Video Transcript
In this video, we will learn about the four major types of tissues found in animals. We’ll learn about their functions and how those functions are supported by their structures. We’ll take a look at examples of muscular, nervous, epithelial, and connective tissue and how different tissues come together to make a functioning organ.
A tissue is a group of cells that work together to perform a specific function. There are four main types of tissues in complex multicellular animals like humans. These are epithelial tissue, muscular tissue, nervous tissue, and connective tissue. The human body contains approximately 11 organ systems, which each possess several organs. And each individual organ is usually made up of at least three of these tissue types.
Each of the four major types of tissue is defined by its function. The main function of muscular tissue is movement. Any part of the body that can move or change shape likely has some muscular tissue associated with it. You’re likely aware that skeletal muscle controls the movement of our body. Some other important examples of the function of muscular tissue can be found within the heart, which rhythmically contracts and relaxes to pump our blood.
The organs of the digestive tract must move and mix our food. Tiny muscles within the eye control the size of the pupil and the thickness of the lens. And muscles within blood vessels allow them to change diameter, adjusting the rate of blood flow and blood pressure in different parts of the body.
Nervous tissues’ main function is communication. Nervous tissue allows communication between parts of the body and between the body and the outside world. It allows us to sense our surroundings and react to changes. Nervous tissue is the primary tissue of the nervous system. Nervous tissue in the brain and spinal cord can be divided into gray matter and white matter. Gray matter is adapted for information processing, and white matter is adapted for the transmission of information. We have nervous tissue in almost every organ in our body. This allows the nervous system to monitor their status, as well as control their activity.
Connective tissue gets its name because it’s found between other types of tissue nearly everywhere in the body. Connective tissue functions to connect, attach, support, protect, and bind other structures. Some examples of connective tissue are tendons, which connect muscles to bones, and ligaments, which connect bones to other bones. Bone tissue itself is a type of connective tissue that supports the structure of the body, as well as cartilage, which cushions are joints. Adipose, or fat tissue, and blood are other examples of connective tissues.
Epithelial tissue is lining tissue. It protects the internal and external surfaces of our organs and our body. It also functions in absorption and secretion. Epithelial tissue makes up the outer layer of our skin. It lines the small intestine where it absorbs nutrients. And it lines our airways where it secretes mucus. Epithelial cells are replaced frequently as they wear out or rub off.
In biology, we know that structure and function are always directly related. Tissues are made of cells. So the types of cells found in that tissue determine the job that that tissue can do. Muscular tissue is adapted for movement. And it contains muscle cells. The muscle cells are filled with special proteins and other structures which allow them to contract. Nervous tissue is adapted for communication. It contains special communication cells called neurons. Neurons are built for transmitting signals and processing information.
Epithelial tissue lines and covers various structures. So epithelial cells form one or more cohesive layers. And they’re adapted to be relatively easily replaced. Connective tissue has various functions such as attachment, support, and protection. It does many different jobs. So it comes in different forms, each with different types of cells. Connective tissue almost always consists of living cells suspended in a nonliving medium.
Next, we’ll take a closer look at the structures of each of these types of tissues and some examples. There are three types of muscular tissue. They are skeletal, cardiac, and smooth muscle. Skeletal muscular tissue is found attached to the bones of our skeleton. It controls our voluntary bodily movements. Under a microscope, skeletal muscle has long, continuous fibers with stripes called striations. Cardiac muscle is only found in the heart, and it allows our heart to beat continuously and automatically. Under a microscope, cardiac muscle looks like branched fibers, and it also has striations.
Smooth muscle is found surrounding our internal organs. It allows them to contract, dilate, and change shape. Smooth muscle consists of spindle-shaped muscle cells. And it’s called smooth because it lacks striations.
Nervous tissue contains neurons which are specialized in communication as well as various types of support cells. There are glial cells, which carry out functions such as providing nutrients for the neurons. There are cells called oligodendrocytes, which provide the myelin sheath for the neurons within the central nervous system. Oligodendrocytes are another type of glial or support cell. Schwann cells provide the myelin sheath for neurons found outside of the central nervous system. These various types of cells work together to allow nervous tissue to carry out its function.
Epithelial tissue is characterized by the number of layers it possesses and by the shape of the cells in the outermost layer. The structure of epithelial tissue consists of cells which are attached to a basement membrane underneath of which you find connective tissue. Epithelial tissue with only one layer of cells is called simple epithelial tissue. Epithelial tissue with multiple layers of cells is called stratified epithelium.
If the cells found in the outermost layer of epithelium are roughly square-shaped, we call it cuboidal epithelium. The two descriptions combined into the name of the tissue. If there are one layer of cells, we would call this simple cuboidal tissue. But if there are multiple layers of cells, we would call it stratified cuboidal tissue.
If the cells of the outer layer are oblong-shaped, we refer to them as columnar. And if the cells in the top layer are flat, we refer to it as squamous. Depending on the function and the location, some epithelial tissue may possess cells with special features. One example is microvilli, which aid in absorption. Some epithelial cells possess cilia, which move in a sweeping motion and push materials from place to place. Another variation are goblet cells, which secrete substances such as mucus.
Connective tissue is the most varied type of tissue, and it does a number of different jobs. Connective tissue is often divided into two categories by type: proper connective tissue and special connective tissue. Proper connective tissue comes in two different types: loose and dense. These both consist of cells and fibers surrounded in what’s called a ground substance. Examples of loose connective tissue include adipose tissue and something called areolar tissue. Loose connective tissue has less fibers and more lubricating ground substance. So it serves the function of cushioning and lubricating the surfaces between different organs. Examples of dense connective tissue are tendons and ligaments.
Dense connective tissue has more fibers and less ground substance than loose connective tissue. Special connective tissue consists of living cells suspended in some sort of nonliving medium. Some examples are cartilage, bone, and blood, all of which possess specialized cells that are suspended in some sort of nonliving medium that may or may not possess fibers.
Before we move on to our practice questions, let’s take a look at a couple of organs and how they’re made up of different issues.
Here, we have a diagram of a section of skin. I’ve drawn the muscular tissue in red, the connective tissue in yellow, the epithelial tissue in pink, and the nervous tissue in blue. And we can see that this complex organ is made up of all four of these types of tissues. Epithelial tissue makes up the epidermis and lines the sweat glands. The dermis and hypodermis are both types of connective tissue. Our skin is full of sensory nerves, which are made of nervous tissue, and even contains specialized muscles, which are made of muscular tissue. I chose red for the blood vessels, even though they’re complex organs themselves, made up of all four types of tissue.
Let’s take a look at another example diagram. This diagram represents a section of the small intestine. We can see that it consists of many layers of muscular tissue and connective tissue. The small intestine is lined inside and out with epithelial tissue, and it contains a network of nervous tissue in order to monitor and regulate its activity.
Let’s take a moment to wrap up our lesson by reviewing what we’ve learned. In this video, we learned about the four main types of animal tissues. These are muscular tissue, nervous tissue, epithelial tissue, and connective tissue. We learned about their structure, their functions, and examples of each. And then we learned how many tissues come together to form one organ.
