All right, we're getting ready to do the rat dissection. So first things first, we have two rats here that we're going to be dissecting. One is male and one is a female. Before we get going, we just want you to be aware that we are going to be opening these rats up. We will be seeing the internal organs, so sort of viewer discretion is advised.
And just to make sure you know what we're expecting, for these rats, we're going to have a list on D2L of sort of what we call fair game organs. Anything that's on that list, you should be able to identify in an image what you're going to be dissecting. or if we show you an image and something's labeled, you should know what organ or appendage that is, and then you should be able to tell us what the function of that is. Now, the rats that we're using here in class, we've purchased from a biological supply company, and they've been reared specifically for the purpose of dissections for educational purposes.
And we just want to make sure that this, as with any dissections that you do at Washburn, that you are always respectful towards the animals or specimen. If you go on to take advanced anatomy. it might very well one day be a human cadaver. Regardless of whether you're dissecting a rat, a human, or any other animal here at Washburn, we expect you to be respectful towards the specimen in your language and your actions towards them should be respectful as well. Now, since these have been intentionally reared and prepared for the sake of educational dissections, they've been preserved in a specific way to help with that process.
And specifically what they've done is they've drained all of the blood out of these rats when they were euthanized. And in doing so, they've drained the blood and they've added into the circulatory system dyes that highlight where the circulatory vessels are. So I just want you to be aware that real rats don't have these vibrant blue and vibrant pink vessels in their circulatory system. That's merely the dye that has been added to sort of help contrast and help you as you learn. Now, before we actually get into the dissection itself, we just kind of want to start with some external features.
Some people get really excited about, hey, what's inside? And that's great. But there's a lot to be learned from the exterior as well.
So first things first, what kind of organism are we looking at here? I mean, obviously, yes, it's a rat. We told you that. But rats are mammals.
And there's sort of two features that we can see exterior that are features characteristic of mammals. One, mammals have hair. Rats both have hair. Another characteristic of mammals is that they nourish their young with milk produced from the female via mammary glands.
This is our female rat here. If we go ahead and flip her over, you can see her mammary glands on the bottom, which is where milk would be produced after offspring were yielded. Okay, so we have some mammals here, and specifically these are rodents. And they have sort of one really obvious external feature that keys us into the fact that they're rodents.
Rodents have continuously growing, a pair of continuously growing incisors, which are these really long front teeth. If you've ever possessed a rodent as a pet, so a hamster, guinea pig, gerbil, something along those lines, you know that you have to give them something to gnaw on to kind of keep those dulled down since they are continuously growing. Now, we also, like we said, we have two different biological genders here, or biological sexes.
We have a male and a female. And there's a couple of things about the external anatomy that can tell us if it is a male or female. So let's start with the female first.
A couple of characteristics of the females are the presence of mammary glands. Now, this female's mammary glands are much more pronounced or engorged than some. So she's a mature female.
And not only is she mature, the fact that these are as engorged as they are, might suggest that she's pregnant. And so we'll have to just see when we open her up. We should be able to tell during the dissection.
Now, female rats have three external openings just like humans. The first opening, which is right here, is the urogenital opening. And what's inside of this opening is the urethra, which urine would leave the body through. Beneath the urogenital opening, let me grab another probe.
Beneath the urogenital opening is the vaginal opening. So this would be the opening through which the menstrual cycle would occur, but also is the birth canal. So any offspring born would come through this opening. And then beneath that is the rectum, which is the opening for fecal manner. Now, if we look at the male, here's what really trips people about the male in terms of external anatomy.
One... Obvious landmark of a human male externally is the penis. Male rats also have a penis, but it doesn't hang. externally like it does in males. So the males, like the females, have a urogenital opening through which the penis would extend during reproduction.
Okay, so we'll be able to expose it, but the penis essentially is lying just beneath the skin, and the urethra, which runs the length of the penis, ends here in the urogenital opening. In addition to the urogenital opening, males also have a rectum. underneath the scrotum through which fecal matter would leave.
And the most obvious sign of a male externally on the rat would be the scrotum. So the scrotum is this right here. And it's essentially a sac that holds the testes away from the body. And the importance of this is that sperm that are produced in the testes have to manufacture at a certain temperature.
And that temperature is lower than body temperature. Our internal body temperature, as with the rats, is too warm for optimal sperm production. And so the scrotum helps keep the testes away from the body so that they can be cooler.
And there's actually muscles that allow the testes within the scrotum to contract or relax based on the temperature that the rodent is in. So if the rodent became very cold, these muscles could contract and pull the testes up closer to the body and therefore the body heat, allowing them to maintain a warmer temperature. And likewise, if the rat was really warm, those muscles could relax.
The testes could drop further away from the body slightly. And then that would allow them to be cooler. Okay. So now that we have a sense of the external anatomy for male and female, let's just talk about some terms that we use for dissections to indicate directionality. Okay.
So two sets of terms that we will use are anterior and posterior. And they are in reference to this plane right here. Anterior refers to regions that are more towards the head of the rat.
And then as you're moving posterior, you're getting closer to the rear or sort of what I call the tail region of the rat. So anterior, posterior is in reference to this plane right here. We also have a set of terms that refer to sort of more of the horizontal plane, and that would be ventral and dorsal.
Ventral refers to areas that are more towards the stomach of the organism, or you might say the underside. And then dorsal would refer to more of the back of the organism. So ventral, dorsal. Another set of terms that we use are a set of relative terms, where you have to have a focal point, and then the terms refer to how close something is to that focal point. So for instance, the heart of the rat is roughly here in the body.
So if I was referring to the heart as a focal point, I could use the words proximal and distal to say relatively how far something is relative to that point, the heart. So for instance, the forepaws of the rat are more proximal to the heart, whereas the hind legs are more distal to the heart. Proximal refers to something that is in closer proximity to your focal point.
Distal refers to something that is further away to that focal point. Again, it's relative to whatever you set as your focal point. And then proximal and distal tell you relatively how far you are from that point.
Finally, the good old right and left also still apply in many cases. However, one thing to keep in mind is that the right and left, when used in dissections, are in reference to the specimens. left and right.
And where this can get confusing is that a lot of dissections happen with the specimen on their back. So the vast majority of our dissection, minus a lot of this little preamble, is going to have the rat on its back faced up. So we'll have a ventral view of the rat during the dissection.
What that means is that when we're dissecting, the right of the rat is actually going to be on our left. So the terms right and left... apply, but they are the right and the left of the thing that you are dissecting, not necessarily your right and left. And if you're dissecting something on its back, that's going to mean that your directions are opposite. So that's just something to keep in mind.
Now that we have a sense of what we're dissecting, what they look like externally, and we have down our directions, let's go ahead and start opening up our female rat.