Descripción morfológica e histológica del aparato digestivo del calamar Illex argentinus (Cephalopoda: Ommastrephidae)
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The morphology and histology of the digestive tract of the Argentine short-finned squid Illex argentinus are described. The structures involved are the buccal mass, oesophagus, vestibulum, stomach, caecum, intestine, digestive gland and digestive duct appendages. A differential development of the tissular components in relation to the function of each organ is observed. The musculature of the buccal mass, oesophagus and stomach, organs involved in the mechanical degradation of food is strongly developed. This development is weaker in the caecum where enzymatic digestion and absorption take place and in the intestine. For the same reason, the epithelia of the mucosae of the oesophagus and stomach secrete a thick cuticle whereas those of the caecum and intestine are ciliated and mucous-secretory. The oesophagus has a small diameter, the stomach and the caecum have a small volume, but they all share the characteristic of being highly distendable. The caecum is divided in two parts: the spiral portion where the mucosa is folded forming caecal leaflets and the simple caecal sac. The digestive gland is the largest structure of the digestive tract. It is formed by tubules lined with glandular epithelium and has the following functions: enzymes synthesis and secretion, nutrients absorption, storage of lipid reserves and excretion of digestion residues. Each tubule represents a functional unit and is composed of vacuolated cells whose appearance and content vary in relation to the function the gland is accomplishing. The secretion of the digestive gland is conducted to the caecum by the digestive ducts which are surrounded by the digestive duct appendages, a tubulo-alveolar formation that takes part in the absorption processes.