In this video, we're going to look at the absorption of the nutrients that we have broken down into monomers. So nearly all food, 80% of electrolytes and the majority of the water is going to be absorbed in the small intestine. And most of this is going to be before the illiam. Really the only thing in the illium that gets reclaimed are the bile salts. So most of the absorption is going to be dependent on energy. So it's active transport into the bloodstream and the exception is going to be the lipids when we get to it. So let's see how carbohydrates are absorbed. So when we look at the three monossaccharides we discussed glucose and galactose on the apical side of these epithelial cells they're going to and let's just mark the apical side here. So this is the apical side here's the basil lateral side. So on the apical side glucose and galactose are actively transported using the energy in the sodium gradient. Fructose on the other hand is going to go through facilitated diffusion. So that's a passive process down its concentration gradient. And on the basolateral side likewise fructose in addition glucose and galactose are going down their gradient. So it's passive on the basolateral side. So it's going to be facilitated but it's going to be secondary active for glucose and galactose on the apical basolateral side. So once it's in the ISF it will again go down its gradient into circulation into the capillary beds that are found in the villi. As for proteins, the most the majority of amino acids are going to use a very similar secondary active transport that is coupled to the sodium ion or the sodium gradient. uh there are instances where deptides and even tripeptides can be co-ransported with hydrogen ions and then inside the cell they are further digested back into uh single amino acids and they will enter the blood through facilitated diffusion. Now when we get to lipids, the absorption of monoglycerides and fatty acids are a little bit more complicated. In the earlier video, we showed basically an image of this, but basically what happens is they will cluster with bile salts and a specific phospholipid called lecithin. So this is a phospholipid that will help to produce these myels. So these are small little circular vesicles uh that hide away a lot of the fats and these myels because they're in general they're fairly small they're hydrophobic they can diffuse across the cell membrane. Now once it is inside the cell they're going to combine with more lcithin other phospholipids cholesterol and are then coated with proteins and they form a structure called a kyom micron and let me just jump to that initial image that we had here. So here are lecithan the bile salts the fatty acids and the monoglycerides and they form these myels which are then absorbed. Once it is here, this is where they produce the kyomicrons and they're going to be readily absorbed through the lactal through the lymphatic system. Not through the capillaries because the capillaries are not as permeable as the uh lactals. So once it's in the lactals, it's going to be transported to the systemic uh circulatory system and there you're going to hydrayze the free fatty acids and glycerols. Uh you're going to hydrayze to free fatty acids and glycerol using an enzyme called lipoprotein lipase. And this is an enzyme that is found in the capillary endothelia. And it is at this point where the cells can now use these molecules for either energy or in atapost cells store them as fat. In the case of very short fatty acids, uh these can diffuse directly into the portal blood for distribution. But your traditional fatty acids are not shortchain fatty acid chains. As for nucleic acids, these are going to be absorbed via active transport in directly into the bloodstream. So, fairly straightforward here. For vitamins, vitamin absorption is primarily going to occur in the small intestines. uh the fat soluble vitamins A, D, E, and K. These are going to be carried by my cells um and go through the process that we just talked about for lipids. While the water soluble vitamins, the C's and the B's, they're going to be absorbed by diffusion or through an active or passive transporter mechanism. Vitamin B12 is unique, however. It is a large charged molecule and it has to bind to intrinsic factor. So recall intrinsic factor was a protein that was produced in the stomach. So vitamin B12 has to complex with intrinsic factor and then in the small intestine the dadum specifically it will get absorbed. As for vitamin K and some of the B vitamins that the entic bacteria are producing, these are going to be absorbed in the large intestine. For electrolytes, most electrolyte absorption is going to be active usually along the lengths of the small intestine. iron and calcium they're going to be absorbed in the douadinum and their absorption is going to be dependent on need. Uh so ionic iron is usually stored in mucosal cells but it's toxic. It's a neurotoxin. So in many cases it's going to have to be bound to a protein. And the protein that it is bound to is called feritin. So this is the protein that we use for iron storage. And when the iron is transported in the circulatory system, it binds to a different protein. This is a plasma protein called transference. So we'll call this iron transport. So for example, in your liver where you stockpile a good amount of iron, that iron is bound to feritin. If I'm transporting that iron to the spleen to be used, then it's going to be use uh excuse me, yeah, then it's going to be excuse me, if I'm transporting iron away from the spleen, then it's going to be using transferin. So when we look at electrolytes, uh usually sodium absorption is coupled with active absorption of glucose and amino acids. We talked about that in the context of secondary active transport. Chloride ions are usually transported actively using ATP. Potassium is going to diffuse in response to osmotic gradients. Um, however, if we have poor water absorption, we're usually going to have poor potassium absorption. Uh, and then calcium absorption is going to be dependent on hormonal signals. So parathyroid hormone uh as well as vitamin D is going to serve as a very important co-enzyme that facilitates the absorption of calcium. This is sort of the reason why if you look at milk for example it's fortified with vitamin D to facilitate the absorption of that calcium in the milk. When we look at the absorption of water, about nine lers of water, most of which comes from GI tract secretions is going to be absorbed in the small intestine via osmosis. Okay. The remaining water is going to be absorbed via the large intestine where again there's a balance that needs to be played where you can't absorb too much otherwise you'll have constipation or too little otherwise you'll have diarrhea. Uh water uptake is usually going to be coupled with solute uptake because the golden rule for water transport or osmosis is water chases solutes.