Anatomy and physiology study guide

Frogs How astonishing Are They

Frogs are assuredly available in the tropic and subarctic regions but majority of the species are found in the tropical rain forests. They form the diverse group of vertebrates and about 5,000 species are known till present. Some species are any way on the verge of extinction. Frogs are separate from the toads as the toads prefer to live in dry habitats and this discrepancy is made on the basis of convergent evolution. The word frog has been derived from an Old English word frogga which means to jump.

Taxonomy

The order Anura encompasses about 4,810 species under 33 families out of which Leptodactylidae includes 1100 species, Hylidae includes 800 species and Ranidae includes 750 species. 88% of the amphibian species are the frogs. All the members of Anura are frogs but those belonging to the family Bufonidae are thought about as true toads. The skin of the frogs is moist and plane while that of the toads is dry and warty except the fire bellied toad Bombina bombina whose skin is slightly warty. Frogs and toads are broadly classified under three suborders. The first one is Archaeobatrachia, which comprises 4 families of primitive frogs. Second is Mesobatrachia, which includes 5 families of more evolutionary intermediate frogs and the third one is Neobatrachia, which is the largest group and contains the remaining 24 families of "modern" frogs,found throughout the world. Neobatrachia is supplementary divided into the Hyloidea and Ranoidea. Some species of frogs can be hybridized assuredly for example the common edible frog Rana esculenta is the hybrid of Pool frog R.lessonae and the Marsh frog R.ridibunda.

Morphology and Physiology

Frogs are quite peculiar among the amphibians. Among the two groups of amphibians, the salamanders and the caecilians they are unusual as the adults lack tail and their hind legs are adapted more to jumping as compared to walking. Their physiology is similar to other amphibians as oxygen can assuredly perforate through their moist skin. This highlight enables them to breathe through their skins. The oxygen is assuredly dissolved in the moist layer of the skin in the form of a film and is passed to the blood from where it is portable later on. The frogs all the time keep their skin moist. This mode of respiration also makes frogs susceptible to the toxins dissolved in water and is responsible for decline of people of unavoidable frog species. Frogs have long hind legs with elongated ankle bones. Their vertebral column is also short comprising of about ten vertebrae followed by a fused tail bone called as coccyx.

The body size of frogs range from 10 mm to 300 mm. The skin loosely covers the body as there is no connective tissue. The texture of the skin may be smooth, warty or folded. They have three eyelids. One is transparent which protects the eyes underwater and the two are translucent to opaque. They have tympanum on either side of the head which helps in hearing. They have pedicellate teeth. Most frogs have teeth only on the upper jaw and vomerine teeth on the roof of their mouth. The teeth are basically for retention the prey in place from where it is swallowed.

Feet and Legs

The legs and feet vary in buildings depending upon the habitat of the frogs either they live on trees, ground, water and in burrows. The frogs are supposed to be very quick to capture their prey and escape from their predators and must be suitably adapted to their environment. Frogs those living in water have webbed toes but the degree of toes to be webbed is directly proportional to the time spent in water by the frog. The African dwarf frog has completely webbed toes as it is completely aquatic whereas Whites tree frog has half webbed toes. The frogs adapted to arboreal mode of life have toe pads located on the ends of the toes for gripping on the vertical surfaces. The pads are made up of interlocking cells that have very small gap between the adjacent surfaces. When the frog applies pressure on the pads the interlocking cells help in gripping the irregular surface. The small gaps between the cells help in gripping by capillary performance and this also allows the frog for pronounce grip on the plane covering also. The ground dwelling frogs lack all the adaptations that are gift in the aquatic ad arboreal frogs. They have very small toe pads and very microscopic or no webbing at all. Some burrowing frogs have a toe extension called the metatarsal tubercle which helps in burrowing.

Jumping

Frogs are generally thought about as exceptional jumper but maybe the best jumpers of all the vertebrates. The Australian rocket frog can leap about 50 times higher than its body distance resulting in jumps of about 2 meters. The acceleration of the jump may be twice as that of gravity. The potential of jump, distance of jump varies with the species. The musculo-skeletal morphology is highly modified for performing the jumping activity. The bones tibia, fibula and the tarsals are fused into a particular strong bone just like the radius and ulna in the forelimbs. The metatarsals are also elongated and help in jumping. The ilium is fused with the sacrum and aids in jumping especially in the Ranids and Hylids and functions as the power victualer for jumping. The elongation of limbs is the basic factor which governs the height as well as the distance of the jump.

The muscular theory is also highly modified according to the habitat of frogs. In contemporary frogs almost all muscles are complex in performing the jumping movements and only few are complex in bringing back the body to its primary posture. The muscles are also greatly enlarged in size and the muscles that are complex in jumping form about 17% of the body mass of the frog. Presently it is hypothesized that the frogs store their vigor by stretching their tendons and use it like spring and release the store vigor in one stroke only.

Skin

Many frogs are reported to store water and oxygen through their skin near the pelvic area. However, the permeable skin is also responsible for water loss. Some tree frogs have a waterproof layer over their skins which help in reducing the water loss. Other frogs also minimize water loss by becoming nocturnal, living under the shades While the daytime and advent out in night for capturing the prey. Some frogs rest in such a way that their skins are in direct caress with each other and this helps in reducing water loss.

Majority of the frog species use camouflage as their prime defensive weapon. Most camouflaged frogs are nocturnal in habit which adds a good source of their survival from the predators. Some frogs have the potential to change colour but they are capable of acquiring shades of only one or two colours like the Whites tree frogs vary in shades of green and brown. Warts and skin folds are generally found in the ground dwelling frogs and the arboreal frogs have plane skin as they can assuredly cover themselves under the leaves. Some forgs change their colour While the day and the night time as the light and moisture article helps in contraction and expansion of the pigment cells.

Poison

Many frogs bear mild poisons that make them unpalatable by their predators. All the toads have poison gland called the parotid gland located behind the eyes on top of the heads. Some poison dart frogs are completely toxic. The chemicals gift the toxins of the frogs may vary from irritants to hallucinogens, convulsants, nerve poisons and vasoconstrictors. Many predators of frogs are capable of protecting themselves from the poisons of frogs. Others together with human beings may be severely affected by the toxins of frog. Some species of frogs gather poison from the ants and the arthropods they eat and furnish an alkaloid that is toxic and this alkaloid is not derived from the food they eat. Some native people of South America excerpt poison from the poison dart frogs also. The alkaloid epibatidine, a painkiller which is derived from the poison dart frogs is 200 times more potent than morphine. Other chemicals that have been isolated from the frogs are opinion to be useful against the rehabilitation of Hiv infection. The dart and arrow poisons are under investigation for use in therapeutic drugs. The skin secretions of some toads contain bufotoxins especially the bufotenin is psychoactive.

Respiration and Circulation

The skin of the frog allows entry of oxygen as well as carbon dioxide. The skin houses large amount of blood vessels. When the frog is underwater the oxygen is absorbed through the skin and is portable directly to the bloodstream. On land lungs are used for respiration. The lungs look as if human lungs but the chest muscles are not complex in respiration an also the frogs lack ribs and diaphragm. While breathing through lungs the frogs take air through the nostrils and compress it at the floor of the mouth and then the compressed air is sent to the lungs.

The heart of frogs is three chambered. In the three chambered heart the oxygenated blood from the lungs and the deoxygenated blood from the tissues enters the atria which are cut off and which later on enters the aorta by spiral valve. The blood ultimately enters the pulmonary artery. The spiral valve prevents the mixing of two types of blood and enables the frog to pronounce higher metabolic rates and remain active. Some frogs are even able to survive in oxygen deficient water also.

Digestion and Excretion

The digestive theory of frogs begins with the mouth. The upper jaw bears teeth called the maxillary teeth which are used for milling the food before swallowing. These teeth are very weak and cannot be used for catching the prey. The frogs use their sticky tongues for catching the prey. The food after milling enters the stomach through esophagus. The food then enters the small intestine where most of the digestion takes place. The pancreas secretes pancreatic juice and the liver produces bile which enters the intestine and mixes with the food and thus the frog extracts nutrients. The food after digestion enters the large intestine where water is absorbed and then the waste products are passed towards the cloaca. All the waste products leave the body through cloaca and cloacal vent.

Nervous System

The fogs bear a highly developed nervous theory consisting of brain, spinal cords and nerves. Many parts of the brain look as if with that of the humans. The medulla oblongata is responsible for controlling the activities of digestion, respiration and other self-operating functions. Cerebellum controls the muscle coordination and body posture. The relative size of cerebrum is smaller in comparison to that of the humans. There are ten cranial nerves and ten pairs of spinal nerves. The ear has semicircular canals that are responsible for balancing and orientation.

Life Cycle

The life stages of frogs are similar to that of other amphibians together with egg, tadpole, metamorphosis and adult. The breeding behaviour of frogs is very piquant as they furnish a mating call in order to attract the female. After mating the female lays thousands of eggs wrapped in a gelatinous covering in water. The eggs are highly vulnerable to predation so frogs use a amount of diverse techniques in order to save their progeny from predators. In the colder atmosphere the embryo is black in colour in order to discharge more heat from the sun which fastens the development of the frog. Some frogs lay their eggs in small packets of leaves which they make in order to save them from the predators and contribute vital moisture to them. In some frogs the tadpoles after hatching directly jump into water. The eggs hatch into tiny tadpoles which have oval bodies and vertically flattened tails. Only one species have semi-terrestrial tadpoles. The tadpoles are completely aquatic and they lack eyelids, lungs, front and hind legs and possess a cartilaginous skeleton. Like fishes the tadpoles also have lateral line system, gills for respiration and tails with dorsal and ventral folds of skin foe swimming. Some species which hatch from the eggs as tiny frogs do not have gills. Tadpoles also lack true teeth but they have keratinized structures in their upper jaws called keradonts and the lower jaw also bears three keradonts surrounded by a horny beak.

The tadpoles feed on algae and diatoms which are filtered by the gills indicating that they are herbivorous. Some species are carnivorous and also show cannibalism. Tadpoles are at the risk of being assuredly caught by the fishes, birds especially the kingfishers, newts and predatory diving beetles. Tadpoles of some species are also toxic to their predators. Some tadpoles have the potential of overwintering and then metamorphosing in the next year. The tail of the tadpole also contains some vertebral structures that give rise to the urostyle in later part of the life and the tail also lacks solid segmental structures but it bears a notochord. When fully developed the tadpole undergoes metamorphosis which includes transition from larval stage to the adult form. Metamorphosis includes many drastic changes that help the tadpole to compose into an adult. These changes contain development of fore and hind limbs, loss of gills and development of lungs and loss of tails. The distance of the intestine also shortens as they transform their feeding habit from herbivorous to carnivorous. The eyes also migrate rostrally and dorsally and are adapted for the binocular foresight as found in the adult frog. The final stage of transformation of a tadpole to the adult frog involves apoptosis which means programmed cell death and loss of tail.

After completing metamorphosis the frogs leave water and start their terrestrial lives and if they are aquatic then they may live in the water as well. almost all species of frogs especially the adults are carnivorous feeding on gastropods, arthropods and annelids. Frogs are also consumed by many mammals and birds. Frogs are also consumed by humans. The median life span of frogs is about 40 years and some species especially those of the temperate region are also known to hibernate While the winters.

Reproduction

When the frogs reach maturity they assemble near a water source which may be a pond of stream. Some also reach back to the places where they were born. While the breeding season the male frog calls a female by a extra sound called the mating call or croaking and it becomes a chorus used by the males to attract the females towards themselves. The mating call is unique for every species. The females do not croak at all. After that the male and female undergo amplexus where the male tightly holds the female with his forelegs. The reproduction is external the female releases the eggs covering her body and the male soon releases a sperm explication over them resulting in the swelling of the eggs which attain a protective covering. The eggs are brown or black with a clear gelatinous covering. Most temperate species reproduce between the late autumn and early spring. Reproducing in the early season ensures good availability of food as well as faster development of the tadpoles.

Parental Care

20% species of frogs show parental care and this topic needs supplementary concern. Some species of poison dart frogs lay their eggs on the forest floor and safe them by continually guarding them and also urinate on them to keep them moist. After hatching the parent carries the eggs to a water retention bromeliad and feeds them on unfertilized eggs. Some frogs safe their eggs by retention them inside their bodies. Some frogs keep their eggs inside their vocal sacs and release the tadpoles after hatching of the eggs.

Call

The sound of some species is so loud that they can be heard from miles away. The call of a frog is unique for a species. Frogs call by passing air through the larynx in the throat which is then amplified by the vocal sacs. Some species lack vocal sacs but can furnish loud calls as they have greatly enlarged buccal cavity acting as the resonance accommodation that amplifies their call. The species of frog that lack vocal sacs and are not able to furnish large calls gather near the flowing water and narrate by other means. The main imagine of producing a call is to attract a female by the male. Males either call singly or in groups. All calls are produced by the males by retention their mouths closed. When frogs are in danger they also furnish a distress call by retention their mouths open resulting in high pitch sound.

Distribution

Frogs are distributed all over the world except Antarctica and many oceanic islands. The diverse people of frogs is gift in the tropical areas as abundance of food is available and the temperature range is suitable according to their need and also they are capable of defending themselves. The people of frogs has declined since 1950s resulting in faultless extinction of 120 species and one third has joined the class of threatened species by 1980s. Habitat loss, change in atmosphere conditions, pollution, infectious diseases together with chytridiomycosis. Many environmental scientists believe that frogs are good biological indicators as they partake actively in the food chain as well as in the food web. Many programmes together with the conservation of frogs have been started since 2007. They have also been shifted to zoos and aquarium in some countries and the year 2008 has been declared as the Year of the Frog. The earliest frogs evolved in the Jurassic (188-213 million years ago). The major evolutionary changes contain shortening of the distance of body and loss of tail. The fossils of frogs have been recorded all over the world except Antarctica.

Uses

Frogs play a very foremost role from commercial point of view. They are a source of food as frog legs are a source of delicacy in China, Philippines and France. Dead frogs are also used for dissection in the schools and colleges for studying the anatomy and physiology but this custom has been banned as the people of frogs is declining. Frogs are also used as model organisms since the history of science. Galvani discovered the association between electricity and nervous theory by studying the physiology of frogs. The human chorionic gonadotropin found in enormous quantities in urine of the pregnant females when injected into the frog Xenopus laevis induce her to lay eggs. Robert Briggs and Thomas King cloned a frog by the technique of somatic cell nuclear change in 1952 and later on through this technique the sheep Dolly was cloned. Frogs are used in the investigate of embryology as they look as if very closely with that of the development of human embryo. Xenopus laevis is a very productive experimental frog used in the concepts of human pregnancy. The genome sequence of X. Leavis is under study and will be completed newest by 2015.

Frogs have also been a part of fairy tales from a long time as they are ugly, clumsy and are thought about very talent. The Moche people of Peru are celebrated for worshiping frogs. We can close that frogs are very foremost in assorted fields of our life.

Posted by lazina at 8:45 AM

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