Morphologie fonctionnelle du tube digestif d'Holothuria tubulosa Gmelin (Echinodermata,Holothuroidea)
Massin, C. (1980). Morphologie fonctionnelle du tube digestif d'Holothuria tubulosa Gmelin (Echinodermata,Holothuroidea), in: Jangoux, M. (Ed.) Proceedings of the European Colloquim on Echinoderms, Brussels, 3-8 September 1979 = Actes du Colloque Européen sur les Echinoderms, Bruxelles, 3-8 septembre 1979. pp. 261-270, plates
In: Jangoux, M. (Ed.) (1980). Proceedings of the European Colloquim on Echinoderms, Brussels, 3-8 September 1979 = Actes du Colloque Européen sur les Echinoderms, Bruxelles, 3-8 septembre 1979. A.A. Balkema: Rotterdam. ISBN 90-6191-077-3. XVIII, 428 pp., meer
The digestive tract of Holothuria tubulosa is roughly divided in three loops, from mouth to anus: the foregut, the midgut and the hindgut.The first part of the foregut or oesophagus (part before the muscular inversion point) is mainly a stocking zone of sand. The oesophagus is characterized by a cuticule covering the digestive epithelium. Its wall is greatly extensible. The second part of the foregut, just after the oesophagus, is characterized by special cells with mixed secretions (proteins and glucids). These cells secrete a gel spilling in the alimentary canal. The extra-cellular enzymes could be embedded in such a gel, preventing their dilution in the intestinal lumen. This gel could also lubricate the digestive tract and protect the digestive cells against sand attrition. An apical mucus in the lining cells characterizes the midgut and the hindgut. This mucus is supposed to protect cells against sand attrition. Midgut and especially the first part of the hindgut possess typical mucus cells which presumably elaborate the mucus coating of the fecal pellets. The end part of the hindgut accumulates the fecal pellets and would be able to eliminate some metabolic wastes. The lining cells of the foregut (including oesophagus), midgut and hindgut (mainly first part) are able to absorbe organic matter and assume the intracellular digestion. The product of intracellular digestion by the lining cells is supposed to pass in the underlaying hemal system. The possible origins of extracellular enzymes are briefly discussed.
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