Your trachea, or windpipe, is one part of your airway system. Airways are pipes that carry oxygen-rich air to your lungs. They also carry carbon dioxide, a waste gas, out of your lungs.

When you inhale, air travels from your nose, through your larynx, and down your windpipe. The windpipe splits into two bronchi that enter your lungs.

Problems with the trachea include narrowing, inflammation, and some inherited conditions. You may need a procedure called a tracheostomy to help you breathe if you have swallowing problems, or have conditions that affect coughing or block your airways. You might also need a tracheostomy if you are in critical care and need to be on a breathing machine.

Your throat is a tube that carries food to your esophagus and air to your windpipe and larynx. The technical name for your throat is the pharynx.

Throat problems are common. You've probably had a sore throat. The cause is usually a viral infection, but other causes include allergies, infection with strep bacteria or the leaking of stomach acids back up into the esophagus, called GERD.

Other problems that affect the throat include

• Tonsillitis - inflammation of the tonsils
• Cancer
• Croup - inflammation, usually in small children, which causes a barking cough
• Laryngitis - swelling of the voice box, which can cause a hoarse voice or loss of voice

Most throat problems are minor and go away on their own. Treatments, when needed, depend on the problem.

Croup is an inflammation of the vocal cords (larynx) and windpipe (trachea). It causes difficulty breathing, a barking cough, and a hoarse voice. The cause is usually a virus, often parainfluenza virus. Other causes include allergies and reflux.

Croup often starts out like a cold. But then the vocal cords and windpipe become swollen, causing the hoarseness and the cough. There may also be a fever and high-pitched noisy sounds when breathing. The symptoms are usually worse at night, and last for about three to five days.Children between the ages of 6 months and 3 years have the highest risk of getting croup. They may also have more severe symptoms. Croup is more common in the fall and winter.

Most cases of viral croup are mild and can be treated at home. Rarely, croup can become serious and interfere with your child's breathing. If you are worried about your child's breathing, call your health care provider right away.

Food or small objects can cause choking if they get caught in your throat and block your airway. This keeps oxygen from getting to your lungs and brain. If your brain goes without oxygen for more than four minutes, you could have brain damage or die.

Young children are at an especially high risk of choking. They can choke on foods like hot dogs, nuts and grapes, and on small objects like toy pieces and coins. Keep hazards out of their reach and supervise them when they eat.

When someone is choking, quick action can be lifesaving. Learn how to do back blows, the Heimlich maneuver (abdominal thrusts), and CPR.

The trachea (windpipe) extends from the larynx toward the lungs (Figurea). The trachea is formed by 16 to 20 stacked, C-shaped pieces of hyaline cartilage that are connected by dense connective tissue. The trachealis muscle and elastic connective tissue together form the fibroelastic membrane, a flexible membrane that closes the posterior surface of the trachea, connecting the C-shaped cartilages. The fibroelastic membrane allows the trachea to stretch and expand slightly during inhalation and exhalation, whereas the rings of cartilage provide structural support and prevent the trachea from collapsing. In addition, the trachealis muscle can be contracted to force air through the trachea during exhalation. The trachea is lined with pseudostratified ciliated columnar epithelium, which is continuous with the larynx. The esophagus borders the trachea posteriorly.

Trachea

Figure 22.9 Trachea (a) The tracheal tube is formed by stacked, C-shaped pieces of hyaline cartilage. (b) The layer visible in this cross-section of tracheal wall tissue between the hyaline cartilage and the lumen of the trachea is the mucosa, which is composed of pseudostratified ciliated columnar epithelium that contains goblet cells. LM × 1220. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)

From the nasal cavity, air passes through the pharynx (throat) and the larynx (voice box) as it makes its way to the trachea (Figure 16.9). The main function of the trachea is to funnel the inhaled air to the lungs and the exhaled air back out of the body. The human trachea is a cylinder, about 25 to 30 cm (9.8–11.8 in) long, which sits in front of the esophagus and extends from the pharynx into the chest cavity to the lungs. It is made of incomplete rings of cartilage and smooth muscle. The cartilage provides strength and support to the trachea to keep the passage open. The trachea is lined with cells that have cilia and secrete mucus. The mucus catches particles that have been inhaled, and the cilia move the particles toward the pharynx.

The end of the trachea divides into two bronchi that enter the right and left lung. Air enters the lungs through the primary bronchi. The primary bronchus divides, creating smaller and smaller diameter bronchi until the passages are under 1 mm (.03 in) in diameter when they are called bronchioles as they split and spread through the lung. Like the trachea, the bronchus and bronchioles are made of cartilage and smooth muscle. Bronchi are innervated by nerves of both the parasympathetic and sympathetic nervous systems that control muscle contraction (parasympathetic) or relaxation (sympathetic) in the bronchi and bronchioles, depending on the nervous system’s cues. The final bronchioles are the respiratory bronchioles. Alveolar ducts are attached to the end of each respiratory bronchiole. At the end of each duct are alveolar sacs, each containing 20 to 30 alveoli. Gas exchange occurs only in the alveoli. The alveoli are thin-walled and look like tiny bubbles within the sacs. The alveoli are in direct contact with capillaries of the circulatory system. Such intimate contact ensures that oxygen will diffuse from the alveoli into the blood. In addition, carbon dioxide will diffuse from the blood into the alveoli to be exhaled. The anatomical arrangement of capillaries and alveoli emphasizes the structural and functional relationship of the respiratory and circulatory systems. Estimates for the surface area of alveoli in the lungs vary around 100 m². This large area is about the area of half a tennis court. This large surface area, combined with the thin-walled nature of the alveolar cells, allows gases to easily diffuse across the cells.

VISUAL CONNECTION

Figure 16.9 Air enters the respiratory system through the nasal cavity, and then passes through the pharynx and the trachea into the lungs. (credit: modification of work by NCI)

Tracheobronchomalacia (TBM) is a rare condition that occurs when the walls of the airway (specifically the trachea and bronchi) are weak. This can cause the airway to become narrow or collapse. There are two forms of TBM. One typically develops during infancy or early childhood (primary TBM). The other is an acquired form usually seen in adults (acquired or secondary TBM). Some people with TBM may initially have no signs or symptoms. However, the condition typically is progressive (worsening over time) and most people will eventually develop shortness of breath, cough, sputum retention (inability to clear mucus from the respiratory tract), and/or wheezing or stridor with breathing.

Most cases of primary TBM are caused by genetic conditions that weaken the walls of the airway, while the acquired form may occur due to trauma, chronic inflammation, and/or prolonged compression of the airways. The acquired form is often seen in adults with common respiratory conditions such as asthma, chronic bronchitis, and emphysema. In many cases, the cause is not known.

Treatment may only be needed if signs and symptoms are present, of there is complete or near-complete collapse of the airway. Depending on severity, treatment options may include continuous positive airway pressure (CPAP), stenting, surgical correction (tracheobronchoplasty), and tracheostomy.