Breathing in Other Animals

The process of respiration involves inhalation of oxygen from the atmosphere which is distributed in the body cells to carry out functions and in turn, energy is released in the form of carbon dioxide by burning of food. This process is called as exhalation. Respiration is the chemical process and breathing is the physical process that involves the exchange of gases between the body and the atmosphere. In higher vertebrates like human beings, the process of respiration is carried out mainly by lungs and the process of breathing is carried out through nostrils. But the system of breathing and respiration is not the same in all the organisms living on this Earth. It varies in different species and organisms. 

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Breathing in Mammals 

Breathing is an activity that is most essential for every life form on this Earth. While different organisms have different ways to respire. In mammals, the function of respiration is carried out through the lungs. The primary responsibility to carry out the mechanism of breathing depends upon the respiratory system by inhaling the oxygen from the atmosphere into the body and exhaling carbon dioxide from the body back into the atmosphere. However, the other systems also play a critical role in the exchange of gases like the circulatory system that is responsible for the exchange of oxygen and carbon dioxide in the cells of the body. The respiratory system in mammals begins through the airways that are often lined with hairs to filter the air prior to entering the lungs. The mechanism of breathing in most mammals depend upon the muscular structure that lies beneath the lungs known as Diaphragm. This muscular structure works by pulling the lungs downward to increase the lung volume hence the air can rush into the lungs. Slowly when the Diaphragm pushes the lungs upward reducing the lung capacity thus the air is released outside. This inhalation and exhalation process is referred to as breathing. The mechanism of breathing is different in all mammals. Some inhale air through nostrils while others inhale through the mouth. Mammals have a pair of lungs to carry out the respiratory function.

The function of respiration is cannot be carried out properly if the lungs are filled with any liquid. The presence of liquid in the lungs disrupts the gaseous exchange process that is carried out by the lungs. As a result, the blood cells of the body receive less oxygen. In severe situations, the oxygen supply is completely blocked resulting in the death of the mammal. 

In humans, there are different types of breathing, the processes of each vary. There are 4 types of breathing:

• Hyperpnea: This is forced breathing in which there will be muscle contractions in both inspiration and expiration

• Eupnea: This is the normal breathing resulting from the contraction of the diaphragm and intercostal muscles.

• Costal Breathing: This is a form of shallow breathing in which the intercostal muscles contract 

• Diaphragmatic Breathing: This is deep breathing in which we can see the contraction of the diaphragm.

Breathing in Birds 

When compared to other mammals birds have lungs that do not expand or contract. Rather they have extensive air sacs that are spread across their bodies. Birds do not have a diaphragm or any pleural cavity. The environmental air is yelped into the air sacs and the spent air is expelled from the body once it passes through the lungs. The air sacs are not directly involved in the process of gas exchange but it provides extensive support to the lungs and increases its efficiency. Alveoli are the main unit of respiration in mammals, however, in birds, these are replaced by parabronchi. The parabronchi are richly supplied with capillaries and is the main site in the avian respiratory system where the exchange of gases takes place. 

The process of breathing in birds begins with inspiration, during which the air sacs in the posterior region of the body expand thus pulling air into the primary bronchi. Some of the air also reaches the secondary bronchi further reaching the parabronchi. During this most of the air reaches the posterior group of air sacs. Similarly, the air from the parabronchi is pulled back to the secondary bronchi and into the anterior air sacs resulting in the expansion of the anterior air sacs. At the time of expiration, the air sacs tend to contract resulting in the movement of air from the posterior group of air sacs through parabronchi and the air from anterior air sacs move to the primary bronchi followed by air reaching the trachea and then finally it is released out from the body. The avian respiration follows the one-way flow of air. The air sacs in birds also act as thermoregulators since every flight activity in birds produces excessive heat and unlike mammals, birds lack in the heat controlling sweat glands. 

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Breathing in Amphibians 

Amphibians are the vertebrates that survive in a moist environment. In these animals, the lungs and the skin both play a vital role to carry out the process of respiration. Toads and frogs come under the category of amphibians. Except for a few species of frog, rest all varieties of amphibians begin their lifecycle in water as tadpoles. While in this stage, the process of gas exchange is carried out by the thin skin and the gills. In few tadpoles of the frogs, the tail fins are responsible for the process of respiration since it has a large surface area and is richly supplied with blood capillaries. As they begin to grow and there will be the development of lungs while the gills and the tail fin degenerate. When the paired lungs are still developing these larvae take the trips to the water surface which enables them to take breaths. Once the lungs are fully developed the process of respiration is then completely carried out by the lungs. There are a few species in amphibians like the salamanders in which the larvae stage is not completely converted into the adult stage. In such species, though the lungs are fully developed and carry out their process, the gills are also retained by the body for their whole life. While in some other varieties of salamanders, while they reach the adult stage, the lungs do not develop and the gills start to degenerate. Therefore, in such species, the process of breathing and respiration is carried out by the skin.  

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Breathing in Reptiles

The reptiles include the snake, tortoise, lizards, crocodiles, etc. Reptiles do not have a larval stage like amphibians. Reptiles breathe through the lungs. Though in some reptiles the body is adapted to their respective environmental condition like the aquatic turtles developing permeable skin but the process of respiration is not completely executed without the lungs. The lungs in reptiles comprise of very fine alveoli that are many in number when compared to that of mammals. 

The lungs of the lizards and crocodiles have a larger surface area since it has partitions containing alveoli. The diaphragm in crocodiles is highly muscular. It has the capacity to pull the pubis back bringing the liver down. As a result, there is more surface area in the lungs and they can expand more freely. In most variety of crocodiles, there is a presence of secondary palate due to which they are capable of breathing even underwater. In snakes, the lungs are small and sac-like that have alveoli on the walls. Unlike diaphragm in crocodiles, snakes have extended trachea that enables them to swallow their prey without lacking breathe. 

In turtles, a hard shell covers the top of the body. The lungs of turtles are attached to the inside of their shell. Generally when the turtle retracts its limbs inside of the shell the air from the lungs is released, when the turtle brings its limbs outside of the shell, the internal pressure inside the lungs is reduced therefore the air can easily enter the lungs. 

Breathing in Fish 

The process of respiration in fishes is carried out by the organs known as gills. These are the organs that are situated at the side of the mouth cavity in most aquatic animals especially fishes. Fishes need to absorb dissolved oxygen from the water to carry out its functions. The water is passed in large quantities through the gills to the absorption surface to get oxygen. There is the presence of filaments over the gills where the exchange of gases takes place. In a bigger variety of fishes, these gills are covered and protected by flaps of skin.  When the water is ingested through the mouth, it passes to the gills and hence the chambers of the gills enlarge in size. After this, the mouth is closed thus preventing the water to flow out through the mouth. The water present inside the mouth is now forced over the gill chambers allowing the chambers to contract thereby the water is emptied through the opercular openings. There is a membrane on the ventroposterior border of the operculum that prevents the water to flow back into the gill chambers at the time of the inhalatory phase of respiration. Due to the action of the mouth cavity and the gill chambers, the proper flow of water in one direction is maintained over the gills.

Breathing in Invertebrates 

Invertebrates are the animals deprived of bony skeleton and backbone. Most of the insect varieties are included under invertebrates along with few aquatic species like corals, jellyfishes and, mollusks that include squids, octopus, snails, etc. The main respiratory organs in Invertebrates are the gills and trachea. In most of the insect varieties, the trachea is the main organ to carry out the respiratory function. Insects have an external opening known as spiracles. The air enters the body through these spiracles and reaches the internal respiratory system that is the trachea. The muscularity around the opening of the spiracle is such that it opens and closes only when required so as to prevent the moisture loss. The muscle needs to relax in order to open the opening of the spiracle. Although the muscle action is controlled by central nervous system, this can even happen by the response of the external stimuli at times  The trachea is a dense network of tubules that has the capacity to maintain pressure throughout the body. The tracheal tubes are subdivided into smaller tubes that reaches every part of the body. There is a presence of a special cell called tracheole that is present at the end of each branch of the trachea. The tracheole provides a surface where the exchange of gases between the atmosphere and the cells of the body take place. 

The gills in fishes lie within the cavity whereas in a few invertebrates they open directly to the atmosphere. In invertebrates, we can find the gills as a thin extension of the surface of the body that comes directly in contact with the surrounding. The heart of a few varieties of mollusks pumps blood that contains the oxygen capturing molecule known as Haemocyanin. The respiratory system in such varieties is similar to that of a vertebrate fish.

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