Animal Tissues - Online Tutor, Practice Problems & Exam Prep

Animal physiology explores the relationship between anatomy and function, emphasizing adaptations and acclimatizations. Adaptations are heritable traits enhancing survival, while acclimatizations are short-term responses. Fitness trade-offs limit perfect adaptations due to finite energy resources. Tissues, derived from germ layers, include connective, muscle, nervous, and epithelial types, each serving specific functions. For instance, connective tissue supports and connects, while epithelial tissue separates environments. Understanding these concepts is crucial for grasping how organisms function and evolve in their environments.

Animal Physiology and Fitness Trade-Offs

Hi. In this video, we're going to talk about the basics of animal physiology and cover the major types of tissues found in animals. Now, anatomy is the study of an organism's physical structures. A very famous study in anatomy is this image here, the Vitruvian Man, drawn by Leonardo da Vinci. Physiology is the study of the functions of those structures. So here, you can see the human cardiovascular system, which is a network of veins, arteries, and capillaries, and, of course, the heart. Those are the structures; the function, the physiology of this, is to pump blood and mainly to deliver oxygen to tissues in the body by pumping the blood around. So, there you have the difference between anatomy and physiology. Now, organisms are going to have adaptations that they acquire through evolution. These are going to be traits that they are able to pass down to their offspring, heritable traits, that will improve their chances of surviving and reproducing in their environment.

One of my all-time favorite examples of an adaptation is with these moths behind my head. You see, prior to the industrial revolution, most of this species of moth appeared like this; they were white. The industrial revolution in England brought on tons of smog and pollution, and generally darkened the air, and stained dark, you know, just the environment around these factories. And so over time, the population of moths shifted from mostly having this white appearance to mostly having this black appearance. And the reason for that is these white moths stuck out like sore thumbs in the post-industrial world, making them easy targets for predators, meaning they had a lower chance of surviving, and they, therefore, a lower chance of effectively reproducing. So now, this species of moth is mostly in this appearance, or mostly has this appearance.

Now, these adaptations should not be confused with acclimatizations. Acclimatizations are short-term, basically short-term adaptations to changes in the environment. These are going to be things like, the amount of oxygen that your red blood cells can carry. I mean, there's a famous example. Lots of runners want to train at high altitudes because the thinking is, by training at high altitudes, they'll acclimatize to the high altitude, and they'll, their blood cells will be able to suck up more oxygen, and therefore, they'll be able to deliver more oxygen to their tissues. The problem with this is as soon as these runners go back to a normal, lower altitude, they're going to lose this effect. It actually goes away so quickly that it's, in some respects, almost not even worth the trouble.

So, adaptations are going to be long-term, passed down through generations; acclimatization happens within an individual in a short span of time. Now, the thing about evolution is it's not going to lead to perfect adaptations. There's this idea called fitness trade-offs, which is essentially a limit to an organism's ability to adapt to its environment. And this is in part due to a finite energy capacity. Essentially, an organism has only so many resources it can commit. Right? I really like to think about this if you've ever played a role-playing game. Right? Your character has different stats. You can only commit a certain number of stat points though. Right? You can't make your guy really, really strong and really, really fast or something. Right? You only have a set number of resources that you can allocate. Well, the same is true with adaptations. Organisms can't make everything perfect because they only have a finite resource pool to draw from. So what you get is essentially a cost-benefit compromise for the energy investment in adaptations. Basically, you want to expend the least amount of energy for the biggest effect.

Now, adaptations are also going to be limited by existing alleles in ancestral genes. I mean, organisms can only modify or really only work with the genes that came before, the genes that are available to them. So that's going to constrain the possibilities in terms of an organism's adaptations. For example, our spines are actually terribly designed for us standing upright. That's why, basically, all humans have back problems. The reason is, we weren't intended to be upright creatures. The spine came from creatures that walked on all fours, but that was our constriction. Right? Those were the confines within which we had to work, so you gotta live with the back problems.

Now, there's also a trade-off between the reproductive success of an organism and its chance of survival. You know, the way I like to think of this is, if you commit too much to having one successful reproduction, you might actually be losing out when you could have had, you know, 2 mildly successful reproduction periods. So I guess what I'm trying to say is sometimes, it's more important to ensure the survival of the organism so that they can reproduce another day than to just commit all the way to just getting that one reproduction done. You know, one of the ways this often comes up in terms of survival is the immune system. You know, it takes a lot of energy for animals to mount an immune response. And sometimes it's worth it to sacrifice reproduction in order to ensure the organism survives and, again, can reproduce another day. So, basically, what this all comes down to is if a mutant allele alters a feature in an individual, and it allows that individual to survive and reproduce more efficiently, that allele is going to increase in frequency in the population. This is getting back to that idea of Hardy Weinberg population genetics, with the frequency of genes appearing in a population. You know, the idea is that if an individual survives and reproduces more effectively, they're going to have more offspring that have that mutant allele, and those offspring are going to survive and reproduce more effectively, so they're going to pass on that allele, so it's going to become more prevalent in the population. Now, just to illustrate this idea of fitness trade-offs with some real-world examples, I want to talk about the cheetah. Now, cheetahs are known for their ability to run super fast, and the way this actually works is if their legs are longer, they're able to actually run faster. But they only have a finite resource pool. Right? If you make the legs too long, the bones are too brittle. The cheetah will risk breaking its legs all the time. You don't want to make the legs too short because then it's not going to run fast enough. So you need to find this cost-benefit compromise. The longest you can make the legs while the bones are still sturdy enough that the cheetah's not going to risk breaking its leg every time it sprints after a gazelle or whatever. Another beautiful example of this, also with another animal from Africa, the giraffe. As you can see here, and as I'm sure you know about giraffes, they've got this really crazy long neck. And part of the reason for that is they're able to reach vegetation that's higher up than other herbivores can reach. Right? They can get the vegetation that's in the treetops that other herbivores can't get to. This allows them to survive more effectively because they don't have to compete with a bunch of other organisms for food. Right? They're really just competing with other giraffes, others who can reach all the way up there. Here's the problem, that neck is really big, and really heavy, and really energy expensive to make. So, you know, you could have the best neck in the world, but that's not going to be efficient. You want that cost-benefit compromise. You want the neck to be just long enough that it can reach that vegetation, and the organism will easily be able to secure food, whereas at the same time, it's not going to waste tons of energy, in having an overly long neck. I mean, just think about the amount of muscle in there alone, and all the energy demands that muscle has just to keep the organism's head up. So with that let's flip the page.

Tissues and Organs

In living systems, structure is always related to function. There is no room to waste energy on frivolous reasons. You can see this relationship between structure and function all the way down at the molecular level. Consider a membrane protein that needs to span the hydrophobic plasma membrane, yet interact with the hydrophilic environments inside and outside the cell. Also, a lot of these membrane proteins, for example, transport ions, which are charged molecules. Right? Or charged particles, I mean. Now with the membrane protein, it's going to have hydrophobic regions. Right? Those hydrophobic regions are going to interact with the membrane, and in part, anchor it into the membrane, and it's going to have hydrophilic regions which will interact with the intracellular and extracellular environment, and, assuming, for example, it's transporting an ion, it will have a hydrophilic internal environment to get that charged particle through.

We also see this relationship between structure and function at the cellular level. Consider cells that perform secretion. Right? They need to export lots of molecules. What is the organelle involved with exporting stuff? The Golgi apparatus. Here you can see a nice, electron microscope view of a cell that is chock full of Golgi apparatus. All this foldy stuff here is Golgi apparatus, and that's because this is a secretory cell, it's a cell that plays a role in secreting substances in the body, so it's going to be chock full of Golgi apparatus to carry out that function efficiently.

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And, of course, we see this on the organ and the whole organism level as well. The famous example, of course, being the flower that Darwin saw, which you can see right here, and this flower has a really long tube, it's kind of hard to see in this image, but just take my word for it, this tube that leads to the nectary, the nectar-producing portion of the flower, can be almost a foot long. And when Darwin first saw it, he said, you know what? I bet there's an animal out there that has a proboscis that can reach all the way down there and get that nectar. And there it is. This moth right here, with this huge proboscis, you can see it uses to feed on nectar from this flower. So structure is going to fit function.

Now when we talk about an organism's anatomy and physiology, we're going to be talking a lot about tissues and organs. A tissue is going to be a group of cells that carries out a specific function. And here you can see a sample of some tissue from a lung. These cells that are stained in this color are part of a tissue, they're going to carry out a specific function, and they're going to work in concert with other tissues in the lung to carry out the function of the lungs to perform gas exchange. The lungs themselves are an organ, which is basically composed of multiple tissues and will carry out some specialized functions. So, for example, in the lungs, you need tissues where gas exchange can occur, there's also tissues that produce a mucus substance to help prevent the lungs from collapsing. There's a lot of stuff that goes into just carrying out that one specialized function of the organ. It takes multiple tissues working together. And then those organs will actually work in concert with each other in what we call organ systems. This is a group of organs that works together to carry out some function. Right? So while the lungs might perform gas exchange, they need other structures to carry out the function of breathing. Let me jump out of the way here, and here you can see the respiratory system. This is the organ system responsible for breath. And you can see it has multiple components, of which the lungs, these guys, which you can see in pink over here, the lungs are only one organ in this system. It requires many other things working in concert to talk about tissues.

Embryonic and Adult Tissues

Tissues are complex structures made of highly specialized cells. They don't form overnight. In fact, an organism begins to develop its tissues early on in embryo development following what's known as gastrulation. After gastrulation, these cell layers called germ layers develop. These are kind of like embryonic tissues and there are 3 types: the outer layer or the ectoderm, the internal cells which are called the mesoderm, and the innermost cells, the endoderm. And you can see those depicted in the gastrula here. And, if you don't remember what a gastrula is, I recommend you go back and check out our video on development that covers this whole process of blastulation and gastrulation and talks about how you get to a weird ball of cells like that.

Now, adult tissues come from these tissues and there are 4 types of adult tissues. You have nervous tissue which will come from the ectoderm, muscle tissue which comes from the mesoderm, connective tissue which also comes from the mesoderm, and epithelial tissue that comes from both the endoderm and the ectoderm depending on what type of epithelium you're dealing with. You can see some examples of the final products of these germ layers and what they will wind up as right here.

With that, let's turn the page.

Connective and Nervous Tissues

Connective tissue plays a major support role in the animal body. It connects, separates, and cushions other tissues and is basically made up of some cells scattered within an extracellular matrix. Hopefully, you remember, extracellular matrix is an array of proteins and this gel-like substance called ground substance. This functions as a support structure outside of eukaryotic cells in order to kind of play the role that a cell wall might, for example. It has a lot of other properties too, but you can think of it as a sort of surrogate cell wall, providing structural support. Now, loose connective tissue is the most common type of connective tissue found in vertebrates. It helps hold organs in place and attaches epithelial tissue, a topic we are going to discuss in just a moment. The most notable type of loose connective tissue is adipose tissue or fat. Adipose tissue is mostly made up of these cells called adipocytes or fat cells. You can see an example of loose connective tissue here in these two images; both are loose connective tissues.

Another type of connective tissue is dense, or sometimes it is called fibrous connective tissue, and this tissue is dense with collagen fibers. Most notably, it makes up tendons, which connect muscle to bone—very important—and ligaments, which connect bone to bone—also very important. That's how your body moves. You can see an example of this fibrous connective tissue right here above my head. Now, you also can have supportive connective tissue, such as bone and cartilage. These tissues provide structural integrity. You can see examples of bone and cartilage here; this is bone, and right behind my head, you have some cartilage. These tissues form a hard extracellular matrix, which is what gives them that structural integrity.

Lastly, there's fluid connective tissue, which is essentially blood. Blood cells have a liquid extracellular matrix we call plasma. Here, you can also see a nice little example of how connective tissue functions with other tissues. The stuff stained in blue in this image is connective tissue, and the purple stuff that it is surrounding is a type of epithelial tissue. So, you can see how the connective tissue is supporting that epithelium.

Nervous tissue is very important. This is how I am thinking these thoughts and speaking to you right now. This tissue conducts electrical and chemical signals and is divided between the central and peripheral nervous systems, which we'll discuss when we explore the nervous system in general. The main type of cell that gets all the credit in the nervous system is our neurons. These receive and transmit the electrical signals. You can see a neuron here. It transmits these electrical signals by transporting ions across the membrane in what we call the action potential. We will talk about that again when we cover the nervous system. The main components of a neuron are the axon, this portion here, and the dendrites. The branch-like structures out here, that I have circled, are the dendrites.

The axon can be thought of as the wire; it is the structure that can be very long sometimes, and this is what transmits the electrical signal. The dendrites are the branch structures that receive signals and determine how the cell needs to respond. Now, the reason I talk about neurons as though they get all the attention but don't necessarily deserve it is because of these other cells in nervous tissue, glia. Glia do not get nearly enough credit; they are super important as support cells for neurons, essential to their survival. Neurons would not live without these glia, and they also help the neurons with their functioning. We'll get to the specifics of their roles when we talk about the nervous system, but let me just say that this beautiful astrocyte that my head was covering, this glia right here, is probably responsible for much more of the functions of the nervous system than it actually gets credit for. A lot of current research in neuroscience is showing that glia play a much more important role than they are initially given credit for, and they also are involved in signaling, albeit in a different way from neurons. So super important stuff. Don't write off glia. Alright. With that, let's turn the page.

Muscle and Epithelial Tissues

Muscle tissue is unique to animals and is capable of contraction. That's how animal locomotion works. There are actually 3 types of muscle tissue that we'll talk about. These are skeletal muscle, which is attached to bone and used for locomotion and posture. And you can see right here, we have some skeletal muscle. Then, we also have cardiac muscle, which you can see right here. This is cardiac muscle only found in the heart and its job is to contract the heart and help the heart pump blood. And it's got some super interesting features that relate to signal transduction in the nervous system sense. Well, I'm getting ahead of myself because I'm excited, but we'll get to all that in a later lesson. Lastly, we have smooth muscle. This is found in the walls of organs and vasculature and is what allows them to contract. And you can see some smooth muscle, right behind my head here. Boom, smooth muscle.

Now, the last type of tissue that we'll talk about is epithelial tissue. This lines organs and body surfaces and its main job, the thing that makes it so important, is it can separate interior and exterior environments. This allows organisms to create unique environments which allow for some drastically different chemical and physical conditions. This is super important. I mean, think about it. Your stomach is full of acid, right? You need that for digestion. But, obviously, if that stuff leaked out into your body, you would be done for. Thankfully, we have epithelium that will line our stomach and keep those environments separate. You can see an example of epithelial tissue right here. This darkened line that crosses through them is meant to represent the barrier that they create between the two environments. And there's a little bit of terminology that you should know. The apical side of the epithelium faces away toward the exterior environment. So here, we have our apical side. The basal side faces the interior of the animal or the organ, for example. And lastly, there's a special type of extracellular matrix on the basal side that epithelium sits on. This is called the basal lamina, and you can see a nice image of it here. We are looking at a small portion of the exterior or the sort of outer edge of a cell here. This is the inside of the cell. This is the outside of the cell. And this dark line right here is that basal lamina that the epithelium will sit on. That's all I have for this lesson. I'll see you guys next time.