Introduction to Epithelial Tissue: Study with Video Lessons, Practice Problems & Examples

Epithelial tissue, or epithelia, is a primary tissue type that covers body surfaces, lines cavities, and forms glands. It consists of tightly packed cells adjacent to open spaces, providing protection, regulating transport, and allowing sensations. Epithelial tissue is categorized into covering and lining epithelium, which protects and regulates absorption, excretion, and filtration, and glandular epithelium, which produces secretions like sweat and hormones. Understanding these functions is crucial for grasping the role of epithelial tissue in maintaining homeostasis and facilitating interactions with the environment.

Intro to Epithelia

In this video, we're going to begin our introduction to epithelial tissue. And so recall from our previous lesson videos that epithelial tissue is one of just four primary types of tissue found in the human body. And epithelial tissue is commonly abbreviated as just epithelia without the "l" and without the "tissue". And so epithelia or epithelial tissue is tissue that covers body surfaces, many organs, lines internal body cavities and ducts, and makes up glands or cellular structures that are specialized for secretion or releasing products. And so covering, lining, and glands are key terms that are very often associated with epithelial tissue in your textbooks.

However, one of the key defining features of most epithelial tissue is that it consists of a single sheet or multiple sheets of tightly packed cells on a boundary immediately adjacent to open space. In fact, if we take a look at our illustration down below, you'll notice that we're highlighting a few examples of where epithelial tissue can be found in the human body. And what you'll notice is that in each of the micrographs for these examples, we can clearly see that epithelial tissue is going to consist of sheets of tightly packed cells on a boundary adjacent to open space. In fact, we can actually highlight the open space in each of these micrographs. And so notice on the far left over here, you can see the open space is right here in this region.

In the second micrograph, you can see that there's open space right over here. In this third micrograph, you can see that there are small bits of open space in these highlighted small regions that you see there. And then in this final micrograph, once again, you can see that there are small bits of open space in these highlighted regions right there. And so over here in the micrograph on the far left, notice that it is indicating that the outermost layers of our skin are going to be epithelial tissue. And we know that our skin covers our entire body surface.

And so the outermost layers of the skin are a classic example of epithelial tissue. Now we also know that epithelial tissue is important for lining internal body cavities, including the lining of our airways. And so notice that this second example is showing that the lining of our airways is going to contain epithelial tissue. And we also know that epithelial tissue is important for forming or making glands. And so that's going to include salivary glands.

And salivary glands are going to be found in our mouth and they are going to secrete or produce saliva. And then last but not least, we know that epithelial tissue is important for lining ducts and forming tubules as well. And so notice in this last example, we're showing you that the ducts and tubules found in our kidney are going to contain epithelial tissue. And so once again, this is just our brief introduction to epithelial tissue. And as we move forward in our course, we're going to continue to learn a lot more about epithelial tissue.

And so this concludes this introduction, and I'll see you in the next video where we'll talk more about the functions of epithelial tissue.

Functions of Epithelial Tissue

In this video, we're going to begin our lesson on the functions of epithelial tissue. Before we get started, it's important to note that the functions of epithelial tissue are quite diverse. Instead of making an exhaustive list of all of the different functions of epithelial tissue, in this video, we're going to provide a big picture view and talk more broadly about the functions of epithelial tissue. Epithelial tissue can be broadly categorized into 2 major functional groups, as indicated below in our image. These 2 major functional groups are:

1. Covering and lining epithelium, found in the far left block of the image.
2. Glandular epithelium, located in the far right block of the image.

The covering and lining epithelium, as its name implies, is essential for covering body surfaces and many organs, and lining internal body cavities and ducts. The functions of covering and lining epithelial tissue can be grouped into 3 major functions, outlined below in our image:

1. Provide protection: Serving as tissue on a boundary, it acts as a physical barrier, functioning like a shield protecting against mechanical stresses, pressures, microorganisms such as bacteria, and extreme temperatures.
2. Regulating transport: This epithelial tissue is selectively permeable, allowing control over the transport of substances across the boundary. It regulates transport both into the open space above and deeper into the tissue below.
3. Allow sensations: In close connection with nervous tissue, this epithelial tissue is involved in detecting stimuli from the outside world and activating nervous tissue to process these stimuli. This includes detecting sensations such as touch.

The glandular epithelium, as the name suggests, is crucial for forming glands which are cellular structures specialized for producing secretions. These secretions are released into an open space, as depicted below. Examples of these secretions include sweat, saliva, milk, oil, enzymes, hormones, and mucus.

This concludes our brief introduction to the functions of epithelial tissue. As we progress, we will delve deeper into these topics and apply these concepts practically. I'll see you all in our next video.

Introduction to Epithelial Tissue Example 1

So here we have an example problem that says to use an x to indicate the primary function or functions associated with the epithelium in each body location. And so notice that we've got the body location listed in the far left column, and we've got the functions from our last lesson video listed across the top. And so if we take a look at our very first body location, we could see that it is the skin. And so we know that the outermost layers of our skin are going to be covering and lining epithelial tissue. And we know that the skin is going to cover our entire body surface.

And so the skin is going to have a primary function of protection. It is going to protect us from environmental factors, such as, for example, mechanical stresses and microorganisms that might try to penetrate into our body and cause us disease, and it can also protect us from really hot or cold substances. Now, we also know from our last lesson video that the epithelia in our skin can also have an important role in sensation. And so recall that the epithelia in our skin connect us to the outside world, and so it can be important for detecting stimuli in the outside world, such as, for example, touch or pressure or temperature. And the epithelia that detects those initial stimuli can then go on to activate nerve endings of nervous tissue that it is in close connection with to allow for sensation.

And so we can indicate that protection and sensation are primary functions of the skin. Now, in terms of secretion, this is more of a function of glandular epithelial tissue. And so the sweat glands of our skin, that would be more so glandular epithelial tissue, but not so much the epithelial tissue in our skin, the covering and lining epithelial tissue in our skin. And then also, in terms of transport, that's not really a primary function of the epithelial tissue in our skin. If anything, the skin is going to be preventing transport, but, it does so in a protective manner.

For example, preventing the transport of microorganisms in order to protect us from those microorganisms. So moving on, the next body location that we have here is the lining of the bladder, which we'll learn later in our course is also known as transitional epithelium or urothelium. And so the lining of our bladder is going to have a primary function of protection once again. Its job is to essentially protect the rest of the body from the waste products that are found in the urine that can actually cause us damage and harm if those waste products are reabsorbed into our body. And so, the lining of the bladder is going to have a protective function.

It's also going to have a primary function of sensation as well. And so there are nerve endings that are going to allow for us to detect if our bladder is full and needs to be empty. Now, in terms of secretions, again, that's more so of a glandular epithelial function, not a covering and lining epithelial function. And in terms of transport, regulating transport, again, this is not a primary function of the lining of the bladder. If anything, it is going to be preventing the transport of the urine, but in a protective fashion.

Now, moving on here, we have the capillary blood vessels and the capillary blood vessels are going to be lined with a very thin epithelium. And so that is going to be a lining epithelium. And, the capillary blood vessels are going to have a primary function in regulating transport. And so, the capillary blood vessel epithelium is going to be regulating the transport of nutrients and gases from the blood into the tissues, such as glucose being transported from the blood into the tissues and oxygen gas being transported from the blood into the tissues. And it will also regulate the transport of waste products from the tissues back into the blood, such as, for example, carbon dioxide gas being produced by the tissues.

It will regulate the transport of that CO₂ back into the blood. Now in terms of secretion again, that's more of a function of glandular epithelial tissue, not lining epithelial tissue. Sensation is not really a primary function of capillary blood vessels. And protection, once again, probably not a primary function. It's more so regulating the transport, the exchange of materials between the blood and the tissues. Now, last but not least here, what we have is the salivary gland. And the salivary gland, it gives it away with this gland here.

It is going to be a glandular epithelial tissue. It's going to produce saliva in our mouth, which is going to have enzymes that help us break down our foods in our mouth. And, the salivary gland, of course, is going to have a primary function of secretion. And so, in terms of these other functions, this is not really the primary function of the salivary gland, it's mainly to secrete. And so this here concludes our brief example, and we'll be able to get some practice applying these concepts as we move forward.

So I'll see you all in our next video.

Which statement is true about nearly all epithelial tissue?

• A. All epithelial tissue produces specialized secretions. 
• B. All epithelial tissue has one surface that is adjacent to an open space.  
• C. All epithelial tissue consists of a thick layer of cells in order to provide protection. 
• D. All epithelial tissue allows for the diffusion of molecules into other adjacent tissues.

When considering an internal organ like the heart or liver, based on what you know about epithelial tissue, do you think that most of the tissue that makes up that organ would be epithelial tissue or some other kind of tissue?

• A. Mostly epithelial tissue.
• B. Mostly some other kind of tissue.

A nutrient in the small intestine is absorbed into the bloodstream. In doing so, it moves from being dissolved in the chyme present in the small intestine to being dissolved in the plasma of the blood. How many times did the nutrient pass through epithelial tissue when moving from the intestine to the blood?

• A. 0
• B. 1
• C. 2
• D. 3

Here’s what students ask on this topic:

What are the main functions of epithelial tissue?

Epithelial tissue has several key functions. Firstly, it provides protection by acting as a physical barrier against mechanical stresses, microorganisms, and extreme temperatures. Secondly, it regulates transport by being selectively permeable, allowing certain substances to pass while blocking others. This includes absorption of nutrients, excretion of wastes, and filtration of substances. Lastly, epithelial tissue allows sensations by detecting stimuli from the external environment and activating nervous tissue to process these signals. Additionally, glandular epithelium forms glands that produce secretions like sweat, saliva, and hormones.

Where is epithelial tissue found in the human body?

Epithelial tissue is found in various locations throughout the human body. It covers body surfaces, such as the outermost layers of the skin. It lines internal body cavities and ducts, including the airways and digestive tract. Epithelial tissue also forms glands, such as salivary glands in the mouth, which produce saliva. Additionally, it lines ducts and tubules in organs like the kidneys, playing a crucial role in filtration and secretion processes.

What is the difference between covering and lining epithelium and glandular epithelium?

Covering and lining epithelium primarily serves to cover body surfaces and line internal cavities and ducts. Its main functions include providing protection, regulating transport of substances, and allowing sensations. On the other hand, glandular epithelium is specialized for forming glands that produce and release secretions. These secretions can include sweat, saliva, milk, oil, enzymes, hormones, and mucus. While both types of epithelial tissue are essential, their roles and locations in the body differ significantly.

How does epithelial tissue contribute to homeostasis?

Epithelial tissue contributes to homeostasis by performing several vital functions. It provides a protective barrier against physical damage, pathogens, and harmful substances, maintaining the integrity of internal environments. By regulating the transport of nutrients, waste products, and other substances, epithelial tissue ensures that essential materials are absorbed and harmful ones are excreted. Additionally, glandular epithelium produces secretions like hormones and enzymes that regulate various physiological processes. Together, these functions help maintain a stable internal environment, crucial for the body's overall health and function.

What are some examples of secretions produced by glandular epithelium?

Glandular epithelium produces a variety of secretions essential for bodily functions. Examples include sweat, which helps regulate body temperature; saliva, which aids in digestion and oral hygiene; milk, produced by mammary glands for nourishment; oil, which lubricates and protects the skin; enzymes, which catalyze biochemical reactions; hormones, which regulate physiological processes; and mucus, which protects and lubricates internal surfaces. These secretions play crucial roles in maintaining homeostasis and facilitating interactions with the environment.