Argenzio R A, Stevens C E
Proc Nutr Soc. 1984 Jan;43(1):13-23. doi: 10.1079/pns19840022.
The rumen and the mammalian large intestine are similar in many respects. Microbial protein appears to be synthesized and degraded in the digesta of both organs in a comparable manner. The VFA end-products of carbohydrate fermentation are produced in similar concentrations. Digesta pH is maintained with buffer added by the saliva or ileal fluid, HCO3 released into the lumen and rapid absorption of the organic acids. VFA are absorbed at equivalent rates by rumen epithelium and large intestinal mucosa. Over-production of VFA produces similar adverse effects. There is a considerable amount of species variation in the relative length and volume as well as the extent of sacculation of the large intestine. The caecum is the primary site for retention of digesta and microbial fermentation in the large intestine of rabbits, rodents and a few other species. However, the proximal colon is the major site of retention and fermentation in most mammals. Absorptions of Na and VFA appear to account for absorption of most of the water removed during passage of digesta through the large intestine. A relatively slow rate of Na absorption and release of HCO3 appears to provide the fluid and buffering capacity needed for efficient microbial digestion in the rumen and in the large intestine of some species. A more rapid absorption of Na by the large intestine of other species would aid in the conservation of Na and water. The many similarities between the large intestine and the rumen suggest that further comparison can provide additional information on both the function and diseases of these two organs. The rumen has proved to be accessible to a variety of procedures useful for the study of microbial digestive processes and its epithelium has provided a non-glandular tissue for studies of inorganic ion transport as well as the transport and metabolism of VFA. Comparative studies of the large intestine also can provide a better understanding of the functions and malfunctions of the human large intestine. The pig and some species of monkey would appear to be most suitable for examining the effects of diet and carbohydrate malabsorption. The equine large intestine provides a good system for studying events, such as those associated with the recycling of nitrogenous compounds. Furthermore, as demonstrated by comparative studies of the kidney and other organs, a great deal of information can be gained through examination of the various mechanisms that have been developed to serve similar functions.
瘤胃和哺乳动物的大肠在许多方面相似。微生物蛋白似乎在这两个器官的消化物中以类似的方式合成和降解。碳水化合物发酵产生的挥发性脂肪酸（VFA）终产物浓度相似。消化物的pH值通过唾液或回肠液添加的缓冲剂、释放到肠腔中的HCO₃以及有机酸的快速吸收来维持。瘤胃上皮和大肠黏膜对VFA的吸收速率相当。VFA产生过多会产生类似的不良影响。大肠的相对长度、体积以及袋状化程度存在相当大的物种差异。盲肠是兔子、啮齿动物和其他一些物种大肠中消化物滞留和微生物发酵的主要部位。然而，在大多数哺乳动物中，近端结肠是滞留和发酵的主要部位。钠和VFA的吸收似乎是消化物通过大肠时去除的大部分水分吸收的原因。相对较慢的钠吸收速率和HCO₃的释放似乎为瘤胃和某些物种大肠中高效的微生物消化提供了所需的液体和缓冲能力。其他物种大肠对钠的更快吸收有助于钠和水的保存。大肠和瘤胃之间的许多相似之处表明，进一步比较可以提供关于这两个器官功能和疾病的更多信息。事实证明，瘤胃适用于各种有助于研究微生物消化过程的程序，其上皮为无机离子转运以及VFA的转运和代谢研究提供了一种非腺性组织。对大肠的比较研究也可以更好地理解人类大肠的功能和功能失调。猪和某些种类的猴子似乎最适合研究饮食和碳水化合物吸收不良的影响。马的大肠为研究诸如与含氮化合物循环相关的事件提供了一个良好的系统。此外，正如对肾脏和其他器官的比较研究所表明的，通过研究为实现类似功能而发展出的各种机制，可以获得大量信息。
