Difference Between Gills and Lungs

Gills vs Lungs

Gills and lungs are the main tissues that provide gas-exchanging surfaces for the respiratory function of most of the higher animals. Primarily fish has gills while amphibians, reptiles, birds, and mammals have lungs for respiration or gas exchange. It would primarily comply that aquatic animals have gills and terrestrial animals have lungs, but the aquatic mammals and some of the fish species have lungs. This article intends to discuss the most important and primary differences between lungs and gills with regard to form and function.


Gills are the respiratory organs that are capable of extracting dissolved oxygen in water, and those are found in evolutionarily higher and complex aquatic animals. However, the microscopic and simple aquatic organisms do not require a gill apparatus to extract oxygen from water, as their body surface can absorb adequate amounts. The structure of a gill is interesting, and it has a filtering system to trap particles other than water while gas exchange takes place. In fishes, the water is taken from the mouth, projected through gills to absorb oxygen, and sent out through the gill slits (cartilaginous fish) or operculum (bony fish). The primary function of a gill involves a counter current system of flowing blood in the gill and water around the gill in opposite directions. In addition, the comb-like filaments of the gill called gill lamellae aids in increasing the surface area of gas exchange. There are slight differences between the gills of bony fish and cartilaginous fish in structure, but the function of extracting oxygen with ventilation of gills is performed in both types. Other vertebrates such as amphibians have externally exposed gills for respiration in their larval stages. The embryonic developmental stages of higher vertebrates such as birds, mammals, and even reptiles possess gills to fulfil the respiration functions inside the womb or egg. Therefore, it could be envisaged that most of the aquatic animals with complex body systems possess gills for their respiration. Moreover, gills in fishes are capable of diffusing excretory products along with the respiratory wastes into the water.


Lungs are the main respiratory surface of the air-breathing higher vertebrates and some of the terrestrial invertebrates. However, the vertebrate lungs are structurally different and better adapted to extract more oxygen than the invertebrate lungs. The vertebrate lung receives the atmospheric oxygen through the nasal and oral cavity and trachea through inhalation, extract the oxygen into blood capillaries and diffuse the carbon dioxide out at extremely thin-walled alveoli, and exhale through the same way. There are millions of alveoli formed in the lungs, to increase the surface of gas exchange. However, the excretory waste products are not diffused through the walls of alveoli. The lungs are located in the thoracic cavity of mammals, and the intercostal muscles contract with the diaphragm to increase the volume and reduce the inside pressure so that the inhalation takes place, and the exhalation process takes place in the other way around. In addition to its main function respiration, lungs are important in maintaining the pH of blood, getting rid of unwanted blood clots, providing airflow for the pharynx to produce sound, repelling dust and other particles from the air tract, and many other functions.


What is the difference between Gills and Lungs?

• Both organs are vital as gas exchanging surfaces, but gills are important to extract dissolved oxygen in water while lungs are important to extract atmospheric oxygen.

• Gills are found in aquatic organisms, whereas lungs are found in terrestrial air-breathing animals.

• Gills are able diffuse excretory products but not the lungs.

• Gills could be either interiorly or exteriorly located organs, whereas lungs are only interior organs.


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