Understanding the Digestive System Essentials

Hi everyone, this is the first video for Chapter 22, the digestive system. So as you're watching this video, I'd like for you to follow along with your outline notes. So just a quick overview of the digestive system. Essentially, the digestive system consists of two major parts. One is the alimentary canal, or commonly called the gastrointestinal tract, or the GI tract, and that's the long tube. that starts with our oral cavity or our mouth. And if you were to trace that tube, right, all the way down, that's the entire GI tract, all the way from mouth, all the way to the opening of the anus. Then we have accessory structures. And accessory structures are not part of the tube. They just secrete substances into the tube or into the tract. And those accessory structures are located right here. the liver, the gallbladder, and the pancreas. So the digestive system, as you can see, sits right here. You can see on the left side how it sort of fits in with all of the other organs of the different organ systems of the human body. But let's just trace like a piece of food along the GI tract, and we'll talk about the different the different structures that that food would would go through. So first we have the oral cavity. That's pretty easy. That's the mouth and the other accessory structures that are located in the mouth. So we have the tongue, the teeth, and then of course we have the salivary glands. They are paired glands. So one on each side of the mouth. They are the parotid, the submandibular. and the sublingual glands. So they are salivary glands. They too are accessory structures. Again, food or food substance will not pass through accessory structures. The accessory structures secrete into the digestive tract. So the tract itself is the oral cavity to the pharynx. The pharynx is your throat. Okay. Remember, the pharynx is part of the respiratory system too. And that should make sense to you. If you were to breathe in air, you know that air goes into your throat or your pharynx. And when you chew and swallow food or drink water, you know that that also goes into your throat, right? It goes into your pharynx. So the pharynx or your throat is the shared structure. And it's shared between the respiratory system and the digestive system. So again, oral cavity to pharynx to this long, smooth tube called the esophagus. Then the food would go into the stomach. And after it passes the stomach, it moves into the small intestine. There are three portions of the small intestine. We'll talk about those later on. And then the food won't move. It's really not called food at this point. But the food substance will move into the large intestine. And anything that's not absorbed as nutrients is packed into waste product and excreted through the anus as feces. So, again, moving on or repeating, I should say. Let's go. Oral cavity. pharynx, esophagus, stomach, small intestine. The small intestine is small because of the lumen, right? Not the length of it, but the lumen size. Large intestine, again, large because of the lumen size, anus. The accessory structures, again, the accessory structures are structures that secrete substances. What are substances? Enzymes or hormones. Bile, so it depends on the accessory structure. So salivary glands are an accessory structure. They secrete their substance into the mouth. Oops, sorry about that. Another accessory structure is the liver. The liver secretes its substance, predominantly secretes bile, and the bile is stored in the gallbladder. So the gallbladder is another accessory structure. And then we have this fish-shaped structure called the pancreas. The pancreas and the gallbladder secrete directly into the first portion of the small intestine called the duodenum. So they are the major accessory structures, salivary glands, liver, gallbladder, pancreas. And then of course we have the alimentary canal or the GI tract, and that's the long tube starting with mouth, ending with anus. It's kind of an overview of the major structures of the digestive system. Now, before I move on, I want to talk about the major functions of the digestive system. Now, of course, you know, the digestive system involves eating. and creating waste product, right? The important part of the digestive system is to take what we eat and break that down into its very basic forms, its smallest forms, so we can absorb those nutrients. The whole name of the game is to absorb the nutrients so the cells can use the nutrients to continue. to do their jobs, right? So the nutrients are also part of that job and continuing to make ATP in order to continue to live and thrive. If we don't get nutrients, the cells can't function properly. If cells don't work, tissues don't work, organs don't work, et cetera, et cetera. The digestive system has a bunch of different functions. One is ingestion. That's just bringing in food. Secretion. deals with secreting different enzymes, different hormones. Propulsion is another function of the digestive system. And propulsion is just the movement of the food and food products through the entire digestive tract. So propulsion is accomplished by rhythmic movement of smooth muscle. So in Biology 109, you probably learned that there's a lot of smooth muscle that is found in our digestive system. So as smooth muscle contracts, that moves food or food substance along our digestive tract. Remember, smooth muscle is involuntarily controlled. So that means we are not consciously moving our food from our stomach to our small intestine. That would be too much work, right, to think about that. You don't want to move your piece of pizza. Like, okay, time to move to the duodenum now. We don't do that. So it's involuntarily controlled. And the actual definition of rhythmic contractions of smooth muscles, that term is called peristalsis. And when you think of peristalsis, I want you to think of a tube. Actually, I think it's easy to think of a tube of toothpaste, right? When you squeeze your tube of toothpaste to get the toothpaste on your toothbrush, you squeeze from the back and you squeeze forward to get the toothpaste onto the toothbrush. I hope this makes sense. This is the same way we have peristalsis along the digestive tract. So the smooth muscle is contracting behind the food, pushing the food. in this case, down, right? It's pushing it down the digestive tract. So the contraction would be here and the food would be here, moving it along. Think of squeezing a tube of toothpaste. Okay. So that's peristalsis. We got to move the food along the digestive tract, right? We don't rely on gravity. We rely on smooth muscle movements. The next two are really important. I'm looking at your outline. So again, please follow along. One is digestion. Obviously, digestion occurs in the digestive system. Two is absorption. So there are two types of digestion that occur in our digestive system. One is mechanical digestion. And the second is chemical digestion. Usually when we just refer to the word digestion, we're referring to chemical digestion. But mechanical digestion is just breaking a large piece of food into smaller pieces of food. If I eat a peanut butter and jelly sandwich and I chew it, right, with my teeth, breaking apart that peanut butter and jelly sandwich, right, one bite of the peanut butter and jelly sandwich to little tiny pieces of peanut butter and jelly, that's mechanical digestion. In chemistry class, we call that a physical change. It's. Breaking something large into smaller pieces, but not disrupting any chemical bonds. So I take a piece of peanut butter and jelly sandwich. I chew it. It's still peanut butter and jelly. I haven't chemically changed it at all. That's an example of mechanical digestion. Make sense? If I churn my stomach and break things apart, right? I'm not breaking bonds. I'm just breaking a big piece of food into smaller food. That's mechanical digestion versus chemical digestion. Chemical digestion needs to occur for absorption to occur. And chemical digestion breaks apart big macromolecules, big molecules into smaller molecules. Let me show you here. See if I can write here. Okay, so let's talk about peanut butter and jelly. I'm eating peanut butter and jelly. I'm chewing it. Chew, chew, chew, chew, chew. I still have peanut butter and jelly. That's an example of mechanical digestion. Now, as I swallow that peanut butter and jelly, right? And let's trace it. I swallow it. It goes past my larynx, through my esophagus, into my stomach. Now it's churning with some enzymes. And we know that enzymes help speed up chemical reactions. So now we're going to break that down. What's a peanut butter and jelly? It has carbohydrates. It has lipids. It has protein. So let's start with those three macromolecules, right? Carbs, lipids, proteins. Big old carbohydrates, big starch molecules, right? From my bread. They are too big to be absorbed. And when I say absorbed, I mean, it's going from this tube, the digestive tract. into our bloodstream. That's what absorption means. It's going from the digestive tract into the blood. Cause listen, if it remains in the digestive tract, right? If it remains in this tube, where does it go out to the environment? So we have to get it out of the tube into the blood that's absorption. So with carbs, we would start with like, um, I keep moving my computer. I'm sorry. With carbs, we would start with big carbohydrates. They are called polysaccharides. I'm going to abbreviate it. You don't abbreviate it. So polysaccharides cannot be absorbed. They're too big. Poly, many saccharides, too big. So there are enzymes. I'm not going to mention them yet, but we will learn them. Enzymes. that break the chemical bonds and make those big polysaccharides into their building blocks. And the building block, the goal is to get monosaccharides, mono one. And the monosaccharides, if digestion is complete and we end with monosaccharides, that's a star. And we end with monosaccharides. Monosaccharides can be absorbed. That means they can get to our bloodstream and our cells can use them. Polysaccharides cannot be absorbed. So I eat my bread, right? And if it just stays bread throughout the digestive tract, nothing is absorbed. But through the help of enzymes, we break down those polysaccharides into monosaccharides. And they're able to be absorbed into our bloodstream to be used by ourselves. Okay, so that's the carb example. Let me clear it. Now let's do a lipid example. Okay, so we can eat and consume many different kinds of lipids. What are lipids? Lipids are fat. right so we can consume many different kinds of lipids some of which are called triglycerides there's many others we'll just start with triglycerides big triglyceride is a big lipid right can we absorb it as is no we can't too big too big can't get it to the bloodstream So by the work of enzymes, again, we will learn the specific enzymes. By the work of enzymes, we break down those big fats into little fats. And one example of little fats, little tiny fats that we can absorb are called free fatty acids. So we break down big lipids with the help of enzymes in our digestive tract to get free fatty acids. Free fatty acids, boom. If we digest completely. the lipids we consume and get free fatty acids, free fatty acids can be absorbed. They're absorbed through the lymph system rather than blood. And we'll get to that later on, but still we have absorption, which is a good thing. We need absorption. So our, our cells can get the fuel they need to continue to be active, productive, make ATP, right? We've been saying cells need oxygen to make ATP. Cells need oxygen to make ATP. They also need nutrients. So here it is. This is why we have to eat clear. Last one that I'm going to talk about right now, proteins, right? I'm eating my peanut butter and jelly sandwich. It has peanut butter. Peanut butter has protein in it. Proteins are big, right? They are big, organic. molecules, too big to be absorbed, right? Too big to be absorbed. Sometimes proteins are referred to as polypeptides, right? I couldn't write that down. Polypeptides. Sometimes they're just referred to as proteins, regardless, it's too big. So we use enzymes to help break them down in the digestive tract. in this tubing here. When the enzymes work and they chemically break the bonds of the polypeptide, we get the building block of protein. The building blocks of our proteins are called amino acids. Boom. If we get amino acids, we get nutrient absorption. We have to break proteins all the way down to amino acids in order to get absorption of those amino acids. into the bloodstream, the cells then use the amino acids for a variety of things. I hope this makes sense. So we have digestion and then we have absorption. Two very important processes. If you cannot digest, you cannot absorb, right? If you have a problem with something that aids in digestion, like enzymes, if you have a problem here, and you can't get to here, not only can you not digest, you can't absorb. So if you can't absorb, your cells are not going to be healthy. They can't function properly. That's an important concept. Okay. Let's see here. Regulation of motility, regulation of movement through the digestive system. We know that the autonomic nervous system controls. our organs and there's two branches of the autonomic nervous system. We have sympathetic nervous system, fight or flight, and we have parasympathetic nervous system, rest and digest. The one that drives the digestive system is rest and digest, which is the parasympathetic nervous system. We also have hormones that help also regulate motility through the digestive system, digestive tract. Continuing with the digestive system part A, you can take a look at the oral cavity. We briefly talked about the oral cavity. That's the mouth, teeth, tongue, salivary glands. As you move through the digestive system, I suggest that you take different color highlighters. or crayons or pens, whatever it is, because we have a lot of enzymes that you'll be memorizing. I, and, and along with that, you'll also be memorizing different hormones and you'll be memorizing different reflexes, different organs. So I would assign a highlighter color for each one, like organs, digestive organs would be. yellow. So every time I looked in my notes inside digestive organ, right, oral cavity, pharynx. um, esophagus, like any part of the digestive tract, I would highlight in yellow. Maybe I would even assign accessory structures, a different color, teeth, tongue, salivary glands, all a different color green. Maybe then I would, every time we talked about enzymes, um, I would use a different color highlighter, maybe pink, right? So every time you see an enzyme throughout your notes, it would be highlighted in pink. So when you're going back and you're studying, everything that's pink would be an enzyme. Everything that's orange would be a hormone. Everything that's yellow would be an organ of the alimentary canal, something like that. I think that's just an easier way to organize your notes so that when you're going back and you're reviewing everything, it kind of makes more sense rather than like searching and being like, what is that? Is that a hormone? Is that an enzyme? I can't remember. Just, you know, as you're moving through. I would do that. I'm just looking here, esophagus. So you can move through the salivary gland. Salivary glands is the first gland that will secrete enzymes into the mouth. So digestion actually very much begins right in our mouth. The enzyme that really is working in our mouth is called salivary amylase. Any amylase will start digesting carbohydrates. So what we just wrote before for carbohydrates, that's the digestion of polysaccharide eventually into monosaccharides. Obviously in our mouth, we don't have complete digestion, but it's starting the process. The pharynx is the throat. That's just kind of like a through way. Let me see here. And then we hit the esophagus. The esophagus, the tissue, the epithelial tissue associated with the esophagus is stratified squamous epithelium. That is that epithelium stratified is many layers. That's a protective epithelium. So it aids in protection. And then the important thing that's happening during the, within the esophagus. is the swallowing reflex, and that's called deglutition. So swallowing is in three phases. This is an image from your textbook, figure 22.9. Swallowing occurs when the food, we call it a bolus. So the bolus is the chewed food that's mixed with salivary amylase and lingual lipase, and it's going to be swallowed. So the first phase is the voluntary phase. That's you chewing and moving it back. towards your pharynx, towards your throat. Once it hits that, then we're off to the races. So this is where the reflex begins. And this second phase is called the pharyngeal phase. This is when the bolus moves into the actual pharynx, the soft palate and uvula lift to close the nose, right? So we only want the bolus to move down into the esophagus. We don't want it to go up. out your nose. So we have to have that uvula, that little punching bag that's in the back of your, I won't show you, but the little punching bag that's in the back of your throat, that has to lift when we're swallowing. So it blocks off the nasal cavity. We don't want the food to go up and out the nose. We just want it to go down the esophagus. The other thing that happens during the pharyngeal phase is this little flap of elastic tissue called the epiglottis seals off the larynx. So the food doesn't go down the trachea. The food only goes down the esophagus. If you've ever been, if you've ever like taken a sip of water and accidentally take a breath in or take a sip of water and try to talk and you have that coughing reflex and then like you stop and you're like, oh, sorry, that went down the wrong pipe. That's this process being bothered. So if you're doing that and you accidentally have your epiglottis not cover your larynx, food or liquid could go down your trachea and that triggers one heck of a response because we certainly don't want food or liquid going down our trachea because then that would reach our lungs. We don't want that to happen. So we have that terrible coughing reflex to get whatever touched the trachea up and out of the trachea. So that's the tube you're talking about when you say, woo, went down the wrong pipe. It went down the trachea and we don't want that. And then finally we have the esophageal phase and you can see the waves of peristalsis that's moving the bolus of food from the pharynx down the esophagus eventually leading to the stomach. So here is the stomach. This is where I'll stop with video one and I'll continue stomach, small intestine, large intestine, and accessory structures for video two for chapter 22. Thanks for tuning in, everybody. I'll see you for video two.

Essentially, the digestive system consists of two major parts. One is the alimentary canal, or commonly called the gastrointestinal tract, or the GI tract, and that's the long tube. that starts with our oral cavity or our mouth. And if you were to trace that tube, right, all the way down, that's the entire GI tract, all the way from mouth, all the way to the opening of the anus. Then we have accessory structures.

And accessory structures are not part of the tube. They just secrete substances into the tube or into the tract. And those accessory structures are located right here. the liver, the gallbladder, and the pancreas.

So the digestive system, as you can see, sits right here. You can see on the left side how it sort of fits in with all of the other organs of the different organ systems of the human body. But let's just trace like a piece of food along the GI tract, and we'll talk about the different the different structures that that food would would go through.

So first we have the oral cavity. That's pretty easy. That's the mouth and the other accessory structures that are located in the mouth.

So we have the tongue, the teeth, and then of course we have the salivary glands. They are paired glands. So one on each side of the mouth. They are the parotid, the submandibular. and the sublingual glands.

So they are salivary glands. They too are accessory structures. Again, food or food substance will not pass through accessory structures.

The accessory structures secrete into the digestive tract. So the tract itself is the oral cavity to the pharynx. The pharynx is your throat. Okay.

Remember, the pharynx is part of the respiratory system too. And that should make sense to you. If you were to breathe in air, you know that air goes into your throat or your pharynx.

And when you chew and swallow food or drink water, you know that that also goes into your throat, right? It goes into your pharynx. So the pharynx or your throat is the shared structure. And it's shared between the respiratory system and the digestive system. So again, oral cavity to pharynx to this long, smooth tube called the esophagus.

Then the food would go into the stomach. And after it passes the stomach, it moves into the small intestine. There are three portions of the small intestine. We'll talk about those later on. And then the food won't move.

It's really not called food at this point. But the food substance will move into the large intestine. And anything that's not absorbed as nutrients is packed into waste product and excreted through the anus as feces.

So, again, moving on or repeating, I should say. Let's go. Oral cavity. pharynx, esophagus, stomach, small intestine.

The small intestine is small because of the lumen, right? Not the length of it, but the lumen size. Large intestine, again, large because of the lumen size, anus. The accessory structures, again, the accessory structures are structures that secrete substances. What are substances?

Enzymes or hormones. Bile, so it depends on the accessory structure. So salivary glands are an accessory structure. They secrete their substance into the mouth. Oops, sorry about that.

Another accessory structure is the liver. The liver secretes its substance, predominantly secretes bile, and the bile is stored in the gallbladder. So the gallbladder is another accessory structure.

And then we have this fish-shaped structure called the pancreas. The pancreas and the gallbladder secrete directly into the first portion of the small intestine called the duodenum. So they are the major accessory structures, salivary glands, liver, gallbladder, pancreas. And then of course we have the alimentary canal or the GI tract, and that's the long tube starting with mouth, ending with anus. It's kind of an overview of the major structures of the digestive system.

Now, before I move on, I want to talk about the major functions of the digestive system. Now, of course, you know, the digestive system involves eating. and creating waste product, right? The important part of the digestive system is to take what we eat and break that down into its very basic forms, its smallest forms, so we can absorb those nutrients.

The whole name of the game is to absorb the nutrients so the cells can use the nutrients to continue. to do their jobs, right? So the nutrients are also part of that job and continuing to make ATP in order to continue to live and thrive.

If we don't get nutrients, the cells can't function properly. If cells don't work, tissues don't work, organs don't work, et cetera, et cetera. The digestive system has a bunch of different functions.

One is ingestion. That's just bringing in food. Secretion. deals with secreting different enzymes, different hormones. Propulsion is another function of the digestive system.

And propulsion is just the movement of the food and food products through the entire digestive tract. So propulsion is accomplished by rhythmic movement of smooth muscle. So in Biology 109, you probably learned that there's a lot of smooth muscle that is found in our digestive system.

So as smooth muscle contracts, that moves food or food substance along our digestive tract. Remember, smooth muscle is involuntarily controlled. So that means we are not consciously moving our food from our stomach to our small intestine.

That would be too much work, right, to think about that. You don't want to move your piece of pizza. Like, okay, time to move to the duodenum now. We don't do that. So it's involuntarily controlled.

And the actual definition of rhythmic contractions of smooth muscles, that term is called peristalsis. And when you think of peristalsis, I want you to think of a tube. Actually, I think it's easy to think of a tube of toothpaste, right? When you squeeze your tube of toothpaste to get the toothpaste on your toothbrush, you squeeze from the back and you squeeze forward to get the toothpaste onto the toothbrush.

I hope this makes sense. This is the same way we have peristalsis along the digestive tract. So the smooth muscle is contracting behind the food, pushing the food. in this case, down, right? It's pushing it down the digestive tract.

So the contraction would be here and the food would be here, moving it along. Think of squeezing a tube of toothpaste. Okay. So that's peristalsis.

We got to move the food along the digestive tract, right? We don't rely on gravity. We rely on smooth muscle movements. The next two are really important. I'm looking at your outline.

So again, please follow along. One is digestion. Obviously, digestion occurs in the digestive system.

Two is absorption. So there are two types of digestion that occur in our digestive system. One is mechanical digestion. And the second is chemical digestion. Usually when we just refer to the word digestion, we're referring to chemical digestion.

But mechanical digestion is just breaking a large piece of food into smaller pieces of food. If I eat a peanut butter and jelly sandwich and I chew it, right, with my teeth, breaking apart that peanut butter and jelly sandwich, right, one bite of the peanut butter and jelly sandwich to little tiny pieces of peanut butter and jelly, that's mechanical digestion. In chemistry class, we call that a physical change. It's.

Breaking something large into smaller pieces, but not disrupting any chemical bonds. So I take a piece of peanut butter and jelly sandwich. I chew it.

It's still peanut butter and jelly. I haven't chemically changed it at all. That's an example of mechanical digestion.

Make sense? If I churn my stomach and break things apart, right? I'm not breaking bonds.

I'm just breaking a big piece of food into smaller food. That's mechanical digestion versus chemical digestion. Chemical digestion needs to occur for absorption to occur. And chemical digestion breaks apart big macromolecules, big molecules into smaller molecules.

Let me show you here. See if I can write here. Okay, so let's talk about peanut butter and jelly. I'm eating peanut butter and jelly.

I'm chewing it. Chew, chew, chew, chew, chew. I still have peanut butter and jelly.

That's an example of mechanical digestion. Now, as I swallow that peanut butter and jelly, right? And let's trace it.

I swallow it. It goes past my larynx, through my esophagus, into my stomach. Now it's churning with some enzymes. And we know that enzymes help speed up chemical reactions. So now we're going to break that down.

What's a peanut butter and jelly? It has carbohydrates. It has lipids. It has protein.

So let's start with those three macromolecules, right? Carbs, lipids, proteins. Big old carbohydrates, big starch molecules, right?

From my bread. They are too big to be absorbed. And when I say absorbed, I mean, it's going from this tube, the digestive tract. into our bloodstream.

That's what absorption means. It's going from the digestive tract into the blood. Cause listen, if it remains in the digestive tract, right? If it remains in this tube, where does it go out to the environment? So we have to get it out of the tube into the blood that's absorption.

So with carbs, we would start with like, um, I keep moving my computer. I'm sorry. With carbs, we would start with big carbohydrates.

They are called polysaccharides. I'm going to abbreviate it. You don't abbreviate it.

So polysaccharides cannot be absorbed. They're too big. Poly, many saccharides, too big.

So there are enzymes. I'm not going to mention them yet, but we will learn them. Enzymes.

that break the chemical bonds and make those big polysaccharides into their building blocks. And the building block, the goal is to get monosaccharides, mono one. And the monosaccharides, if digestion is complete and we end with monosaccharides, that's a star.

And we end with monosaccharides. Monosaccharides can be absorbed. That means they can get to our bloodstream and our cells can use them.

Polysaccharides cannot be absorbed. So I eat my bread, right? And if it just stays bread throughout the digestive tract, nothing is absorbed. But through the help of enzymes, we break down those polysaccharides into monosaccharides. And they're able to be absorbed into our bloodstream to be used by ourselves.

Okay, so that's the carb example. Let me clear it. Now let's do a lipid example. Okay, so we can eat and consume many different kinds of lipids. What are lipids?

Lipids are fat. right so we can consume many different kinds of lipids some of which are called triglycerides there's many others we'll just start with triglycerides big triglyceride is a big lipid right can we absorb it as is no we can't too big too big can't get it to the bloodstream So by the work of enzymes, again, we will learn the specific enzymes. By the work of enzymes, we break down those big fats into little fats.

And one example of little fats, little tiny fats that we can absorb are called free fatty acids. So we break down big lipids with the help of enzymes in our digestive tract to get free fatty acids. Free fatty acids, boom. If we digest completely.

the lipids we consume and get free fatty acids, free fatty acids can be absorbed. They're absorbed through the lymph system rather than blood. And we'll get to that later on, but still we have absorption, which is a good thing.

We need absorption. So our, our cells can get the fuel they need to continue to be active, productive, make ATP, right? We've been saying cells need oxygen to make ATP. Cells need oxygen to make ATP.

They also need nutrients. So here it is. This is why we have to eat clear. Last one that I'm going to talk about right now, proteins, right?

I'm eating my peanut butter and jelly sandwich. It has peanut butter. Peanut butter has protein in it.

Proteins are big, right? They are big, organic. molecules, too big to be absorbed, right? Too big to be absorbed. Sometimes proteins are referred to as polypeptides, right?

I couldn't write that down. Polypeptides. Sometimes they're just referred to as proteins, regardless, it's too big.

So we use enzymes to help break them down in the digestive tract. in this tubing here. When the enzymes work and they chemically break the bonds of the polypeptide, we get the building block of protein.

The building blocks of our proteins are called amino acids. Boom. If we get amino acids, we get nutrient absorption. We have to break proteins all the way down to amino acids in order to get absorption of those amino acids.

into the bloodstream, the cells then use the amino acids for a variety of things. I hope this makes sense. So we have digestion and then we have absorption.

Two very important processes. If you cannot digest, you cannot absorb, right? If you have a problem with something that aids in digestion, like enzymes, if you have a problem here, and you can't get to here, not only can you not digest, you can't absorb. So if you can't absorb, your cells are not going to be healthy.

They can't function properly. That's an important concept. Okay. Let's see here. Regulation of motility, regulation of movement through the digestive system.

We know that the autonomic nervous system controls. our organs and there's two branches of the autonomic nervous system. We have sympathetic nervous system, fight or flight, and we have parasympathetic nervous system, rest and digest.

The one that drives the digestive system is rest and digest, which is the parasympathetic nervous system. We also have hormones that help also regulate motility through the digestive system, digestive tract. Continuing with the digestive system part A, you can take a look at the oral cavity.

We briefly talked about the oral cavity. That's the mouth, teeth, tongue, salivary glands. As you move through the digestive system, I suggest that you take different color highlighters.

or crayons or pens, whatever it is, because we have a lot of enzymes that you'll be memorizing. I, and, and along with that, you'll also be memorizing different hormones and you'll be memorizing different reflexes, different organs. So I would assign a highlighter color for each one, like organs, digestive organs would be. yellow. So every time I looked in my notes inside digestive organ, right, oral cavity, pharynx.

um, esophagus, like any part of the digestive tract, I would highlight in yellow. Maybe I would even assign accessory structures, a different color, teeth, tongue, salivary glands, all a different color green. Maybe then I would, every time we talked about enzymes, um, I would use a different color highlighter, maybe pink, right? So every time you see an enzyme throughout your notes, it would be highlighted in pink.

So when you're going back and you're studying, everything that's pink would be an enzyme. Everything that's orange would be a hormone. Everything that's yellow would be an organ of the alimentary canal, something like that.

I think that's just an easier way to organize your notes so that when you're going back and you're reviewing everything, it kind of makes more sense rather than like searching and being like, what is that? Is that a hormone? Is that an enzyme?

I can't remember. Just, you know, as you're moving through. I would do that. I'm just looking here, esophagus.

So you can move through the salivary gland. Salivary glands is the first gland that will secrete enzymes into the mouth. So digestion actually very much begins right in our mouth. The enzyme that really is working in our mouth is called salivary amylase.

Any amylase will start digesting carbohydrates. So what we just wrote before for carbohydrates, that's the digestion of polysaccharide eventually into monosaccharides. Obviously in our mouth, we don't have complete digestion, but it's starting the process.

The pharynx is the throat. That's just kind of like a through way. Let me see here.

And then we hit the esophagus. The esophagus, the tissue, the epithelial tissue associated with the esophagus is stratified squamous epithelium. That is that epithelium stratified is many layers. That's a protective epithelium.

So it aids in protection. And then the important thing that's happening during the, within the esophagus. is the swallowing reflex, and that's called deglutition. So swallowing is in three phases.

This is an image from your textbook, figure 22.9. Swallowing occurs when the food, we call it a bolus. So the bolus is the chewed food that's mixed with salivary amylase and lingual lipase, and it's going to be swallowed.

So the first phase is the voluntary phase. That's you chewing and moving it back. towards your pharynx, towards your throat. Once it hits that, then we're off to the races. So this is where the reflex begins.

And this second phase is called the pharyngeal phase. This is when the bolus moves into the actual pharynx, the soft palate and uvula lift to close the nose, right? So we only want the bolus to move down into the esophagus. We don't want it to go up. out your nose.

So we have to have that uvula, that little punching bag that's in the back of your, I won't show you, but the little punching bag that's in the back of your throat, that has to lift when we're swallowing. So it blocks off the nasal cavity. We don't want the food to go up and out the nose. We just want it to go down the esophagus. The other thing that happens during the pharyngeal phase is this little flap of elastic tissue called the epiglottis seals off the larynx.

So the food doesn't go down the trachea. The food only goes down the esophagus. If you've ever been, if you've ever like taken a sip of water and accidentally take a breath in or take a sip of water and try to talk and you have that coughing reflex and then like you stop and you're like, oh, sorry, that went down the wrong pipe.

That's this process being bothered. So if you're doing that and you accidentally have your epiglottis not cover your larynx, food or liquid could go down your trachea and that triggers one heck of a response because we certainly don't want food or liquid going down our trachea because then that would reach our lungs. We don't want that to happen. So we have that terrible coughing reflex to get whatever touched the trachea up and out of the trachea. So that's the tube you're talking about when you say, woo, went down the wrong pipe.

It went down the trachea and we don't want that. And then finally we have the esophageal phase and you can see the waves of peristalsis that's moving the bolus of food from the pharynx down the esophagus eventually leading to the stomach. So here is the stomach. This is where I'll stop with video one and I'll continue stomach, small intestine, large intestine, and accessory structures for video two for chapter 22. Thanks for tuning in, everybody.

I'll see you for video two.

Transcript for:Understanding the Digestive System Essentials

Transcript for:
Understanding the Digestive System Essentials