Lung Volumes And Capacities
The intake of air rich in oxygen present in the environment and the release of air rich in carbon dioxide produced within the body is called breathing. Inspiration is inhaling which means taking in air while expiration is exhaling which is giving out air from the body. Respiration is defined as the oxidation of food to release energy. The organs involved in the process of respiration are called respiratory organs. The various respiratory organs/structures of human beings are as follows:
- External nostrils: These are holes that lead into the nasal chamber of the nasal cavity through the nasal passage.
- Nasal chambers: These are two narrow passages lined by pseudostratified epithelial cells secreting mucus.
- Internal nares: These are the openings of the nasal cavity into the nasopharynx.
- Nasopharynx: It is the part of the pharynx through which only air passes.
- Larynx: aka sound/voice box and helps in sound production. The pharynx opens through the larynx into the trachea.
- Trachea: It divides at the level of the 5th thoracic vertebra into the right and left primary bronchi.
- Bronchi: Each bronchus divides into secondary, tertiary bronchi, and bronchioles which further open into the alveoli.
- Alveoli: These are balloon-like structures helping in the exchange of gases. There are around 300 million alveoli in the two lungs.
- Lungs: These are two in number. Alveoli present within the lungs are the main site of the exchange of gases.
On average, a healthy person breathes 12-16 times per minute. The volume of air involved in breathing movements can be estimated by a Spirometer which helps in the clinical assessment of pulmonary functions.
Respiratory Volumes and Capacities
The lung capacities of different animals vary widely based on their activities. For eg, the lung capacity of cheetahs is much higher than that of humans. This is because their muscles require a large amount of oxygen for more energy production which helps them in running faster. The lung capacity of elephants is also higher due to their large body size. The maximum amount of air a human lung can hold is approximately 6 liters. The volume of air involved in the breathing process can be evaluated with the help of an instrument called a spirometer. It is equipment that is used to examine the total volume of air inhaled and exhaled by the lungs. It is also used in testing pulmonary function. The air in the lungs is measured in terms of lung volume and lung capacity. Lung/Respiratory volume refers to the volume of gas in the lungs at a given time during the respiratory cycle. Lung volume tells about the amount of air involved during inhalation or exhalation. Whereas, lung capacity measures how much air can be inhaled from the end of a maximal exhalation. Lung/Respiratory capacities are derived from a summation of different lung volumes. Respiratory Volumes and Capacities play an integral part in pulmonary function tests. They depend on various factors like the depth of respiration, ethnicity, gender, age, body composition, and on certain respiratory diseases.
In breathing, the lungs are neither completely filled with air nor completely emptied. Recording the volume movement of air into and out of the lungs is called spirometry. It is done with the help of a spirometer. Generally, the air in the lungs is divided into four different ‘respiratory volumes’ in man.
- Tidal Volume (TV): It is the volume of air inspired or expired during normal breathing. Its value is approximately 500ml per breath.
- Inspiratory reserve volume (IRV): It is the additional volume of air inspired during forceful inspiration. Its value is 2500-3000ml.
- Expiratory reserve volume (ERV): It is the additional volume of air that expired during forceful expiration. This volume averages 1000-1100ml.
- Residual volume (RV): It is the volume of air remaining in the lung even after forceful expiration. It is about 1100-1200ml.
Combinations of two or more ‘respiratory volumes’ are called ‘pulmonary capacities’. They are of the following types:
- Inspiratory Capacity (IC): It is the total volume of air a person can inspire after a normal expiration. It includes:(Tidal volume + Inspiratory reserve volume= Inspiratory Capacity).
- Expiratory Capacity (EC): It is the total volume of air a person can expire after a normal inspiration. It includes: (Tidal volume + Expiratory Reserve Volume= Expiratory Capacity).
- Functional Residual Capacity (FRC): It is the volume of air that remains in the lungs after normal expiration. It includes:(Expiratory Reserve volume + Residual Volume= Functional Residual Capacity).
- Vital Capacity (VC): It is the maximum volume of air a person can breathe in after forceful expiration or the maximum volume of air a person can breathe out after forceful inspiration. The vital capacity is higher in athletes, mountain dwellers than in plain dwellers, in men than women, and in the young ones than in the old persons. (ERV+TV+IRV=VC).
- Total Lung Capacity (TLC): It is the total volume of air present in the lungs and the respiratory tract after maximum inspiration. (RV+ERV+TV+IRV=TLC or VC+RV=TLC).
FAQs on Respiratory Volumes and Capacities
Question 1: Write the values of all the respiratory capacities.
Question 2: Name the instrument used for estimating the various respiratory volumes.
A spirometer is used for estimating the various respiratory volumes.
Question 3: Which volumes can’t be determined using a spirometer?
FRC, RV, and TLC.
Question 4: List the different types of respiration.
- Pulmonary respiration through the lungs.
- Cutaneous respiration through the skin.
- Branchial respiration through the gills.
Question 5: The type of respiratory organ an animal possesses depends on which features.
Habitat and Level of organization.
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