Human Respiratory System: Function and Anatomy
Respiratory System: Function and Anatomy
Function: Exchange of gases between the body and the atmosphere.
Human respiratory, or pulmonary, respiration consists of:
Driving System
Nostrils, mouth, pharynx, larynx, trachea, bronchi (main, lobar, segmental), and bronchioles.
Exchange System
Alveolar tubes and sacs. The anatomic dead space, or respiratory zone (no gas exchange) of the bronchial tree, includes the first 16 bronchial generations, and its volume is 150 ml.
The respiratory function is to move volumes of air from the atmosphere to the lungs and vice versa. This is possible through a process known as ventilation.
Ventilation is a cyclical process and consists of two stages: inspiration, which is the entry of air into the lungs, and exhalation, which is the output. Inspiration is an active phenomenon, characterized by the increase in thoracic volume that causes a negative intrapulmonary pressure and determines the displacement of air from outside into the lungs. Contraction of primary inspiratory muscles, the diaphragm and external intercostals, is responsible for this process. Once intrapulmonary pressure equals atmospheric pressure, inspiration stops. Then, thanks to the elastic force of the rib cage, it retracts, creating a positive pressure that exceeds the atmospheric pressure, determining the flow of air from the lungs.
During normal breathing, exhalation is a passive process. Active respiratory muscles are able to further reduce the intrathoracic volume, increasing the amount of air that travels abroad, which happens in forced expiration.
While this series of air exchanges occurs in the alveoli, the gases involved in gas exchange, oxygen and carbon dioxide, diffuse along their concentration gradient. This is the oxygenation and detoxification of the blood.
The volume of air entering and leaving the lungs per minute has some synchrony with the cardiovascular system and the circadian rhythm (reducing the frequency of inhalation/exhalation at night and while asleep). It ranges from 6 to 80 liters, depending on demand.
Care should be taken with the dangers of pulmonary ventilation. Along with the air, solid particles also enter and can clog and/or poison the body. Larger ones are trapped by hairs and mucous material from the nose and respiratory tract, which are then drawn by ciliary movement until they are swallowed, expelled by spitting, or sneezed out. At the bronchial level, lacking cilia, macrophages and phagocytes are used to clean particles.
Definition of Organs
Nasal Cavity
Consists of two large cavities whose function is to allow the entry of air, which is moistened, filtered, and heated to a certain temperature through structures called turbinates.
Pharynx
A muscular, membranous tube that helps the air pour into the lower airways.
Epiglottis
A lid that prevents food from entering the larynx and trachea during swallowing. It also marks the boundary between the oropharynx and laryngopharynx.
Larynx
A conduit whose main function is to filter the inspired air. It also allows the passage of air into the trachea and lungs and closes to prevent the passage of food during swallowing. It also has the function of the vocal body, i.e., producing sound.
Trachea
Provides an avenue open to the air inhaled and exhaled from the lungs.
Bronchus
Conducts the air that goes from the trachea to the bronchioles.
Bronchiole
Conducts the air that goes through the bronchi and terminates in the alveoli.
Alveolus
Allows gas exchange, i.e., inside the blood, it removes carbon dioxide and picks up oxygen (hematosis).
Lungs
The lungs’ function is to carry out gas exchange with the blood, so the alveoli are in close contact with capillaries.
Intercostal Muscles
The main function of the respiratory muscles is to mobilize a volume of air that serves to deliver oxygen to different tissues after proper gas exchange.
Diaphragm
Striated muscle that separates the thoracic cavity (lungs, mediastinum, etc.) from the abdominal cavity (intestines, stomach, liver, etc.). It is involved in respiration, decreasing the pressure within the chest cavity and increasing the volume during inhalation, and increasing pressure and decreasing volume during exhalation. This process is carried out mainly by contraction and relaxation of the diaphragm.
The nasal passages are made up of:
- Sensitive cells
- Olfactory nerve
- Pituitary
- Turbinates
- Nostrils
Composition of Dry Air
| Oxygen | 21% |
| Nitrogen | 78% |
| Carbon Dioxide | 0.03% |
| Argon and Helium | 0.92% |
| Water Vapor | 0% |
Composition of Alveolar Air
| Oxygen | 16% |
| Nitrogen | 77% |
| Carbon Dioxide | 5% |
| Water Vapor | 2% |