okay this is consul on of our absorption and excretion unit and we are gonna start with talking about the digestive system and if you're in my class we're gonna do kind of an intro inquiry activity because I want to see how much you already know about this system because this tends to be one that students are more familiar with so we're gonna do a fun activity but for now we're just for the sake of the video we're just gonna dive into these notes so a little overview of the system the overall function of your digestive system is to convert the food that we eat into the energy and raw materials that will build and fuel our bodies so we're gonna break down the food that we eat release energy from it to use it and then use those raw materials that I've made up the food we eat to then build whatever it is that our body needs at that time so the macromolecules and our food those carbs lipids proteins that we've been talking about since biology one they get broken down mechanically and chemically into their simplest form so we're physically gonna like break them down so they have a lot of surface area and then we're gonna use enzymes to digest them chemically as well and we really want to be as efficient as possible and not waste things which is kind of a theme you'll see throughout this unit and so that's something that your body has gotten really good at doing from there these simplest forms of these molecules that we eat they can be absorbed into our blood and then transported via capillaries and of course the rest of our blood vessels to to wherever the nutrients are then needed in our body at that point in time so our last unit in unit 4 we talked about blood and how it is our transporter of nutrients in the body well this is where those nutrients are coming from that our blood is transporting it's coming from the digestion of our food and I love this picture it doesn't show every structure of the digestive system as you'll see on the next slide it's only highlighting a few because your oral cavity in your head that would be up here that plays role also but I like it because you can see some of the key organs of the digestive system within the context of some of the organs that were in the respiratory and cardiovascular systems that we covered in unit 4 transport so you can kind of see here how your esophagus which connects to your stomach runs behind your trachea or your windpipe and remember your trachea connects to your lungs with your heart right here kind of in the middle you can kind of see how your esophagus runs back there we're gonna go through each of the structures the digestive system in detail in some Discovery stations and one of my favorite parts about these discovery stations is that we're also gonna talk about health issues and diseases associated with the different organs of the digestive system so we'll talk about things like heartburn how it's actually not in your heart it's in your esophagus but because it runs behind your heart or posterior to your heart it feels like it's in your hearts in your chest so those are all things we're gonna get into throughout this unit so let's continue with our ovary to you to talk about the structures so when we're thinking of the digestive system we're typically thinking of the structures that make up the alimentary canal this is another word for this is your gastrointestinal tract or your GI tract this so I'm gonna use alimentary canal and then like GI tract interchangeably so just don't referring the same thing this is essentially just a hollow muscular tube that runs from your mouth and they'll hold us there all the way to your anus which is another hole in your body and this tube is where the digestion and absorption of nutrients from our food is going down if we were to stretch out your alimentary canal it would be about nine meters or thirty feet long which is crazy so in your actual body it's not that long just because of muscle that you have all of these we'll see you have an assortment of like smooth muscles up in them but just think that's 9 meters or 30 feet long is the pathway that your food is traveling through just to go from your mouth all the way out of your body which is kind of crazy so when we're referring to the alimentary canal or the GI tract we're talking about your mouth your Fair Nicks your esophagus stomach small intestine and large intestine but there are also accessory or support structures like your teeth your tongue salivary glands gall bladder liver and pancreas so we're going to talk about each of these things in our discovery stations so before we get to that though I'm actually gonna do an overview of the digestion process so that then when you're reading about each of the individual organs in the alimentary canal you'll have the context of the role that they play within digestion so think of digestion as like a disassembly line of your food so we're taking of our part your food piece by piece and we divided into six kind of overall steps but these aren't necessarily sequential some of them are happening simultaneously they're happening in multiple places at once but just for the sake of understanding I'm numbering them into six steps but again don't think of them as after number two then comes number three and then only after three is done then comes four that's not the case at all a lot of this is going on all at once so first is ingestion this step is actually only oh sorry I'll say that a minute then we have propulsion mechanical breakdown chemical digestion absorption and defecation and ingestion is only happening in your mouth these next four are happening in multiple organs along your GI tract and they're all kind of working together cooperatively to accomplish these four steps and then defecation is occurring only in your large intestine okay I want to talk through each of these briefly so that you'll have some context before the discovery station so first ingestion what is that that's just eating that's all it is your teeth are an accessory structure in the ingestion process they start mechanical breakdown by chewing up your food so we're already talking about the second step or excuse me the third technically numbered step here so again there's overlap so your teeth start crunching up your food your salivary glands another accessory structure they start the chemical digestion by releasing enzymes like amylase i'm just start digesting foods like starches already in your mouth right there after ingestion which is happening in your oral cavity or your mouth then we have propulsion so this is the movement of food through your gastrointestinal tract and this is happening throughout the whole entire process through every structure really it starts with voluntary swallowing of the bolus bolus is just what we would refer to the ball of chewed up food that's in your mouth we refer to that as a Bullis so it starts with you choosing to swallow that and then most of the rest is an involuntary process called peristalsis which we can see pictured here where essentially they're your smooth muscles that are in your esophagus and your stomach and your intestines they can tract and relax in order to propel or move the bolus and your digested food through the alimentary canal and then eventually out of your body the mechanical breakdown is just the physical breakdown of the food you eat and the purpose of that is to is twofold one to increase the surface area of the food that you've eaten because that's gonna help us with absorption that's gonna help us maximize what nutrients are absorbing but then also think about as you're chewing and foods moving around in your mouth you're mixing it with enzymes as well in your mouth and in other parts of your body and that's going to help then with the chemical digestion portion portion chemical digestion is for using secreted enzymes and all these different structures of your body to chemically break down the food molecules that you need into their simplest forms basically monomers if you remember that term from biology one so that then we're able to absorb into the blood what we need to use and then transport it via the blood to whatever cells need these nutrients absorption is the process of that transport of the end results of our digested food through the walls of the GI tract and into your blood or it can also be absorbed into lymph which is something we're gonna talk about in unit 6 which is our protection unit so we'll talk about the lymphatic system then so for now just really think of blood and then it can then be transported so these monomers these vitamins minerals they'll be then be used for cellular respiration in ourselves so going back to biology one that's where the glucose that we talked about in cellular respiration that's where it's coming from or just whatever other process is needed at the time maybe we're gonna take amino acids and reassemble those into proteins that certain cells need to accomplish a process it's totally dependent on what the cell needs and when and then last is defecation which is a fancy term for the elimination of the indigestible substances through the anus as feces or poop so we are gonna stop in class and talk about all these different structures I've been mentioning in some detail through these stations and you're gonna label a big body diagram of them but for the sake of the video I'm gonna keep trucking along so back in unit 1 we talked about histology and tissues and I want to kind of bring those up again and talk about that some of the tissues very briefly that make up the gastrointestinal tract because you remember one of the major themes of anatomy and physiology is that form dictates function and so you're gonna see how the structure or the form of the tissues that make up the GI tract or how the GI tract is able to do all the different roles that it does in accomplishing the digestion of our food so most of the structures in our GI tract have four main layers to them so these are the actual layers of the organs and if you remember or from your text or from forever ago we didn't enter to histology you have the perineum which is a serous membrane that's are some serious memories that are lining your abdominal pelvic cavity so we're not talking about that we're talking about the actual organs within your abdominal pelvic cavity cavity excuse me and the layers of those tissues so the innermost layer is mucosa and it secretes mucus enzymes and hormones and it also absorbs nutrients into the blood and protects against infectious diseases the submucosa is the next layer and it's kind of a middle layer and it's made of loose areolar connective tissue and it gives the tube elasticity and some flexibility then you have the muscularis externa which is a middle layer of smooth muscle or it can be you know multiple layers of smooth muscle and these play a role in peristalsis which is that propulsion process of how we move the food through the tract and then we have serosa which is the outermost layer of loose connective tissue and that when you look at this kind of close-up here we can see and you can kind of see some other parts too but that's where nerves and blood vessels and lymphatic vessels for each structure are going to be are gonna be nourishing and and playing a part continue with this ology just again this is such a brief overview epithelial tissue also plays an important role in many of the organs by creating a selectively permeable lining so specifically stratified squamous epithelial cells and your mouth esophagus and anus are there to protect against abrasive foods so think of when you've eaten something like really crunchy like a ruffle potato chip that he said those that layer of epithelial cells is keeping your mouth from getting scratched essentially by that and then we also have simple columnar epithelial cells that line our stomach and intestines and those are critical for absorption and secretion of substances all right so connecting back all the way to biology one into unit one intro to anatomy where we reviewed basic biology concepts I want to do a brief overview of some of the digestive enzymes that are playing a role in making the chemical digestion of our food possible and where they are and what they're digesting so amylase is a digestive enzyme it's mainly in your saliva your salivary glands secrete it and it starts the digestion of starches which are if you remember from biology one or complex carbohydrates so it starts that process in your mouth and amylase is trying to break those starches down into a simpler sub component of it which is maltose which is a disaccharide another digestive enzymes are pepsin and HCl hydrochloric acid which are in the gastric juices that the stomach secretes they help to digest proteins and what they form is just partially digested protein so they're starting the process of breaking down proteins protease is lipases and amylase like we mention up here also are in the pancreatic juice that your pancreas secretes and these help break down those proteins fats that are in the bile um that are surrounded by bile and also starches which we started digesting here and they can break down those proteins into peptides and amino acids and break down those thoughts into fatty acids and glycerol and break down starches into things like maltose which is just a type of sugar peptidases sucrase lactase and maltase are all intestinal enzymes that your intestines secrete they digest peptides which are just short chains of amino acids and then also sucrose lactose and maltose put your sugars lactose is specifically the sugar in milk and it's gonna break down those peptides and amino acids and then sucrose lactose and maltose into monosaccharides like glucose fructose and galactose so even simpler sugars then where we're trying to get them down to their simplest forms in order for them to be absorbed and at last are bile salts that are in your liver bile bile they're not technically enzymes but they help with the breakdown of fats we couldn't break down thoughts without them and they break down your thoughts into fat droplets then how are easier to be digested by the body and absorbed okay so how is this all regulated we're gonna do a brief overview before we wrap up so the enteric nervous system that prefix and tear or inter it looks like inter is just referring to get so anything that has that prefix is just referring to your gut so it's like your guts nervous system this is an in-house nerve supply that's just for your GI tract for regulating activities of the digestive system it's considered part of your autonomic nervous system which they actually be a very familiar term from unit 3 control and coordination and it has receptors that respond to external stimuli such as seeing smelling tasting or thinking about food I mean you can think about something that you really want to eat like fresh pizza and it'll make your mouth water and that is because you have receptors that are responding to that but also internal stimuli too so an internal stimulus can be mechanical like the actual stretching of your stomach for instance or it can be chemical like a change in pH or the presence of a certain end product can then cause some sort of signal so this is all part of the enteric nervous system so it's actually crazy so we'll talk about the vagus nerve on the next slide but it's actually been studies that found that if we sever the vagus serve which is the cranial nerve that runs from your brain all the way into your abdomen that the enteric nervous system can still function independently so it's almost like an entirely independent secondary nervous system in your body which is kind of crazy and pretty cool so it communicates with your central nervous system via that vagus nerve I just mentioned which is the longest cranial nerve in the body starts up here and goes all the way through your abdomen and all these different organs it has both sensory receptors and then also motor functions as well and again it connects the brain to the GI tract and other things but it's not just the nervous system your endocrine system has a role too of course because it is also part of controlling and coordinating everything in your body so hormones have a significant role tons of examples of hormones like G cells they produce a hormone called gastrin your inter endocrine cells so your gut into current cells release hormones like serotonin and histamine and then these are hormones can increase and activate the release of things like hydrochloric acid and stimulate muscle contractions in your stomach and intestines and do all these things that make those six steps of the digestion process happened and make it possible alright last gastric fluid secretion specifically so the that's what the fluid that's getting secreted into your stomach is controlled in three phases and/or places so I want to mention this under regulation before moving on so first there's the cephalic phase which is our reflex phase that's occurring in your brain so this is before food even enters your stomach you have external stimuli like we mentioned seeing her smelling food those signal your hypothalamus and your the medulla oblongata and your brain which triggers parasympathetic fibers in the vagus nerve to start prepping your food or your stomach to say that foods gonna be coming we should be stimulating the secretion of gastric fluid you also have the gastric phase of regulation which is actually happen in the stomach so mechanical stimuli get activated by stretch receptors in your stomach and that causes the secretion of more gastric fluid chemical stimuli activate chemo receptors in your stomach as well which cause your G cells to release gastrin which is the hormone that signals the increase of that HCl secretion and then also your intestinal phase so this is happening in your intestine receptors in the duodenum receive time and that causes intestinal cells to again secrete more gastrin these are all examples of how each of these phases have stimulatory events but similar signaling mechanisms work in these phases in the opposite direction in order to inhibit the secretion of gastric fluid so we can work both ways and this is how we are able to control the rate that the stomach is digesting food and thus emptying and the small intestine is taking that on so that your small intestine doesn't get overloaded because once food is enter your small intestine you can't throw it up anymore and so we don't want to overload that system in your body all right that is concept one and we and class are now we're going to practice modeling the digestive system just so we can understand it a bit better