Trachea

Trachea

The trachea is also known as the windpipe.  The trachea is the only route from the oral and nasalTwo small rectangular bones forming the bridge of the nose. cavities. It leads to the gas-exchanging cul-de-sacs of the alveoliMicroscopic air sacs in the lungs where gas exchange occurs between air and blood. in the lungs.  The trachea is located anteriorThe front of the body or toward the front when standing in the anatomical position. to the esophagusThe muscular tube that transports food from the pharynx to the stomach via peristalsis..  This hollow tube is unlike the esophagus. The trachea is held open all the time by these C-shaped cartilageA flexible connective tissue found in joints, the ear, nose, and rib cage. Cartilage can be of three rings. On the other hand, the esophagus collapses when not in use.  This makes sense…you can’t live without air.  These C-shaped rings, colored in blue in this picture, wrap around the trachea. They give it the ability to stay open. At the same time, they provide flexibility and mobility within the thoracic cavityThe body cavity housing the heart and lungs..  The thoracic cavity is constantly changing shape and pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange. and the trachea is OK with that.

Tracheal Cartilages

I use this histological picture often.  It’s a good one.  The esophagus’s lumenThe inside space of a hollow organ or structure. and mucosaThe innermost lining of the digestive tract that contains mucus-secreting cells for protection and a are wavy. It collapses when there is no food in it. The lumen of the trachea is held open by this C-shaped cartilage ring.  Upon closer inspection, it is, infact, hyaline cartilageThe most abundant cartilage type, found in joints, ribs, and the nose. with chondrocytes in lacunaSmall spaces in bone tissue where osteocytes reside. carve our of the gelatinous background.  Hyaline cartilage likes to take up that dark purple stain, just a mucosa. Hyaline cartilage has that glassy appearance to it matrix.

If these cartilage rings were an O shape instead of a C shape, they could possibly get squished closed. This might happen as a huge food bolusA rounded mass of food mixed with saliva that is ready for swallowing. passes through the esophagus.  A C-shape never fully closes.  Pack animals, like dogs and wolves, will take enormous bites of food. They do this as they all compete for a limited food supply.  They, too, have a C-shaped cartilage ring so that they don’t choke as they take too-big-bites.

Tracheal Mucosa

The mucosa of the trachea is pseudostratified ciliated columnar epithelium with mucus cellsThe basic structural and functional units of life. scattered between the cells.  There are just a few at this bottom right corner of the picture.  There are fewer mucus cells than there were in the nasal mucosa, which was also pseudostratified ciliated columnar.  The ciliaHair-like projections on the surface of some cells that move fluids or particles. are on the apical sides of the cells, or the sides facing the lumen.  Just as in the nasal cavityThe internal space behind the nose that filters, warms, and humidifies incoming air., these cilia trap particulates before descending into your bronchiThe large airways that branch from the trachea into the lungs, dividing into smaller bronchioles..

These purple bubbles are submucosal glandsGlands in the airway walls that secrete mucus.. They are on the border between the dense irregular-ish submucosa and the thin layer of smooth muscle around the trachea.  Somewhere, there is a duct cutting trough the submucosa and spilling out its content onto the lining of the lumen.  These submucosal glands contain cells similar to those in the salivary glands that produced mucus.  There are also simple cuboidal cells in these glands. They secrete a more watery substance. These cells are very few compared to the salivary glands.

Mucociliatory Escalator

The mucociliary escalatorThe mechanism by which cilia move mucus and trapped particles up toward the throat for removal. is part of the respiratory defense system. It uses coordinated movementA fundamental property of life involving motion of the body or its parts. of cilia to transport mucus and trapped particles upward. This process prevents infections. Particles get trapped by the mucus lining the trachea. Then, the cilia wave in unison to move the particles upward to your pharynxThe muscular passageway connecting the mouth to the esophagus and larynx.. You then cough, and immediately swallow that mucus into your digestive system. Smoking damages cilia and mucus production, leading to a smoker’s cough. A smoker does not have this fluid movement of cilia. They will have a hacking cough as they forcibly move the mucus. If a smoker quits, the cilia can regenerate within a few days.