（一）大肠的结构及功能：
1、大肠是人体消化系统的重要组成部分，位于人体小肠之后，血管支原始网状皱襞从大肠过渡到肠系膜。大肠由结肠、盲肠和回肠组成，其中大肠长约约1.5米，两侧各有一个穹窿，其内壁肌层细胞很多，具有挤挤及吸收作用，因而它的功能也是各由的。
2、大肠的主要功能有收集、稀释、挤压、运转和吸收，它充当着消化和吸收液体营养物质和有机废物以及维持水平血浆电解质平衡等重要功能。在大肠中，肠套反射可以补充吸收。大肠还有一定的合成功能，它还可以合成Vitamin K(凝血酚)、氨基酸、细胞色素等，促进消化。
3、除此之外，大肠还可以调节乳酸及胆汁酸的吸收，大肠内除有大量异养芽孢杆菌外，还有一些病原生物，当某些条件下过多的菌落的出现，将会导致相应的疾病，水平血在其中起着重要作用。特别是大肠癌，由于出现过多的菌群而发生，所以要注意保持正常水平血，以减少肠癌发病。
（二）大肠的疾病：
1、大肠炎：大肠炎是一种消化性疾病，它以炎症和发热为特征。临床上，大肠炎不同类型有着不同的特点，其可以分为慢性和急性两种，急性大肠炎临床常见的症状表现多为腹痛、发热、腹泻等，慢性大肠炎的表现则有发热的症状，而且持续时间较长，且伴随大量的排气和便秘等症状。
2、结肠癌：结肠癌是一种发生在大肠的恶性肿瘤，它的病因是由于组织的细胞突变或免疫功能低下，而导致细胞癌变。这种绝大多数结肠癌是慢性长期受损所致，其主要症状是体重下降，发热，血便，呕吐，腹部肿胀等，常在早期出现腹痛、肠便增多等症状。同时，结肠癌在晚期可出现无菌性腹膜炎、肠梗阻等症状。
（三）大肠的预防：
1、坚持良好的作息时间，保证每天7个小时以上的睡眠时间。
2、多吃新鲜蔬菜水果，少吃富含脂肪和高热量食物。
3、多喝水，每天六、七杯白开水，可以促进消化。
4、多参加运动，促进体内废碱和毒素排出，平衡肠道菌群。
5、适当补充维生素，留意维生素A、维生素B、维生素C和维生素E及其他矿物元素的补充。
6、少吃裹粉等淀粉类食物，因为人体对裹粉的消化能力较低。
7、减少吸烟和饮酒，以防发生结肠癌等疾病。
8、定期检查，及早发现大肠疾病，及早治疗，减少肠癌发病。
I. Overview of the Blood Circulation of Colon
The blood circulation of colon can be divided into three broad categories according to its pathways: the arterial circulation, the venous circulation and the lymphatic circulation.
1. Arterial Circulation
The arterial circulation of colon is supplied by the superior and inferior mesenteric arteries. The superior mesenteric artery supplies in anterosuperior manner and the inferior mesenteric artery supplies in posteroinferior manner. The superior mesenteric artery originates from the abdominal aorta and supplies the ascending, transverse and descending portions of the colon, whereas the inferior mesenteric artery originates from the aorta below the superior mesenteric artery and supplies the sigmoid colon, the rectum, and the rectosigmoid junction.
2. Venous Circulation
The venous drainage of the colon is varied, but it mainly follows the arterial circulation and drains into the superior or inferior mesenteric veins. The inferior mesenteric vein drains into the portal system.
3. Lymphatic Circulation
The lymphatic circulation of the colon is mainly composed of the superior and inferior mesenteric lymphatic vessels and their associated lymph nodes. They receive lymph from the rectum and the distal descending and sigmoid colon.
II. Anatomical Nomenclature
The colon consists of the ascending, transverse, and descending colon, and the sigmoid colon. The ascending and descending colon are likewise separated by the flexure of the splenic, ileocecal, and hepatic flexure.
III. Arrangement of the Layers
The wall of the colon is comprised of four layers, from the innermost to the outermost: the mucosa, the submucosa, the muscular layer, and the serosa.
1. Mucosa
The mucosa is the innermost layer of the colon and consists of a single layer of simple columnar epithelium lined by numerous glands, crypts, and goblet cells.
2. Submucosa
The submucosa is an acellular, chiefly collagenous connective tissue layer and consists of loose stroma. Its primary function is to bind the mucosa and the muscular layer.
3. Muscular Layer
The muscular layer is composed of two layers of smooth muscle fibers: the inner circular layer, and the outer longitudinal layer. The inner circular layer thickens towards the lower rectum.
4. Serosa
The serosa is a thin, smooth, delicate membrane and consists mainly of connective tissue and adipose tissue. It is composed of the visceral peritoneum and is continuous with the parietal peritoneum.
IV. Development of the Layers
1. Mucosa
The mucosa is the first layer to be visible in the fourth week of gestation and is the innermost layer to be completed in the sixth week.
2. Submucosa
The submucosa is formed during the sixth week and consists of few submucosal glands at first. Its complexity increases as the fetal life progresses.
3. Muscular Layer
The muscular layer consists at first of few muscle cells, but increases drastically during the 16th week of gestation.
4. Serosa
The serosa is the outermost layer to be completed, and is not fully formed until the sixteenth week of gestation.
如果觉得《大肠 大肠癌》对你有帮助，请点赞、收藏，并留下你的观点哦！
