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Hormones in Digestion_Final

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>> The Greek physician Galen viewed the stomach as a feeling being that knew when it was empty or full. He believed that nature granted the stomach the ability to feel when there's a lack of food, which then motivated a person to go out and seek food. Does the stomach feel? In this lecture, we're going to talk about what the organs sense and how they communicate in order to perform the complex tasks of emptying the organs, changing pH levels, releasing enzymes, and more. It may not work quite like Galen thought, but there's an extensive network of hormones and neurotransmitters that send signals back and forth from the gut to the brain or from the gut to various organs. Even if there are many signals going back and forth, the gut doesn't rely on the brain to operate. There are neurons in the gut that control mobility, nutrients absorption, and the release of enzymes so that digestion can keep going no matter how distracted we get. Hormones and neurotransmitters are the chemical signals that help keep digestion moving forward. These hormones are released by endocrine cells in the gut and the pancreas. To clarify, endocrine cells are a collection of cells that secrete hormones in the body. The gut has more endocrine cells than anywhere else in the body. It is the largest endocrine organ. Think of hormones as communication signals, taking a piece of information from one area and sending it to another, like a telegram with encoded information. These messages regulate many of our bodily functions. Much of this signaling is done in response to the presence of nutrients as if the entire body is saying, "Hey, guys, dinner's ready. Grab the crew, and let's eat." There are five hormones present in all mammals which regulate digestion. They are gastrin, secretin, cholecystokinin, gastric inhibitory peptide or GIP, and motlin. When food arrives and expands the stomach, it triggers gastrin to be secreted. Gastrin is the messenger that tells the stomach to release hydrochloric acid and pepsin for digestion. It's as, "Hey, guys, let's sterilize and demolish this stuff." Gastrin keeps going until the pH is lowered enough to adequately do its job of decontamination and breaking down proteins. Pepsin loves to work in a low pH environment. Gastrin also stimulates the growth of stomach lining and mobility. Gastrin is also stimulated by caffeine, alcohol, and undigested proteins. A low pH inhibits this hormone because when the pH is lowered, it knows its job is done. Secretin is a hormone that helps regulate water and pH. Once food passes from the stomach into the duodenum, secretin is notified that there's low pH coming its way in the form of moist food. It knows to stimulate the pancreas to release sodium bicarbonate to raise the pH. That way, the enzymes needed for the next phase can activate, as they prefer the higher pH. This also prepares the small intestine for absorption. Secretin stimulates bile production in the liver. This is in perfect concert with our next hormone that makes sure that bile production has a place to go since bile is needed to break down any fats along the way. Cholecystokinin is also released in the duodenum. This hormone stimulates the gall bladder to release its bile by sending a signal for it to contract. It also releases digestive enzymes in the pancreas when fat is present. The next hormone is gastric inhibitory peptide or GIP. It's an enzyme that slows down the churning of the stomach and inhibits the acid as it releases partially digested food, or chyme, into the small intestine. It also induces insulin. Insulin is a hormone that is made by the pancreas. Since sugar cannot go into cells directly, we rely on our friend the pancreas to help us out. When we eat sugar, insulin attaches itself to the cell wall and helps it absorb the sugar. Sugar is a great energy source when eaten in moderation and from the right sources. Another great thing insulin does is signal the liver to store extra sugar for those cold and barren winter nights. Now many of us don't face that type of struggle or deprivation anymore, but you can see why this was a useful trick for our ancestors and how it can be useful in times of emergency. Onto our next hormone, motilin. In the duodenum, this hormone increases what we call migrating myoelectric motor mobility. Myoelectric motor mobility is a wave of electrical activity that passes through the intestines during a regular fasting period. Think of this like a night shift janitor. This janitor comes in and cleans and sweeps when no one else is around, picking up the undigested pieces. The intestine likes to keep a clean house. The sound of growling that we come to associate with hunger is actually the sound of the stomach being cleaned. Let's take a minute and look at this often overlooked process. Fasting was a part of many cultures, for spiritual purpose or lack of resources, but only now are we starting to understand the importance of this phase of digestion in overall gut health. We know that during the migrating motor complex, any bacteria that have traveled into the small intestine are ushered back into the large intestine. This is the time for the rest of the phase of rest and digest. This often overlooked function is one of the most important. Now that we've covered these five digestive hormones, let's talk about the famous hunger hormones, ghrelin and leptin. Ghrelin, even just sounds like a hungry stomach. Pardon me, ya'll, that's just my stomach ghrelin. Ghrelin is released by the stomach and targets the pituitary gland signaling the brain that the stomach is empty and needs to eat. Maybe this is what Galen was talking about. On the opposite team is leptin, made by fat cells. This hormone decreases appetite. Now let's all go out, bottle up leptin and sell it. I'm kidding. There are, however, ways to help increase your body's natural production. We'll go over this later on in the course when we discuss nutrition. As I mentioned at the beginning of this lecture, hormones and neurons regulate the digestive tract. These neurons are part of the enteric and central nervous system. Haven't heard of the enteric nervous system? It's the brain in your gut, the one that operates completely independently from the brain in your head. Don't worry if this is a new concept for you, we'll cover it in detail later on. In short, for now, the digestive tract has 100 million neurons from mouth to anus. These neurons coordinate what we called long and short reflexes. Long reflexes are controlled by sensory neurons that send signals to the central nervous system and to the brain. So when you think about that freshly baked cookie in the bakery case and you start to salivate, it's because the message was just sent to your hippocampus that food is coming. That's the long reflex. Short reflexes are messages passed around the gut by hormones and neurons. These are messages that don't have to go to the brain. They happen in the gut, they're sent in the gut, and they're received somewhere in the gut. All of this is done using its enteric nervous system so that reflex can happen quickly and automatically based on what's needed in the moment. So for example, when your stomach distends because you just ate a few slices of pizza, your body starts to secrete enzymes and hydrochloric acid. This all happens outside of your conscious awareness while you're typing report and scarfing down your lunch. As many of us do, you may even forget your eating or not notice that you're full because your brain doesn't have to tell your stomach to start digesting. This has its perks and it has its setbacks. There are also reflexes that control everything from movement to waste leaving the anus. When we put together hormones and reflexes, we can see that digestion is influenced by these signals which regulate glands, and instruct them to secrete enzymes, and influence motility and movement of food via muscle contraction. Gastrointestinal hormones were discovered by Bayliss and Starling in 1902. This is the same team that discovered that the gut could continue its process of reflexes for digestion even when no longer connected to the brain. To them, this signified that the gut has its own nervous system. As we said at the beginning of this lecture, we now know that the gut has more neurons than the entire spinal cord. Through this chemical network of hormones and neurons, we're able to keep an incredible complicated system running smoothly. Isn't that impressive? We have a number of reflexes, some that come from the brain and others come from within the gut. Through this process, we're able to sift through and digest just about anything. Here's a challenge for you. Next time you have a judgmental thought about your body, think about how many parts and systems are perfectly coordinating inside of you every day, making tasks like digestion look simple and easy. Your body is like a super intelligent computer. Thank you for joining me to learn about the hormones that play a role in digestion. Now it's time for you to rehearse your new found knowledge by completing the hormones and digestion fill-in-the-blanks handout in your Learning Center. I hope you enjoyed this lecture, I know I enjoyed sharing this information with you. See you soon.

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Duration: 9 minutes and 20 seconds
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Language: English
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Posted by: ninaz on Mar 21, 2018

Hormones in Digestion_Final

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