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Gastrointestinal tract
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Parts of a Chicken Digestive Tract

Avian Digestive System

Around 51 species are thought to occur in the country. Some 16 species have been recorded in Etosha National Park. They spend most of the year underground in Etosha in dried mud, waiting for the next rainy season. None of them are truly aquatic as they do not depend on water throughout the year. All species avoid the pan as it is too salty. The Giant African Bullfrog is the most commonly observed, but only in periods of brief rain to breed.

Once they are above the surface the race is on to consume enough food to sustain them through the dry winter months. Frogs are cannibals though and can swallow any animal it can fit into their mouths.

Other species found in Etosha include the bushveld rain frog, ornate frog and Namibia's rarest, the spotted rubber frog.

Amongst the leopard and mountain zebra tracks of the Naukluft Mountains, amphibians are common. River frogs abound amongst the fountains and pools of crystal-clear water.

Large tadpoles are more easily observed than adults and the sound of marbled rubber frog precedes their appearance. Common platanna reside in remaining Naukluft pools or in the ephemeral Tsondab River.

Widely distributed and close to the dunes is the tremelo sand frog. The desert rain frog is an inhabitant of the Sperrgebiet, one of Namibia's true surviving wilderness areas. Those fortunate to have lived and worked there can appreciate this vast stretch of the Namib Desert. Banned for public access due to diamond mining restrictions, the rather unusually attractive desert rain frog can emerge form their underground hide-outs for short winter periods when the winds have died.

They enjoy cooler temperatures and take advantage of the seasonal moisture. Almost all frogs have the same body structure less for variable size and colour differences. Females are invariably larger than males.

Front legs are short, hind legs are large and the body and head are flat and bereft of a neck. The tongue is attached to the front of the mouth, a feature that allows them to flick it out quickly to capture prey. They have internal organs such as a heart, liver, lungs and kidneys and although frogs breathe by lungs, they also breath through their skin.

The skin is thin and moist and many species have poison glands in their skin which irritates an attackers mouth, causing the predator to release the frog. There is only 1 species of frog that has hair the African hairy-frog, what else? With such large eyes, you would expect frogs to have good eyesight. Their eyes bulge out enabling them to see in almost any direction to capture food and stay safe. Frogs that hunt at night have a better sense smell than those that don't and they have a delicate sense of touch, particularly when in water.

Tongues and mouths have numerous taste buds enabling them to spit out bad-tasting food. Species such as the painted reed frog are very beautiful. Unfortunately frogs have been branded as cold and slimy, ugly and repulsive but a different opinion can be formed if they are handled and studied a bit. There are no poisonous or dangerous frogs in the country and you won't catch warts from picking up a toad either! Frogs are difficult to recognize. They make distinctive sounds, as do birds, calling out to females in the mating season in a louder voice than that of a female.

To find a frog it is best to go out at night or in the rain with a torch. This is not advisable if you in the Okavango Delta when other potentially dangerous nocturnal creatures are around doing the same thing less the torch but many species are likely to occur in the vicinity of lodges and camps. So after your traditional early morning or late afternoon game drive in Etosha National Park or Naukluft National Park, it might be possible to go on an accompanied night 'frogging safari'.

There are 3 stages in the life of a frog. Egg, tadpole and a 4-limbed adult. They possess both renal and hepatic portal circulations, and predominantly excrete ammonia, urea, or uric acid depending on their evolutionary adaptations. Their RBCs are nucleated, and their metabolic rates are lower than those of mammals. All reptiles exhibit ecdysis—a normal process by which the outer skin is periodically shed. Diurnal species require broad-spectrum light for vitamin D 3 synthesis and calcium homeostasis.

Fertilization is internal, and females may produce eggs oviparous or live young ovoviviparous. Reptiles are not considered highly social creatures, and multiple-male groups can lead to intraspecies aggression. Single-male, multiple-female groupings can work well for certain species, but the solitary reptile is often the healthiest pet.

The life span of many reptiles can exceed 10—20 yr, requiring a longterm commitment from owners. Reptiles possess a common cloaca, which receives the lower GI, reproductive, and urinary tracts. In addition, lungs are simpler and composed of vascular pockets, more like a cavitated sponge than alveoli. Lizards and chelonians are quadrupeds and have a familiar pentadactyl limb arrangement. Reptiles lack a true diaphragm; in many species, all organs are contained within a single coelomic cavity.

Boas and pythons are primitive snakes and have both left and right lungs; however, other snakes lack a developed left lung. Squamates have incomplete tracheal rings, and males have paired copulatory organs hemipenes. The chelonians are characterized by their shell, which comprises a dorsal carapace and ventral plastron. The internal organs are separated by two thin membranes. The heart is located within a cardiac membrane, while the lungs are dorsad and separated from the remaining viscera by a postpulmonary membrane or septum horizontale.

Chelonians have complete tracheal rings, and males have a single copulatory phallus. Treatment is with praziquantel , repeated in 2 wk. Plerocercoids of the genus Spirometra may be found as soft swellings in the subcutis. These larval stages may be removed surgically.

Nematodes are found in all orders of reptiles, and several genera are important. Strongyloides spp frequently inhabit the intestinal tract of reptiles; larvae are seen in the respiratory tract and respiratory exudate. In snakes, the larvae have been seen within granulomas distributed throughout the body wall, suggesting that the larvae may be able to penetrate the skin.

Overwhelming parasitism is common when poor hygiene results in highly contaminated environments. Rhabdias and related species have been found in the lungs of a variety of snakes; embryonated ova may be found in the oral cavity and in lung aspirates.

Embryonated ova and free larval forms may be seen in the feces. Larvae resembling Rhabdias also have been seen in the gingiva of snakes with stomatitis. Infections often are subclinical but may be associated with secondary bacterial pneumonia. In severe cases, death may result. Stomach worms of the genus Physaloptera are seen in lizards.

Gastric ulceration may occur in severe infections. Ova are elliptical and may be embryonated. Numerous snakes are infected by Kalicephalus spp. This hookworm, capable of transcutaneous infestation, prefers the upper GI tract and causes erosive lesions at sites of attachment. Ova are similar to those of Physaloptera spp.

Large granulomas caused by the above species have also caused GI obstruction in snakes. Ascarids frequently infect reptiles. Ova are similar to those of ascarids from mammalian hosts. Severe lesions and death may be seen in infected snakes. Clinically infected snakes frequently regurgitate partially digested food or adult nematodes and are anorectic.

The major lesions are large granulomatous masses in the GI tract; they may abscess and perforate the intestinal wall. Many other nematode species may be found in reptiles.

Capillarid, trichurid, and oxyurid ova may be found on fecal examination. The nonpathogenic larval and oval forms of parasites of prey items eg, Syphacia obvelata , the mouse pinworm may be found when infected prey is consumed. Treatment should be attempted when evidence of parasitism is present. Some larval forms of nematodes are suspected or confirmed to penetrate the skin eg, Strongyloides and Kalicephalus , bypassing the oral reinfection route.

The subtle nature of reinfection by this route often goes unnoticed until the reptile is overwhelmed by parasites. Close attention to the immediate removal of excreta and fastidious sanitation help reduce parasite burdens in captivity. Dermal lesions caused by the spirurid worm Dracunculus spp may be seen. Numerous species of spirurids infect the mesentery, coelomic cavity, and blood vessels. These worms require a mechanical vector, so their incidence is reduced in captive-bred reptiles or in reptiles that have been in captivity longterm.

Pentastomes are found in a wide variety of reptiles, with variable pathogenicity. Pentastomid infections are occasionally associated with pneumonic signs, but these primitive arthropods can inhabit any tissue, and symptoms will vary with their migration path and tissues responses. Pentastomes were initially found primarily in tropical poisonous snakes; however, as more necropsies on reptiles were performed, more were found.

Necropsy results from 88 bearded dragons showed that 11 were infested with pentastomes. The most novel approach has been to endoscopically locate and mechanically remove all the adult pentastomes. Recognition of pentastomal infestations is important, because these parasites are thought to present a zoonotic risk. Numerous protozoans are found on reptiles; most are harmless commensals.

The most serious protozoal pathogen of reptiles is Entamoeba invadens.

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