What is the Difference Between Gills and Lungs

The main difference between gills and lungs is that gills are the type of respiratory organs specialized to breathe in water, whereas lungs are the type of respiratory organs specialized to breathe in the air. Furthermore, fish use gills while mostly tetrapods use lungs. Gills are made up of rows of filaments through which water continuously flows while lungs contain sacs connected to the outside through a network of breathing tubes. 

Gills and lungs are the two types of respiratory systems in vertebrates. Generally, they are responsible for the exchange of respiratory gases: oxygen in and carbon dioxide out. Moreover, blood vessels run near them to facilitate gas exchange. 

Key Areas Covered 

1. What are Gills
     – Definition, Structure, Function
2. What are Lungs
     – Definition, Structure, Function
3. What are the Similarities Between Gills and Lungs
     – Outline of Common Features
4. What is the Difference Between Gills and Lungs
     – Comparison of Key Differences

Key Terms 

Fish, Gills, Lungs, Tetrapods, Vertebrates

What are Gills 

Gills are the main type of respiratory organs in animals that live in water. Generally, they mainly occur in fish but, amphibians, arthropods and annelids also have gills. Gills are a type of convoluted growths surrounded by blood vessels. Additionally, a thin epithelial layer covers them. However, the gills in fish and crabs are internal while gills in amphibians are external. Typically, gills are arranged in a series of plates right behind the head. Moreover, there are a series of openings from the esophagus to the exterior. In addition, a cartilaginous or bony gill arch supports each gill. 

Figure 1: Gills

Furthermore, the series of comb-like filaments in gills are known as gill lamellae, which increases the surface area of gills. Generally, during breathing, fish intake a mouthful of water and draw through the sides of the throat, forcing water through the openings of the gills. Moreover, bony fish have three pairs of gill arches while cartilaginous fish have five to seven pairs. However, water contains less oxygen concentration when compared to air. Therefore, breathing inside water is less efficient. 

What are Lungs 

Lungs are the most advanced form of the respiratory system found in animals including humans, mammals and most of the other vertebrates. Moreover, a few fish and some snails also have lungs. Generally, in vertebrates, there is a pair of lungs in the thorax on either side of the heart. The main function of the lungs is to extract oxygen from the atmosphere while transferring it into the bloodstream.

Figure 2: Lungs

Moreover, the lungs are ingrowths consisting of a series of tubes, which carry air towards a large number of small sacs. Both these tubes and sacs are covered by the pleura. Generally, lungs begin at trachea at the lower respiratory system. Then, these trachea further branch into bronchi and bronchioles. After that, bronchioles branch into alveolar ducts, which form alveolar sacs, containing alveoli. In the meanwhile, small capillaries surround alveoli through which the gas exchange occurs. 

Similarities Between Gills and Lungs 

• Gills and lungs are the two types of respiratory systems that occur in vertebrates. 
• Their main function is to facilitate gas exchange.  
• They are surrounded by blood vessels. 
• They help to take oxygen from the outside environment while eliminating carbon dioxide to the outside. 
• Both have a respiratory membrane with a large surface area to increase the efficiency of gas exchange.  

Difference Between Gills and Lungs 

Definition 

Gills refer to the respiratory organ of aquatic animals, such as fish that breathe oxygen dissolved in water while lungs refer to a pair of breathing organs located with the chest, which remove carbon dioxide from and bring oxygen to the blood. 

Significance 

While gills are external extensions of the body surface, lungs are internal folds. 

Type of Oxygen Breathing 

Moreover, gills help to breathe oxygen dissolved in water while lungs help to breathe oxygen in the air. Thus, this is the main difference between gills and lungs.

Occurrence 

Also, another difference between gills and lungs is that gills mainly occur in fish while lungs mainly occur in tetrapods. 

Structure 

Further, their structure is also a major difference between gills and lungs. Gills are made up of rows of filaments through which water continuously flows while lungs contain sacs connected to the outside through a network of breathing tubes. 

Type of Diffusion 

Gases diffuse between water and capillaries in gills immersed in the flow of water while gases diffuse between inhaled air entering the lungs and capillaries occurs within the lungs. 

Type of Heart 

Animals with gills usually have a two-chambered heart while the animals with lungs have a four-chambered heart. 

Conclusion 

Gills are the type of respiratory system found in animals in water such as in fish. They contain rows of filaments through which water continuously flows. On the other hand, lungs are the type of respiratory system present in animals that live on the land. Therefore, they help to take oxygen in the air. Moreover, lungs contain tubes, which carry air to the sacs where the gas exchange occurs. Thus, the main difference between gills and lungs is the structure and the type of gas exchange. 

References:

1. Farabee, M J. “THE RESPIRATORY SYSTEM.” Respiratory System, Available Here.

Image Courtesy:

1. “Figure 39 01 04” By CNX OpenStax (CC BY 4.0) via Commons Wikimedia   
2. “Lung structure normal” By National Heart Lung and Blood Institute – National Heart Lung and Blood Institute (Public Domain) via Commons Wikimedia