Abstract
Abstract The purpose of this study was to describe the structure of the midgut (hepatopancreas and intestine) in the endemic species, Macrobrachium carcinus. Thirty specimens were collected, and the midgut was fixed in Bouin's solution for histological and histochemical analyzes by light microscopy. The hepatopancreas consists of two lobes that connect to the end of the stomach by primary ducts, which originate secondary tubules or hepatopancreatic ducts, that branch into hepatopancreatic tubules. The hepatopancreatic duct presents a columnar epithelium composed of R- and F- cells with evident brush borders for absorption and storage. The hepatopancreatic tubule is lined by epithelium with five cell types (E, F, R, B, and M). The distal region presents all cell types, with a predominance of E-cells that correspond to epithelial renewal. The middle region presents F- and B- cells, characteristic of extracellular and intracellular digestion. The proximal region, with B- and R- cells, performs the final digestion, storage, and extrusion of the cells with waste material. The intestine is lined by a single cell type with an evident brush border, suggesting luminal absorption. This cellular arrangement along the length of the midgut proposes distinct morpho-functional characteristics of digestion, absorption, and storage in this species.
Highlights
The digestive system of decapod crustaceans comprises an internal tube subdivided into three parts according to their embryological origin: the foregut and the hindgut originate from the ectodermal layer, and the midgut originate from the endodermal layer in decapods (McLaughlin, 1983; Felgenhauer, 1992; Icely and Nott, 1992; Ceccaldi, 1998; Sonakowska et al, 2015)
Each primary duct divides into the secondary tubules or hepatopancreatic ducts (Fig. 1D, E) that branch into the hepatopancreatic parenchyma and give rise to numerous blind ending hepatopancreatic tubules
Histological and histochemical characteristics of the hepatopancreatic ducts The hepatopancreatic ducts or secondary tubules are lined with columnar epithelium, which is supported by a thin layer of connective tissue that presents isolated muscle cells in circular and longitudinal arrangements (Fig. 1F)
Summary
The digestive system of decapod crustaceans comprises an internal tube subdivided into three parts according to their embryological origin: the foregut (esophagus and stomach) and the hindgut originate from the ectodermal layer, and the midgut (hepatopancreas and intestine) originate from the endodermal layer in decapods (McLaughlin, 1983; Felgenhauer, 1992; Icely and Nott, 1992; Ceccaldi, 1998; Sonakowska et al, 2015). The hepatopancreas occupies a large part of the cephalothorax and projects into the abdomen in some species This organ has great relevance for crustaceans, since it is directly involved in the synthesis and secretion of digestive enzymes and, subsequently, in absorption, nutrient assimilation and waste excretion (Barker and Gibson, 1977; Gibson and Barker, 1979; Vogt et al, 1985). It stores important nutrients, such as lipids, glycogen and other organic and inorganic compounds (Felgenhauer, 1992). These compounds are transported to other organs and used for body growth as well as for the development and maturation of sexual structures (Al-Mohanna and Nott, 1989)
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