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Digestive System I

Digestive System I . FIRST CATCH YOUR FOOD. Oral (buccal) cavity adapted to the way food is gathered and type of food ingested. Tunicates, cephalochordates, lamprey larvae are jawless and filter feeders .

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Digestive System I

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  1. Digestive System I

  2. FIRST CATCH YOUR FOOD Oral (buccal) cavity adapted to the way food is gathered and type of food ingested Tunicates, cephalochordates, lamprey larvae are jawless and filter feeders. Water drawn in by cilia, expansion of buccal cavity etc. Food particles trapped in mucous, mucous moves down gut by ciliary action.

  3. JAWS – larger prey Fish are suction feeders (mostly e.g. bony fish) or ram feeders (overtake prey with mouth open e.g. sharks). Open – virtually all the elements move (kinetic skull) to rapidly expand the pharynx and generate great suction force Similar suction feeding in aquatic salamanders http://www.youtube.com/watch?v=Bs1wv2x_VrI

  4. Sharks – combination of suction and ram-feeding • Open = • Epaxial muscles lift head • hypaxial muscles • hyoid muscles • mandibular muscles • Lower jaw to produce enormous gape. • Some enlargement of pharynx to produce suction

  5. Close http://www.youtube.com/watch?v=yp9YKEO9e1w&feature=related

  6. TERRESTRIAL VERTS One of the major changes in evolution onto land was feeding mechanism. No water to suck in. Co-ordinated movements of mandible and tongue replace it. 4 phases of feeding cycle in all terrestrial verts: 1. Slow opening Kinetic skull - transverse hinge across skull. Pterygoid muscles move pterygopid bones forward & snout lifts up. Slight lowering of mandible

  7. 2. Fast opening Sudden opening to max gape – depressor mandibulae, mandibulohyoideus 3. Fast closing Mandible brought back into position –adductor mandibulae

  8. 4. Slow closing/power stroke Crushing, cutting, slicing of prey The champions of cranial kinesis

  9. Cranial kinesis in birds, allows a good repertoire of abilities for different foods, shock absorption for woodpeckers.

  10. MAMMALS – same 4 phases, NON-KINETIC SKULLS. New muscles e.g digastric (opening) and temporalis (closing), new movements – grinding, cutting, depending on carnivore or herbivore

  11. MUSCULAR TONGUE – tetrapods – very important for moving and swallowing food Derived from several areas of floor of pharynx Often rough e.g. cats Often used in food gathering – frogs, salamanders, lizards, ant-eaters http://www.youtube.com/watch?v=C9cITqEbT7o

  12. Tongue also site of tastebuds Snakes – detects olfactory cues Speech!

  13. NOW KEEP IT/CUT IT UP -TEETH Homodont Mammals - heterodont

  14. START TO DIGEST IT - ORAL GLANDS Fish don’t have them except for occasional mucus secreting cell Lampreys have pair of glands that secrete anti-coagulant. Terrestrial verts have well developed salivary glands. SALIVARY GLANDS Exocrine glands, eccrine secretion Modified in some snakes to produce neurotoxins & vampire bats to produce anti-coagulants Produce saliva = lubricates, moistens, begins digestion (a-amylase), antiseptic (IgA & lysozyme)

  15. mandibular • sublingual • parotid • Some species have • zygomatic, buccal, • molar

  16. Different glands have different serous:mucous proportions • serous cell – dark staining, produces a watery, thin secretion • mucus cell – pale staining, produces a thick secretion

  17. Secretions stored in cytoplasm until signal to release, then released by eccrine

  18. ESOPHAGUS – function - conduction Usually a simple tube to conduct food from pharynx to stomach, quite muscular. Mostly short in amphibians & reptiles, longer in amniotes as the neck gets longer Sometimes specialised.

  19. Grain & seed-eating birds – esophagus = crop, sac serves to store and soften, produces milky secretion for young. Hoatzin has a fermentation chamber to break down cellulose. Egg eating snakes – esophagus crushes the egg

  20. Stratified squamous epithelium –cornified for protection Skeletal muscle at top, mixed in the middle, smooth muscle at bottom Submucosal glands for lubrication protective

  21. STOMACH – function – mechanical & chemical breakdown Tunicates, amphioxus, hagfish, lamprey – NO stomach. May have been primitive craniate condition and stomach evolved when feeding became intermittent (see next slide). HCl production could have been for killing bacteria and preserving food for storage. Stomach secondarily lost when food is very small particles as in lungfish, carp-like fish.

  22. Intermittent feeders!

  23. Usually J-shaped, but straight in slender long bodies (eels, snakes). Has different regions – fundus, body & pylorus Pyloric sphincter keeps food in until it has been mechanically & chemically broken down. body fundus Pyloric sphincter

  24. How does it mechanically & chemically digest? 1. 3 layers of muscularis externa RUGAE

  25. 2. Gastric pits = secretory

  26. GASTRIC PITS Mucous cells (mucous) Parietal cells (0.1M HCl) Peptic cells (pepsin)

  27. Mucous cells (mucous) Parietal cells (0.1M HCl) Peptic cells (pepsin)

  28. Variations: • chitinase produced by amphibians, reptiles, birds • renin (curdles milk) produced by young mammals • GIZZARD from posterior stomach in some fish, some reptiles and all birds, proventriculus from anterior stomach in birds Gizzard contains stones for grinding – no teeth!

  29. Herbivores Plant food abundant and easy to ‘catch’ but very poor in energy & protein content. Need large volumes and slow passage to digest it – alter STOMACH OR COLON Hippos, giraffes, camels, ruminants have large multi-chambered stomachs

  30. Stomach = rumen, reticulum, omasum, abomasum. Only abomasum has glands, rest have stratified squamous like esophagus. Bacteria & protozoa produce cellulase, ferments cellulose to organic acids, CO2, methane. Cow = 200L methane/day (147kg methane/yr) Ruminates

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