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Biology: The Fate of Absorbed Nutrients


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  • Type: Video Tutorial
  • Length: 15:58
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 170 MB
  • Posted: 07/01/2009

This lesson is part of the following series:

Biology Course (390 lessons, $198.00)
Biology: Animal Systems and Homeostasis (63 lessons, $84.15)
Biology: The Digestive System (6 lessons, $9.90)

Taught by Professor George Wolfe, this lesson was selected from a broader, comprehensive course, Biology. This course and others are available from Thinkwell, Inc. The full course can be found at The full course covers evolution, ecology, inorganic and organic chemistry, cell biology, respiration, molecular genetics, photosynthesis, biotechnology, cell reproduction, Mendelian genetics and mutation, population genetics and mutation, animal systems and homeostasis, evolution of life on earth, and plant systems and homeostasis.

George Wolfe brings 30+ years of teaching and curriculum writing experience to Thinkwell Biology. His teaching career started in Zaire, Africa where he taught Biology, Chemistry, Political Economics, and Physical Education in the Peace Corps. Since then, he's taught in the Western NY region, spending the last 20 years in the Rochester City School District where he is the Director of the Loudoun Academy of Science. Besides his teaching career, Mr. Wolfe has also been an Emmy-winning television host, fielding live questions for the PBS/WXXI production of Homework Hotline as well as writing and performing in "Football Physics" segments for the Buffalo Bills and the Discover Channel. His contributions to education have been extensive, serving on multiple advisory boards including the Cornell Institute of Physics Teachers, the Cornell Institute of Biology Teachers and the Harvard-Smithsonian Center for Astrophysics SportSmarts curriculum project. He has authored several publications including "The Nasonia Project", a lab series built around the genetics and behaviors of a parasitic wasp. He has received numerous awards throughout his teaching career including the NSTA Presidential Excellence Award, The National Association of Biology Teachers Outstanding Biology Teacher Award for New York State, The Shell Award for Outstanding Science Educator, and was recently inducted in the National Teaching Hall of Fame.

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So now you have observed all this food. You have eaten this hamburger or whatever it is you eat, maybe tofu and so you have got all these things that you have broken down in your small, first in your stomach, then your small intestine and now absorbed into your blood and into your lymph system. The question now is where does it all go? I mean what's next and we actually have it detailed into two groupings. One is called the absorptive state and the other is called the postabsorptive state. I like to call them when you are not hungry and when you start to get hungry because you are obviously past absorption and I want to start out with the absorptive state. Now let's take a look at this chart, here. You know in the absorptive state you have got all these nutrients floating around in your blood, okay and you have got some of these nutrients floating around in your lymph and they are eventually going to end up in your blood. Let's take a look at where they will go and let's start out with amino acids, alright. Now amino acids are going to end up as proteins. That's just the way it goes. You see we can't store amino acids. Amino acids are made to make proteins and the other thing about this is if you have excess amino acids you have either got to do something special with them which we will get to later or you have got to get them out of your body. So amino acids, the simplest one, they come on down. They go to all your tissues through your blood. They go to the liver and what happens? Protein synthesis, you know you get that DNA makes RNA, RNA makes protein, the amino acids are put together, bam you get protein synthesis. You get protein synthesis. Amino acids, simple. It gets a little bit more complicated when we get to monosaccharides. In the monosaccharide we are going to concentrate on is glucose. Why glucose? Well remember glucose is that particular molecule that we use for energy in respiration and you may want to look back at those respiration lectures to really review that because it's a pretty complex process. So what's going to happen with glucose? Again one thing in particular but two things could happen. The first thing is it's going to get shunted to the liver. Why? Well one of the first stops after the intestine is blood is going to get scooted to the liver. A lot happens in your liver. It has way over a dozen different functions many of which are going to occur in the absorptive and the postabsorptive state. So what's going to happen there? Well when it goes to the liver depending on the levels of glucose in your blood it's going to end up stored as glycogen. Now one thing I do want to mention, you remember insulin, okay. Well insulin is a hormone that's going to do these things. In fact it's going to do all of this. It's going to cause the glucose it's going to cause the amino, it's going to cause the lipids to be used during this absorptive state and in this case it's going to get stored as glycogen. Now does that mean all of your glucose stays in your liver as starch, this long complex starch called glycogen? Well of course not because you take in a lot of glucose over the course of the day or in the course of a meal. So a lot of it will pass right through the liver again depending on levels and end up going to all your other tissues, okay and once it goes to all those other tissues what's it gong to do. Look back at those respiration lectures, ATP production. Now lipids, remember lipids were a little bit different. When they went into the villus alright they went into the lacteal, when they went into the lacteal they went into the lymph and the lymph eventually ends up emptying it into your blood stream through the thoracic duct. But let's take a look at what happens to those lipids. Well for the most part lipids are going to be stored as fat. Why? Because they are fat, alright and so, they are going to end up as these things called triglyceride molecules. Alright now the other fate of these lipids is they could end up believe it or not in your muscles and get burned. Now why is that? Let me do a quick review of something that I always thought was really cool. Now what was really cool was the reason fats work so well in respiration. Remember what fats were. Fats were these, first of all this was a molecule that by itself would be called glycerin and this is why these are called triglycerides or [1]glycerol alright and they were these chains of carbons that were going to, there was an oxygen here you know and there were these big old long chains of carbons and they ended up like so. What was so great about these lipids is that when you broke this off, this fatty acid chain off you had these big old long chains of carbons and I want you to think back to respiration. After you broke down your glucose there is a process of glycolysis. So remember that you had glucose. You put it through glycolysis. You broke the chains off and the next step was something called the Acetyl CoA step and Acetyl CoA was you eventually needed to end up with two carbon little pieces. Well look at this. There is a fatty acid you could break it right there. You could break it right there and imagine big old long chains of this. Gee wiz you could put this right into the Acetyl CoA step and you are good to go. So fats are definitely an energy molecule of choice but they are an energy of molecule of choice for everything in the body except the brain. I don't want to talk to you about now what happens. So where are we? We just went through the absorptive state, okay. We have put all the stuff in the blood and the lymph. We scooted around the body. Every organ in the body is really, really happy. So what we have done is we have taken the glucose. We have stored it as glycogen in the liver. We have taken those lipids. Oh you know one another thing we can do with those lipids which is very cool. Remember these big old long molecules. Well you know there is not much difference between a chain of molecules and a glucose molecule. In fact glucose is found in a linear form sometimes. We could even take these lipids and store them and we could turn them into glucose and then once we turn them into glucose we can even store that in glycogen. In fact we can even see that on this chart here that we had up where the lipids can also come down and besides being stored as triglycerides can also end up as being stored as glycogen too if we choose not to use them as energy at that point. But anyway I want to talk about postabsorption now. Alright postabsorption now take a look at this chart and we will scoot this around but we are going to start on the far left. So what does postabsorption mean? It means you know what it's been about 5 or 6 hours since my last good meal and I have got nothing scooting around my blood. What about all that stuff you stored? Hook me up with some nutrients here. And I want to start out where it's easy, over to fat. Some of us have more fat than others and what I am doing with every extra pound I gain is I am saving for the future and that future is the day I decide that really I probably ought to exercise. And so but that being said I have got these nice triglycerides. We already know triglycerides. They are going to be released into the blood. They are going to be used for ATP production. We just went through that. That's good but the difference here between this and the aborptive state is we are literally putting we are taking them out of storage and into ATP production. Now let's move in this direction and we are going to get more complicated alright. So in your muscles you have taken some of that glucose and stored it as glycogen and also by the way as we will see in a minute we have also taken some of that glucose and stored it as glycogen in the liver. Well let's go back to the muscles. What's going to happen to that? And this is another cool thing you may want to look back on the lectures from, those respiration lectures. Let me show you because you probably haven't. You remember that what ends up happening is that glucose in a process called glycolysis, the first thing that happens is it gets phosphorylated. Remember we were getting the glucose molecule all charged up and it became glucose with a phosphate attached. So put that right there. And then that glucose with the phosphate went through another step. Now this is regular glucose molecule and it got diphosphorylated. So we had glucose with two phosphates on it, okay. And eventually fructose came into play and this is not electron respiration. But in this case what happens is the glycogen when it's converted into glucose, okay so it's broken down, can be immediately plugged into the chain of events that leads to ATP. So what's going to happen is this glycogen giving rise to glucose actually pops off a glucose with a phosphate already attached and now you have entered the glycolysis a little bit earlier and it actually takes if you remember one less ATP to get that going. But you could do that in your spare time. Let's move on here. So we are going to make ATP from this glycogen, okay. But wait a minute. There was another thing I am hoping you remember from respiration and it's this. That sometimes well definitely the first step of glycolysis is to make a substance called pyruvate. Now pyruvate is not something you want scooting around your body. Why? Well two reasons. You would love to turn it into ATP or convert it to energy because you don't turn pyruvate into ATP but take the energy out of the pyruvate and make ATP with it. But sometimes we get in this condition called an anaerobic state which means you go into oxygen debt. What do you do? You walk upstairs? What do you do? You think while you are watching a Thinkwell lecture. What do you do? You play football. And in this state of oxygen debt the pyruvate builds up. Well you don't want pyruvate to build up. So if you were bacteria you would turn it into alcohol but that's not a cool thing for humans because they need to be drunk all the time. So instead we turn it into lactic acid. So one aspect of this postabsorptive state is the glycolysis also creates a build up of pyruvate and lactic acid. Now here is the thing and I am coming to the central theme of all of this and the central theme is right down here okay and that's the brain. You see your brain needs glucose. All your other organs in your body could use glucose but they generally use lipids. So the theme here as we start moving to the liver is this. We have got to keep our brain alive. So we keep our brain alive with glucose. So check this out. We can actually take this pyruvate and lactic acid and turn it into glucose. Now you don't do photosynthesis. Up till now you thought that's how we made glucose with photosynthesis. Well you are not vegetables. You don't do that but you take the pyruvate and lactic acid and actually you could take any two or three or four carbon thing floating around in your blood and actually through a process called Gluconeogenesis you can make glucose alright. Now what else is in your liver? Glycogen. What's that? Big starch, lots of glucose molecules. So either by Gluconeogenesis or the glycogen we can then produce glucose for the brain. Get it? It's all about the brain. Your brain dies you die. You have got to feed your brains, okay. Now let's think back to that absorptive state. I said to you proteins, amino acids you can't store them. You have just got to be able to do something with them. You are going to make proteins or excrete them but you don't just excrete amino acids because you want to be able to use anything you possibly can. So there is this process called deamination, quick review of amino acids. I am sure you know but let's just make sure. Remember amino acid has something like this. It's called an amino acid because it has an amine group and a carboxyl group and then has H over here and R over here. Well there is a lot of bonds here and some of these R groups which is a very versatile group can be, big old molecules sticking off of there with lots of bonds. So think about it. You don't want to waste this. So what are we going to do? We are going to deaminate. We do a process called deamination. This NH2 is broken off which is a problem because it forms a substance called ammonia. Bad, you don't want ammonia in your blood. Did you ever smell ammonia? Well that hurts because it hurts tissues. You sure don't want it coursing through your brain and lungs and heart and places like that. So what we do is in the liver we do a cycle called the ornithine cycle but eventually that's going to be converted through a cycle into urea which you know is an execratory product and out it goes. Now check this out. We have got all sorts of bonds in here that we can use and all sorts of organics that we can use and we can do great things with those things. For the most part because that thing has a double bonded oxygen to it we call it a ketone that thing meaning that amino acid, there is my double bonded oxygen. So we are going to call that a ketone. This is not an organic chemistry class but that's good enough, right. And these ketone bodies can now be used to generate glucose. So you can even use your amino acids for energy. So the next question I am sure you are asking me is this. If we can use amino acids for energy why don't you tell me we use proteins for energy? Well in the case of starvation you can use your proteins for energy but that means you have got to start breaking down your own tissues. You only do that when you are desperate. What makes you desperate? Not enough energy for the brain. So it all comes down to feeding the brain. So as a summary I like to make you think. So I am going to ask you guys one question. You know the glucose is used for energy. You know that glucose is different than fats. So I have one question for you. Why does glucose, why does eating sugar which you know is a carbohydrate that looks something like this, why do sugar make you fat? I mean that's what people say, oh you are gaining weight, okay. You are gaining weight from eating sugar. Why do you gain weight when you eat sugar? Think about that. Oh I will tell you the answer. The reason and I am going to go right back to this, okay. The reason that happens is once again your glucose doesn't, may turn into fat. Your glucose can actually once it has been literally brought into your body if it is not used for glycogen storage and if it is not used for ATP production if you have enough of it, you can actually turn that into fat. Why? Because it's made of CH and O and that's all glucose is and that's all lipids are. This is very cool stuff. So the next time you eat a meal remember absorptive state is when you are full, postabsorptive state is when you are hungry and real different things will happen in your body each time. I think it's time for break. Go eat something.
Animal Systems and Homeostasis
The Digestive System
The Fate of Absorbed Nutrients Page [1 of 3]


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