Human Anatomy: Upper Respiratory Tract

Upper Respiratory Tract

• The upper respiratory tract includes the nasal cavities, paranasal sinuses, larynx, and trachea.
• The respiratory functions of the nasal cavities and paranasal sinuses include warming, moistening, and filtering the inspired air.
• The nasal cavities are surrounded by blood vessels that exchange heat with each breath.

Nasal Cavities

• The nasal cavities are divided by a midline septum.
• The lateral walls of the nasal cavities have folds called conchae, which resemble the shape of a conical shell.
• The nasal cavities contain mucus glands and serous glands that humidify the inspired air.
• The nasal cavities are more efficient at heat and moisture exchange than the mouth.

Paranasal Sinuses

• The paranasal sinuses are extensions of the nasal cavities.
• They connect with the nasal cavities and are involved in the respiratory process.

Conducting Versus Respiratory Zones

• The conducting portion of the airway runs from the trachea to the terminal bronchioles.
• The respiratory bronchioles and alveoli are capable of gaseous exchange.
• Alveoli are lined by alveolar type 1 and alveolar type 2 cells, with the latter producing surfactant to reduce surface tension.

Pulmonary Circulation

• The pulmonary circulation supplies the lungs with deoxygenated blood.
• The pulmonary trunk emerges from the right ventricle and divides into the right and left pulmonary arteries.
• The pulmonary arteries carry deoxygenated blood to the alveoli, where gas exchange takes place.
• Oxygenated blood is then carried back to the left atrium of the heart via the pulmonary veins.

Bronchial Arteries

• The bronchial arteries supply oxygen-rich blood to the conducting portions of the airways.
• The walls of the conducting airways are too thick to permit diffusion, so they require their own oxygen-rich supply.

Immune Cells of the Airways

• Macrophages and immune cells can usually deal with microorganisms that enter the airways.
• Once the microorganism is phagocytosed, the macrophage presents microbial antigens on the surface to activate B and T cells.
• Activated B and T cells produce more antibody and/or activate the macrophage.

Coughing

• The cough reflex is a mechanism for clearance of the lungs.
• There are four distinct phases to a normal cough: irritation, inspiration, compression, and expulsion.
• The cough reflex can be triggered by inflammatory, mechanical, chemical, or thermal stimuli.

Larynx

• The larynx is a vital structure that protects the lungs.
• The larynx contains cartilages and membranes that play a crucial role in the respiratory process.
• The laryngeal inlet is a narrow passage that allows air to enter the lungs.
• An emergency laryngotomy may be required if the glottis is obstructed.

Emergency Laryngotomy

• The procedure involves penetration of the cricothyroid membrane with a sharp implement to establish an airway.
• Care must be taken to avoid damage to the thyroid gland.
• The patency of the opening needs to be maintained to prevent obstruction.

Learn about the definition and contents of the upper respiratory tract. Understand the parts of the respiratory system and their functions.