Bile Salts: Fat Digestion in the Small Intestine – Composition of Bile (Nursing)

00:01 Now, this might feel kind of complicated but I don't want you to to think that.

00:06 Let's kind of walk through it in what we're looking at.

00:09 We're talking about fat in the small intestine.

00:12 Now, we drew it like a pipe just to make it simple.

00:15 That's not a blood vessel.

00:17 We're talking about your intestines there.

00:19 So that's that pink color is to help you recognize the intestines.

00:23 Then you've got kind of a greenish color coming in because that represents where the bile is dumping into the small intestine.

00:31 Now, what other kind of juices are in that bile? We talked about six things.

00:37 Say what you can remember in six parts of bile.

00:39 How many of those can you remember? Good. Now, with those six parts, we also have bile and what comes from the pancreas - pancreatic enzymes.

00:52 Good job.

00:53 Okay, so you've got coming off from the left of that picture.

00:56 We've got fat droplets coming in from the stomach.

00:59 We've got bile from the liver and the gallbladder and then we've got these bile cells of bile salts cholesterol and lecithin.

01:08 So this is where it's all coming together.

01:10 The fat droplets from the stomach, the bile salts cluster on lecithin coming from draining down from that liver in that gallbladder.

01:18 See, the small intestine receives the bile and pancreatic juices right through that ampulla of Vater.

01:25 Do you remember what that is? That's the little opening into the small intestine.

01:29 And what is the gatekeeper? What's the sphincter? Right, the sphincter of oddi.

01:35 Good job.

01:36 We're going to talk a little bit about what a micelle is.

01:40 Now, I know we've got that blown up really big on the screen for you.

01:44 That's because we want to talk about the hydrophilic head and the hydrophobic tail.

01:49 Now remember as I eat fat it's going to move through my stomach and enter my intestine in these large pieces, right? But the large lipid and fat droplets as they're moving into my small intestine, mix with bile.

02:03 Remember we saw that in our previous drawing.

02:05 So the large ones mix with bile and then they become much smaller lipids.

02:11 Now the smaller lipids arrange themselves in a shape of a tiny sphere.

02:16 That's what you're looking at in the picture.

02:18 That's what a micelle is.

02:20 Its hydrophilic on the outside, hydrophobic on the inside.

02:25 Now in case those words are new to you, hydrophilic means it has a tendency to mix with, dissolve in, or be wetted by water.

02:34 So that's around the outside.

02:36 Remember it looks big but it's actually really really tiny.

02:40 We just blew it up so you can see what it looks like.

02:43 So the heads - the outside of the sphere is hydrophilic, it can interact with water.

02:49 But the inside, the tails as we call it, repel water.

02:53 They're hydrophobic.

02:55 So when you see that word hydrophobic, it doesn't mean the tail is afraid of water, but it doesn't mix well with water.

03:01 It fails to mix with water.

03:03 So part of the purpose of the micelle, they act as emulsifiers in fat.

03:09 They help the small intestine absorb essential lipids and vitamins.

03:15 So what does micelles do? They are emulsifiers and they help the small intestine absorb essential lipids and vitamins.

03:23 So we absorb things like complicated lipids like lecithin and lipid soluble vitamins like A, D, E and K.

03:31 That all happens in the small intestine.

03:35 So those bile salts that are formed in the liver and secreted by the gallbladder allow the micelles of fatty acids to form.

03:43 So would we have micelles without bile and bile salts? No, we need those for the micelles to be formed and these micelles allow the absorption of complicated lipids and lipid soluble vitamins which you know to be A, D, E, and K.

03:59 This happens within the micelle by the small intestine.

04:03 Okay, we're back to our picture of the small intestine.

04:06 Let me give you the three fancy steps.

04:08 Now that we've broken it down and you know what it means, You know we're looking at a small intestine.

04:14 you see fat from the stomach coming in as big ones, then it mixes with the bile and the bile salts, and we end up with smaller pieces of fat, right? So step 1 is the emulsification of fat droplets by bile salts.

04:26 We've already looked at that in detail with the micelles, but in step 2, you have hydrolysis of the triglycerides and an emulsified fat droplet into fatty acids in monoglycerides.

04:38 Triglycerides meaning three, monoglycerides meaning one.

04:43 In step three, the fatty acids are dissolved and the monoglycerides become micelles to produce the mixed micelles.

04:51 Why is it a mixed micelle? Hydrophobic on the inside, hydrophilic on the outside.

04:59 So we're doing a lot of talking about what happens to fat.

05:03 I know fat gets a bad rap, but we need it for so many things in our body.

05:08 We can't use it unless all of these pieces are working.

05:12 You need to an appropriate intake, you need a functioning liver, a functioning gallbladder, a clear hepatobiliary tract, and an intestine that's working well, otherwise, we can't break down the important things we need or get the vitamins and nutrients that we need.

05:29 So pancreatic lipase does the next thing.

05:33 It breaks the fat into free fatty acids and monoglycerides.

05:37 Now, these guys are small enough to pass through the epithelial cells on villi on the wall of the small intestine.

05:44 Now, you can't see those on this model of the small intestine, but we are going to show you that.

05:51 So take just a minute, pause the video, work your way through this picture, and make sure that all makes sense as we go on to the next section.

06:05 So where did the pancreatic lipase come from? Well, there's a clue in lipase, right? - Ase means it's an enzyme.

06:12 The name before it should be pretty clear as to where it comes from.

06:16 It comes from the pancreas, but it travels right through those structures we've already talked about.

06:22 Remember the ampulla of Vater, that is the opening into the small intestine.

06:26 The sphincter of oddi is the - that's the gatekeeper, the muscle that opens and closes depending on whether the body needs to drain bile into the small intestine or stop it.

06:40 So more about fat in the small intestine.

06:43 I promise you this is really important.

06:45 Let's look at it all together.

06:48 You've got bile from the liver and gallbladder hitting the fat from the stomach.

06:52 You've got the fat droplets.

06:54 We've got micelles being formed, fat being ripped apart.

06:57 And so we can start to use the nutrients that we want and we need.

07:02 Now, look at this small intestine.

07:04 We're going to break down the layers of the small intestine for you.

07:08 Now, those are mesentery vessels that come off the gut.

07:11 Those are the vessels that take the nutrients from the intestine carry it in the mesentery vessels back up to the portal vein to the liver.

07:21 Right, that's another really important part of the digestive process in your body.

07:25 But the small intestine has some muscles.

07:27 It's got different muscle layers there.

07:29 We just put those there to kind of remind you but in the deepest layer right on the very innermost part of the small intestine, you've these circular folds that are called villi.

07:42 Now that gives us an increased area, instead of being just flat.

07:47 when we have villi like this we've got more surface area to work with.

07:51 So inside the villi are these little blood capillaries and lymph capillaries? Okay, this ties back into what we've been talking to with the lymph system earlier in the video series.

08:03 So on top of these little villi there are the blood capillaries and lymph capiliaries.

08:10 Now you see the big drawing of the small intestine on the left.

08:13 You see the villi.

08:15 But then you've got a magnification drawing next to it.

08:18 So that helps you see.

08:20 Okay, look at that. You see the capillaries.

08:23 You see that we've got the lymph capillaries. That's pretty cool.

08:26 And now it makes sense why you have a greater surface area with villi.

08:30 And the greater the surface area, the more work space we have that's available for absorption of nutrients.

08:37 Now when we absorb things, where does it go? It goes through those vessels back up to the portal vein and to the liver to be processed.

08:47 Now, fats are absorbed into the lymph capillaries and transported back to the liver just like the nutrients.

08:52 I didn't want you to miss that point.

08:55 So bile is comprised of bile salts.

08:59 Remember it mixes with ingested fats and it promotes absorption of fats from the GI tract.

09:05 I want you to pause here.

09:06 This is one of our study techniques that we use to help you remember.

09:11 So pause here and without looking at your notes, see what specifics you can write in here about just how fat is broken down and where in the GI tract that happens.