Chordates breathe by gills, gills and lungs (sometimes helped by the skin), or lungs alone when the embryonic period has passed. Gills are clusters of capillaries in the gill-slit walls that allow water to flow from the throat. They are found on all vertebrates except fish. Humans and other mammals breathe through our noses and mouths, but most fishes breathe through their gills. Fish with lungs also need to breathe periodically because they cannot swim for very long without breathing.
Anatomy and physiology of breathing in animals including humans. Includes information on how amphibians, reptiles, birds, and mammals breathe. Also covers topics such as the respiratory system, air sacs, lung function, and blood gas changes during respiration.
Respiratory system is the set of organs responsible for oxygenation of the blood and removal of carbon dioxide from the body. It consists of a pair of ducts, one for each side of the body, called the bronchi. These lead to a large network of passageways called bronchioles which branch out until they end in tiny tubes called alveoli where gas exchange takes place. The alveoli are covered by a membrane called the pleura. This is why chest x-rays show both lungs have a good supply of air.
Non-chordates breathe through the body surface, gills, or trachea, whereas chordates breathe through the lungs or gills. Chordates have a hollow and dorsal central neural system, whereas non-chordates have a solid central nervous system that is either ventral or lateral inside the body. Also see our next post for more information.
A third chordate trait is pharyngeal slits, which are holes between the pharynx, or throat, and the outside world. They have undergone considerable changes as a result of evolution. These slits are utilized by primitive chordates to filter food particles from the water. As animals grow larger, they need a stronger gill system for breathing. Therefore, the number of filaments in their gills will increase while the size of the slit between each pair of filaments will shrink.
After evolution developed limbs instead of gills, these openings were no longer needed for respiration. However, they are still present in many modern-day fish, such as trout and salmon.
Pharyngeal slits can be seen in both vertebrate and invertebrate chordates. However, not all chordates have them. Fish are members of the class of vertebrates that do have pharyngeal slits. The other major group of vertebrates without pharyngeal slits are amphibians. Amniotes (reptiles and birds) have a complete set of teeth on the bottom of their mouth that is used to chew their food before swallowing it. Fish and amphibians swallow their food whole; therefore, they cannot chew it first like amniotes can.
In conclusion, chordates have pharyngeal slits. Fish are a type of chordate.
Nereis dumerilii does not have gills. The parapodia and dorsal integument lobes take up the role of breathing. As a result, these areas are densely packed with blood vessels. In Nereis virens, the physiology of breathing is well understood. It is known that oxygen enters the body through the surface area provided by the dorsal integument lobes. Because of this reason, many organisms living in or on the soil tend to be gill-less.
Gastropods such as sea snails and freshwater snails possess a shell that acts as both body armor and an oxygen reservoir. Inside their protective shells, gastropods have a fluid-filled cavity that is analogous to our stomach. This is where the vital organs are located- the heart, lungs, and liver. Unlike other mollusks, however, they have no muscle tissue between the inside and outside of their shells. So, how do they move things around inside their bodies if they have no tentacles or other external appendages with which to grab or trap food? They use the power of gravity! As water flows into their shell, it increases the pressure inside the shell. This pressure then forces open the valve of the gonad sac, allowing sperm to flow out into the water supply. If there are no males in the population, then the only way for females to reproduce is by laying eggs directly into the water column.
Non-chordates breathe using distinct organs. Although the organs differ in form, they all have a large surface area in contact with the surrounding environment and are well supplied with blood arteries and capillaries. This means that oxygen is taken up from the air and carbon dioxide is released into the air.
Fish breathe through their skin, using gills on either side of their head that filter water to pull in oxygen from the atmosphere and dump out carbon dioxide. Seawater contains about 32% oxygen, while fresh water has around 15%. However, due to the higher concentration of salt in marine water, fish need to bring extra plasma from their bloodstream to replace what's lost through breathing.
Amphibians have a similar system for breathing as fish, but instead of gills they have lungs. While it is sleeping, an amphibian breathes slowly through its mouth and nose just like us humans. But when it senses danger, it secretes mucus from its stomach up its throat into its mouth, which forms a protective layer over the lungs. Then it stops breathing and waits for the threat to go away!
Reptiles also have lungs but they're located inside their bodies rather than on their skin. They breathe by expanding and contracting their chest muscles, much like we do when we breathe in and out.