0:00 In this video we will learn about the anatomy and the physiology of the large 0:06 intestine, 0:07 also known as the colon. 0:09 Finally, towards the end of the video I will introduce colon cancer. 0:15 The colon or large intestine is approximately 150 centimeters in length. 0:21 It is divided into a few sections. 0:24 The small intestine here will join to the first part of the large intestine, 0:27 known as 0:28 the secum. 0:30 Then there is the ascending colon, the transverse colon, descending colon, zygm 0:36 oid colon and 0:37 finally the rectum. 0:40 Waste is excreted through the rectum in anus. 0:45 The appendix here is a pouch structure that connects the secum and is stored to 0:49 have a 0:49 role in the immune system. 0:53 The colon's major role is to absorb vitamins, water and ions, as well as the 0:58 transfer and 0:59 storage of waste. 1:03 Let's take a section of the colon. 1:07 These three longitudinal fibers that run along the colon are called Tine Coli. 1:13 The Tine Coli runs along all segments, except the rectum. 1:20 Now let's look at the layers of the colon. 1:23 The very top layer of the colon closest to the lumen is the mucosa layer. 1:29 These are the colon cells which are mostly columnar epithelial cells. 1:35 These cells they form crypts and these are all crypts. 1:41 The next layer is the submucosa, sub as in below, so below the mucosa. 1:48 The submucosa is the connective tissue layer that contains nerves, blood supply 1:55 and lymphatics. 1:57 Here we have the arteries that supply the cells and veins that leave the area. 2:03 Then there is the muscularis, which is the muscle layer. 2:06 There are actually two muscle layers. 2:09 We have the inner muscle layer where we have circular muscles and then the 2:13 outer muscle 2:14 layer where we have longitudinal muscles. 2:18 The outer most layer of the large intestine is connective tissue layer called 2:24 the serosa. 2:25 After the serosa we can find various structures such as lymph nodes that 2:31 connect with lymph 2:32 vessels that reach the mucosa layer. 2:37 Let's have a closer look at the mucosa layer and at these columnar epithelial 2:45 cells here. 2:46 So here we have the colon cells. 2:49 Above the colon cells we have mucus which is a liquid type substance that helps 2:55 lubricate 2:56 food as well as protect the lining of the digestive tract from dangerous 3:01 microbes as well as from 3:02 toxic substances. 3:05 Now in the colon there is a relatively thick mucus layer and then a thin mucus 3:10 layer on 3:10 top of that. 3:14 Coming above the mucus and within the lumen are bacteria. 3:20 These bacteria are called the gut microbiota. 3:24 Humans and their gut microbiota have a symbiotic and mutualistic relationship. 3:32 The colon cells they all arise from the cells within the crypts because within 3:36 the crypts 3:36 we have stem cells that migrate up. 3:42 These transit cells will move up where they will finally differentiate into 3:46 different types 3:47 of cells and after some time once they progressively move up they will begin to 3:54 shed allowing new 3:56 cells to arise from the bottom again. 4:00 Therefore you can think of it as a cycle where cells keep renewing. 4:05 The stem cells will eventually differentiate into four main types of cells. 4:10 These are the goblet cells that secrete mucus. 4:14 Your regular colonocytes which are your again typical columnar epithelial cells 4:22 . 4:22 Stem cells can also differentiate into endocrine cells that secrete hormones 4:26 and peptides 4:27 that maintain homeostasis of the gut. 4:32 Now in the colon there can also be paneth cells that arise from stem cells 4:37 during development. 4:39 However these paneth cells are confined in the small intestine after some time. 4:56 Now that we have a better understanding of the colon, let us focus on colon 5:03 cancer. 5:05 Colon cancer is where there is uncontrolled growth of colon cells and these 5:10 cells can 5:10 later invade other tissues. 5:14 So let us look at an example. 5:18 Here we have a colon. 5:20 These red mushy looking things are tumours. 5:24 Tumours are abnormal growths. 5:28 Neoplasia is another word that is used interchangeably with tumour. 5:34 Neoplasia essentially means new growth. 5:38 Now cancer is a type of tumour that usually grows rapidly and is malignant. 5:46 So what does malignant mean? 5:49 Well let us first have a look at a simple explanation of the development of 5:55 cancer. 5:56 So here we have a normal colon. 5:59 The chromosome, the DNA of this normal colon, have minimal to no mutations and 6:05 so is quite 6:06 healthy. 6:08 However, mutations can and do occur in our body. 6:14 And so this normal colon can develop a benign polyp. 6:19 A polyp is a tumour but it is not cancerous because it is benign. 6:28 Sometimes polyps are called adenomas if they are big enough. 6:32 Polyps are slow growing, capsulated and non-invasive. 6:38 A polyp develops because of possible mutations in the DNA that give rise to 6:46 them. 6:46 Usually people undergo surgery called colonoscopy to remove these polyps in 6:52 case they are or 6:53 can become cancerous. 6:57 Now some adenomas, they can progress and become carcinomas. 7:04 Carcinomas are the deadly ones, they are malignant. 7:08 Carcinomas are cancerous, they grow rapidly, are uncapsulated and are invasive. 7:16 For colon carcinomas to develop for example, we would expect to see multiple 7:20 mutations 7:21 in the DNA of many chromosomes. 7:26 Carcinomas and big tumours also usually have a lot of blood supply as these 7:32 abnormal growing 7:33 cells require many nutrients. 7:36 Therefore, in and around tumours, a process called angiogenesis occurs which is 7:42 the formation 7:43 and maturation of blood vessels. 7:48 A good way to understand what is happening in tumours and cancer is that there 7:53 is more 7:53 cells dividing than there are cells dying. 8:01 Now let us look at the stages of colon cancer. 8:05 Some people have different classifications of cancer and colon cancer. 8:09 This is one of them. 8:11 Now there are five stages in total. 8:15 Briefly looking at the anatomical layer of the colon, from the top we have the 8:20 mucosa, 8:21 the submucosa, the muscularis and serosa. 8:25 We can also find lymph nodes following these layers. 8:32 Stage zero is basically when we have abnormal cells in the mucosa layer that 8:36 will keep dividing 8:38 forming a polyp. 8:40 The polyp is usually benign. 8:45 Stage one is where the tumour has spread to the muscle layer and things may be 8:51 getting 8:51 serious. 8:55 Stage two, the tumour has spread through the colon wall towards the serosa. 9:09 Stage three, the tumour has spread through nearby lymph nodes. 9:16 And then we have stage four, which is a terminal stage called metastasis. 9:21 This is where the cancer cells have metastasized and have begun invading other 9:27 tissues and organs 9:30 by travelling through the blood or and lymphatics. 9:36 The cancer cells can invade other organs, such as the liver, lungs and bone. 9:46 And that concludes the video on the colon and an introduction to colon cancer. 9:51 There will be another video that will look into greater detail at colon cancer, 9:55 specifically 9:56 colon cancer carcinogenesis.
