Faculty of Biosciences, University of Heidelberg, Im Neuenheimer Feld 234, 69120, Heidelberg, Germany.
Zoology (Jena). 2021 Aug;147:125945. doi: 10.1016/j.zool.2021.125945. Epub 2021 Jun 10.
The ∼15.000 decapod crustaceans that are mostly omnivorous have evolved a structurally and functionally complex digestive system. They have highly effective cuticular chewing and filtering structures in the stomach, which are regularly renewed by moulting. Decapods produce a broad range of digestive enzymes including chitinases, cellulases, and collagenases with unique properties. These enzymes are synthesized in the F-cells of the hepatopancreas and are encoded in the genome as pre-pro-proteins. In contrast to mammals, they are stored in a mature form in the lumen of the stomach to await the next meal, and therefore, the enzymes are particularly stable. The fat emulsifiers are fatty acyl-dipeptides rather than bile salts. After mechanical and chemical processing of the food in the cardiac stomach, the chyme is filtered by two unique filter systems of different mesh-size. The filtrate is then transferred to the hepatopancreas where the nutrients are absorbed by the R-cells, mostly via carriers, resembling nutrient absorption in the small intestine of mammals. The absorbed nutrients are used to fuel the metabolism of the hepatopancreas, are supplied to other organs, and are stored in the R-cells as glycogen and lipid reserves. Export lipids are secreted from the R-cells into the haemolymph as high density lipoproteins that mainly consist of phospholipids. In contrast to mammals, the midgut tube and hindgut contribute only little to food processing and nutrient absorption. The oesophagus, stomach and hindgut are well innervated but the hepatopancreas lacks nerves. Hormone cells are abundant in the midgut and hepatopancreas epithelia. Microorganisms are often present in the intestine of decapods, but they are apparently not essential for digestion and nutrition.
大约 15000 种十足目甲壳动物大多为杂食性，它们进化出了结构和功能复杂的消化系统。它们的胃中有高效的角质咀嚼和过滤结构，这些结构通过蜕皮定期更新。十足目动物产生广泛的消化酶，包括几丁质酶、纤维素酶和胶原酶，具有独特的性质。这些酶在肝胰腺的 F 细胞中合成，并以前原蛋白的形式编码在基因组中。与哺乳动物不同的是，它们以成熟形式储存在胃腔中，等待下一顿饭，因此，这些酶特别稳定。脂肪乳化剂是脂肪酸二肽，而不是胆汁盐。在心胃中对食物进行机械和化学处理后，食糜通过两个独特的不同网眼大小的过滤系统进行过滤。滤液然后被转移到肝胰腺中，营养物质被 R 细胞吸收，主要通过载体，类似于哺乳动物小肠中的营养吸收。吸收的营养物质用于为肝胰腺的新陈代谢提供燃料，供应给其他器官，并以糖原和脂质储备的形式储存在 R 细胞中。出口脂质作为主要由磷脂组成的高密度脂蛋白从 R 细胞分泌到血液中。与哺乳动物不同的是，中肠管和后肠对食物加工和营养吸收的贡献很小。食管、胃和后肠都有很好的神经支配，但肝胰腺没有神经。激素细胞在中肠和肝胰腺上皮中丰富。微生物通常存在于十足目动物的肠道中，但它们显然不是消化和营养所必需的。
