Respiratory Tract of Humans

In animals, the respiratory tract is the subdivision of the respiratory system that is responsible for the process of respiration. The respiratory tract is bordered by mucosa or epithelium. Through the nose, the air is drawn into the nasal cavity, where a layer of nasal mucosa works as a filter, trapping toxins and other hazardous compounds in the air. Following that, air enters the pharynx, a passageway that connects the oesophagus and the larynx. The larynx’s aperture is protected by a unique cartilage flap called the epiglottis, which opens to enable air to pass through but shuts to prevent food from entering the airway.

Air enters the trachea from the larynx and descends to the carina, where it branches to form the right and left major (main) bronchi. Each of these bronchi branches into a secondary (lobar) bronchus, which branches into tertiary (segmental) bronchi, which branch into smaller airways called bronchioles, which eventually connect to tiny specialised structures called alveoli that perform gas exchange functions.

The rib cage protects the lungs, which are positioned in the thoracic cavity. The diaphragm is a strip of skeletal muscle located at the base of the lungs. The diaphragm is a muscular structure that separates the lungs from the stomach and intestines. Additionally, the diaphragm is the primary respiratory muscle involved in breathing, and it is controlled by the sympathetic nervous system.

The lungs are surrounded by a serous membrane that folds inward to form the pleurae — a two-layered protective barrier. The inner visceral pleura covers the lungs’ surface, while the outer parietal pleura is related to the thoracic cavity’s inner surface. Pleurae enclose a hollow known as the pleural cavity, which is filled with pleural fluid. This fluid is utilised to reduce the amount of friction experienced by the lungs during respiration. 

Structure 

The upper and lower airways make up the respiratory tract. One’s upper respiratory tract or upper airways are comprised of the nose and nasal passageways as well as paranasal sinuses (cords). The trachea, bronchi, and bronchioles are all part of the lower respiratory tract, which includes the larynx below the vocal folds. Alveolar ducts, alveolar sacs, and alveoli make up the lower respiratory tract, although they may also be seen as independent entities. An important difference in the respiratory tract is whether it is carrying or exchanging gases. In addition to the lungs themselves, the conducting zone comprises the nose, pharynx, larynx, and throat, as well as the bronchi and bronchioles. Breathing in air that has been filtered, warmed, and moistened is carried along via the conduction zone. It covers the first through the sixteenth divisions of the respiratory system. Excluded from this zone is a section of the respiratory tract that serves as a conduit for the lungs to receive and expel gases. Additionally, the conducting zone serves as a low-resistance conduit for airflow. Its filtering skills play a vital defensive role.

Oxygen and carbon dioxide are exchanged with the blood in the respiratory zone, which comprises the respiratory bronchioles, alveolar ducts, and alveoli. One-tenth of the gas exchange occurs in the bronchioles and alveoli of the lungs. The alveoli are responsible for 90% of the total. The 16th through the 23rd divisions of the respiratory tract makes up the respiratory zone.

Divided tubes from the bronchi get smaller and smaller until they reach an alveolus, which has an estimated 20 to 23 divisions.

Upper respiratory tract 

Above the cricoid cartilage or the vocal folds are considered to be portions of the upper respiratory tract, which may refer to any of these components of the respiratory system. Upper and lower airways both involve the larynx at times.  Known as the voice box, the larynx is made up of cartilage that creates sound. This comprises the nasal cavity, the paranasal sinuses, and the pharynx, which includes the nasopharynx, laryngopharynx, and larynx. 

Lower respiratory tract 

The trachea, bronchi (primary, secondary, and tertiary), bronchioles (including terminal and respiratory), and lungs make up the lower respiratory tract (including alveoli). [8] The larynx may also be included on occasion. The trachea, bronchi, and bronchioles make form the tracheobronchial tree, which describes the branching anatomy of the airways feeding the lungs with air.

The function of the respiratory system

Respiration 

Inhalation draws air into the lungs’ alveoli, where it is discharged by expiration. This breathing process is known as respiration. The trachea, bronchial tubes, and lungs all play a role in the process of inhalation. The whole digestive system is shielded by the rib cage, spine, and sternum. You breathe oxygen into your lungs, where it enters your blood and travels throughout your body. Carbon dioxide (CO2) is expelled via the lower respiratory tract and then the upper respiratory tract to complete the breathing process.

As opposed to the trachea and the bronchi, the airway in the nose and throat may be collapsed and retracted with ease. Suction forces caused by the diaphragm contracting rhythmically while sucking air into the lungs are an absolute need. Genioglossus (tongue) and hyoid muscles are used to do this by contracting at an alternating rate. Additionally, the motor neurons controlling the muscles receive tonic innervation from the respiratory centre in the medulla oblongata, which establishes a baseline degree of stiffness and size. Diaphragm muscles enable lung expansion and contraction via their principal role. The external intercostal muscles, which are located between the ribs, aid in this procedure.

Conclusion 

Several organs comprise the respiratory system, also known as the pulmonary system, which is responsible for oxygenating the body via the act of respiration (breathing). The exchange of gases happens during this process, with oxygen being absorbed from the air and carbon dioxide being released from the body. At the level of the vocal cords, the respiratory system is separated into two sections: the upper and lower respiratory tracts. When it comes to airflow in the upper respiratory system, the nasal cavity, paranasal sinuses, throat, and larynx are all part of it. This comprises the larynx, below the vocal cords, trachea and bronchioles as well as the lower respiratory tract.