L17 Digestive system I - Digestive System I Oral cavity...

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Digestive System I Oral cavity & teeth
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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. FIRST CATCH YOUR FOOD
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JAWS – larger prey Fish are suction feeders (mostly) or ram feeders (overtake prey with mouth open). 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
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Suction feeders e.g. bony fish Increase in number and motility of bony elements Open – virtually all the elements move (kinetic skull) to rapidly expand the pharynx and generate great suction force Similar suction feeding in aquatic salamanders
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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.
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