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DIGESTIVE SYSTEM

DIGESTIVE SYSTEM. Mrs. Ofelia Solano Saludar Department of Natural Sciences University of St. La Salle Bacolod City. Name the divisions of the coelomic cavities of a fish, amphibian, reptile/bird, mammal.

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DIGESTIVE SYSTEM

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  1. DIGESTIVE SYSTEM Mrs. Ofelia Solano Saludar Department of Natural Sciences University of St. La Salle Bacolod City

  2. Name the divisions of the coelomic cavities of a fish, amphibian, reptile/bird, mammal. Name the linings of the coelom, and the remnants of some of its regions in the mammalian gut. Discuss the phylogeny of the following vertebrate structures: Mouth Teeth Tongue Pharynx Stomach Small intestine Large intestine Describe the ruminant way of eating.

  3. EMBRYOGENESIS • The digestive tract is formed from splanchnic mesoderm. • Epithelial lining is derived from endoderm lining the primitive gut.

  4. Digestive tube differentiates into foregut, midgut, hindgut • Organs arise as diverticula from these regions. • Stomodealandproctodeal invaginations establish an entrance (mouth), and exit (anus or vent)

  5. In all vertebrates except birds & mammals, the COELOM is divided into 2 compartments: the pericardial cavity(heart), & the pleuroperitoneal cavity(viscera). The transverse septum separates the 2 cavities • In cyclostomes, fishes & urodeles, the pericardial cavity is anterior to the pleuroperitoneal cavity. • Due to the posterior descent of the heart, it lies ventral to anterior part of the latter starting with anurans.

  6. With the transverse septum, a pericardial sac forms around the heart. Dorsal to the heart are the pleural cavities. • In birds & mammals, folds join the transverse septum to produce the oblique septumin birds, or the muscular diaphragm in mammals. • Birds & mammals have 4 coelomic cavities: pericardial, 2 pleural, peritoneal

  7. The COELOM has 2 linings: Parietal peritoneum & Visceral peritoneum • The dorsal and ventral mesenteries are the 2 folds of peritoneum • The dorsal mesentery supports the digestive tract in all vertebrates.

  8. The ventral mesentery is absent in adult vertebrates except in the regions of the liver and the gall bladder (falciform ligament) • There are special mesenteries for the gonads and their ducts. • In mammals, the mesentery of the stomach develops a special prolongation called the greater omentum.

  9. DIVISIONS OF THE VERTEBRATE ALIMENTARY CANAL

  10. Accessory organs include the tongue, teeth, oral glands, pancreas, liver, and gall bladder. • Differences in the anatomy of vertebrate digestive tracts is often correlated with the nature and abundance of food: • readily absorbed (e.g., hummingbirds) vs. requiring extensive enzymatic activity (e.g., carnivores) • constant food supply (e.g., herbivores) vs. scattered supply (e.g., carnivores)

  11. Filter-feeding is the oldest craniate method of acquiring food. It is still employed by lampreys, a few jawed fishes, and baleen whales

  12. OROPHARYNGEAL CAVITY • The oral cavity begins at the mouth & ends at the pharynx. • FISHEShave a very short oral cavity, while tetrapods typically have longer oral cavities. • Primary palate- roof of the oral cavity of fishes & amphibians; 20 palate in reptiles & mammals

  13. Nasal passageways open into the oropharyngeal cavity in lobe-finned fishes, and into the oral cavity in tetrapods with primary palate. • Multicellularoral glands open onto the roof, walls & floor of cavity • May contain: venom, saliva, including several enzymes, anticoagulant (lampreys, bats) nutrients in catfish, mucus • Oral glands are scarce in fishes

  14. MAMMALS: • The mouth is specialized to serve as a suckling and masticatory organ (with muscular cheeks). • An oral vestibuleseparates the gums or alveolar ridges from the cheek and the mouth. • Oral cavity leads to pharynx; transition passageway is called the isthmus of fauceswith 2 pillars • A fleshy uvula hangs from the caudal border of soft palate into oral pharynx. • Pharygeal & lingual tonsils are present.

  15. Mammals have 3 pairs of salivary glands that can differ in both the volume & composition of their secretions. • Parotidglands secrete a serous fluid; largest gland in many herbivores • Submaxillary(submandibular) and sublingual glands tend to contain large amounts of mucus; the submaxillary gland of the giant anteater is extremely large and provided with a storage bladder.

  16. In rodents an opening leads from the vestibule into the cheek pouchin which grains maybe stored. It is emptied by shaking the head vigorously. A hamster with mumps!

  17. TONGUE Gnathostomes& primitive amphibians: primary tongue is a simple crescent- shaped elevation in the floor of the oral cavity caused by the underlying hyoid skeleton Most amphibians- primary tongue (hypobranchial eminence) + glandular field (tuberculumimpar) is stuffed with hypobranchialmusculature Reptiles & mammals- primary tongue + glandular field (tuberculumimpar) + lateral lingual swellings (more hypobranchial muscle) Birds- lateral lingual swellings are suppressed & intrinsic muscle is usually lacking

  18. Functions of vertebrate tongues: capturing & gathering food, taste, manipulate fluids & solids in oral cavity, swallowing, grooming, thermoregulation, human speech

  19. Tongue mobility: • Turtles, crocodilians, some birds, & whales- tongue is largely immobilized in the floor of the oral cavity & cannot be extended • Snakes, insectivorous lizards, amphibians, & some birds - tongue is sometimes long and may move in and out of the oral cavity • Mammals- tongue is attached to the floor of the oral cavity (via the frenulum) but can still be extended out of the oral cavity

  20. TEETH • Derivations of the fish dermal armor • Odontoblastsdeposit dentin; crown of enamel from the ameloblasts of the enamel organ, & thecementum(anchors teeth to jaw) • Placoidscales - show gradual transition to teeth at the edge of the jaw

  21. EVOLUTION OF VERTEBRATE TEETH: • Vary in number, distribution, degree of permanence, mode of attachment, & shape • Have tended toward reduced numbers & distribution • Fishes - teeth are numerous & widely distributed in the oral cavity & pharynx • Early tetrapods- teeth widely distributed on the palate; most amphibians & some reptiles still have teeth on the vomer, palatine, & pterygoid bones • Crocodilians, toothed birds, & mammals- teeth are limited to the jaws; diastema are toothless areas on the jaw

  22. SETS OF TEETH • POLYPHYODONT – many sets, typical of most vertebrates • DIPHYODONT– two sets, most mammals • MONOPHYODONT– one set, platypus • Most vertebrates have succession of teeth • Most vertebrates (except mammals) replace teeth in ‘waves’ (back to front; every other tooth) • Mammals generally develop 2 sets of teeth: milk (deciduous) teeth & permanent teeth

  23. HOMODONT- all shaped alike • HETERODONT- varied • Incisors: cutting plant food • Canines: slicing and tearing meat • Molars: grinding grass and other plants

  24. What’s on your menu?

  25. MODE OF ATTACHMENT • ACRODONT – peak of jaws, teleosts • PLEURODONT– inner surface of jaws, amphibians, lizards • THECODONT– sockets, crocodiles, extinct birds and mammals

  26. MOLARS- tricuspid cusps • Secodont- 2 or 3 cusps interconnected by sharp ridges of enamel (carnivores) • Selenodont- sharp, crescentric enamel ridges; side-to-side, forward-backward chewing movements (bovine molars) • Lophodont- long, grinding teeth (proboscidians) • Bunodont- have low rounded cusps instead of sharp edges & pointed cusps (higher primates)

  27. Examples of modified incisors

  28. Specialized fangs (Viperidae) deliver venom which kills prey, as well as starts digestion • In other venomous snakes, teeth are less derived but can deliver venom • Some lizards (Gila monster) deliver neurotoxin • Others have bacteria that takes down prey (Komodo dragon)

  29. Toothless vertebrates: agnathans, sturgeons, some toads, turtles, birds (jaw modified into beaks), & baleen whales.

  30. PHARYNX • Pharyngeal pouches may give rise to gill slits • Fishes– gills & gill slits • Tetrapods- includes: • Glottis (slit leading into the larynx) • Openings of auditory (Eustachian) tubes • Opening into esophagus • Location of tonsils in mammals

  31. Caudad to the pharynx, the wall of the gut are composed of 4 layers:

  32. ESOPHAGUS • A distensible muscular tube connecting the pharynx & the stomach • Fishes- closes so stomach doesn’t become filled with respiratory water • Birds-may have a diverticulum called the crop which has digestive enzymes & allows hoarding of food • Pigeon milk is an esophageal secretion in doves for nestlings

  33. STOMACH Muscular chamber(s) at end of esophagus that serves as storage & macerating site for ingested solids & secretes digestive enzymes Vertebrate stomachs: Cyclostomes- weakly developed; similar to esophagus Fish, amphibians, & reptiles - increasing specialization (more differentiated from the esophagus)

  34. Birds- store large quantities of food temporarily in the crop, releasing it for digestion as needed. • Stomach is divided into: proventriculus(glandular stomach) and ventriculus(muscular stomach, or gizzard) • Lacking teeth, they swallow small stones which lodge in the muscular gizzard (the opening of the pyloric sphincter is very tiny, preventing these gizzard stones from escaping). • As the gizzard churns, the stones grind against the food like numerous tiny millstones. • Birds must constantly replace their gizzard stones by swallowing new gravel.

  35. Mouth – usually • relatively simple • Esophagus – may be widened at • midpoint to form crop (storage area) • Proventriculus – glandular • stomach which is highly acidic 4. Gizzard – thick muscular walls and sandpaper like surface stomach 5. Small intestine – food digestion and absorption • Caecum – bacterial breakdown • of cellulose 7. Large intestine 8. Cloaca – final holding area

  36. RUMINANT STOMACH • Stomach serves mainly as a storage sac for large quantities of vegetable matter. • In the absence of cellulase, little digestion takes place in the small intestine, and food is diverted into a long dead end side branch, the caecum. • The caecum houses a huge population of bacteria, some of which produce enzymes that convert cellulose to sugars, while others manufacture amino acids and other nutrients. • Micromolecules are absorbed directly through the epithelium of the caecum, and the waste material is released into the colon for disposal.

  37. A relatively inefficient system, but since the supply of cellulose is so great, herbivores modified the lower part of the esophagus and the stomach into "four stomachs".

  38. Four compartment stomach • Reticulum – form • food bolus and initiate • regurgitation • Rumen – digestive • and fermentation vat, • contains anaerobic microbes, • site of fatty acid absorption • Omasum – lined by muscular • folds, reduces particle size, • absorbs water (and any • leftover fatty acids) • Abomasum – true • glandular stomach where • bacteria and pathogens • are killed

  39. What do the microbes provide to the ruminants? 1. Digestion of cellulose 2. Provision of organic acids Symbiotic Microorganisms • Provision of protein by • recycling waste nitrogen cellulose • Provision of B vitamins, • essential amino acids X cellulase 5. Detoxify compounds

  40. What do the ruminants provide to the microbes? 1. Housing with reliable heat Symbiotic Microorganisms 2. Adequate nutrition 3. Garbage removal 4. Neutral environment

  41. INTESTINES Located between the stomach & the cloaca or anus Vertebrate intestines are differentiated to varying degrees into small & large intestines

  42. Cartilaginous fishes-have a short, thick, tapering intestine with a spiral valve where food passes slowly as it moves toward the colon. • The colon is not required for resorption of water, since a shark is essentially isotonic with its environment. • Specialized salt glands, which remove excess ocean salts from the blood dump their waste into the colon, where it can be eliminated.

  43. Amphibians - intestines differentiated into coiled small intestine and short, straight large intestine • Reptiles & Birds- coiled small intestines & a relatively short large intestine that empties into the cloaca • Mammals - small intestine is long & coiled and differentiated into duodenum, jejunum, & ileum. The large intestine is often relatively long.

  44. Typhlosoles, coils, villi and CECA increase absorptive area of intestines • Fishes- pyloric & duodenal ceca are common in teleosts; these are areas for digestion & absorption (are not fermentation chambers) • Tetrapods - ceca are present in some herbivores; may contain bacteria that aid in the digestion of cellulose

  45. MIDGUT & HINDGUT FERMENTERS • Enlarged caecum or colon- rodents, horses, zebras, sheep, rhinos, apes, elephants • Break down of cellulose and carbohydrates • Forms short-chain fatty acid • B vitamins- not utilized, lost in feces • Coprophagy– rabbits eat special soft feces

  46. Chamber at end of digestive tract that receives the intestine, & urinary & genital ducts below placental mammals; opens to the exterior via thevent • Lampreys, ray-finned fishes, & mammals (except monotremes)- shallow or non-existent • If no cloaca is present, the intestine opens directly to the exterior via anus. CLOACA

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