Digestive System Midgut

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2.5.1. Digestive system

The digestive tract of the penaeidae shrimp is divided into three regions (Figure 4): namely, foregut, midgut and hind gut. The embryological origin of the epithelial cells in the foregut and hindgut are derived from the ectodermal and covered with cuticle. However, the epithelial cells of the midgut are derived from the entodermal origin. This region of the gut is lack of cuticle; however, it is lined by a peritrophic membrane (Lovett and Felder, 1989, 1990a, 1990b). Figure4. The digestive tract of P. vannamei (https://nutriad.com/2015/01)
Key: E= Esophagus, GM=gastric mill, HP= hepatopancreas, MG=mid gut, HG=hind gut, and A= anus

The foregut starts at the mouth which is located rostro-ventrally in the cephalothorax
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This gut is composed of the anterior midgut ceca, posterior midgut, hepatopancreas (digestive gland) and intestine (midgut trunk) (Icely and Nott, 1992, Martin and Chiu, 2003). The peritrophic membrane, epithelium, basal lamina, haemocyte layer (granulocytes), and connective layer of the circular and longitudinal muscles and the outer intima are composed within the wall of the midgut (Martin and Chiu, 2003). The peritrophic membrane is produced by the epithelial cells in the midgut. The function of the membrane is to protect the gut from mechanical damage, pathogens, toxins and other harmful chemicals (Lehane, 1997). The hepatopancreas covers a large part of the cepahalothorax, and it is the master digestive gland. The main functions of this gland are the synthesis and secretion of digestive enzymes, absorption of nutrients, storage of mineral reserves and organic substances, metabolism of lipid and carbohydrate and calcium absorption (Johnson, 1980, Icely and Nott, 1992, Ceccaldi, 1997, 1998). The water and ion balance of the shrimp are also regulated by the epithelial cells of the digestive system (Ahearn et al., 1999, Wheatley,

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