Human Anatomy Part 1 - K. A. Dyubenko, A. K. Kolomiysev, Yu. B. Chaykovsky 2002

Special Part
Respiratory System, systema respiratorium [respiratory apparatus, apparatus respiratorius] - General Overview

The Respiratory system, systema respiratorium, consists of Organs that facilitate gas exchange between ambient air and Blood. It comprises the conducting zone, which delivers air to the Lungs during inspiration and removes it during expiration—including the External Nose, Nasal cavity, Pharynx, Larynx, Trachea, and Bronchi—and the respiratory zone, which directly performs gas exchange, namely the lungs (Fig. 280).

In a broad sense, gas exchange is a fundamental component of METABOLISM; it involves the uptake of oxygen from the environment by the Organism and the elimination of carbon dioxide. The respiratory apparatus performs only The first phase of gas exchange, known as pulmonary or external respiration, which encompasses the exchange of gases between atmospheric air and alveolar air, as well as the diffusion of gases along the alveolar-capillary gradient. The subsequent two phases—gas transport by the blood to and from Tissues, and tissue respiration (the uptake of oxygen and release of carbon dioxide by tissues)—constitute Functions of The Cardiovascular system and all body Cells.

A crucial structural feature of the respiratory tract is the rigidity of its walls, which are supported by osseous or cartilaginous tissue. This ensures the patency of the airways during various body postures and movements. The respiratory tract is divided into the Upper Respiratory Tract—comprising the external nose, nasal cavity, and pharynx—and the Lower Respiratory Tract—comprising the larynx, trachea, and bronchi.

During inspiration, air normally enters the pharynx through the nose, a process known as nasal breathing, which is the physiological norm. As it passes through the nasal cavity, the air is moistened, warmed, and filtered. Irritation of the nasal mucosa triggers the sneeze reflex or excessive mucus secretion, serving a protective function. Furthermore, this area houses the olfactory region, regio olfactoria, which is an integral component of the olfactory analyzer.

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Fig. 280. Respiratory apparatus, apparatus respiratorius

When nasal breathing is obstructed, air may enter the pharynx through the Mouth during inspiration, a condition known as oral breathing, which is pathological. This bypasses the aforementioned Functions of the nasal cavity to a significant degree, potentially leading to respiratory disorders. From the pharynx, air passes into the larynx. In addition to conducting airflow, the larynx serves several other functions. Its mucous membrane acts as a reflexogenic zone, where irritation triggers a cough reflex or even laryngospasm. The larynx is also The Organ of phonation, which is particularly vital for humans as it enables speech and verbal communication.

In the Trachea and Bronchi, inspired air continues to be moistened and warmed, but arguably their most critical function is drainage, facilitated by the ciliated epithelium lining the mucosa. The bronchial walls contain Cytology/cytology/32.html">Smooth Muscle tissue. The contraction or relaxation of myocytes alters the bronchial lumen, thereby regulating the volume of inspired air.

In addition to gas exchange, the lungs participate in Water balance, with 15–20% of the body's water being eliminated via the lungs. By excreting carbon dioxide, they help maintain acid-base Homeostasis. They also eliminate volatile substances such as alcohol, acetone, ammonia, ether, and chloroform. Furthermore, the lungs play a role in thermoregulation, releasing up to 10% of body heat into the environment during expiration. The lungs act as a blood reservoir and are involved in the Regulation of Blood coagulation.

The protective function of the respiratory apparatus is further reinforced by the extensive presence of mononuclear phagocyte system elements within its mucous membrane. Numerous lymphoid follicles are embedded in the walls of the larynx, trachea, and bronchi. The Tonsils (described alongside the pharynx) also play a certain protective role within the respiratory system. The lungs contain abundant alveolar phagocytes that engulf microorganisms and dust particles.