- Gastrointestinal system questions
- Meet the gastrointestinal tract!
- Small intestine 1: Structure
- Small intestine 2: Digestion
- Small intestine 3: Absorption
- Hepatic lobule
- Biliary tree
- Exocrine pancreas
- Endocrine pancreas
- Colon, rectum, and anus
- Control of the GI tract
Small intestine 3: Absorption
Created by Raja Narayan.
Want to join the conversation?
- is it possible to survive without a small or large intestine?(4 votes)
- Yes it is very possible to live with out the large intestines, many women have this procedure when they suffer from colonic inertia (a rare disease, but appears more common in women). They have to adjust to some changes such as the large intestine not absorbing a lot of fluids anymore and several other factors, but it is very possible to live without it. Not sure about the small intestines. I'm sure you can live with out a portion of it, but doubt all of it since major absorption of nutrients etc happens here.(15 votes)
- what is active transport and passive transport?(4 votes)
- Active transport transports materials against the concentration gradient by using energy.
Passive transport transports materials towards the concentration gradient without using energy.(10 votes)
- Thanks the video was very informative. My question is what happens if someone is diabetic and can't absorb sugar does it mean there is something amiss with the pancreas or is it something else going on what do you think?(4 votes)
- Depends on the type of Diabetes - you can be Insulin dependent (Type 1) or Non Insulin Dependent (Type 2); if you are insulin dependent, your pancreas does not produce insulin and your body can't use it to absorb glucose from the bloodstream. If you are Non-Insulin dependent, your body develops insulin resistance which causes your cells to not respond to circulating Insulin in the bloodstream properly.(6 votes)
- At the end of the video, you discuss what happens to the fatty acid tails, but what happens to the triglyceride head?(3 votes)
- The triglyceride head would simply be a glycerol molecule once the fatty acids have been cleaved from it. Glycerol can be transported back to the liver to be used to create more triglycerides or be broken down for energy.(5 votes)
- Is there really only one mechanism for fat absorption? I thought it depended on the size of the fatty chains.(3 votes)
- You are right. First materials are absorbed into intestinal cells. Then long chain fatty acids are absorbed into the lymphatic lacteals and travel to the left subclavian artery, getting into the blood that way. The short chain fatty acids are absorbed into the intestinal capillaries and go into the blood to the liver.(7 votes)
- At minute2:52, you say that as a sugar leaves the enterocyte and enters a blood capillary, that a Na+ ion is also entering the enterocyte by flowing down its concentration gradient.
How does the cell maintain this low concentration gradient of Na+ ions if the passing of monosaccarhides into and out of the cell are constantly increasing the concentration of Na+ within the enterocyte? I'm sure there's something going on here, otherwise the process would stop. I'm just curious about what's going on.
- The comments say that the explanation of amino acid absorption at0:51is mistaken because amino acids use a secondary active transporter. Does the mean the whole explanation is wrong and they are actually broken down using ion gradients like monosaccharides, or did Raja just misspeak? And in a more general sense, what is the difference between primary and secondary transporters?(4 votes)
- How different is primary active transport than secondary active transport?(2 votes)
- Fairly different. Primary active transport uses the direct hydrolysis of ATP to drive the movement of different substances arcades a membrane. For secondary active transport rather than directly using ATP as an energy source, secondary active
transport makes use of concentration gradients set up by primary active transport
- Lacteals can passively absorb chylomicrons, which are much larger than the other nutrients; this means that the lacteal vessels have much larger fenestrations than those present in the capillaries. So why wouldn't the other nutrients (i.e. monosaccharides, amino acids, vitamins, etc.) be absorbed into the lacteal?(2 votes)
- There are specific transport mechanisms for all molecules. AAs, monosaccharides, and even SCFAs go through specific channels to get to the portal system. Chylomicrons are too large for this- that's why they go to the lymph vessels.(1 vote)
- What organs in the GI system can people NOT live without?(2 votes)
- You can live without any of the GI organs but not all at the same time.(1 vote)
Voiceover: All right, great. So, now we have all of our monomers ready to be absorbed. How does the absorption process work? Let's take a look. So, now we're so close. We've got all of our monomers, but we need to figure out how the heck are we going to get them inside our blood stream. Well, starting with our amino acids here. These guys are going to be shuttled into cells using what's called primary active transport, primary active transport. Now, if I say primary here, what does that specifically indicate as used? Now, you might recall when we use active transport, that means we need a little bit of energy to get something to happen. And the form of energy that we use in primary active transport comes from ATP, the energy, the unit of life, adenosine tri as an three, phosphate. And so if we look at a single enterocyte or an intestinal cell, there would be a protein that's here on the cell membrane. This protein would break apart our ATP, cleaving off one of the phosphate groups to release adenosine diphosphate, so that's two, diphosphate. And in doing so, would allow our amino acid to enter into our enterocyte or our intestinal cell. From there, the amino acid could undergo a couple of different steps, but eventually will leave the enterocyte and go to a blood capillary, where it enters the blood stream and then can be shuttled anywhere else in the body for use. Monosaccharides are sugars, sort of have a similar thing going on, but instead of primary active transport, we have what's called secondary active transport going on. So, if we use the ATP for primary active transport, what do we use for secondary? Well, the fact that we're saying this is still active transport means that there was some energy that was used at some point, and the energy actually was invested in sending up an ion gradient. And so the ion gradient then could be used by allowing something like sodium to flow down its gradient, to go from the place of high concentration to low concentration where it can relax. And by allowing that to occur, energy is then harnessed allowing a monosaccharide or a sugar to enter into our enterocyte. And just to make sure we're complete, I'm going to draw the protein transporter we have here as well as one on the other side, and show that there is a sodium ion that's flowing into our enterocyte down its concentration gradient to end up in the enterocyte with the sugar. And sort of the same thing happens on the other side, except as the sugar leaves, sodium on this side is entering. So, the sodium is still flowing down its concentration gradient, but it ends up inside the enterocyte while the sugar leaves and goes to the blood capillary. So this also ends up in our blood stream and can go anywhere in the body to be used. The nucleoside in the base sort of use the same mechanism that amino acids do. So, I'm just going to write primary active transport right here. And you can take a look above to see how that happens. And by doing that, you can imagine where they are going to end up. That's right, the blood capillary as well. And that takes us to our last macro molecule, fat. Now, the thing about fat that's rather redonkulous is that because it's got this really nonpolar tail. If it ever shows up next to an enterocyte like this guy, all it has to do is just diffuse across the membrane, and then it ends up on the inside. In the enterocyte, all of our fatty acids are going to be reorganized into what are called chylomicrons, chylomicrons. And like the name, chylomicrons themselves are too big to fit directly into a blood capillary. I couldn't even fit it here in this enterocyte. So, it doesn't actually directly go into the blood capillary. It is too big to do that. Too big to go to the blood capillary. Instead, chylomicrons will be absorbed into what are called lymphatic, lymphatic capillary, also known as a lacteal, a lymphatic capillary. And these are big enough to accommodate our chylomicrons. Here, they're going to be further digested and broken down into smaller bits, and by the time that happens, they will end up in veins. That will send the digested fat through the heart and eventually to arteries. That can then distribute them wherever they need to go in the body. And so you can appreciate a lot it's going on here. We've talked about how all four of our major macromolecules are digested in the duodenum, the place where the most digestion occurs in the GI tract. And now, we just talked about how they are absorbed, most likely in the jejunum, right. Because the jejunum is where the most absorption occurs anywhere in the GI tract. And that's how our small intestine works.