0:00 Hello, in this video we're going to talk about the physiology of vomiting. 0:08 Vomiting is also known as emesis and throwing up, amongst many other terms, and 0:14 it is an 0:15 involuntary, forceful expulsion of the contents of one stomach, essentially 0:21 through the mouth. 0:23 We will look at the so-called "ematic reflex," which is the vomiting reflex. 0:29 And in order to understand the vomiting reflex, we need to talk about the brain 0:34 . 0:34 So here is the brain and the brain stem. 0:36 There's an area of the brain stem called the medulla oblandata, where we find 0:41 what's called 0:42 the vomiting center. 0:44 The vomiting center contains essentially muscularic receptors, types of 0:49 receptors, and when these 0:51 receptors are stimulated, within the vomiting center, this will trigger the 0:56 vomiting reflex, 0:57 so the process of vomiting. 1:01 Close to the vomiting center, also near the medulla oblandata of the brain stem 1:05 , is another 1:06 area called the chemoreceptor trigger zone, or CTZ for short. 1:13 Now, the CTZ, as the name suggests, gets triggered by chemicals. 1:20 But the CTZ contains a few types of receptors, and these are the dopamine 2 1:26 receptors and 1:27 the 5-HT receptors, 5-HT essentially is serotonin, so these are serotonin 1:34 receptors. 1:36 It's easy to remember CTZ because we know that chemotherapy stimulates this 1:43 chemoreceptor 1:44 trigger zone. 1:46 So when the chemoreceptor triggers on the CTZ is stimulated, it will then 1:51 stimulate the 1:52 muscularic receptors of the vomiting center, and when the muscularic receptors 1:57 of the vomiting 1:58 center are stimulated, this will cause the vomiting reflex, the ematic reflex. 2:06 Though the chemoreceptor trigger zone is located in the medulla, like the 2:11 vomiting center, 2:12 the chemoreceptor trigger zone is located conveniently outside the blood brain 2:18 barrier. 2:18 Now, the blood brain barrier is a barrier preventing circulating substances in 2:24 the blood 2:25 from making contact with the brain and areas of the brain stem. 2:31 Because the chemoreceptor trigger zone is situated outside the blood brain 2:34 barrier, it 2:35 is thus more permeable to circulating substances such as cytotoxic agents 2:42 chemotherapy. 2:44 Motion sickness is a very common thing people experience, and the cause of 2:49 motion sickness 2:50 actually comes from the inner ear, a bony structure called the labyrinth. 2:57 The labyrinth is made up of many areas, one of which is called the vestibule, a 3:01 structure 3:01 important for balance in space. 3:06 Problems here will send electrical signals to the brain stem via the vestibular 3:11 cochlear 3:12 nerve, and the signals will get sent to an area specifically in the brain stem 3:17 called 3:18 the vestibule nuclei, which is located in the pongs of the brain stem. 3:24 The vestibule nuclei contain histamine 1 receptors, and also muscarinic 3:33 receptors. 3:35 So when the vestibular nuclei is stimulated during, let's just say motion 3:40 sickness, or 3:41 during also morning sickness, these signals will then be passed on to the chem 3:48 oreceptor 3:49 trigger zone. 3:51 And from here, the chemoreceptor trigger zone will then send signals to the 3:54 vomiting 3:54 center in the medallablongata to trigger the vomiting reflex. 4:00 Another cause of vomiting are things that occur from the cerebrum, or the brain 4:06 , after 4:06 it has processed all this sensory information. 4:10 So what I mean is that, for example, when people are emotionally overwhelmed, 4:17 or when 4:18 people are in severe pain, or when they smell something really bad, or they see 4:24 something 4:25 repulsive, something really bad, essentially all this stuff will get sensed by 4:30 the brain 4:31 by the higher centers of the brain. 4:33 And from the higher brain centers, this will then, this signal then travel down 4:39 to the 4:39 vomiting center to stimulate the vomiting center to initiate the vomiting 4:45 reflex. 4:45 This makes sense, because some people get really nauseous when they see blood, 4:51 or guts, 4:51 or they smell something like a type of food that just smells horrible. 4:56 Again, the higher brain centers stimulate the vomiting center through muscar 5:02 inic receptors. 5:04 Other causes of vomiting occur in the stomach. 5:06 So let's just recap some anatomy here. 5:09 So we have the mouth, which connects to the esophagus, which will travel down 5:14 through 5:14 the diaphragm, which is the muscle muscular structure. 5:18 The esophagus will then join onto the stomach, and the stomach joins onto the 5:24 small intestine. 5:26 If we were to zoom into the stomach, we can see they form deep pits, deep pits 5:32 and glands. 5:34 And these are lined up by many different types of cells, one of which are 5:38 called enterochromophen 5:40 cells. 5:42 The enterochromophen cells release serotonin in response to cytotoxic agents. 5:49 Which is also, which is thought to stimulate then five HT3 receptors on sensory 5:56 nerve fibers 5:57 around the area. 6:00 And stimulation of this sensory nerve fiber, which is actually the vagal nerve, 6:04 will bring 6:05 this information to the vomiting center to trigger the vomiting reflex. 6:13 In summary, all the causes of vomiting we talked about essentially will 6:19 stimulate the 6:19 vomiting center, which is the output from which the vomiting reflex or the em 6:25 etic reflex 6:26 is initiated. 6:28 Let's focus on what the vomiting reflex is and actually what happens during the 6:33 process. 6:34 First, it actually causes the lower esophageal sphincter to relax, which makes 6:39 sense because 6:40 we need food to come up towards the mouth when we vomit. 6:45 We also need the diaphragm to contract and also the abdominal muscles to 6:50 contract so 6:51 that it will help push the food back up. 6:54 And this happens because we are increasing intra-abdominal pressure when we 6:59 contract 6:59 our muscles. 7:03 There are also autonomic changes such as tachycardia, which is increase in 7:08 heart rate. 7:09 And we also increase salvation as well as peristalsis. 7:14 The vomiting reflex also causes the epiglottis to close at the top part because 7:19 we don't 7:20 want food to travel down to the lungs. 7:23 And once the vomiting reflex does all these things, then the vomit or the food, 7:29 expulsion 7:29 of food can happen. 7:33 So that was the physiology of vomiting, the emetic reflex, the vomiting reflex.
