall is flat and flexible rather than rigid. On a CT scan, this gives the trachea a distinctive D-shape: a curved front wall supported by cartilage and a straight soft-tissue wall in the back.
The C-Shaped Cartilage Rings
The trachea’s segmented look comes from 16 to 20 rings of cartilage stacked on top of one another. Each ring is shaped like the letter C, not a full circle. The open side of the C faces backward, toward your spine. A strip of smooth muscle called the trachealis bridges the gap at the back, creating a flexible wall that sits right against the front of the esophagus.
This open-backed design is intentional. When you swallow food, the esophagus expands slightly, and the flexible posterior wall of the trachea can bow inward to accommodate it. The trachealis muscle can also contract to narrow the airway, which helps generate the burst of air pressure needed for coughing.
Where It Sits in Your Body
The trachea begins just below the larynx (voice box) at about the level of the sixth cervical vertebra in your neck. It runs straight down, slightly behind the notch at the top of your breastbone, passing through the neck and into the upper chest. The thyroid gland wraps around the front and sides of the upper trachea, with its connecting bridge (the isthmus) crossing over the second and third cartilage rings. Connective tissue ligaments anchor each lobe of the thyroid directly to the trachea, which is why you can sometimes feel your windpipe move when you swallow.
Behind the trachea, the esophagus runs parallel for the entire length. In front, layers of strap muscles in the neck cover and protect it. You can feel the trachea’s ridged rings by pressing gently on the front of your throat just below your Adam’s apple.
Where It Splits: The Carina
At its lower end, roughly at the level of the fourth thoracic vertebra (behind the upper part of your breastbone), the trachea divides into the left and right main bronchi. The point of this split is marked by a small cartilage ridge called the carina, which is a projection of the last tracheal ring. It sits in the midline and acts like a divider, directing air into each lung. Doctors viewing the inside of the airway with a camera see the carina as a sharp keel-shaped ridge where the single tube becomes two.
What It Looks Like Inside
Viewed through a bronchoscope (a thin camera threaded into the airway), the interior of a healthy trachea is smooth and glistening, with a pale pink mucous membrane. The cartilage rings are visible as evenly spaced horizontal ridges beneath the lining, and the flat muscular back wall looks slightly different in texture from the ringed front and sides. A thin layer of clear mucus coats everything.
That mucous lining is covered in millions of tiny hair-like projections called cilia. Each cell on the surface carries 200 to 300 of them, and they beat rapidly, around 8 to 20 times per second, in coordinated waves that push mucus upward toward the throat. Scattered among the ciliated cells are goblet cells, which produce the sticky mucus that traps dust, bacteria, and other particles you inhale. Together, the cilia and mucus form a self-cleaning escalator that continuously sweeps debris out of the airway. Beneath both of these cell types sit small basal cells that act as stem cells, ready to replace damaged surface cells as needed.
How It Looks on Medical Imaging
CT scans are the standard imaging tool for evaluating the trachea. On a cross-sectional CT slice, the trachea appears as a dark air-filled oval (because air shows up black on CT) surrounded by a thin bright ring of tissue and cartilage. The D-shape is clearly visible, with the flat posterior membrane distinguishing the back wall from the curved cartilaginous front. Surrounding structures like the esophagus, thyroid, and major blood vessels are all identifiable in relation to it.
Dynamic CT imaging, taken during both inhalation and exhalation, can reveal how much the trachea changes shape with breathing. In a condition called tracheomalacia, where the cartilage rings are weakened, the back wall collapses forward during exhalation, creating what radiologists call the “frown sign” because the posterior wall bows inward and the airway narrows by more than 70%.
Infant vs. Adult Trachea
A newborn’s trachea is dramatically smaller: only about 4 cm long with a diameter of roughly 3.6 mm, barely wider than a pencil eraser. This is one reason small objects pose such a serious choking risk for infants and toddlers. The trachea grows proportionally with the child, eventually reaching adult dimensions during the teenage years. The cartilage rings are softer and more pliable in infants, which makes the young airway more prone to compression and collapse.