0:00 Throughout most of human history, we have felt at war with microbes. 0:07 However, the human body is colonized by a vast number of microbial population, 0:13 known as the human microbiome. 0:16 Trillions of bacteria colonize our bodies. 0:19 We can find them in various locations, such as our throat, 0:25 our gut, and even our skin. 0:30 In a healthy adult human body, there are approximately ten times more bacteria 0:38 than there are human cells. 0:41 Humans and their microbiota, which is bacteria, have a symbiotic and mutual 0:47 istic relationship, 0:49 which means that us humans and the bacteria work together, work with each other 0:55 , 0:56 benefit off each other, and depend on each other for survival. 1:02 There is a growing number of research into the field of the human microbiota. 1:08 For example, the association between the gut microbiota and our health. 1:14 It's an ongoing research, and you insight on the mutualistic symbiotic 1:19 relationship 1:19 are emerging rapidly. 1:21 Most of these studies and research are based on in vitro studies, as well as 1:26 animal studies. 1:29 Another important terminology we should learn is the microbiome, 1:34 which essentially means a community of bacteria. 1:37 So, for example, if I say the human-oral microbiome, 1:41 it means the community of microbes or bacteria that live within our oral cavity 1:48 . 1:49 In this video, we will investigate and focus on the bacteria that live in our 1:55 gut. 1:56 When we talk about the community of bacteria that reside in our gut, 2:00 we can refer to them as the human gut microbiome. 2:04 We will first learn about what they are and what's and some interesting facts 2:08 about them, 2:09 and then we will look into the effects they have on the human body, 2:14 which is, as I mentioned, an exciting and relatively new field of research. 2:20 So, we begin here with the digestive tract. 2:23 Looking at the digestive tract, which is made up of the esophagus, stomach, 2:27 small intestine, 2:28 and large intestine, these microorganisms are mostly found in the large 2:35 intestine, 2:36 though it is important to understand that we do find these bacteria also in the 2:40 small intestine just not as much. 2:43 So, let us recap the regions of the large intestine. 2:48 Here is a small intestine that joins with the large intestine. 2:52 The large intestine is made up of the sacrum, the ascending colon, the trans 2:57 verse colon, 2:58 the descending colon, sigmoid colon, and rectum. 3:03 We also have the appendix that joins with the sacrum. 3:09 You might be thinking, though, if bacteria are inside our body, 3:13 wouldn't it initiate some form of immune response? 3:17 Well, that is true, but the digestive tract, as well as other tracts, are 3:21 special, 3:23 in that it contains mucus, right? 3:25 So, if we zoom into the large intestine here, we have the lumen of the large 3:28 intestine, 3:29 and here are the colon cells. 3:32 Above the colon cells, we have mucus, which acts as a barrier between the micro 3:36 be community 3:38 within the lumen and the human cells. 3:42 The highly dense microbial community and the host intestinal cell linings 3:47 are separated by a thick layer of mucus in the large intestine. 3:52 Interestingly, if we compare this to the small intestine, 3:57 the small intestine and the microbes are only separated by a thin layer of muc 4:04 us, 4:05 much thinner compared to the mucus layer of the large intestine. 4:12 Therefore, we can see how that mucus helps keep these bacteria from causing any 4:19 harm. 4:20 Also, the antibodies that are part of the mucosal system, 4:25 as well as the tight junctions between the intestinal cells, help in this 4:29 respect. 4:31 So, there is a lot of barrier here, allowing these bacteria to live within us 4:37 in a symbiotic mutualistic relationship. 4:42 So, why do we have it? 4:44 Why do we have these bacteria living in our gut? 4:47 Well, the gut microbiota become established at birth 4:51 and continue to change in composition throughout development. 4:55 In fact, many factors influence the amount of microbes we have inside our body, 5:01 such as taking medications, diet, and lifestyle. 5:04 All are factors that influence the composition, the amount, and the different 5:09 types of microbes we have. 5:12 And therefore, each individual is unique in that each individual has a unique 5:17 amount composition of microbes. 5:24 In the large intestine, the bacteria are mainly found in the proximal colon, 5:29 because this is where substrate availability is highest. 5:33 But there are still so much bacteria everywhere else, such as the transverse 5:38 colon, as well as the descending colon. 5:44 And so, we can say that the bacterial density will increase from the duodenum 5:49 of the small intestine to the large intestine. 5:54 We find especially a lot of bacteria in the proximal colon. 5:59 As well with this increase in density, there is also an increase in bacterial 6:04 diversity, 6:05 so there are more bacterial species as we move towards the end of the colon. 6:11 With the increase in bacterial diversity and density, there is also an increase 6:17 in mucus thickness. 6:21 Now, the normal gut microbiota is dominated by anaerobic bacteria, 6:26 but there are some aerobic and facultative anaerobic bacteria that are found in 6:30 the intestine. 6:32 In total, there are up to 1,000 species of bacteria living in our gut, 6:37 that interestingly only belong to a few known bacterial species. 6:43 The most abundant bacteria come from the filler from acutes and bacteroidities. 6:52 Our gut microbiota play many fundamental roles in our body. 6:57 Let us learn a bit about the effects the gut bacteria have on the host 7:04 physiology. 7:05 The main impact gut microbes have on host physiology is on metabolism. 7:11 The gut microbiota has been shown to help absorb nutrients. 7:19 But the main effect on metabolism is that the gut microbiota have a big role in 7:23 fermentation. 7:25 You see, foods that are not digested and absorbed in the small intestine, 7:30 such as non-digestible carbohydrates, will reach the large intestine. 7:36 And here, the carbohydrate will undergo fermentation by the bacteria. 7:41 So let us have a closer look at this process. 7:44 So here we have the colonocytes with mucus on top, and here is a blood supply. 7:50 Within the lumen of the colon, we find the bacteria communities, waiting for 7:54 food to come. 7:56 The non-digestible carbohydrate particles will reach the colon, and will be 8:00 then fermented by the bacteria. 8:04 Through this fermentation process, the bacteria will produce a byproduct, a 8:09 substance known as short-chain fatty acids. 8:14 Some of these short-chain fatty acids, such as butyrate, are used as energy by 8:18 the colon cells. 8:20 Up to 70% of the energy used by colon cells come from short-chain fatty acids. 8:28 Short-chain fatty acids that are absorbed into the blood can have other effects 8:32 around the body. 8:34 There is some evidence that short-chain fatty acids will influence adiposity by 8:41 increasing lipogenesis. 8:42 Short-chain fatty acids have also shown to influence the immune system in many 8:46 ways, 8:47 as well as they have been shown to play a key role in the health of colon cells 8:54 . 8:55 Another fundamental effect the gut microbiota play in our body is its effect on 8:59 gut morphology, so gut structure. 9:11 These effects include increasing the amount of mucus in the intestinal tract, 9:17 decreasing intestinal cell permeability, 9:20 deepening the crypts of the intestine, increase vascular flow, and stimulate 9:26 tissue repair and renewal, particularly the villi. 9:32 All of these effects, essentially, will promote barrier integrity, as well as 9:37 the function of the digestive system. 9:40 The reason as to how the gut microbiota modulate most of these activities 9:46 remains elusive, 9:48 but most of the research suggests that it is attributed to the production of 9:52 the short-chain fatty acids, 9:54 following fermentation of non-digestible foods. 10:01 The gut microbiota has also shown to have effect on the immune system. 10:08 For example, it has shown to influence the maturation and development of lymph 10:13 oid tissues, 10:14 such as payous patches in the mucosal system, as well as the lymph nodes. 10:21 The gut microbes are also able to regulate production of some immune mediators, 10:26 including increasing concentration of secretory IgA antibodies. 10:31 Recently, it has been found that the bacteria are able to influence the 10:36 composition of T-cells in the laminopropia. 10:41 The gut microbiome also has effects on the nervous system. 10:46 Most of these effects are based on animal studies, and include decreasing 10:50 synaptic connectivity 10:52 and promoting anxiety-like behaviors, as well as pain perception. 10:58 There is also suggestions that the gut microbiota influences bone homeostasis 11:04 by regulating bone density, as well as increasing the reabsorption of calcium 11:10 from the gut. 11:12 Now, we're still only scratching the surface of our understanding of gut 11:16 microbes and how they affect our health. 11:18 It is an ongoing and exciting field of research. 11:22 I hope you enjoyed this video. Thank you for watching. 11:28 (gentle music)
