1 00:00:00,012 --> 00:00:04,905 Now that we've learned about the macronutrients, let's look at nutrient 2 00:00:04,905 --> 00:00:08,464 processing, how we take what we eat, break it down, 3 00:00:08,464 --> 00:00:13,380 absorb it and get it into our body. When you think of the GI tract, you can 4 00:00:13,380 --> 00:00:16,542 still think of this as being outside your body. 5 00:00:16,542 --> 00:00:21,492 It is a system that still protects us from outside invaders. 6 00:00:21,492 --> 00:00:27,211 It's very important in proper immune health, in addition to all of it's 7 00:00:27,211 --> 00:00:32,372 digestive properties. So as we focus now on digestion, what is 8 00:00:32,372 --> 00:00:38,833 digestion? It is the breaking down of our food into smaller pieces. It occurs both, 9 00:00:38,833 --> 00:00:44,056 both mechanically and chemically. Once we've digested our food, we'll be 10 00:00:44,056 --> 00:00:49,645 able to absorb it. Absorption is simply the movement of these smaller pieces from 11 00:00:49,645 --> 00:00:53,454 this external portion of our body into circulation. 12 00:00:53,454 --> 00:00:58,238 Finally, we can also consider transport as part of nutrient processing. 13 00:00:58,238 --> 00:01:03,021 This is the movement of nutrients from one part of the body to another. 14 00:01:03,021 --> 00:01:06,893 For example, from the liver out towards the body's cells. 15 00:01:06,893 --> 00:01:11,271 As we review the digestive tract, we're going to start at the mouth. 16 00:01:11,271 --> 00:01:16,283 For anyone interested in a career in dentistry, or practicing dentistry, or 17 00:01:16,283 --> 00:01:20,077 someone that's just interested in good oral health, 18 00:01:20,077 --> 00:01:24,977 a healthy mouth is key to proper nutrition, as it is the forefront of your 19 00:01:24,977 --> 00:01:30,527 digestive process Without healthy teeth, its much harder to break your food down. 20 00:01:30,527 --> 00:01:35,527 If we can't properly break our food down, we won't be able to absorb it into our 21 00:01:35,527 --> 00:01:39,578 systems. In addition an unbalanced diet can be 22 00:01:39,578 --> 00:01:45,811 detrimental to oral health. So good nutrition, good teeth, go hand in 23 00:01:45,811 --> 00:01:50,000 hand. As we chew our food we'll process further 24 00:01:50,000 --> 00:01:55,192 along into the stomach down to the small intestine. 25 00:01:55,192 --> 00:02:00,403 and finally, the large intestine. This figure gives you an overall idea of 26 00:02:00,403 --> 00:02:04,319 what's broken down where, and where things are absorbed. 27 00:02:04,319 --> 00:02:09,661 It also illustrates that we have two systems for absorbing nutrients, both the 28 00:02:09,661 --> 00:02:14,248 portal system, blood, and the lacteal. This is the lymph system, 29 00:02:14,248 --> 00:02:17,657 and it's where we absorb our fat-based foods. 30 00:02:17,657 --> 00:02:25,089 When we think about nutrient processing, the proper breakdown and absorption and 31 00:02:25,089 --> 00:02:30,848 utilization of our food is key to maintaining all body systems, 32 00:02:30,848 --> 00:02:37,671 the skeletal system, circulatory system, the nervous system, the respiratory 33 00:02:37,671 --> 00:02:42,179 system, our muscles, and of course, the digestive tract itself. 34 00:02:42,179 --> 00:02:45,971 Proper nutrition is key to a healthy digestive system. 35 00:02:45,971 --> 00:02:51,122 When we talked about carbohydrates, we mentioned fiber being an important 36 00:02:51,122 --> 00:02:56,712 component to digestive health. It keeps the stomach and intestinal 37 00:02:56,712 --> 00:03:02,393 muscles strong and healthy. All right, so let's start from the 38 00:03:02,393 --> 00:03:07,406 beginning, the mouth. Here we have both mechanical and 39 00:03:07,406 --> 00:03:12,409 enzymatic digestion. Of course, the most important part of 40 00:03:12,409 --> 00:03:18,526 digestion is the mechanical digestion. In the mouth, besides the teeth and the 41 00:03:18,526 --> 00:03:25,165 tongue moving foods around, we also have salivary glands, producing saliva as well 42 00:03:25,165 --> 00:03:30,052 as salivary amylase, lingual lipase, fluids, mucus, and 43 00:03:30,052 --> 00:03:33,746 lysosomes. The enzymes, salivary, amylase, and 44 00:03:33,746 --> 00:03:38,993 lingual lipase only break down a small portion of our food, but you can 45 00:03:38,993 --> 00:03:42,914 understand how these work with a simple experiment. 46 00:03:42,914 --> 00:03:48,270 Try biting into a slice of bread. Don't swallow it, but continue to chew 47 00:03:48,270 --> 00:03:51,270 it. Lingual lipase will slowly break down 48 00:03:51,270 --> 00:03:56,554 some of that carbohydrate into sugars. Over time, if you don't swallow, you will 49 00:03:56,554 --> 00:04:01,270 notice this sweet taste in your mouth that didn't start out as sweet, but 50 00:04:01,270 --> 00:04:05,146 started out as bread. The other components of saliva are very, 51 00:04:05,146 --> 00:04:08,504 also very important. Of course, the fluid keeps the 52 00:04:08,504 --> 00:04:13,612 consistency in the mouth, mucus protects the GI tract and the oral 53 00:04:13,612 --> 00:04:18,657 surfaces, and lysosomes have antibacterial properties to protect the 54 00:04:18,657 --> 00:04:24,387 mouth from bacterias entering the mouth. Continuing, we go to the stomach. 55 00:04:24,387 --> 00:04:30,117 Between the mouth and the stomach, we do have sphincters that are helpful in 56 00:04:30,117 --> 00:04:33,592 making sure food goes in the right direction, 57 00:04:33,592 --> 00:04:36,610 and stays there. At the end of this lecture, we'll talk a 58 00:04:36,610 --> 00:04:40,606 little bit about problems in digestion, and one of these, GIRD, can occur if 59 00:04:40,606 --> 00:04:44,842 these sphincters don't work properly and some of the foods that have entered the 60 00:04:44,842 --> 00:04:48,100 stomach return to the mouth. They don't return as whole foods 61 00:04:48,100 --> 00:04:52,361 obviously, but they do return in acidic from, creating that acid environment in 62 00:04:52,361 --> 00:04:57,955 the mouth and the upset stomach. Looking at the stomach, it's important to 63 00:04:57,955 --> 00:05:01,078 understand that it is a muscular structure. 64 00:05:01,078 --> 00:05:06,484 The muscles of the stomach move food around, breaking it down and allowing the 65 00:05:06,484 --> 00:05:10,322 enzymes and chemicals in the stomach to work on food. 66 00:05:10,322 --> 00:05:13,277 In the stomach we will find hydrochloric acid. 67 00:05:13,277 --> 00:05:17,607 This is why we want to make sure that food does stay in the stomach, and 68 00:05:17,607 --> 00:05:21,702 doesn't return to the esophagus. The esophagus is a far less acidic 69 00:05:21,702 --> 00:05:26,182 environment than the stomach. Acid reflux, or GIRD, as I mentioned, is 70 00:05:26,182 --> 00:05:29,108 when these acids go back towards the mouth. 71 00:05:29,108 --> 00:05:34,539 The goal of the stomach digestion is to move food slowly, towards the bottom of 72 00:05:34,539 --> 00:05:40,103 the stomach and the pyloric sphincter. This is the barrier between the stomach 73 00:05:40,103 --> 00:05:44,102 and the initial part of the small intestine, the duodenum. 74 00:05:44,102 --> 00:05:49,002 At the end of this lecture, we'll also talk a little bit about the impact of 75 00:05:49,002 --> 00:05:54,577 gastrointestinal surgeries on nutrition. Most of these focus on changing the size 76 00:05:54,577 --> 00:05:59,577 of the stomach to aid in weight loss. Once we've gone past the stomach, we do 77 00:05:59,577 --> 00:06:03,802 enter the intestinal tract. There are several areas of the intestinal 78 00:06:03,802 --> 00:06:07,767 tract that are important. The duodenum is the site of most 79 00:06:07,767 --> 00:06:13,717 digestive processes. Further down in the intestinal tract, we'll see an increase 80 00:06:13,717 --> 00:06:17,407 in absorption. In the duodenum, we see significant 81 00:06:17,407 --> 00:06:21,522 enzymatic digestion. We also see a buffering of the foods 82 00:06:21,522 --> 00:06:26,087 coming from the stomach. Foods that have been broken down in the 83 00:06:26,087 --> 00:06:30,827 stomach, and are entering the intestinal tract, are called chyme. 84 00:06:30,827 --> 00:06:36,596 It's now a mixture of what you've eaten, stomach acids and stomach fluids. 85 00:06:36,596 --> 00:06:42,278 In the duodenum, bicarbonate will be released, to help bring down the pH to 86 00:06:42,278 --> 00:06:48,196 protect the intestinal tract, because we don't want that acid to come into the 87 00:06:48,196 --> 00:06:55,022 intestinal tract and damage the tissues. As we go on to talk about the 88 00:06:55,022 --> 00:06:59,488 macronutrients individually, we'll talk about what enzymes are present 89 00:06:59,488 --> 00:07:02,823 in the duodenum for digestion. As we continue down, the Jejunum and the 90 00:07:02,823 --> 00:07:07,738 Ileum are where we start to see absorption take place. 91 00:07:07,738 --> 00:07:13,085 This figure shows you exactly what types of nutrients are absorbed where. 92 00:07:13,085 --> 00:07:17,304 There is both passive, active and facilitated transport. 93 00:07:17,304 --> 00:07:20,551 We'll talk a little bit about what those are. 94 00:07:20,551 --> 00:07:24,642 First off, let's look at different types of digestion. 95 00:07:24,642 --> 00:07:28,962 So, let's review the Enzymatic Digestive processes. 96 00:07:28,962 --> 00:07:33,191 Digestive enzymes work just like any other enzyme. 97 00:07:33,191 --> 00:07:37,172 This is an example here of breaking down sucrose. 98 00:07:37,172 --> 00:07:41,078 Enzymes work to facilitate chemical processes. 99 00:07:41,078 --> 00:07:47,136 In this case, they facilitate the hydrolysis of the disaccharide sucrose 100 00:07:47,136 --> 00:07:51,620 into independent molecules of glucose and fructose. 101 00:07:51,620 --> 00:07:56,767 Enzyme function is very specific and enzymes will only target specific 102 00:07:56,767 --> 00:08:00,445 compounds. As you read through this, try to learn 103 00:08:00,445 --> 00:08:04,902 the different enzymes that act on specific nutrients. 104 00:08:04,902 --> 00:08:12,047 In addition to chewing, physical processes of digestion that occur in the 105 00:08:12,047 --> 00:08:18,802 stomach and intestinal tract include peristalsis and segmentation. 106 00:08:18,802 --> 00:08:23,775 Peristalsis is the muscular movement that pushes foods forward in the GI tract 107 00:08:23,775 --> 00:08:28,773 while segmentation helps breaks foods up into smaller amounts, so that as they do 108 00:08:28,773 --> 00:08:33,351 enter locations where they are acted on enzymatically, we can increase the 109 00:08:33,351 --> 00:08:36,671 surface area, and make digestion more efficient. 110 00:08:36,671 --> 00:08:41,719 The link below is a useful animation for you to understand what this looks like, 111 00:08:41,719 --> 00:08:46,044 and review the digestive process, in addition to reading your text. 112 00:08:46,044 --> 00:08:51,067 In the stomach, peristalsis is very important in mixing the foods and 113 00:08:51,067 --> 00:08:56,408 creating the chyme. As I have already mentioned, the goal is to move the chyme 114 00:08:56,408 --> 00:09:01,522 towards the pyloric sphincter, to release the chyme, in a regulated manner, into 115 00:09:01,522 --> 00:09:07,365 the intestinal tract. Again, the stomach environment is highly acidic. Look at 116 00:09:07,365 --> 00:09:11,061 this chart here. You can see that gastric juice is more 117 00:09:11,061 --> 00:09:18,047 acidic than lemon juice and orange juice. Of course not, as acidic as battery acid, 118 00:09:18,047 --> 00:09:24,218 but nonetheless, significantly acidic. A healthy sphincter here, as well as the 119 00:09:24,218 --> 00:09:29,606 upper sphincter, is very important in controlling flow into the GI tract. 120 00:09:29,606 --> 00:09:35,235 Depending on what you eat, the movement of the food from the stomach into the 121 00:09:35,235 --> 00:09:41,337 intestines may happen at different rates. Fiber, for example, will actually slow 122 00:09:41,337 --> 00:09:45,708 down stomach emptying. This is why it's useful for people with 123 00:09:45,708 --> 00:09:49,122 diabetes. In someone with diabetes, if they do have 124 00:09:49,122 --> 00:09:54,121 a certain amount of carbohydrate in the diet, that is broken down to sugars. 125 00:09:54,121 --> 00:09:59,608 By adding fiber, we slow the release, and help the body process the sugar a little 126 00:09:59,608 --> 00:10:02,659 bit at a time. So now, let's look at some of the 127 00:10:02,659 --> 00:10:05,782 enzymatic and hormonal controls of digestion. 128 00:10:05,782 --> 00:10:12,152 This is a basic overview of the different hormones that control the digestive 129 00:10:12,152 --> 00:10:16,655 processes, including how quickly food moves through. 130 00:10:16,655 --> 00:10:22,052 When we eat, food hits the stomach wall, and gastrin is released. 131 00:10:22,052 --> 00:10:26,602 Gastrin will activate the release of hydrochloric acid. 132 00:10:26,602 --> 00:10:30,953 We certainly wouldn't want an acidic environment to be maintained at all times 133 00:10:30,953 --> 00:10:35,562 in the stomach, even though the stomach does have mucosa to protect its cells, 134 00:10:35,562 --> 00:10:39,034 the cells of the stomach, these endothelial cells are protein. 135 00:10:39,034 --> 00:10:43,094 If we have acids all the time, we can actually break down the cell walls and 136 00:10:43,094 --> 00:10:46,127 damage the stomach lining. Ulcers are just that. 137 00:10:46,127 --> 00:10:51,462 Ulcers are when we do have damage in these stomach linings, and these damaged 138 00:10:51,462 --> 00:10:55,657 areas can become infected. This is very painful and causes 139 00:10:55,657 --> 00:11:00,095 significant problems. In addition to hydrochloric acid, gastrin 140 00:11:00,095 --> 00:11:04,271 activates the enzyme pepsin. Just like hydrochloric acid, we don't 141 00:11:04,271 --> 00:11:09,288 necessarily want proteolytic enzymes, those are enzymes that break up proteins, 142 00:11:09,288 --> 00:11:13,471 sitting around active all the time. We don't want them to act on body 143 00:11:13,471 --> 00:11:16,348 proteins. So pepsin sits as an inactive protein 144 00:11:16,348 --> 00:11:21,135 until gastrin activates it. Gastrin will also activate stomach 145 00:11:21,135 --> 00:11:24,973 emptying. That way, the stomach can rest when 146 00:11:24,973 --> 00:11:31,211 there's no food to be processed. Other important regulators of, of gastric 147 00:11:31,211 --> 00:11:35,212 function include Gastric Inhibitory Peptide, 148 00:11:35,212 --> 00:11:41,053 secretin, and Cholecystokinin. Gastric Inhibitory Peptide, or GIP, will 149 00:11:41,053 --> 00:11:47,256 actually slow stomach emptying and trigger the release of insulin. 150 00:11:47,256 --> 00:11:54,420 This is important in regulating how much carbohydrate material is released into 151 00:11:54,420 --> 00:11:58,727 the duodenum. We don't want too much at once, 152 00:11:58,727 --> 00:12:03,119 or the body's insulin system won't be able to keep up. 153 00:12:03,119 --> 00:12:07,200 Secretin will actually decrease pepsin release. 154 00:12:07,200 --> 00:12:13,334 This helps slow the digestive process. And Cholecystokinin slows stomach 155 00:12:13,334 --> 00:12:17,093 emptying, with a movement into the duodenum. 156 00:12:17,093 --> 00:12:22,455 It's also important for releasing bile. This will be the released into the 157 00:12:22,455 --> 00:12:25,741 intestinal tract. We've talked a little bit about this 158 00:12:25,741 --> 00:12:28,565 already. Bile is generated in the liver and and 159 00:12:28,565 --> 00:12:32,966 stored in the gall bladder. If someone does not have a gall bladder, that's 160 00:12:32,966 --> 00:12:35,567 fine. They can still make bile and release it 161 00:12:35,567 --> 00:12:38,828 directly from the liver. Cholecystokinin also triggers the release 162 00:12:38,828 --> 00:12:42,428 of digestive enzymes. So if we review this figure, gastrin is 163 00:12:42,428 --> 00:12:47,484 responsible for getting the stomach working, while the others, GIP, secretin 164 00:12:47,484 --> 00:12:53,423 and Cholecystokinin, are responsible for prepping the duodenum for its work, and 165 00:12:53,423 --> 00:12:58,664 for controlling the movement of chyme from the stomach into the intestinal 166 00:12:58,664 --> 00:13:02,179 tract. As we move into the intestines, we'll see 167 00:13:02,179 --> 00:13:07,392 that certain anatomical structures are very important to digestion. 168 00:13:07,392 --> 00:13:13,261 The villi help increase surface area of our intestinal tract to make sure that we 169 00:13:13,261 --> 00:13:17,144 have enough time to both digest and absorb our foods. 170 00:13:17,144 --> 00:13:22,578 If we take a closer look at these finger-like projections on the surface of 171 00:13:22,578 --> 00:13:27,952 our intestinal tract, we see that they are made up of even smaller villi, 172 00:13:27,952 --> 00:13:35,347 and that within these villi are the actual absorptive cells, the lacteal, the 173 00:13:35,347 --> 00:13:42,127 capillaries of the blood system, as well as other important components. 174 00:13:42,127 --> 00:13:49,115 As we move into the intestines, we will note that the intestinal tract, in 175 00:13:49,115 --> 00:13:55,150 addition to being significantly long itself, is made up of villi. 176 00:13:55,150 --> 00:14:01,756 This further increases the surface area of the intestine, to ensure that we have 177 00:14:01,756 --> 00:14:06,377 sufficient capacity to both digest and absorb our food. 178 00:14:06,377 --> 00:14:13,008 Within each villi, are the vessels that will carry nutrients from the GI tract to 179 00:14:13,008 --> 00:14:17,325 the bladder. The capillaries carry water-soluble 180 00:14:17,325 --> 00:14:24,153 substances towards the liver, while the lacteal carry fat-soluble substances to 181 00:14:24,153 --> 00:14:28,134 the liver. We talked briefly, when we talked about 182 00:14:28,134 --> 00:14:33,982 carbohydrates and fiber, about the fact that intestinal cells turn over. 183 00:14:33,982 --> 00:14:38,382 New intestinal cells will start at the bottom in the crypts. 184 00:14:38,382 --> 00:14:43,759 They'll move slowly up the villi until they reach the top where they can be 185 00:14:43,759 --> 00:14:47,264 sloughed off. Fiber and other substances in our 186 00:14:47,264 --> 00:14:50,972 digestive product help slough these cells off. 187 00:14:50,972 --> 00:14:58,518 Certain auto-immune conditions, such as Crohn's disease, can actually damage 188 00:14:58,518 --> 00:15:03,873 intestinal villi and reduce absorptive capacity. 189 00:15:03,873 --> 00:15:10,582 As I mentioned, there's different ways that we do absorb nutrients. 190 00:15:10,582 --> 00:15:16,615 The first is facilitated diffusion. With this, we do see the importance, 191 00:15:16,615 --> 00:15:20,843 important role of proteins. Proteins are the transporters. 192 00:15:20,843 --> 00:15:26,160 These proteins change shape to allow for specific nutrients to cross over, and 193 00:15:26,160 --> 00:15:31,490 keep things we don't want going in, like bacteria keeping those out. 194 00:15:32,718 --> 00:15:38,982 Diffusion is a simpler form of substances crossing, and they can do so either 195 00:15:38,982 --> 00:15:44,709 between the cell walls, between, actually, those Phospholipids, that we've 196 00:15:44,709 --> 00:15:51,169 already discussed in the lipids section, or through the proteins. 197 00:15:51,169 --> 00:16:00,074 Active transport requires energy. Minerals are often carried through by, by 198 00:16:00,074 --> 00:16:07,482 active transport as are our proteins. So here we can see that it takes 199 00:16:07,482 --> 00:16:14,861 calories, energy, ATP to digest our food. When we talk a little bit about basal 200 00:16:14,861 --> 00:16:19,912 metabolism, this is part of that basal metabolsim, 201 00:16:19,912 --> 00:16:27,062 the amount of energy required to keep our body functioning, even when we're really 202 00:16:27,062 --> 00:16:31,912 doing nothing. Finally, endocytosis is where the cell 203 00:16:31,912 --> 00:16:38,012 wall breaks itself off, engulfing a substance and bringing it into the 204 00:16:38,012 --> 00:16:41,937 system. As I mentioned, most of the digestive 205 00:16:41,937 --> 00:16:46,314 process really happens in the intestinal tract. 206 00:16:46,314 --> 00:16:50,591 Lets look at some of what happens in the mouth and the stomach. 207 00:16:50,591 --> 00:16:54,254 In the mouth as we know, lots of mechanical breakdown. 208 00:16:54,254 --> 00:16:59,686 Chewing your food is very important. We also have salivary amylase and lingual 209 00:16:59,686 --> 00:17:05,143 lipase working on our starches and fats. In the stomach we'll also continue fat 210 00:17:05,143 --> 00:17:10,672 breakdown with gastric lipase and we'll begin protein breakdown with Pepsin. 211 00:17:10,672 --> 00:17:16,312 Pepsin is, as I mentioned previously, inactive at first and activated as food 212 00:17:16,312 --> 00:17:21,796 enters the stomach and hydrochloric acid increases, and is responsible for 213 00:17:21,796 --> 00:17:26,638 beginning to breakdown polypeptides into smaller peptide chains. 214 00:17:26,638 --> 00:17:32,042 Let's now consider each macronutrient's final digestion and absorption. 215 00:17:32,042 --> 00:17:46,287 Take a moment to review this slide. Carbohydrates, such as starch, will 216 00:17:46,287 --> 00:17:55,045 continue to be broken down from their long chains, until they reach 217 00:17:55,045 --> 00:17:58,660 disaccharides and finally, into simple sugars. 218 00:17:58,660 --> 00:18:04,009 When we reach the disaccharide form, specific enzymes, matching each 219 00:18:04,009 --> 00:18:07,522 disaccharide, will do the final break down. 220 00:18:07,522 --> 00:18:12,122 Lactase for lactose, maltase for maltose, and sucrase for sucrose. 221 00:18:12,122 --> 00:18:17,247 Once carbohydrates are broken down into simple sugars, they can be absorbed. 222 00:18:17,247 --> 00:18:22,272 Absorption of the three monosaccharides will occur through one of the mechanisms 223 00:18:22,272 --> 00:18:26,347 we already discussed. Glucose and galactose are absorbed by 224 00:18:26,347 --> 00:18:30,176 active transport. In fructose, you have facilitated 225 00:18:30,176 --> 00:18:33,492 diffusion. The flow of these monosaccharides in 226 00:18:33,492 --> 00:18:38,655 absorption goes from the lumen of the small intestine to the mucosal, or gut 227 00:18:38,655 --> 00:18:43,540 cell, then towards the capillaries, or into the capillaries within the 228 00:18:43,540 --> 00:18:46,681 intestinal villi. And from those capillaries, 229 00:18:46,681 --> 00:18:50,545 monosaccharides move to the portal vein, and finally, the liver. 230 00:18:50,545 --> 00:18:55,276 Throughout this course, as you read and learn, you will discover how important 231 00:18:55,276 --> 00:18:58,009 the liver is to nutrition and overall health. 232 00:18:58,009 --> 00:19:02,360 It is certainly the center of our factory, where everything is processed 233 00:19:02,360 --> 00:19:07,852 and built to keep the machine running. The digestion of lipids differs from 234 00:19:07,852 --> 00:19:14,347 other macro-nutrients, in that lipids, being fats, will not go into the aqueous 235 00:19:14,347 --> 00:19:19,777 environment of the blood. They'll enter the body through lacteals. 236 00:19:19,777 --> 00:19:26,182 These will still eventually get to the liver, however these lipids are not going 237 00:19:26,182 --> 00:19:31,618 to be transported in the blood. When we think about the break down of 238 00:19:31,618 --> 00:19:36,207 fats, imagine a glass of water with drops of oil added to it. 239 00:19:36,207 --> 00:19:40,710 If you let it sit, the oil will separate out from the water. 240 00:19:40,710 --> 00:19:44,916 These two substances certainly don't mix on their own. 241 00:19:44,916 --> 00:19:50,142 As we've already discussed, bile is a very important substance for the 242 00:19:50,142 --> 00:19:55,822 digestion of lipids, in that it will break lipids up into small droplets that 243 00:19:55,822 --> 00:20:00,846 can be acted upon by enzymes. The result of this micelle activity and 244 00:20:00,846 --> 00:20:06,690 enzymatic digestion are short chain fatty acids, medium chain fatty acids, the 245 00:20:06,690 --> 00:20:12,027 glycerol backbone, as well as a some diglycerides and monoglycerides. 246 00:20:12,027 --> 00:20:17,939 And as a reminder from a previous slide, Cholecystokinin will control the release 247 00:20:17,939 --> 00:20:24,921 of bile from the gall bladder. As I mentioned, the fats are not going to 248 00:20:24,921 --> 00:20:30,214 go into the portal system, they're going to go into the lacteal. 249 00:20:30,214 --> 00:20:35,912 And this image just shows a closer picture of what's happening with these 250 00:20:35,912 --> 00:20:39,922 substances. Eviction of the bile salts, the enzymes 251 00:20:39,922 --> 00:20:44,302 involved in breaking down these droplets of fat, the lipase, 252 00:20:44,302 --> 00:20:49,427 and how we free fatty acids from the monoglyceride, including the glycerol 253 00:20:49,427 --> 00:20:52,623 backbone. If we look at what substances are 254 00:20:52,623 --> 00:20:57,993 actually entering the internal site, we'll see that both monoglycerides and 255 00:20:57,993 --> 00:21:02,349 free fatty acids enter. but once into the intestinal cell they 256 00:21:02,349 --> 00:21:08,742 will actually reconnect as triglycerides. These triglycerides will then be further 257 00:21:08,742 --> 00:21:14,058 packaged into chylomicrons. And it is the chylomicron that is going 258 00:21:14,058 --> 00:21:18,871 into the lacteal to be transported further into the body. 259 00:21:18,871 --> 00:21:24,765 Finally, when we digest and absorb proteins, we'll see similar patterns, as 260 00:21:24,765 --> 00:21:29,767 with the carbohydrates, breaking down long chains into smaller 261 00:21:29,767 --> 00:21:34,453 components. Specifically, we will digest polypeptides 262 00:21:34,453 --> 00:21:38,864 into tripeptides and dipeptides and free amino acids. 263 00:21:38,864 --> 00:21:45,022 Now, to get these components into the blood, we still have to break them down 264 00:21:45,022 --> 00:21:50,759 further into all free amino acids. In the case of protein, unlike fats, for 265 00:21:50,759 --> 00:21:56,826 example, it's the simplest component that's going to be absorbed completely. 266 00:21:56,826 --> 00:22:02,856 Amino acids are going to be actively absorbed and actually couple with sodium 267 00:22:02,856 --> 00:22:09,084 to process through protein transporters. Important enzymes in the breakdown of 268 00:22:09,084 --> 00:22:13,662 proteins include Trypsin, Chymotrypsin and Peptidases. 269 00:22:13,662 --> 00:22:19,877 An interesting note about Trypsin is that some compounds in the foods can actually 270 00:22:19,877 --> 00:22:24,267 destroy Trypsin. These are termed anti-Trypsin factors. 271 00:22:24,267 --> 00:22:29,962 They are actually found in beans, and if we do not cook beans properly, that 272 00:22:29,962 --> 00:22:34,402 anti-trypsin factor will still be active. So in populations where cooking is done 273 00:22:34,402 --> 00:22:41,116 over a fire, if it's not done sufficiently, these anti-Trypsin factors 274 00:22:41,116 --> 00:22:47,370 can significantly impair digestion. To conclude, lets look at some of the 275 00:22:47,370 --> 00:22:52,837 potential problems in digestion We talked a little bit about GIRD, or Gastro 276 00:22:52,837 --> 00:22:59,612 Intestinal Reflux Disease already. this is an extensive form of reflux. 277 00:22:59,612 --> 00:23:05,962 You can certainly have acid reflux without having GIRD but a chronic 278 00:23:05,962 --> 00:23:11,964 condition of reflux could be GIRD. And in this, condition, we are seeing the 279 00:23:11,964 --> 00:23:16,788 sphincter not working properly, so that the acidic substances of the 280 00:23:16,788 --> 00:23:22,520 stomach, that chyme, are released back up the esophagus, potentially damaging the 281 00:23:22,520 --> 00:23:28,547 lining of the esophagus, and doing damage to oral surfaces, including the teeth. 282 00:23:28,547 --> 00:23:31,787 Achlorhydria is a lack of hydrochloric acid. 283 00:23:31,787 --> 00:23:37,147 This is a condition that can happen in aging, and it will impair digestion. 284 00:23:37,147 --> 00:23:42,697 And as hydrochloric acid is important in the breakdown of foods in the stomach 285 00:23:42,697 --> 00:23:46,240 level, if we don't have enough hydrochloric 286 00:23:46,240 --> 00:23:51,719 acid, we won't break down our food sufficiently to be acted upon by the 287 00:23:51,719 --> 00:23:57,475 enzymes in the intestinal tract. Gastric ulcers can also cause digestive 288 00:23:57,475 --> 00:24:02,132 problems, stomach upset, nausea, pain, vomiting and even blood, 289 00:24:02,132 --> 00:24:07,093 or bleeding from the stomach. Gastric ulcers do happen when the mucosal 290 00:24:07,093 --> 00:24:11,978 lining in the stomach is damaged, and these areas where the lining's been 291 00:24:11,978 --> 00:24:16,560 damaged become infected. Continuing on condition, conditions that 292 00:24:16,560 --> 00:24:21,851 affect the intestinal tract include lactose intolerance, Celiac disease and 293 00:24:21,851 --> 00:24:25,689 Chrons disease. With food based conditions, such as 294 00:24:25,689 --> 00:24:31,882 lactose intolerance and celiac disease, the body actually either launches against 295 00:24:31,882 --> 00:24:37,162 itself, so in the Celiac disease condition, antibodies can be synthesized 296 00:24:37,162 --> 00:24:41,474 that attack intestinal cells when one consumes wheat, 297 00:24:41,474 --> 00:24:46,956 damaging these cells, to the extent where we can actually reduce the size of the 298 00:24:46,956 --> 00:24:50,363 villa. In the case of lactose intolerance, these 299 00:24:50,363 --> 00:24:55,616 individuals lack the enzyme lactase. When lactose can't be broken down into 300 00:24:55,616 --> 00:25:00,892 its monosaccharide, it will simply stay in the GI tract, and causes diarrhea. 301 00:25:00,892 --> 00:25:07,157 Chrons Disease is an auto-immune disease that affects the entire GI tract, but 302 00:25:07,157 --> 00:25:13,265 primarily the upper part of the small intestine, and it does also damage the 303 00:25:13,265 --> 00:25:17,353 villi. Ulcerative Colitis is another gastric 304 00:25:17,353 --> 00:25:23,291 disorder related to Chrons disease, but this occurs in the large intestine. 305 00:25:23,291 --> 00:25:29,094 Diverticulosis also occurs in the large intestine, and causes pockets to form in 306 00:25:29,094 --> 00:25:34,212 the intestinal walls, where bacteria can enter and cause infection. 307 00:25:34,212 --> 00:25:42,500 Lastly, in the age of morbid obesity, gastric bypass surgeries and gastric 308 00:25:42,500 --> 00:25:47,463 banding can affect the digestive processes. 309 00:25:47,463 --> 00:25:54,947 In the case of banding where the opening to the stomach is made smaller, 310 00:25:54,947 --> 00:25:59,647 we still have an intact stomach. We still have an intact intestinal 311 00:25:59,647 --> 00:26:03,522 system. This is the least severe of the surgeries 312 00:26:03,522 --> 00:26:08,382 you can have, and it is highly reversible, and indeed, some individuals 313 00:26:08,382 --> 00:26:14,282 even have flexible bands where they can change the size depending on the day. 314 00:26:14,282 --> 00:26:20,937 Whether that's counter-intuitive or not, is up to you to decide, but again this is 315 00:26:20,937 --> 00:26:26,474 one process that one can undergo. In addition to banding, there is the 316 00:26:26,474 --> 00:26:32,075 process of sleeve gastrectomy. This is, has been shown to be effective 317 00:26:32,075 --> 00:26:36,980 in aiding in weight loss. Here we see that the upper portion of the 318 00:26:36,980 --> 00:26:40,362 stomach is stapled, and part of the stomach's removed. 319 00:26:40,362 --> 00:26:44,849 The remaining portion is what we call, is what the sleeve is referring to. 320 00:26:44,849 --> 00:26:49,587 So we still have a stomach, and again, we still have an intestinal tract. Very 321 00:26:49,587 --> 00:26:54,342 importantly, we still have a duodenum. What this does is reduces the size of the 322 00:26:54,342 --> 00:26:58,712 stomach, so someone with the surgery is going to feel full much quicker, and 323 00:26:58,712 --> 00:27:03,348 therefore, eat less. The most invasive surgery is gastric 324 00:27:03,348 --> 00:27:07,984 bypass surgery. In this surgery, you will actually remove 325 00:27:07,984 --> 00:27:12,061 the stomach. and the initial part of the intestinal 326 00:27:12,061 --> 00:27:15,896 tract. So think about what we just talked about, 327 00:27:15,896 --> 00:27:21,482 how important the duodenum is for the complete digestion of our food. 328 00:27:21,482 --> 00:27:27,742 Individuals with gastric bypass surgery certainly have been shown to have 329 00:27:27,742 --> 00:27:34,672 significant weight loss, but after the surgery, good nutrition is essential, and 330 00:27:34,672 --> 00:27:38,850 supplementation is most likely going to be needed.