Frog Dissection Overview and Procedures

Today we're going to be doing the frog dissection. And the first thing we want to do is look at the external anatomy of the frog and see how it's geared up to live for a life both in water and on land. So the first thing we notice is we see the very thin skin here. If you look at the skin, it's very thin, almost like saran wrap. And that is to allow easy gas exchange because the frog breathes mainly through its skin and just a little bit through its lungs. We can also notice the back legs here. Look at the webbed feet designed for swimming in water. Another feature of the frog is the eye. If we take a look at the eye here, we see this membrane right here. This is called a nictitating membrane. And the frog actually uses this when it's in the water. to help protect its eye from any abrasions or anything like that in the water that might come in contact with his eye. So that actually flips up to protect the frog's eye in the water. We also see this other structure right here called the tympanum. That's going to be the ear of the frog. The next thing we want to locate here is the cloaca. Now the cloaca is sort of like an anus. And I've got the probe right there. That's going to be the cloaca. And that's going to be a common opening where both digestive waste comes out of there. Urinary waste comes out of there and sperm and egg, depending upon the sex of the frog, also comes out that same hole. So that's going to be the cloaca. Let's take a look at the size of the frog's legs. You can see the large muscles. They're going to be used for jumping. In addition to that, the frog's spine is also extra strong in his low back. to support the type of jumping and pounding that the spine is going to take. Now, you can see clearly that the frog has two different colorations. A very dark color on his dorsum or back. backside and a very light color on his ventral side. And this is called counter shading. We've seen it before with the earthworm and this helps camouflage the frog. From above it's difficult for a bird to see this frog against the dirt or soil. And if this frog is swimming in the water and fish are looking up, it's very difficult to see the frogs light underside. when it superimposes with the sky and the clouds. So that helps protect the frog against predators. Now, the first thing we want to do in terms of the dissection is to take a look inside the mouth. There's going to be several structures that we need to be familiar with there. To just open the mouth isn't going to work that well because the muscles tend to tighten up. So what we want to do is actually, using our scissors, begin to make a small cut. cut in the corners of the frog's mouth. So I'll make a cut here and another cut on the other side. If the cut isn't deep enough, we might have to go back and do it again. And there we go. So now the mouth should open up fairly easily, which it does. And we can begin to look at some of the parts of the frog's mouth. The first thing we notice here is the tongue flips out. The tongue is actually going to be attached. to the front of the frog's mouth instead of the rear like your tongue is. And that again is because the tongue flips out in order to catch prey. Another thing we're going to notice in the mouth is some teeth but not quite like ours. You're going to have two prominent teeth right here. You can see those two protrusions, one here and one here. Those are called vomerine teeth. And around the sides of the frog's mouth, if I pull back its gum just a little bit here, see if I can get the forceps in there. That side's not working for me. If I pull back the frog's gum a little bit, you can see that it's very, there's a lot of little ridges around the gum. And you can see right here, especially you can feel it with your finger, those ridges, those are called maxillary teeth. And the purpose of the frog's teeth is not so much to chew food because the frog really doesn't do that. The teeth simply hold the prey in. in place while the frog is busy trying to swallow the food whole. And then the frog lets his stomach worry about the details. If we look inside the frog's mouth, we see two openings right next to the probe. These openings are the nostrils. They're actually called internal nares, and these are the frog's nostrils. If we go in a little bit deeper into the frog's mouth, you can see two openings, one here and one right there. And just to confirm, when I put the probe into these openings, I'm going to gently put the probe in there, you can see that it's actually pushing against the eardrum right there. So that's called the eustachian tube, and that allows the frog to equalize perfectly. If we go in a little bit further and I pull this frog's mouth open just a little bit more, we'll see a hole come into view. And I'm going to dry up some of this liquid here. We'll see a hole come into view. Right here you see a little protrusion there and there's actually going to be a hole there. I can stick the probe right into that hole. There we go. This hole is the glottis. So the probe's inside the glottis right now. The glottis is the opening to the lungs. Well, this opening actually goes down through the trachea and eventually into the lungs. and there's an opening right posterior to that, and that opening is gonna be the opening to the esophagus. Just to confirm, once we open up the frog's chest and abdomen, we can actually again put the probe in here and see that the probe is actually going into a lung or the probe is going into the stomach, and we'll do that in just a few minutes. Those are the parts of the mouth that I want you to be familiar with. The next thing we want to do is actually begin the dissection. So we're going to use our scissors, and we're going to cut from the groin up to the mouth of the frog. However, I just want you to cut through the skin. So with your forceps, pull up. the skin, see how thin it is right there. That's all that we want to cut through initially. We don't want to cut through the muscles, we don't want to cut through the organs, just the skin. So I'm going to go ahead and I'm going to stick the scissors. Into the skin, and I'm simply going to cut up through the skin all the way To the mouth and then I'm going to cut down both thighs so I want to take a look at the there and see how thick that muscle really is. So I'm not cutting through the muscle I'm just cutting the skin. Notice my blade is parallel to the muscle and I'm not angling it down into the muscle where it's going to gouge the muscle. Now I'll do the other leg or the other thigh. And again, I'm just cutting through that very thin, moist skin. And I'm going to pull that skin back. Now what you notice when I pull that skin back is all the blood vessels. Now this frog, I think, has been injected with a little bit of dye to make the blood vessels more obvious. But you can see all the blood vessels under the skin there. And again, those blood vessels are are there for a reason. This is where gas exchange takes place. So the skin is going to be very, very vascular, meaning there's going to be a lot of blood vessels there. Because the function of the skin is to try to get the blood and the air in as close a contact as possible. So we've got lots of blood vessels picking up that nice, rich oxygen and returning it to the circulation of the frog. Let's take a look at the other side. And again, we see the same thing, lots and lots of blood vessels because the frog's main respiratory organ is its skin. Under that, you can see some of these abdominal muscles. This is what muscle looks like. See if you can find which way the muscles actually go, the striations in the muscles, because that's the way. If the muscles look like they're going in this direction, then they're going to contract. that direction. So see if you can actually see which way the muscle striations are traveling. If we look down here in the thigh, again, you can see the muscles of the thigh, how large they are and how dependent the frog is on those big thick leg muscles for movement. Again, you can look at the striations, the pattern. in the muscles to determine which way these muscles are actually going to contract. Again, more blood vessels in the skin. The next thing I want to do is cut through the musculature here. But I've got to be careful. The abdominal muscles are not that thick, and I don't want to injure the organs, which are going to be directly below. So I'm going to start with an incision down near the groin. Again, I'm going to keep my blade parallel, my lower blade parallel, so I don't gouge the organs. I'm going to cut right up the center of the frog. I'm going to cut right through here. You might have to cut through a little bit of cartilage and bone there. And I'm going to reflect or peel back the muscles. Now you might have to cut some of this. And I'm going to cut here. And I'm going to cut up here. So I can... more easily reflect the skin of the frog. And I don't really need to worry about this anymore, so I can cut this right off. And that way I don't have it in my way. And I'm going to do the same thing to the other side. I'm going to reflect back the abdominal muscles here. And I'm going to reflect back the skin. I'm just going to remove those so I have more easy access to the organs. Now the first thing that's most obvious here is all this salt and pepper looking structure right here. These are eggs. So this is a female frog. She's about to lay her eggs again Where she's going to lay these eggs somewhere near the water where they can remain moist These eggs are going to kind of get in our way. So we're going to try to remove them them in an orderly fashion in just a minute. Another structure we notice here is this dark structure. This is a lobe of the liver. This is a piece of liver right here. And then under that I see this muscular structure. That's going to be the frog's stomach. So the first thing I guess I want to do in order to see the organs is to try to remove the eggs here. So I'm going to try to get in there with my fingers and gently remove these eggs without making a big mess. So I'm going to try to get in here and remove some of these eggs so we have a more clear view of the organs. Awful lot of eggs here. And remember, most of these eggs will be eaten by predators. So we're not going to see a million frogs or so suddenly appear. Most of these will be eaten by predators. And that's why the frog, one of the reasons why the frog has to lay so many eggs. So we've gotten rid of most of the eggs here in a fairly orderly way. And underneath that, you can see all these small tubes that I've got the forceps in. These tubes are... fallopian tubes are oviducts. This is part of the female reproductive structure. And you see the same thing on the other side here. All this is oviduct. And you can see them there also. Let's take a look at the frog's digestive structures first. I'm going to get rid of some of this here so we can see a little bit more clearly. Again, if any of this tissue gets in your way, feel free to cut it out. And let's take a look at the digestive tract of this frog. So again, this is going to be the stomach here. You see the stomach coming down. The stomach's going to narrow here. And where it narrows, that's where the small intestine begins. Now I've teased away the small intestine. And what you can do is follow the small intestine around. Follow it around until all of a sudden it becomes larger right here. And where it becomes larger, that's going to be the large intestine. Now the small and the large intestine are not named because of their length, but they're named because of their diameter. So the large intestine has a larger diameter. And this large intestine will eventually... We exit through that cloaca, that opening that we showed you earlier. Now, some other structures that I want to go over are the liver. You can see this nice, large liver, and the liver's always, going to be large and a fetal pig it's also quite large and you it's quite large and if we gently lift the liver up we're going to see a small sack like structure right there it almost looks like a P you can see that sack like structure that's going to be the gallbladder. Now the liver produces bile which is going to help in digestion and that bile is going to be stored in the gallbladder and then it's going to be released into the small intestine when food is eaten to help with digestion of fat. Some other structures that I'm looking for around here, here's our stomach again. And on the inside of the stomach, when I say inside, the lesser curvature. This is a large curve here. This would be the greater curvature. So this would be the lesser curvature. There should be a very small, sometimes not so obvious, it's kind of ill-formed pancreas. The pancreas oftentimes is going to be ill-formed. It's not a very well-formed organ and I'm looking for it here and it's not always going to be the easiest to find. But this is where it's usually located. If I tease apart, we can see some tissue here. This tissue helps hold the organ. organs in place this tissue is referred to as mesentery that is called mesentery and before we go on and we find the pancreas if we can find it here I want to talk a little bit about the mesentery and the mesentery comes from something called the peritoneum. The peritoneum is a thin layer of tissue. It's a thin sheet of tissue. And you can see it right here. It's almost like saran wrap. We can see that peritoneum. And that peritoneum is going to line the body cavity and it's also going to line the organs. And it does a couple things. Two of the big things it does is it helps the organs move more freely. and it also helps to protect against infection. The mesentery is actually a piece of peritoneum, and it actually is going to surround blood vessels, and it's going to support and actually hold on to some of the organs. So we can see. some of the peritoneum or mesentery right there, that tissue that's actually surrounding the blood vessels. Underneath, if we lift up the stomach and I look underneath, I see another small structure. It looks kind of purplish. or brown, looks right there, looks almost like a dried up raisin. This is going to be the spleen. That's going to be the spleen of the frog right there. Now I'm still looking for the pancreas, and I have not, I'm unable to see the pancreas. Perhaps this is a small piece of it in here. It's very poorly formed, I think that's actually gonna be it right there. Again, if we look at the lesser curvature, right around here, you might see see a very small sliver of tissue. It's going to look sort of glandular, sort of grainy. That will be the pancreas. When we dissect the fetal pig, that pancreas is going to be bigger and much more obvious. Some of the other structures that we want to take note of here, I'm going to remove some of these, all these fallopian tubes here because they're getting in our way. I'm going to try to gently remove them. And as I do that, we begin to visualize another structure beneath it. You can see this brown structure come into view right here. And that brown structure is a kidney. That's the kidney. right there and that's going to get rid of our nitrogenous waste which in the frog is going to be ammonia and urea so that's going to be a kidney right there Now if we look on the other side, we should see the same thing. I should see another kidney over here. Again, I'm going to have to remove some of these fallopian tubes or oviducts. And we see the other kidney just sitting right there. I'm going to go ahead and I'm going to remove some more of these tubes. And down below, near the pelvis of the frog, this is down here near the pelvis, we can see this pouchy tissue right here. We can see all this pouchy tissue right here. I've got my probe under it. And right here, there it is. That's going to be the frog's urinary bladder. That's the urinary bladder that holds the frog's urine. Again, that urinary bladder is going to exit. through the cloaca, which is that external opening right there. The next thing I want to do is remove the liver so we can get a better shot of the heart and lungs. So I'm going to remove, there's our heart right here. So as I move this liver down, you can see the heart. come into view. Frog has a three-chambered heart and we are looking at the ventricle right here. That is going to be the ventricle and the atria are going to be up here a little bit further. We'll try to visualize a little bit. those in just a few minutes. I'm going to come in here and try to remove this liver without pulling apart. The heart and the liver are very closely connected so we have to be very careful when we remove the liver so as not to damage the heart. too much. So I'm going to come in here and I'm going to try to cut the liver out here very carefully without damaging other structures. I just go to the base of the liver and try to do some small snips taking it slowly and you can see that I removed the liver. Again there's our gallbladder right there and that's going to be our liver. Take a good look at the liver. and here's our stomach before I go up into the chest and talk about the heart and you can see the pink structures right here these are the lungs notice they're very small lungs because the frog relies mainly on the skin to exchange gases rather than the lungs. I want to take a look at the stomach. So I'm going to cut the stomach open and I want to take a look in here. Some Sometimes when you cut the stomach open, I'm going to cut along the greater curvature of the stomach. When you cut the stomach open, sometimes you might see some of the food that the frog has eaten. You might see an insect in there. You might see some other structures. Sometimes you don't see anything. It just depends. So I'm opening that up. You can see there's some food left over right there. And you can see what looks like a nail of some organism. perhaps this frog had a small lizard or something else for lunch. But inside the stomach you can see some of the food there but you can see these folds and these folds when the stomach gets filled up and gets distended these folds obviously are going to allow the stomach to enlarge a little bit. The stomach is very muscular because remember the frog is not going to chew his food he's going to let his stomach do most of the work of digestion. Now if I come down a little bit further into the small intestine I'm going to open up that small intestine and I'm going to put the scissors in there do some small cuts be careful when you're cutting. And you can see how sort of it looks a little fluffy, spongy, I guess. And all those little tiny folds are going to serve to increase the surface area because this is where a lot of your digestion... is going to take place, a lot of enzymes are going to get released to break down the food, and a lot of absorption is going to take place across this small intestine. So we want lots of surface area. Again, wherever diffusion is going to occur, we want lots of surface area. Let's go up and take a look at the heart here. You can see the heart. You can see the large blood vessels coming off of the heart. I've got my probe underneath one blood vessel there. And there's going to be another one going to the other side. See if you can take a look at those blood vessels. They're very thick blood vessels. And that's going to be our heart. I'm going to go ahead and try to remove the heart. Looks like our heart broke apart a little bit here. It's a very delicate heart. You can see the inside of the heart right there. You can see some of the blood on the inside of the heart. This is the ventricle here. You can see one of the atria is very thin. You can see that it's easily deformed when I put my probe onto it because the purpose of the atria is more to store blood temporarily and then pump it into the ventricle, which is then going to pump the blood throughout the entire body. Let's take a look at these two pink structures. And these are going to be the lungs. What I want you to do is remove one of those lungs. Carefully try to remove an entire lung. I'm going to get rid of some more of the fallopian tube there. And I want to remove... lung. Actually before I remove the lung let me go into the frog's mouth and that opening that led to the lungs is going to be called the glottis. So if we open the frog's mouth and we take a look, this little lump right here is going to have a hole in it. And I just, I got the probe inside that hole. Now as I push the probe through here, the probe should go in and you can see it. As I put my probe into the glottis, the probe should come out right around near the lungs, and it does. You can see that I'm actually lifting up that one lung right there. Actually, the probe just went through the lung. you can see that if I go into the esophagus which is further back my probe should go into the stomach and I'm going to push it through a little bit further and you can see that it's going into the stomach. I can't quite, there it is right there, and the probe comes out of the stomach. So I want you to do that. I want you to see if you can actually follow those tubes into their proper structures, the stomach and the lungs. Now let's go ahead and actually remove the lung. We're going to use our scissors and I want to remove this very carefully. So I'm going to snip around the base of the lung here and pull this out. Try not to damage the lung. the lung too much and that's going to be the lung right there that's one of the lungs and the next thing I want you to do is cut this lung right in half we're going to cut it in half remember the lung went in the lung was like this in the frog so I want you to cut it in a horizontal way right across maybe a third of the way down and then I want you to take that lung and sort of open it up and you will see see that the lung of a frog and an amphibian is sort of hollow. You can see that my probe is inside that lung. It's sort of hollow. And I'm opening it up, I'm teasing it open. You can see how hollow that lung is. Now if we were to open up your lung or a fetal pig, which is also a mammal, the lung would appear very solid, like a solid sponge. And if we actually looked at that lung... on a microscopic level, we would see lots of little microscopic sacs called alveoli. Each one of those alveoli serves to increase the surface area of the lung. The frog does not have those alveoli. His lung is essentially hollow, which reduces the surface area, which is why the frog must use its skin as its main organ of gas exchange. As we move up through evolution, we go to a reptile, and as we go to mammals, they're going to have alveoli, which greatly increase the surface area for gas exchange in the lung. So we're going to move that lung out of the way. I'm just going to poke around in here, see if I see anything else of interest. Coming off the heart, our heart was right in here. Coming off of the heart, you can see this major blood vessel right here. Run right down, and you can see the blood vessel there. I'm going to sort of lift up the blood vessel a little bit. And right underneath that blood vessel, probably for protection, is going to be the spine of the frog. That's going to be the spinal column. And your aorta, which is one of the biggest blood vessels in your body, also travels right down the front of your spine. Again, most likely for protection. You can see I'm actually moving the kidney out of the way there so you can see that aorta. And I think we've covered everything that I want you to see. So that is going to be it for the frog dissection.

We can also notice the back legs here. Look at the webbed feet designed for swimming in water. Another feature of the frog is the eye.

If we take a look at the eye here, we see this membrane right here. This is called a nictitating membrane. And the frog actually uses this when it's in the water. to help protect its eye from any abrasions or anything like that in the water that might come in contact with his eye. So that actually flips up to protect the frog's eye in the water.

We also see this other structure right here called the tympanum. That's going to be the ear of the frog. The next thing we want to locate here is the cloaca.

Now the cloaca is sort of like an anus. And I've got the probe right there. That's going to be the cloaca.

And that's going to be a common opening where both digestive waste comes out of there. Urinary waste comes out of there and sperm and egg, depending upon the sex of the frog, also comes out that same hole. So that's going to be the cloaca. Let's take a look at the size of the frog's legs.

You can see the large muscles. They're going to be used for jumping. In addition to that, the frog's spine is also extra strong in his low back.

to support the type of jumping and pounding that the spine is going to take. Now, you can see clearly that the frog has two different colorations. A very dark color on his dorsum or back. backside and a very light color on his ventral side. And this is called counter shading.

We've seen it before with the earthworm and this helps camouflage the frog. From above it's difficult for a bird to see this frog against the dirt or soil. And if this frog is swimming in the water and fish are looking up, it's very difficult to see the frogs light underside.

when it superimposes with the sky and the clouds. So that helps protect the frog against predators. Now, the first thing we want to do in terms of the dissection is to take a look inside the mouth.

There's going to be several structures that we need to be familiar with there. To just open the mouth isn't going to work that well because the muscles tend to tighten up. So what we want to do is actually, using our scissors, begin to make a small cut.

cut in the corners of the frog's mouth. So I'll make a cut here and another cut on the other side. If the cut isn't deep enough, we might have to go back and do it again. And there we go.

So now the mouth should open up fairly easily, which it does. And we can begin to look at some of the parts of the frog's mouth. The first thing we notice here is the tongue flips out.

The tongue is actually going to be attached. to the front of the frog's mouth instead of the rear like your tongue is. And that again is because the tongue flips out in order to catch prey. Another thing we're going to notice in the mouth is some teeth but not quite like ours. You're going to have two prominent teeth right here.

You can see those two protrusions, one here and one here. Those are called vomerine teeth. And around the sides of the frog's mouth, if I pull back its gum just a little bit here, see if I can get the forceps in there. That side's not working for me. If I pull back the frog's gum a little bit, you can see that it's very, there's a lot of little ridges around the gum.

And you can see right here, especially you can feel it with your finger, those ridges, those are called maxillary teeth. And the purpose of the frog's teeth is not so much to chew food because the frog really doesn't do that. The teeth simply hold the prey in. in place while the frog is busy trying to swallow the food whole. And then the frog lets his stomach worry about the details.

If we look inside the frog's mouth, we see two openings right next to the probe. These openings are the nostrils. They're actually called internal nares, and these are the frog's nostrils. If we go in a little bit deeper into the frog's mouth, you can see two openings, one here and one right there.

And just to confirm, when I put the probe into these openings, I'm going to gently put the probe in there, you can see that it's actually pushing against the eardrum right there. So that's called the eustachian tube, and that allows the frog to equalize perfectly. If we go in a little bit further and I pull this frog's mouth open just a little bit more, we'll see a hole come into view.

And I'm going to dry up some of this liquid here. We'll see a hole come into view. Right here you see a little protrusion there and there's actually going to be a hole there.

I can stick the probe right into that hole. There we go. This hole is the glottis.

So the probe's inside the glottis right now. The glottis is the opening to the lungs. Well, this opening actually goes down through the trachea and eventually into the lungs.

and there's an opening right posterior to that, and that opening is gonna be the opening to the esophagus. Just to confirm, once we open up the frog's chest and abdomen, we can actually again put the probe in here and see that the probe is actually going into a lung or the probe is going into the stomach, and we'll do that in just a few minutes. Those are the parts of the mouth that I want you to be familiar with. The next thing we want to do is actually begin the dissection.

So we're going to use our scissors, and we're going to cut from the groin up to the mouth of the frog. However, I just want you to cut through the skin. So with your forceps, pull up. the skin, see how thin it is right there. That's all that we want to cut through initially.

We don't want to cut through the muscles, we don't want to cut through the organs, just the skin. So I'm going to go ahead and I'm going to stick the scissors. Into the skin, and I'm simply going to cut up through the skin all the way To the mouth and then I'm going to cut down both thighs so I want to take a look at the there and see how thick that muscle really is.

So I'm not cutting through the muscle I'm just cutting the skin. Notice my blade is parallel to the muscle and I'm not angling it down into the muscle where it's going to gouge the muscle. Now I'll do the other leg or the other thigh.

And again, I'm just cutting through that very thin, moist skin. And I'm going to pull that skin back. Now what you notice when I pull that skin back is all the blood vessels. Now this frog, I think, has been injected with a little bit of dye to make the blood vessels more obvious. But you can see all the blood vessels under the skin there.

And again, those blood vessels are are there for a reason. This is where gas exchange takes place. So the skin is going to be very, very vascular, meaning there's going to be a lot of blood vessels there. Because the function of the skin is to try to get the blood and the air in as close a contact as possible. So we've got lots of blood vessels picking up that nice, rich oxygen and returning it to the circulation of the frog.

Let's take a look at the other side. And again, we see the same thing, lots and lots of blood vessels because the frog's main respiratory organ is its skin. Under that, you can see some of these abdominal muscles.

This is what muscle looks like. See if you can find which way the muscles actually go, the striations in the muscles, because that's the way. If the muscles look like they're going in this direction, then they're going to contract.

that direction. So see if you can actually see which way the muscle striations are traveling. If we look down here in the thigh, again, you can see the muscles of the thigh, how large they are and how dependent the frog is on those big thick leg muscles for movement. Again, you can look at the striations, the pattern.

in the muscles to determine which way these muscles are actually going to contract. Again, more blood vessels in the skin. The next thing I want to do is cut through the musculature here.

But I've got to be careful. The abdominal muscles are not that thick, and I don't want to injure the organs, which are going to be directly below. So I'm going to start with an incision down near the groin.

Again, I'm going to keep my blade parallel, my lower blade parallel, so I don't gouge the organs. I'm going to cut right up the center of the frog. I'm going to cut right through here. You might have to cut through a little bit of cartilage and bone there. And I'm going to reflect or peel back the muscles.

Now you might have to cut some of this. And I'm going to cut here. And I'm going to cut up here.

So I can... more easily reflect the skin of the frog. And I don't really need to worry about this anymore, so I can cut this right off.

And that way I don't have it in my way. And I'm going to do the same thing to the other side. I'm going to reflect back the abdominal muscles here. And I'm going to reflect back the skin.

I'm just going to remove those so I have more easy access to the organs. Now the first thing that's most obvious here is all this salt and pepper looking structure right here. These are eggs.

So this is a female frog. She's about to lay her eggs again Where she's going to lay these eggs somewhere near the water where they can remain moist These eggs are going to kind of get in our way. So we're going to try to remove them them in an orderly fashion in just a minute. Another structure we notice here is this dark structure. This is a lobe of the liver.

This is a piece of liver right here. And then under that I see this muscular structure. That's going to be the frog's stomach. So the first thing I guess I want to do in order to see the organs is to try to remove the eggs here. So I'm going to try to get in there with my fingers and gently remove these eggs without making a big mess.

So I'm going to try to get in here and remove some of these eggs so we have a more clear view of the organs. Awful lot of eggs here. And remember, most of these eggs will be eaten by predators.

So we're not going to see a million frogs or so suddenly appear. Most of these will be eaten by predators. And that's why the frog, one of the reasons why the frog has to lay so many eggs. So we've gotten rid of most of the eggs here in a fairly orderly way.

And underneath that, you can see all these small tubes that I've got the forceps in. These tubes are... fallopian tubes are oviducts. This is part of the female reproductive structure. And you see the same thing on the other side here.

All this is oviduct. And you can see them there also. Let's take a look at the frog's digestive structures first. I'm going to get rid of some of this here so we can see a little bit more clearly.

Again, if any of this tissue gets in your way, feel free to cut it out. And let's take a look at the digestive tract of this frog. So again, this is going to be the stomach here. You see the stomach coming down. The stomach's going to narrow here.

And where it narrows, that's where the small intestine begins. Now I've teased away the small intestine. And what you can do is follow the small intestine around. Follow it around until all of a sudden it becomes larger right here. And where it becomes larger, that's going to be the large intestine.

Now the small and the large intestine are not named because of their length, but they're named because of their diameter. So the large intestine has a larger diameter. And this large intestine will eventually...

We exit through that cloaca, that opening that we showed you earlier. Now, some other structures that I want to go over are the liver. You can see this nice, large liver, and the liver's always, going to be large and a fetal pig it's also quite large and you it's quite large and if we gently lift the liver up we're going to see a small sack like structure right there it almost looks like a P you can see that sack like structure that's going to be the gallbladder.

Now the liver produces bile which is going to help in digestion and that bile is going to be stored in the gallbladder and then it's going to be released into the small intestine when food is eaten to help with digestion of fat. Some other structures that I'm looking for around here, here's our stomach again. And on the inside of the stomach, when I say inside, the lesser curvature.

This is a large curve here. This would be the greater curvature. So this would be the lesser curvature.

There should be a very small, sometimes not so obvious, it's kind of ill-formed pancreas. The pancreas oftentimes is going to be ill-formed. It's not a very well-formed organ and I'm looking for it here and it's not always going to be the easiest to find. But this is where it's usually located.

If I tease apart, we can see some tissue here. This tissue helps hold the organ. organs in place this tissue is referred to as mesentery that is called mesentery and before we go on and we find the pancreas if we can find it here I want to talk a little bit about the mesentery and the mesentery comes from something called the peritoneum.

The peritoneum is a thin layer of tissue. It's a thin sheet of tissue. And you can see it right here.

It's almost like saran wrap. We can see that peritoneum. And that peritoneum is going to line the body cavity and it's also going to line the organs.

And it does a couple things. Two of the big things it does is it helps the organs move more freely. and it also helps to protect against infection.

The mesentery is actually a piece of peritoneum, and it actually is going to surround blood vessels, and it's going to support and actually hold on to some of the organs. So we can see. some of the peritoneum or mesentery right there, that tissue that's actually surrounding the blood vessels.

Underneath, if we lift up the stomach and I look underneath, I see another small structure. It looks kind of purplish. or brown, looks right there, looks almost like a dried up raisin.

This is going to be the spleen. That's going to be the spleen of the frog right there. Now I'm still looking for the pancreas, and I have not, I'm unable to see the pancreas.

Perhaps this is a small piece of it in here. It's very poorly formed, I think that's actually gonna be it right there. Again, if we look at the lesser curvature, right around here, you might see see a very small sliver of tissue.

It's going to look sort of glandular, sort of grainy. That will be the pancreas. When we dissect the fetal pig, that pancreas is going to be bigger and much more obvious.

Some of the other structures that we want to take note of here, I'm going to remove some of these, all these fallopian tubes here because they're getting in our way. I'm going to try to gently remove them. And as I do that, we begin to visualize another structure beneath it. You can see this brown structure come into view right here.

And that brown structure is a kidney. That's the kidney. right there and that's going to get rid of our nitrogenous waste which in the frog is going to be ammonia and urea so that's going to be a kidney right there Now if we look on the other side, we should see the same thing.

I should see another kidney over here. Again, I'm going to have to remove some of these fallopian tubes or oviducts. And we see the other kidney just sitting right there.

I'm going to go ahead and I'm going to remove some more of these tubes. And down below, near the pelvis of the frog, this is down here near the pelvis, we can see this pouchy tissue right here. We can see all this pouchy tissue right here.

I've got my probe under it. And right here, there it is. That's going to be the frog's urinary bladder.

That's the urinary bladder that holds the frog's urine. Again, that urinary bladder is going to exit. through the cloaca, which is that external opening right there. The next thing I want to do is remove the liver so we can get a better shot of the heart and lungs.

So I'm going to remove, there's our heart right here. So as I move this liver down, you can see the heart. come into view.

Frog has a three-chambered heart and we are looking at the ventricle right here. That is going to be the ventricle and the atria are going to be up here a little bit further. We'll try to visualize a little bit.

those in just a few minutes. I'm going to come in here and try to remove this liver without pulling apart. The heart and the liver are very closely connected so we have to be very careful when we remove the liver so as not to damage the heart.

too much. So I'm going to come in here and I'm going to try to cut the liver out here very carefully without damaging other structures. I just go to the base of the liver and try to do some small snips taking it slowly and you can see that I removed the liver. Again there's our gallbladder right there and that's going to be our liver.

Take a good look at the liver. and here's our stomach before I go up into the chest and talk about the heart and you can see the pink structures right here these are the lungs notice they're very small lungs because the frog relies mainly on the skin to exchange gases rather than the lungs. I want to take a look at the stomach. So I'm going to cut the stomach open and I want to take a look in here. Some Sometimes when you cut the stomach open, I'm going to cut along the greater curvature of the stomach.

When you cut the stomach open, sometimes you might see some of the food that the frog has eaten. You might see an insect in there. You might see some other structures.

Sometimes you don't see anything. It just depends. So I'm opening that up.

You can see there's some food left over right there. And you can see what looks like a nail of some organism. perhaps this frog had a small lizard or something else for lunch.

But inside the stomach you can see some of the food there but you can see these folds and these folds when the stomach gets filled up and gets distended these folds obviously are going to allow the stomach to enlarge a little bit. The stomach is very muscular because remember the frog is not going to chew his food he's going to let his stomach do most of the work of digestion. Now if I come down a little bit further into the small intestine I'm going to open up that small intestine and I'm going to put the scissors in there do some small cuts be careful when you're cutting. And you can see how sort of it looks a little fluffy, spongy, I guess. And all those little tiny folds are going to serve to increase the surface area because this is where a lot of your digestion...

is going to take place, a lot of enzymes are going to get released to break down the food, and a lot of absorption is going to take place across this small intestine. So we want lots of surface area. Again, wherever diffusion is going to occur, we want lots of surface area. Let's go up and take a look at the heart here.

You can see the heart. You can see the large blood vessels coming off of the heart. I've got my probe underneath one blood vessel there.

And there's going to be another one going to the other side. See if you can take a look at those blood vessels. They're very thick blood vessels. And that's going to be our heart. I'm going to go ahead and try to remove the heart.

Looks like our heart broke apart a little bit here. It's a very delicate heart. You can see the inside of the heart right there.

You can see some of the blood on the inside of the heart. This is the ventricle here. You can see one of the atria is very thin.

You can see that it's easily deformed when I put my probe onto it because the purpose of the atria is more to store blood temporarily and then pump it into the ventricle, which is then going to pump the blood throughout the entire body. Let's take a look at these two pink structures. And these are going to be the lungs. What I want you to do is remove one of those lungs. Carefully try to remove an entire lung.

I'm going to get rid of some more of the fallopian tube there. And I want to remove... lung.

Actually before I remove the lung let me go into the frog's mouth and that opening that led to the lungs is going to be called the glottis. So if we open the frog's mouth and we take a look, this little lump right here is going to have a hole in it. And I just, I got the probe inside that hole.

Now as I push the probe through here, the probe should go in and you can see it. As I put my probe into the glottis, the probe should come out right around near the lungs, and it does. You can see that I'm actually lifting up that one lung right there. Actually, the probe just went through the lung.

you can see that if I go into the esophagus which is further back my probe should go into the stomach and I'm going to push it through a little bit further and you can see that it's going into the stomach. I can't quite, there it is right there, and the probe comes out of the stomach. So I want you to do that. I want you to see if you can actually follow those tubes into their proper structures, the stomach and the lungs. Now let's go ahead and actually remove the lung.

We're going to use our scissors and I want to remove this very carefully. So I'm going to snip around the base of the lung here and pull this out. Try not to damage the lung.

the lung too much and that's going to be the lung right there that's one of the lungs and the next thing I want you to do is cut this lung right in half we're going to cut it in half remember the lung went in the lung was like this in the frog so I want you to cut it in a horizontal way right across maybe a third of the way down and then I want you to take that lung and sort of open it up and you will see see that the lung of a frog and an amphibian is sort of hollow. You can see that my probe is inside that lung. It's sort of hollow.

And I'm opening it up, I'm teasing it open. You can see how hollow that lung is. Now if we were to open up your lung or a fetal pig, which is also a mammal, the lung would appear very solid, like a solid sponge. And if we actually looked at that lung...

on a microscopic level, we would see lots of little microscopic sacs called alveoli. Each one of those alveoli serves to increase the surface area of the lung. The frog does not have those alveoli.

His lung is essentially hollow, which reduces the surface area, which is why the frog must use its skin as its main organ of gas exchange. As we move up through evolution, we go to a reptile, and as we go to mammals, they're going to have alveoli, which greatly increase the surface area for gas exchange in the lung. So we're going to move that lung out of the way.

I'm just going to poke around in here, see if I see anything else of interest. Coming off the heart, our heart was right in here. Coming off of the heart, you can see this major blood vessel right here. Run right down, and you can see the blood vessel there. I'm going to sort of lift up the blood vessel a little bit.

And right underneath that blood vessel, probably for protection, is going to be the spine of the frog. That's going to be the spinal column. And your aorta, which is one of the biggest blood vessels in your body, also travels right down the front of your spine. Again, most likely for protection. You can see I'm actually moving the kidney out of the way there so you can see that aorta.

And I think we've covered everything that I want you to see. So that is going to be it for the frog dissection.

Transcript for:Frog Dissection Overview and Procedures

Transcript for:
Frog Dissection Overview and Procedures