Gill slits, which are vertical openings in the sides of the head of many aquatic vertebrates that allow water to pass over their gills, are thought to have begun to disappear during the transition from a water-based to a land-based lifestyle in the evolution of tetrapods.
Early fishes evolved from a lobe-finned ancestor during the Devonian period between 410 and 360 million years ago. During this time gill slits were present, but it is thought that as animals began to adapt to shallow brackish or freshwater habitats, their gills shifted from being located in the throat area to being further back in the body cavity.
Some very early tetrapods, such as Acanthostega, which lived 380 million years ago, still had gill slits and may have been able to breathe underwater. However, as the transition to living on land progressed, subsequent species no longer had visible gill slits and had evolved lungs in order to breathe air.
By the time Homo Sapiens evolved, gill slits had completely disappeared and still remain absent in humans today.
Did gills evolve from pharyngeal slits?
Gills are organ systems that allow aquatic animals to gather oxygen from the water to breathe. Pharyngeal slits are ridges that form on either side of an animal’s throat and lead into the digestive system.
The exact evolutionary relationship between gills and pharyngeal slits is a subject of debate among scientists.
The idea that gills evolved from pharyngeal slits comes from the observation that many of the same proteins found in modern gills are also found in some primitive fish, like lampreys, that have pharyngeal slits.
Though these fish do not use their slits for breathing, the argument is that these proteins may have been repurposed from the beginning stages of gill formation.
Another argument suggests that gills evolved from pharyngeal slits in two distinct steps. In the first step, researchers posit that pharyngeal slits served as sites of circulation where fluids could be exchanged between the outside environment and the animal’s body.
In the second step, with the emergence of ray-finned fishes, some of these same slits were further transformed with the assistance of hormones or other genes to begin forming the structures of modern gills.
Studies of gill development in various species of fish, as well as other evidence from the fossil record, suggest that the formation of gills could have happened via either of these processes. Ultimately, the exact evolutionary relationship between gills and pharyngeal slits remains inconclusive but the notion that gills may have evolved from pharyngeal slits is an area of ongoing research.
What did gills evolve from?
Gills evolved from the lining of the pharynx, which is the tube connecting the mouth to the esophagus. The pharynx was originally a primitive form of breathing, but as aquatic animals evolved, it was replaced by gills.
Gills are made up of thin layers of tissue and contain blood vessels that allow for the exchange of oxygen and carbon dioxide. The water flows over and through these tissues, allowing for the dissolution of oxygen into the blood and the release of carbon dioxide.
In the aquatic environment, gills allow for increased efficiency in gas exchange, resulting in increased oxygen levels to the blood. Additionally, they are more effective at eliminating waste products than the lining of the pharynx.
Over time, gills became the predominant method of gas exchange and respiration in aquatic organisms.
What structure are gills derived from?
Gills are derived from pharyngeal arches, which are structures formed from part of the embryonic branchial arch system that is present in all vertebrates. This branchial arch system consists of five pairs of arches and is made of mesoderm and neural crest tissue.
The pharyngeal arches are present in embryos in most vertebrates at around three weeks of development. These arches will eventually develop into the skeletal and cartilaginous structure of the head and neck, as well as contribute to major structures such as the larynx, jaws, and ears.
Different structures can form from different pharyngeal arches depending on the species. For example, in amphibians, gills typically form from the fourth and sixth arches, while in mammals (including humans) the fourth arch forms structures such as the larynx and Eustachian tubes.
In fish, however, gills typically form from the first, second and third arches. Gill slits or “branchial clefts” are formed when the arches fold together and begin to differentiate into specialized structures, such as the gill filaments.
These gill filaments are comprised of highly vascularized tissue that facilitates oxygen and carbon dioxide exchange with the external environment.
What do pharyngeal slits develop into?
Pharyngeal slits, also known as pharyngeal pouches, are grooves, clefts, and/or depressions located at the side of the embryo’s neck, between the first and second gill arches. They form during embryonic development of all vertebrates, including humans.
The slits form when the pharyngeal arches, which are parts of the embryo’s head and neck, fold into the surrounding tissue.
In fish, the pharyngeal slits are involved in the process of filtering water to extract oxygen and nutrients. The pharyngeal slits eventually develop into the gills and the gill cover. In humans, the pharyngeal slits develop into important parts of the head,neck, and respiratory tract, including the lower jaw, tonsils, palate, parts of the tongue, and the Eustachian tube.
They also provide passage for the lymphatic vessels.
During embryological development, the anterior (closer to the mouth) two slits develop into external structures and are referred to as the external acoustic meatus, the middle ear cavity, and the Eustachian tube.
The posterior (further from the mouth) four slits develop into internal structures, forming the palatine tonsils, the thymus, and the parathyroids. The last pharyngeal slit develops into the laryngeal pouch.
What are the examples of pharyngeal slits?
Pharyngeal slits are a series of grooves in the pharynx, or throat region, of some primitive vertebrates, providing an opening to the outside environment. Examples of organisms with pharyngeal slits include hagfish, lampreys, stingrays, and some species of sharks.
The slits are located on the sides of the animal, beginning in the throat and continuing down along the sides of the body. The slits provide several important functions, including respiration, filtering food, vocalization, and possibly even protection from parasites.
In hagfish, the slits are primarily used for the development of a group of small structures known as palatoquadrate cartilages. These structures form the walls of the pharyngeal slits and act as valves that control the flow of water.
By controlling the flow of water, hagfish can extract oxygen for respiration, filter out food, and expel waste. In some species of stingrays, the slits can also assist with vocalizations.
In some species of sharks, the slits are believed to offer some form of protection from parasites. Sharks have an array of protective mechanisms, including thick skin and an array of special epithelial cells, which are thought to help filter out parasites.
The presence of the pharyngeal slits provides an extra layer of protection, as parasites may struggle to penetrate the grooves.
Overall, pharyngeal slits play multiple important roles in various primitive species of vertebrates, helping with respiration, food filtration, vocalization and possibly even protection from parasites.
What are gill slits called?
Gill slits are a series of openings along the sides of the neck in the pharyngeal region of the body of fish, amphibians and other aquatic animals. They are part of the respiratory system and allow water to flow into the body so the animal can absorb oxygen and release carbon dioxide.
They are also known as branchial clefts or branchial fissures. They are also referred to as pharyngeal clefts, slits or openings. The walls of the gill slits are covered in a thin, membranous tissue called the operculum.
This helps to create suction and forces water through the gill slits, removing oxygen and releasing carbon dioxide.
What is the origin of gill slits?
The origin of gill slits can be traced back to primitive chordates, the animal group which includes modern vertebrates like ourselves. Chordate embryos typically develop a series of openings on either side of their head, called pharyngeal clefts or arches.
These arches are believed to be evolutionary holdovers from gills, which allowed primitive chordates to extract oxygen from the water they lived in.
Gill slits have a variety of functions in aquatic animals and many still retain the gill structures long after they reach adulthood. Fish and amphibians, for example, still rely on gills to extract oxygen from water, while some marine mammals such as whales, dolphins and manatees have modified their gill slits to help them detect and interpret sound underwater.
The development and evolution of gills in the animal kingdom has allowed many aquatic creatures to thrive in their environment by living off oxygen from the water. This adaptation has allowed mankind to explore the wonders of the oceans and aquatic environments for centuries, and given us a glimpse into the rich variety of life existing beneath the waves.
What develops into gill slits in chordates?
Gill slits are a series of paired sacs or grooves in the pharyngeal region of some chordates, such as fish and frogs. They develop from the pharyngeal clefts of the embryo, which are primary parts of the digestive system.
In the early stages of development of the embryo, four pairs of pharyngeal grooves form out of the ectoderm, which is the outermost layer of the embryo. A fifth pair may form but usually disappears shortly after its origin.
As the embryo develops, these clefts elongate and eventually turn into slits that open to the outside of the embryo. These opening are the gill slits. The gill slits form important structures for both aquatic and land-living animals.
Aquatic animals use the gill slits for respiration and filter feeding. The gill filaments inside the slits filter oxygen out of the water and transport it throughout the body. On land, the gill slits in amphibians are still present, but they are not used for respiration.
Instead, they become involved in the development of the organs of the jaw that may be used for eating, or they can help determine the amount of fluid the frog retains in its body.
How are pharyngeal slits formed?
Pharyngeal slits are formed when the embryonic pharyngeal arches, which are initially made up of cell layers from ectoderm and mesoderm, begin to form a groove in the ectodermal wall. This groove eventually breaks through into the pharyngeal endoderm and creates a walled cleft between two pharyngeal arches.
This divide can eventually separate completely and form two distinct slits including the internal and external pharyngeal slits.
The external pharyngeal slit is made up of an external epidermal layer, which is surrounded externally and internally by the pharyngeal endoderm. This external opening is connected to the environment and serves as an entryway for food and water.
The internal pharyngeal slit is a median epidermal slit located between the two pharyngeal arches that form the internal part of the pharyngeal cavity. This internal opening is connected to the oropharynx which is the food path to the esophagus.
As the embryo further develops, the pharyngeal slits will undergo changes over time. The epidermis of the external pharyngeal slits will disappear and its corresponding cleft will be filled with muscles, ligaments, and connective tissues leading to its closure in most vertebrates.
In some species, however, the external slit will remain open and form structures like the gill slit in fish and the Eustachian tube in mammals.
Where do pharyngeal constrictors originate?
The pharyngeal constrictors are four skeletal muscles which originate in the neck and are responsible for constricting the pharynx. The four muscles that make up the pharyngeal constrictors are the superior pharyngeal constrictor, the middle pharyngeal constrictor, the inferior pharyngeal constrictor, and the cricopharyngeal muscle.
The superior and inferior constrictors originate from the pterygoid hamulus, a hook-like process of the medial pterygoid plate in the mandible. They then insert into the superior and inferior parts of the median fibres of the thyroid cartilage, respectively.
The middle pharyngeal constrictor originates from the longitudinal thyroid muscle and inserts into the posterior border of the hyoid bone. Lastly, the cricopharyngeal muscle originates from the cricoid cartilage, which is located below the entrance to the larynx and inserts into the posterior border of the thyroid cartilage.
All four of these muscles come together at the pharyngeal isthmus, located between the pharynx and the larynx, to form the pharyngeal constrictors.
What do gill slits turn into in humans?
Gill slits are the membranous structures that allow for the exchange of oxygen and carbon dioxide in many aquatic creatures, most notably fish. While embryos of all vertebrates share a similarity in appearance during early stages of development where gill slits are clearly recognizable, they eventually take on a different form depending on the species.
In humans, the gill slits develop into branchial arches and branchial clefts before disappearing. The branchial arches are cartilaginous plates that are remnants of the original gill slits, with the first three arches helping to form the lower jaw, middle ear bones and larynx.
Meanwhile, the last two branchial arches serve to form the muscles around the neck and face. The branchial clefts, or pharyngeal pouches, form the lining of the middle ear and the upper portions of the throat, as well as parts of the thymus, parathyroid, and thyroid glands.
Both the branchial arches and branchial clefts disappear when the embryo is in its seventh week of development.
Is pharyngeal gill slits present in human body?
No, pharyngeal gill slits are not present in the human body. Pharyngeal gill slits, also known as pharyngeal arches, are structures present in the embryonic stage of some species, including fish and amphibians, which develop and eventually become pharyngeal clefts and structures of the head and neck.
These structures function as gills, allowing the organism to acquire oxygen from the water. In humans, these structures are initially present during the embryonic stage, but then disappear as they begin to develop into the jaw, ears, and other structures needed for a human life.
Will humans develop gills?
At this time, it does not appear that humans will have gills or other structures that would allow them to breathe underwater. Though humans have a strong evolutionary history of adapting to their environments, the idea of humans evolving to the point of having gills seems highly unlikely.
The unique environment of the water requires special adaptations that humans simply don’t possess.
In order to both survive and find food in the underwater environment, organisms must possess specialized adaptations that make it possible. For example, fish rely on gills that are capable of extracting oxygen molecules from the water, allowing them to remain underwater for extended periods of time.
In addition, they have special internal organs that allow them to maintain balance and respiration at depths of hundreds of feet. For humans, such adaptations would require drastic changes to our bodies, and would likely take millions of years of evolutionary adaptation to achieve.
Given the evolutionary history of humans and our current state of understanding, it does not appear likely that we will ever develop gills. Though never say never, it appears that if humans are ever to enter the underwater environment, we will have to rely on technology and man-made structures to survive.
What does the presence of gill slits in a human embryo suggest?
The presence of gill slits in a human embryo is an indication of our evolutionary history and is a common feature shared by all vertebrates during the early stages of embryonic development. During the early stages of human development, a human embryo will have gill slits, just like other vertebrates.
These gill slits are a remnant of our aquatic ancestry and are absent in the adult human form.
The gill slits form during the second and fourth weeks of human development and remain until the Seventh week when they start to regress and are replaced by pharyngeal arches which form the nasal passages and the lower jaw.
The presence of the gill slits suggest that humans, just like other vertebrates, evolved from aquatic species.
In adult humans, these gill slits do not have any significant purpose and appear not to have any significant effect on morphology and functioning of the human body. Thus, the presence of gill slits in a human embryo is a sign of our aquatic ancestry.
