白鲟消化道形态学与组织学的初步观察

白鲟消化道具有肉食性鱼类的典型特征,其口咽腔结构既适合捕食又适合吞食与滤食水生动物。咽后消化道可分为食道、胃后行支、胃前行支、小肠、瓣肠、直肠与肛门。幽门盲囊似一致密器官,小肠与瓣肠连接处有一特殊淋巴器官,肛门两侧有腹孔。白鲟口咽腔被覆层扁平上皮,上皮内有味蕾分布。咽后消化道组织分层为粘膜(无粘膜肌层)、粘膜下层(小肠及瓣肠前部无)、肌层与外膜。粘膜上皮为单层柱状上皮,由纤毛柱状细胞、一般柱状细胞和杯状细胞组成,其间还散在有颗粒细胞和游走细胞。食道后部与胃的一般柱状细胞为分泌粘液的细胞,肠内的一般柱状细胞为吸收细胞。胃后行支及部分前行支固有膜内有消化腺,其余各部的固有膜为致密层。小肠前中部粘膜形成蜂窝状粘膜窦,无肠腺。除食道前部肌层中有横纹肌外,其余部的肌层均为平滑肌。外膜内结缔组织有的致密有的疏松,外膜表面细胞柱状或立方形或扁平。

PRELIMINARY OBSERVATION ON THE MORPHOLOGY AND HISTOLOGY OF THE ALIMENTARY TRACT OF THE CHINESE PADDLEFISH PSEPHURUS GLADIUS (MARTENS)

The Chinese paddlefish is one of the rare fishes in the world. Just on the ventral surface of the semitranslucent sword-shaped snout, it has an inferior bell-shaped mouth which can protrude for predation. The buccopharyngeal cavity is big with fine teeth located at the floor and roof of the skin. A pair of spiracles are present in the roof as well. The opercular flaps are well-developed and the gill takers are on the sides of the gill arch, forming dense network.Thus, the structure of the cavity is adequate for capturing and filter-feeding. Like most of carnivorous fish, the digestive tract of the Chinese paddlefish is short but complex. It can be divided into esophagus, backward limb of stomach, forward limb of stomach, small intestine, valvular intestine (containing valvula spiralis), rectum and anus. No demarcation line is recognized between esophagus and stomach. The pneumatic cyst attaches and opens to the region of esophagus-gaster transition. Pneumatic duct is not visible outside. Pyloric caecum has no, division or lobes and provides hardly space for chyme. In the conjunction between small and valvular intestine, a particular lymphatic organ is present. There are abdominal pores on each side of the anus and a cloacal orifice on the back extremity. Goezia (Goezia) sp. and a species belonging to acanthocephala parasites in the tract have been found also.The buccopharyngeal cavity is covered by stratified squamous epithelium in which there are mucus-secreting cells and granular cells. Taste buds are found in the skin of the roof and floor of the cavity, also found around the mouth corner, barlets and nearby area. The tract after pharynx consists of mucous membrane (without muscularis mucosae), submucosa (absence in the small intestine and the fore part of valvular intestine), lamina muscularis and adven-titia. The fore part of esophagus bears stratified squamous epithelium, in which there are flat cells having netlike microridges and mucus-secreting cells. The tract posterior to the fore part of esophagus is corved by simple columnar epithelium in which ciliary columnar cells are distributed. The simple columnar cells with microvilli in the rear part of esophagus and stomach are secretory mucus cells and in intestine are absorbing cells (lacking in the rear part of small intestine, the rear part of valvular intestine and rectum). Goblet cells begin to appear in small intestine and become more and more backward. Goblet cells and secretory mucus cells contain glycogen. Wandering cells and granular cells are also found in the simple columna repithelium.The mucous membrane of small intestine is honeycombed. The core of the compact pyloric caecum is honeycombed as well. The distribution of the digestive gland is only confined to the tunia propria of the backward limb and a certain area of forward limb of stomach, while the tunia propria at other parts become stratum compactum. The lamina muscularis in the fore part of esophagus is mainly striated muscle and in the rest parts of the tract is smooth muscle. The cells covering on the adventitia are either columnar or cuboidal or flat.