< back to Topics &
Species lists
> Reference list
THE DIGESTIVE SYSTEM OF
VERTEBRATES
TOPIC: Anatomy of the gastrointestinal tract
Figure 5.1. Digestive tracts of fish: sea lamprey (Petromyzon marinus), chub (Leuciscus cephalus), pike (Esox lucius), trout (Salmo fario), eel (Anguilla anguilla). Articulated jaws are absent in cyclostomes, such as the lamprey, and located in the pharynx (1) of some species such as the chub. The esophagus (2) varies in length and the stomach is absent in cyclostomes and some advanced species, such as the chub. Where present, the stomach (3) may be straight (pike), U-shaped (trout), or Y-shaped with a gastric cecum (eel). The absorptive surface and digesta retention time of the midgut (4) is increased by a spiral valve (5) or pyloric ceca (6) in a number of species. (From Harder 1975a.) < go to CD Chapter 5
Figure 5.2. Digestive strategies of herbivorous marine fish. Surgeonfish and parrotfish are browsers. Mullet and sea bass are grazers. Shaded areas indicate the gizzard-like stomach of the mullet, pyloric ceca of surgeonfish and sea bass, and two regions of sphincters in distal intestine the sea bass (Modified from Horn 1989.) < go to CD Chapter 5
Figure 4.5. Adaptations of the nephron and hindgut in relation to habitat The nephrons of fish, amphibians, reptiles, and birds are limited in their ability to concentrate urine. Urine is excreted into the cloaca of amphibians, reptiles, and birds and refluxed into the hindgut, which aids in the recovery of electrolytes and water from the urine and digesta. Microbial digestion of uric acid also aids in the conservation of nitrogen. The majority of mammals excrete their digesta and urine separately. Recovery of urinary electrolytes is aided by the kidney’s loop of Henle. Nitrogen conservation is aided by diffusion of urea into the intestine where it is digested by hindgut microbes into ammonia and absorbed. (Modified from Smith 1943 by Stevens 1977). < go to CD Chapter 4
Figure 5.3. Gastrointestinal tract of two adult amphibians. Body length in this and the similar drawings of other species represents distance from the most anterior region of the mouth to the anus. (From Stevens & Hume 1995.) < go to CD Chapter 5
Figure 5.4. Gastrointestinal tracts of a carnivorous caiman and snake, an omnivorous turtle, and a herbivorous tortoise and lizard. Note the cecum, larger volume, and greater relative length of the herbivore hindgut, and the baffles provided by projections of tissue into the cecum and colon of the iguana. (From Stevens & Hume 1995.) < go to CD Chapter 5
Figure 5.5. Gastrointestinal tracts of a hawk, budgerigar, and chicken. The hawk drawing also shows the lumen surface of the crop, proventriculus and gizzard. Ceca are small in most carnivores, such as the hawk, and absent in some species, such as the budgerigar, but highly developed in the chicken (From Stevens & Hume 1995.) < go to CD Chapter 5
Figure 5.6. Gastrointestinal tracts of avian herbivores. The crop is absent in the ostrich, but expanded in the grouse and rhea, and both the crop and distal esophagus are expanded in the hoatzin. Note the well-developed ceca in the grouse and rhea, and extremely long colon of the ostrich. (From Stevens & Hume 1995.) < go to CD Chapter 5
Figure 5.8. Examples of mammal stomachs that contain a region of stratified squamous epithelium. (Modified from Stevens & Hume 1995) < go to CD Chapter 5
Figure 5.9. Examples of mammals with an expanded forestomach. E designates esophageal entrance, P designates pylorus, 1 designates omasum, and 2 designates abomasum. (Modified from Stevens & Hume 1995.) < go to CD Chapter 5
Figure 5.10. The large intestine of the human, dog, pig, ox, and horse. Note that the cecum and segments homologous to the ascending, transverse and descending colon of humans vary in their relative length, shape, and volume, and that the proximal or "ascending" segment is extended and expanded in many mammals. (Modified from de Lahunta and Habel 1986.) < go to CD Chapter 5
Figure 5.11. Gastrointestinal tracts of a carnivorous monotreme, cetaceans, and Insectivora. (From Stevens 1980; Stevens & Hume 1995.) < go to CD Chapter 5
Figure 5.12. Gastrointestinal tracts of carnivorous Chiroptera, and Carnivora. (From Stevens 1980; Stevens & Hume 1995.) < go to CD Chapter 5
Figure 5.13. Gastrointestinal tracts of carnivorous Carnivora, marsupials, and primate. (From Stevens 1977; Stevens & Hume 1995.) < go to CD Chapter 5
Figure 5.14. Gastrointestinal tracts of omnivorous species of Insectivora, Carnivora, and Marsupialia. (From Clemens 1980; Stevens & Hume 1995.) < go to CD Chapter 5
Figure 5.15. Gastrointestinal tracts of omnivores species of edentate, rodent, and primates. (From Argenzio & Southworth 1974; Stevens 1980; Stevens & Hume 1995.) < go to CD Chapter 5
Figure 5.16. Gastrointestinal tracts of omnivorous primates, and artiodactyla. (From Argenzio & Southworth 1974; Wrong et al. 1981; Stevens & Hume 1995.) < go to CD Chapter 5
Figure 5.17. Gastrointestinal tracts of herbivorous marsupial, primate, perissodactyls, and proboscidean colon fermenters. (From Stevens 1977; Clemens & Maloiy 1982; and Stevens & Hume 1995.) < go to CD Chapter 5
Figure 5.18. Gastrointestinal tracts of herbivorous rodent, lagomorph and marsupial cecum fermenters. (From Stevens 1977; Clemens 1977; and Stevens & Hume 1995.) < go to CD Chapter 5
Figure 5.19. Gastrointestinal tracts of herbivorous edentate, marsupial, primate, and artiodactyl foregut fermenters. (From Stevens 1977; 1980; 1983; Stevens & Hume 1995.) < go to CD Chapter 5
Figure 5.20. Combination foregut and hindgut fermenters (Hyrax from Clemens 1977. Others from Stevens & Hume 1995.) < go to CD Chapter 5
< top of page