Human Respiratory System: Trachea Structure

Trachea Structure and Function

• The trachea is reinforced with C-shaped rings of hyaline cartilage, making it fairly rigid.
• The open parts of the rings allow the esophagus to expand anteriorly when swallowing, while the solid portions support the trachea walls and keep it patent.
• The trachea is lined with ciliated mucosa that propels mucus, loaded with dust particles and other debris, away from the lungs and towards the throat.

Main Bronchi

• The right and left main bronchi are formed by the division of the trachea.
• Each main bronchus runs obliquely before plunging into the medial depression of the lung on its own side.
• The right main bronchus is wider, shorter, and straighter than the left.

Lungs

• The lungs occupy the entire thoracic cavity, except for the mediastinum, which houses the heart, great blood vessels, bronchi, esophagus, and other organs.
• The narrow, superior portion of each lung is the apex, which is just deep to the clavicle.
• The broad lung area resting on the diaphragm is the base.

Respiratory Volumes and Capacities

• Tidal volume: approximately 500 ml of air moved into and out of the lungs with each breath.
• Inspiratory reserve volume: 2100-3200 ml of air that can be taken in forcibly over the tidal volume.
• Expiratory reserve volume: approximately 1200 ml of air that can be forcibly exhaled after a tidal expiration.
• Residual volume: approximately 1200 ml of air that remains in the lungs after the most strenuous expiration, allowing gas exchange to continue.
• Vital capacity: the sum of tidal volume, inspiratory reserve volume, and expiratory reserve volume, typically around 4800 ml in healthy young men.

Other Respiratory Concepts

• Dead space volume: approximately 150 ml of air that enters the respiratory tract but never reaches the alveoli.
• Volition: voluntary control of breathing is limited, and the respiratory centers can override conscious control when oxygen supply is low or blood pH is falling.
• Emotional factors: modify the rate and depth of breathing through reflexes initiated by emotional stimuli acting through centers in the hypothalamus.
• Chemical factors: levels of carbon dioxide and oxygen in the blood are the most important stimuli that modify respiratory rate and depth.
• Hyperventilation: blows off more carbon dioxide, decreasing the amount of carbonic acid, and returning blood pH to normal range.
• Hypoventilation: allows carbon dioxide to accumulate in the blood, bringing blood pH back into normal range when it becomes slightly alkaline.

Respiratory Diseases

• COPD: can be treated with medicines, oxygen, and pulmonary rehabilitation, but is not curable; main treatments include inhaled medicines that open and reduce swelling in the airways.
• Lung cancer: leading cause of cancer deaths worldwide; risk increases with length and number of cigarettes smoked; quitting smoking significantly lowers the chances of developing lung cancer.
• Symptoms of lung cancer: may include a new cough, chest pain, coughing up blood, hoarseness, shortness of breath, and wheezing.
• Acute bronchitis: secondary bacterial infections of the bronchi, often preceded by common cold or influenza.
• Chronic bronchitis: progressive inflammatory disease resulting from prolonged irritation of the bronchial epithelium, often a consequence of cigarette smoking and chronic exposure to airborne irritants.