BIOL3030 Lecture Notes - Lecture 14: Fish Gill, Mouth, Gnathostomata
21 Feb 2017
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Document Summary
All vertebrates begin in early life with skin. Didnt evolve until later on (unidirectional gills) After evolution of jaws: agnatha and gnathostomes: true gills evolve. True gill on pharngeal arches: pump water past gill surface. Unidirectional flow: water pumped across in one direction across gill surface. Bucha; past gill tissue out posterior of head. Pouches with volume that gas will come into/leave from. Filaments on an arch emitted from back of arch. On filaents: lamellae: from dorsal and ventral side. Through arch and through filaments throgh lamella: blood coursing in one direction. (oxygen poor) blood and water flow oppose each other. Always generating flow of warer in one direction. Oral cavity expands to draw in water: negative pressue. Posterior gill tissue expands (opercular): more negative pressure than oral cavity. Suctioning action: draw water to opercular cavity as buchal cavity reduces volume and pushes water posteiorirly. Old water expelled in opercular cavity as new ater comes in.
