Department of Animal Science, Texas A&M University, College Station, TX, 77843, USA.
Adv Exp Med Biol. 2024;1446:15-38. doi: 10.1007/978-3-031-54192-6_2.
As for other mammals, the digestive system of dogs (facultative carnivores) and cats (obligate carnivores) includes the mouth, teeth, tongue, pharynx, esophagus, stomach, small intestine, large intestine, and accessory digestive organs (salivary glands, pancreas, liver, and gallbladder). These carnivores have a relatively shorter digestive tract but longer canine teeth, a tighter digitation of molars, and a greater stomach volume than omnivorous mammals such as humans and pigs. Both dogs and cats have no detectable or a very low activity of salivary α-amylase but dogs, unlike cats, possess a relatively high activity of pancreatic α-amylase. Thus, cats select low-starch foods but dogs can consume high-starch diets. In contrast to many mammals, the vitamin B (cobalamin)-binding intrinsic factor for the digestion and absorption of vitamin B is produced in: (a) dogs primarily by pancreatic ductal cells and to a lesser extent the gastric mucosa; and (b) cats exclusively by the pancreatic tissue. Amino acids (glutamate, glutamine, and aspartate) are the main metabolic fuels in enterocytes of the foregut. The primary function of the small intestine is to digest and absorb dietary nutrients, and its secondary function is to regulate the entry of dietary nutrients into the blood circulation, separate the external from the internal milieu, and perform immune surveillance. The major function of the large intestine is to ferment undigested food (particularly fiber and protein) and to absorb water, short-chain fatty acids (serving as major metabolic fuels for epithelial cells of the large intestine), as well as vitamins. The fermentation products, water, sloughed cells, digestive secretions, and microbes form feces and then pass into the rectum for excretion via the anal canal. The microflora influences colonic absorption and cell metabolism, as well as feces quality. The digestive tract is essential for the health, survival, growth, and development of dogs and cats.
对于其他哺乳动物来说，狗（杂食性肉食动物）和猫（纯肉食动物）的消化系统包括口腔、牙齿、舌头、咽、食管、胃、小肠、大肠和辅助消化器官（唾液腺、胰腺、肝脏和胆囊）。这些肉食动物的消化道相对较短，但犬齿较长，臼齿的齿数更紧，胃的容量比人类和猪等杂食性哺乳动物更大。狗和猫的唾液α-淀粉酶活性都检测不到或非常低，但与猫不同的是，狗的胰腺α-淀粉酶活性相对较高。因此，猫选择低淀粉食物，但狗可以食用高淀粉饮食。与许多哺乳动物不同的是，用于消化和吸收维生素 B 的维生素 B（钴胺素）结合内在因子是由：（a）狗主要由胰腺导管细胞产生，胃黏膜产生较少；（b）猫仅由胰腺组织产生。氨基酸（谷氨酸、谷氨酰胺和天冬氨酸）是前肠肠细胞的主要代谢燃料。小肠的主要功能是消化和吸收膳食营养素，其次要功能是调节膳食营养素进入血液循环，将内外环境分开，并进行免疫监视。大肠的主要功能是发酵未消化的食物（特别是纤维和蛋白质），并吸收水、短链脂肪酸（为大肠上皮细胞的主要代谢燃料）以及维生素。发酵产物、水、脱落细胞、消化液和微生物形成粪便，然后通过肛门进入直肠排出体外。微生物群影响结肠吸收和细胞代谢，以及粪便质量。消化道对狗和猫的健康、生存、生长和发育至关重要。
