We're now ready to go ahead and open up the rat. So we're going to kind of break this up in stages. There's two primary body cavities within the rat.
There's the abdominal cavity, which kind of takes up this space right here and houses the vast majority of the digestive organs and, well, the majority of the organs we're going to cover. And then we have the thoracic cavity up here where the heart and lungs are located. And these two cavities are going to be separated by a thin sheet of muscle called the diaphragm that we'll be able to see once we open them up. So we're going to go ahead and open up the abdominal cavity. First things first, we're going to go ahead and take our tweezers to pull up on the skin.
One thing we want to keep in mind is that the penis is aligned with the urogenital opening right here, so we want to stay either to the right or the left so that we don't cut it, so that it's intact during our dissection. Now everybody's watched an episode of a medical show, Grey's Anatomy, Chicago Med, whatever, and they think, aha, a scalpel. I know how to use one of those.
We're not going to actually use the scalpel for the whole dissection. It takes a lot of practice to put the right amount of pressure and not nick all of the organs as you're pushing down. Not to mention these things are relatively dull compared to what doctors use.
So we are simply just going to use the scalpel to make a small incision through the skin until we are all the way through. And we're not going to make it very big, just big enough to fit in a pair of scissors. And then we're going to cut.
Using the scissors is generally best because you can kind of pull up on the skin as you cut, and that's going to keep a lot of the underlying organs from being snipped. All right, we're going to cut all the way up until essentially the bottom rib, because that's where the diaphragm is at. Right about... a little higher right here about that's kind of where the rib cage begins and then what we're going to do is we are going to cut down on either side here and down either side here to create two flaps that we can open up now the rule of thumb is the further back you make your cut so the more dorsal you go with your cut towards the back the better you'll be able to lay the flaps down and then you'll have better visualization of the internal organs Let's see what we got here. Our scissors are a little on the dull side too.
They've been dissecting scissors for many moons. Okay, we're going to kind of extend the cut this way to make our flap around the leg. Again, staying around the urogenital opening.
Now we'll kind of cut up around the haunches. Again, the further back we can make our cuts, the better off we're going to be. All right, almost done with this side.
Let me switch scissors. All right, so we have one flap, one side exposed. See how that lays down flat?
Now we're going to go ahead and make incisions down the other side so that we can open the other side up. Alright, once I get it all the way open we'll have better visualization. Okay, and then again, staying so that our penis remains intact and cutting down the other side.
Alright. Okay, so now that we've got our rat opened up, the abdominal cavity, we've got these flaps open, let's go ahead and start identifying some structures and then also commenting on their function. So first thing, I talked about the diaphragm, that thin sheet of tissue. That is what is here. At the very top of the cavity, it's basically acting as a barrier right now between what cavity we have opened, the abdominal and the thoracic cavity, which we'll open later.
Now, the function of the diaphragm isn't just to act as a barrier. The barrier, actually, it's an important piece of respiration. When the diaphragm contracts and relaxes, that changes or helps change the volume of the thoracic cavity, which is what allows the organism to inhale and exhale.
So the diaphragm is really a big part of respiration, allowing the organism to respirate. Next, kind of one of the defining landmarks of the abdominal cavity is the liver. It's the largest organ. in this cavity, and it's got multiple lobes.
So here's a lobe, here's a lobe, there's a lobe here. If I remember correctly, I believe rats have five lobed liver. There's a lobe right there, and if we pick it up, I think we can find another lobe.
Yep, another lobe right here. So one, there's one lobe right there, two, three, four, and then the fifth lobe is down here. All right.
Now, the liver has multiple functions. It functions partially in the digestive system. The liver produces something called bile, and bile helps break down fats that you consume, and so they can be digested.
It also helps break down harmful substances, so it sort of acts as a detox in a way as well. All right. Next, we have, if we pick up the lobe of the liver over here. We have the spleen. The spleen is this long finger-like organ right here that is on the rat's left-hand side of the abdominal cavity.
And the spleen's primary function is in the immune system. It helps recycle red blood cells, which is one of its primary functions. Now beneath the spleen, and this is probably the hardest organ.
because it doesn't have as well of defined shape as a lot of the other ones we've been looking at. Let me see if I can get good visualization real quick. If you kind of pull back the spleen, underneath the spleen, kind of enmeshed in this membrane, is this really brainy-looking material.
And this brainy-looking material is the pancreas of the rat. And like the liver, the pancreas has kind of multiple functions, one of which is within the digestive system. So the pancreas helps secrete a lot of digestive enzymes that help break down those large molecules that you're consuming into their individual building blocks. Remember, those are called monomers. And then the body is able to absorb those into the bloodstream.
But they have to first be broken down via digestion, chemically. And the pancreas is secreting a lot of digestive enzymes that help do that. The other kind of one of the main functions that the pancreas plays is in the endocrine system. So it does help produce a couple of really important hormones, two of which are really critical for regulating your blood sugar levels. The one that people are most familiar with is called insulin.
That helps regulate your blood sugar level. And the other is glucagon. So the pancreas also is producing hormones that help regulate your blood sugar level, in addition to producing digestive enzymes.
And in terms of location, if you pick up the spleen, it's usually attached to a membrane on the underside of the spleen. Now on this side, underneath the liver, is the stomach. So the stomach right here is this organ.
It's not as big as people are expecting. The most common incorrect identification that I see people make is when they see the liver, it's big, it's in your face, and they want to call that the stomach. It's not.
The stomach is smaller than the liver, and it's just underneath on the rat's left-hand side. So if you kind of pull back the spleen, let me see if I can get a better, pull back the spleen, pull back the liver, it's going to be underneath right here. Now the stomach is obviously a big part of digestion. Some digestion happens in the stomach, but actually the majority of digestion doesn't happen in the stomach.
Really, the primary function of the stomach is to act as a holding tank for food that's been consumed. So that an organism can consume more in one sitting. If you didn't have a stomach, you could live. Actually, I know somebody who doesn't have a stomach because it had to be removed.
They had stomach cancer and they're still alive. They just can't eat as large of meals, which means they have to eat more frequently to consume as many calories and get the nutrition that they need. So the stomach, some digestion does happen in the stomach. but also its primary function is to allow you to eat larger quantities in one sitting.
Without it, you'd have to eat smaller amounts more frequently. Now if we kind of follow the stomach, we start to get into the intestines. The very first portion that comes off of the stomach, so if we kind of look, there's the stomach right there.
And here is the intestine coming off the stomach. You can't see it because the stomach is not open right now, but the stomach has two muscular-like rings at the top and the bottom that regulate things moving in and out. And these are called sphincters. So sphincters are essentially contractual rings of muscles that can sort of close like a purse string.
And if we look, we can see... Let me pull it back. If you look right here, you can see where the esophagus is entering the stomach. So the esophagus is connected up to the mouth, and we'll see kind of where it's at in the thoracic cavity. And here's where it's connecting to the stomach.
And then likewise, coming out the bottom, near my finger that I'm wiggling right now, is the beginning of the small intestine. And so in order to keep things in the stomach or to regulate the flow in and out, there's these ring-like sphincters at the top and the bottom. The sphincter that is towards the top that is connected between the esophagus in the stomach, that's called the cardiac sphincter.
And I always remember it because it's closer to the heart, which is up here in the thoracic cavity. And then the sphincter that closes off between the stomach and the small intestine is called the pyloric sphincter. And actually, sort of just a little fun fact, if you ever have heartburn, right, that burning sensation, usually associated with consuming certain kinds of food, Heartburn is like a misnomer.
It's inappropriately named because it really doesn't have anything to do with your heart. When you have heartburn, what's happening is that some of the acid that's in your stomach has splashed up past the cardiac sphincter into the bottom half of your esophagus. Your stomach is lined with a coating to help protect the tissues of your stomach from the acid that's in it, but your esophagus doesn't have that coating. So if some of that stomach acid splashes up, then it causes that burning sensation that we attribute with heartburn. So we got our small intestine here.
And really the function of the small intestine is digestion and absorption. So a lot of the digestion happens here. And then once the molecules have been digested into their smallest format, they are absorbed across the lining of the small intestine into the bloodstream.
And in some cases... the name small intestine can also be a little bit misleading. It's called the small intestine because of its diameter, not necessarily because of its length. Actually, if you were to take the small intestine and the long, the large intestine and put them side by side, the small intestine is a good deal longer.
It's just that the diameter of the intestine is a little bit smaller, which is actually really helpful in giving it a larger surface area to volume ratio. Very critical that this particular organ has a high surface area to volume ratio because it needs to absorb so much from the intestine into the bloodstream. All right, so if we kind of follow the small intestine, it's obviously really convoluted in here, but if you follow it around, eventually you will end up at this sac-like conjunction, just get rid of that, called the cecum, okay? The cecum is situated in between the small and the large intestine. And one of the functions of the cecum, especially in the rat, is that bacteria are housed inside of this organ that help break down plant matter.
So some plant matter, like cellulose, is really difficult to digest by living organisms. They don't produce the necessary enzymes that it takes to digest that material. But some organisms house bacteria in their gut that produce the enzyme that they need to break down cellulose. And that's what's embedded in the cecum of this rat. This rat has bacteria in its gut that produce the enzyme that help break down some plant matter so that it can be digested and is also sort of the meeting point between the small and the large intestine.
So if we kind of look let me sort of just pull this to the side so you can see where the conjunction occurs. There is the small intestine going into the cecum which is this pouch. This pouch is the cecum and there my thumb is going over the small intestine. that is entering the cecum. We can see that coming out the other side, over here, is the large intestine that is leaving the cecum.
The primary function of the large intestine is that water reclamation. So here, the material that's been passing through the intestine, some of it's being absorbed, but not all of it is digested and absorbed by the organism. Okay, some of it's going to be excreted as feces. In the large intestine, a lot of the water from what's going to become the feces is reclaimed, and the feces starts to become more solidified as this process happens.
Some vitamins are also absorbed in this portion of the intestine as well, but it's more common ...remembered by its purpose of water reclamation, which is really important for making sure that organisms stay at the appropriate level of hydration. Just to give you some context, you know, you can swing in either direction. If your intestine does not, your large intestine does not reclaim enough water, then you have the syndrome known as diarrhea.
Watery stool, if it's bad enough and you aren't able to replace the water, you could become dehydrated to the point that it severely impacts your health. The opposite problem would be that your large intestine reclaims too much water, and the stool becomes too solidified too early on, which we would know as constipation. Now, you don't think of constipation as being problematic, and in mild cases, it's not.
But if it becomes bad enough, you can get an impaction where you essentially have a mass of feces that can't continue moving because it's too solidified, and if that maintains for a while, sometimes surgery is needed to... to rectify that. So if we continue to follow the large intestine, we could follow it all the way to the end where it's going to eventually turn into the rectum and come out here through this opening under the scrotum. All right. So we've now covered all of the digestive organs that we're going to tackle, but there is...
one other thing that I want to point out in the abdominal cavity, and that is the kidneys. So the kidneys are very dorsal. They're towards your back.
So if we go ahead and kind of pull to the side, the liver, you can see in the back here this kidney. They have a very distinct shape. The named kidney beans that you can buy from the store are named kidney beans because the shape closely resembles the kidneys inside of living organisms. Let me see if we can get a good shot here. All right, so there's the kidney and you can see the vein coming off of the kidney right there, that blue vessel.
Now, most organisms are born with two kidneys, so we should see one on the other side. And lo and behold, there it is. All right. We've now covered all of the structures in the abdominal cavity that you're going to be responsible for.
Let's go ahead and start tackling some of the reproductive structures of the male rat. We've already kind of identified on the exterior that this is the scrotum which holds the testes. In order to expose the male reproductive anatomy, we need to cut through the scrotum in order to expose the testes, and then we'll need to cut away some skin to expose the penis.
So to do this, we're going to do something similar to what we did when we opened the abdominal cavity. We're going to use a pair of forceps to pull back on the skin so that we don't nick the testes underneath. And then we're going to use a scalpel to sort of carefully separate the tissue away until we get a good opening, in which case we might switch to scissors.
Let's see. Luckily rats have two testes, so if my dissection skills don't turn out to be wonderful here, we can always take two on the other side. But I think I'm getting it. Got a little cut there, but nothing too dramatic. Doing dissections always makes me, I guess, in awe of surgeons.
I think sometimes, oh man, so tedious just to dissect an animal that's already dead. How much more nerve-wracking would it be to try to make cuts on things that you're trying to keep alive? Definitely would add another level.
I guess that's why they go to school for as long as they do. Okay. Alright, we're getting somewhere.
There we go, that's looking good. Alright, let's go ahead and pull the testy out so that we have better visualization. Alright.
And then once we go through the various aspects of the testy, we'll go ahead and dissect out the penis. All right, so let's start first at the testy and then just kind of work our way around to where the sperm would travel. So the function of the testy is that this is where sperm are generated. cell of the male rat.
Now, when those sperm have been produced, they then go to an organ called the epididymis, which is a structure that cups the testes. It's probably best to see it from this angle right here. All right, so you can see the epididymis right here.
This is where the sperm go to mature after they've been produced by the testes. Only after maturation Are they viable potentially for reproduction? Now, when this rat is ready to reproduce, sperm are going to travel from the epididymis, where they mature, down a tube called the vas deferens, which is right here. So the vas deferens is a tube-like structure that connects to the epididymis and carries sperm away from the epididymis down the path that eventually is going to take it out of the body.
Let me open this up a little more so we can see where that kind of loops around. All right. Okay.
Okay. So the epididymis is going to go around and eventually it's going to connect with the urethra. The urethra is the exit point for not only urine in males, but that's also the exit point for the sperm as well.
Now when the rat ejaculates in reproduction, fluid is going to be expelled, a small portion of which is the sperm that are the cells capable of reproduction. But actually the vast majority of the volume of the liquid isn't sperm at all, it's other contributions that aid the sperm. Some of the fluid that is added into what we call the semen. Semen is a collective term for all of the fluid that is ejaculated, including the sperm as well as the other contributions from some other accessory organs. One set of accessory organs that helps add in part of that semen are these two structures.
They're kind of lumpy right here and right here. This is called the seminal vesicle. The seminal vesicle isn't a structure that the sperm moves through, but as the sperm is moving through the vas deferens, this organ adds in fluid that's going to make up a large portion of the semen that's produced. Now it's adding in a couple of things. One thing that it's adding in is fructose, a sugar.
And the reason why the sperm needs the fructose is because that sugar is acting as an energy source for the sperm. they're going to have to be able to swim up the reproductive tract of the female to potentially reach the egg and so that energy source is coming from this organ right here the seminal vesicle another thing that is added in is something to help provide a little coagulation to the semen so that it will better stick to the vaginal walls and increase the likelihood of conception okay and then finally another thing that's added in by the seminal vesicle is an alkaline solution or a basic solution. The reproductive tract of the female is relatively acidic and not the most hospitable, so to speak, to the sperm that have to travel through it.
The alkaline solution that is emitted with the semen help neutralizes the acid and therefore allow the sperm to be viable in the female reproductive tract. What we have right here, we have two organs side by side. This back organ right here is the bladder of the rat that holds onto urine. And then right in front of it, we have the prostate gland, which is another gland that is adding in secretions that are going to help with the formation of the semen. Now we can't see where it turns into the urethra, okay, but we can dissect out the penis and the urethra would be traveling up the base of the penis.
So let's go ahead and turn this to the side and I'll go ahead and dissect out the penis and then we'll just kind of review quickly the male reproductive structures. So you can kind of see it, the penis is sort of in an L shape in the skin right here, but it's currently held within folds of skin. What we need to do is we need to dissect that skin away from the penis so that we can physically see it. So let's go ahead and do that.
We're just gonna kind of pull, give a little tension so that we're able to cut through the skin easier. All right. Always important not to cut yourself during the dissection.
Okay, let me cut off the skin on this other side and then it should be exposed. Okay, all right. Looks pretty good.
All right. So now we have most of the skin cut away from the penis. It's right here.
And the urethra, which connects with the vas deferens, would run through the length of the penis. Now urine and... Semen cannot be released at the same time, but it is a shared pathway.
When the rat is not actively reproducing, then urine would be what travels through the urethra. And then when it is reproducing, it would ejaculate through the urethra out the tip of the penis. Now, really the function of the penis is to be able to deposit the sex cell inside of the female reproductive system. And the reason why that's important is because sperm...
have flagella that allow them to swim. But as I always tell my students, while sperm can swim, they cannot fly. They have to have a liquid to move through.
No liquid, no mobility. We live on land. Land is sort of notoriously a dry environment. And so one...
obstacle that a lot of animals had to overcome when moving to land is how do we continue to reproduce even though we don't live in a environment that is liquid? And one of the solutions to that problem was what we call internal fertilization, or is probably probably more commonly known as sexual intercourse. Sexual intercourse or internal fertilization are ways of getting the sperm into a moist environment, even though the organism lives on land.
By depositing the sex cell into the female reproductive system that in itself is moist, it's putting that cell in close proximity to where the egg will be deposited in an environment where the sperm can then swim through to get to the egg. All right, so let's just kind of reiterate or go back over and name those structures again. First, we have the egg-shaped organ, very smooth. That is the testes where sperm are produced. After sperm are produced, they go to the epididymis.
Oh, let me see. I might be able to get a slightly better view. They go to the epididymis to mature.
After they mature in the epididymis and if they are ready to be released, they travel down the vas daffrons. The vas daffrons here loops around and eventually connects with the utera. Secretions are added to the sperm to create semen from the seminal vesicle, this M-shaped bumpy-looking organ, and from the prostate gland, which sits right in front of the bladder. The penis then deposits the semen, including the sperm, into the female reproductive tract and travels along the length of this out of the urogenital opening.
Now that we have that, let's take a look at the female reproductive system.