What is Epithelium? Let's learn about it simply!

Have you ever wondered how our skin, both inside and outside, is formed and protected? Today we are going to talk about a very amazing and very important type of tissue in our body. We call this epithelium ( epithelium /">epithelium ). You may have heard this word before.

What is Epithelium? Let's understand exactly?

Simply put, epithelium is one of the four main types of tissue in our body. The others are connective tissue, muscular tissue, and nervous tissue. So, this epithelial tissue is what covers all the internal and external surfaces of our body. Not only that, it is also what lines the cavities and hollow organs in the body. It is also the main tissue of our glands.

Think about it, the top layer of your skin, the inside of your mouth, the inside of your intestines, the airways (the way we breathe), the sweat glands – you have epithelial tissue everywhere. It works like a protective suit on our bodies. It also helps with secretion and absorption. The most important thing is that if a substance wants to enter or leave an organ, it has to pass through this epithelial tissue first.

Let's learn about epithelial cells.

Now let's see what this epithelial tissue is made of. These are made up of very small units, which we call epithelial cells . Just like a wall is made up of bricks, this tissue is made up of cells. These cells can be arranged in different shapes and in different layers. It depends on where the cells are in the body and what kind of work they do.

A cell is usually the smallest unit of life. You'd be surprised to learn that there are trillions of cells in our bodies! Each cell has three main parts:

• Cell membrane: This is the covering around the cell. It controls what enters and leaves the cell.
• Nucleus: This is located inside the cell. This is where most of our genetic information , or `DNA (Deoxyribonucleic Acid)`, is located.
• Cytoplasm: This is the liquid part of the cell. Inside this are many other cell parts (organelles), each of which has a specific function.

Some epithelial cells have special structures on their surface that help them do their job properly. Let's take a look at what they are:

What are microvilli?

These are like little fingers that stick out from the surface of the cell. But they don't move. Their main function is to increase the surface area of ​​the cell. This increases the amount of space available for absorption. For example, in our small intestine ( The epithelial cells in the small intestine (SI ) have thousands of these microvilli. These are what absorb nutrients from the food we eat. They also help protect our bodies from bacteria in the gut.

So what is Cilia?

Cilia are tiny, hair-like, motile structures on the surface of cells. They can move an entire cell, or move objects along the surface of the cell. A cell with cilia can typically have hundreds of cilia. These cilia are found in the epithelial cells of our respiratory tract. These cilia trap particles, such as dust, that enter our lungs when we breathe, and push them toward the nasal passages, preventing them from reaching the lungs. Another example is the epithelial cells in the fallopian tubes of women. These cilia help to move an egg from an ovary to the uterus.

Let's also learn about stereocilia!

Stereocilia are a special type of microvilli. They look similar to cilia. They protrude from the surface of some epithelial cells. These stereocilia are essential for hearing and balance in the epithelial tissue of our inner ear.

Are there different types of epithelial cells? How are these distinguished?

Yes, epithelial cells can be classified in different ways, because they differ depending on where they are located in the body and the function they perform.

Sort by shape:

• Squamous epithelium: These cells are flat, like a leaf.
• Cuboidal epithelium: These cells are shaped like a cube. That is, they are the same height, width, and depth.
• Columnar epithelium : These cells are shaped like a pillar. That is, they are taller than they are wide.

Classification according to the way the cells are arranged (number of layers):

• Simple epithelium: This has only one layer of cells.
• Stratified epithelium: This has more than one layer of cells, like layers of cells.
• Pseudostratified epithelium: This is a type of epithelium that has cells of varying sizes, so it looks like there are many layers, but it actually has only one layer of cells. That's why it's called 'pseudo'.

There are several main types of epithelium in our body:

Now, when that shape and number of layers are combined, different types of epithelial tissue are formed. Shall we look at some examples?

• Simple squamous epithelium: These usually line blood vessels and body cavities and control the passage of substances to the underlying tissues.
• Simple cuboidal epithelium: These are often found in glandular tissues (secretory tissues) and kidney tubules.
• Simple columnar epithelium: These are often specialized for absorption. They may have cilia or microvilli on their surface. They line our stomach and intestines.
• Stratified squamous epithelium: The main function of these is to provide protection. For example, they prevent microorganisms from entering the underlying tissues and reduce the loss of water from the body. The top layer of our skin (epidermis) is made up of these stratified squamous epithelial cells.
• Stratified cuboidal epithelium: These are not very common. They are found in the excretory ducts of our salivary glands and sweat glands.
• Stratified columnar epithelium: This is also not very common. It can be seen in the mucous membrane (conjunctiva) that lines the inside of our eyelids. There, they provide protection and secrete mucus.
• Pseudostratified columnar epithelium: These line our upper respiratory tract. They often have a large number of cilia.

There are also epithelial cells that perform special functions!

In addition to this basic classification, some epithelial cells are called differently because of their specific functions.

• Transitional epithelium (Urothelium): This is made up of several layers of cells. The specialty of these is that they flatten when stretched. They line most of our urinary tract. This is why our bladder can grow and expand.
• Glandular epithelium: This type of epithelium is specialized to produce and release substances. These are found in our glands. Glands are specialized organs that can make, store, and/or secrete things like hormones, proteins, and water.
• Olfactory epithelium: This is located inside our nasal cavity. It contains olfactory receptor cells. These cells have specialized cilia-like structures. When we breathe, odor molecules get caught in these cilia. The information then travels to the olfactory bulb in the brain. That's where the brain interprets what the smell is.

What service does epithelial tissue provide to our body?

Epithelial tissue has many essential and important functions that are essential to our lives. Since they are found everywhere in the body, the functions they perform vary depending on where they are located. Let's take a look at the main functions:

• Protection: Epithelial tissue protects many things in our bodies. For example, our skin. It protects things inside the body, such as blood vessels, muscles, and internal organs. Also, the cilia on the epithelial cells that line our intestines protect our bodies from bacteria in the intestines.
• Secretion: Epithelial tissue in glands (glandular epithelium) can secrete enzymes, hormones, and fluids.
• Absorption: The epithelial tissue that lines our internal organs, such as our liver and lungs, can absorb some things. For example, the epithelial tissue that lines our intestines is what absorbs nutrients from the food we eat.
• Excretion: Excretion is the process of removing waste from our bodies. The epithelial tissue in our kidneys excretes waste. The epithelial tissue in our sweat glands excretes sweat.
• Filtration: The epithelial tissue in our respiratory tract filters out dirt and dust particles from the air we breathe, purifying the air. The epithelial tissue in our kidneys filters our blood.
• Diffusion: In biology, diffusion is the movement of particles from a place of high concentration to a place of low concentration. A membrane made up of simple flat epithelial cells allows only selected substances to diffuse through. This process of diffusion helps in functions such as filtration, absorption, and secretion.
• Sensory reception: Our bodies receive information from the external environment through sensory nerve endings located in epithelial tissue. For example, the stereocilia on the surface of the epithelial tissue in our ears are essential for hearing and maintaining balance. Similarly, the taste buds on our tongue are located in stratified squamous epithelium.

What are the diseases that affect epithelial tissue?

Epithelial tissue, which performs such an important function, can also be affected by certain diseases and conditions. Let's take a look at a few of them.

Cancer

The biggest risk with epithelial tissue is the possibility of cancer, specifically two types of cancer called adenocarcinoma and papillary thyroid carcinoma.

Adenocarcinoma is a type of cancer that affects the glandular epithelial tissue that lines organs. It is the most common type of cancer that develops in organs. This is because:

- Almost all prostate cancers.

- Many breast cancers.

- About 96% of colorectal cancers.

- About 95% of pancreatic cancers.

- Non-small cell lung cancers account for about 40% of all lung cancers.

Papillary thyroid carcinoma is a type of cancer that accounts for about 80% of thyroid cancers. It grows slowly. Even if it spreads to the lymph nodes in the neck, it responds well to treatment. It is highly curable and rarely fatal.

Other medical conditions

In addition to cancer, other problems related to epithelial tissue can occur in various organs. Here are some of the most common conditions:

• Asthma: Asthma is a condition in which the airways become narrowed, swollen, and sometimes produce excess mucus. In this, the bronchial epithelium of the airways changes and becomes fragile.
• Celiac disease: When a person with celiac disease eats gluten (a protein found in some grains), their immune system attacks and damages the microvilli in the epithelial cells lining their intestines. This makes it difficult for the intestines to absorb nutrients properly.
• Human Papillomavirus (HPV) types 1-4: HPV can cause warts to form in the flat epithelial cells of the top layer of the skin (epidermis).
• Vertigo: Vertigo is a sensation of spinning that often occurs. It can have many causes. One cause is the abnormal growth of a layer of squamous epithelial cells called a cholesteatoma deep inside the ear. If left untreated, it can cause dizziness (balance problems) as well as hearing problems.

What tests are available to examine epithelial cells?

Because epithelial cells are found in so many important places in our bodies, there are several types of tests that examine these cells to see if they are causing certain diseases. In medicine, the process of examining cells in body tissue or fluid samples in a laboratory to diagnose disease is called pathology. The scientist who examines these cells is called a pathologist.

Here are some examples of tests related to epithelial tissue:

• Epithelial cells in urine: One of the things that is done during a urinalysis is to check for epithelial cells in the urine. A lab technician will look at your urine sample under a microscope to see if the number of epithelial cells is within the normal range. It is normal to have some epithelial cells in your urine. However, if there are too many, it could be an infection, kidney disease, or another serious condition.
• Pap smear: A Pap smear (also known as a Pap test) is a test that checks for abnormal epithelial cells in the cervix, which are cells that are cancerous or that may become cancerous. In this test, a healthcare provider takes a sample of cells from the cervix and examines them under a microscope.
• Some Biopsy Tests: A biopsy is a procedure in which a piece of tissue is removed from a part of the body to be examined, usually under a microscope, to see if there is any evidence of disease. There are several types of biopsies that analyze epithelial cells. For example, in a prostate biopsy, a needle is used to remove epithelial cells from the prostate gland and examine them for signs of cancer. In a biopsy for celiac disease, an endoscopy is used to remove epithelial cells from the lining of the small intestine and examine them for damage to the microvilli.
• Some Cytology Tests: Cytology (also called cytopathology) is the examination of cells from body tissues or fluids to make a diagnosis. There are many cytology tests that involve epithelial cells, such as gynecologic cytology, thyroid cytology, respiratory cytology, and eye cytology.

What is the difference between Epithelium, Endothelium, and Mesothelium?

While these three words sound a bit similar, they refer to three types of epithelial cell layers that line our internal organs, body cavities, and form the outer layer of our skin.

• Epithelium: This normally lines the pathways that open to the outside environment. For example, our respiratory system and digestive system.
• Endothelium: This normally lines the entire inside of the body, for example, our circulatory system (i.e. blood vessels) and the cornea of ​​the eye.
• Mesothelium: This lines our major body cavities. For example, the abdominal cavity (peritoneum), the cavity that covers the lungs (pleura), and the cavity that covers the heart (pericardium). The mesothelium secretes a lubricating substance called serous fluid.

Finally, things to remember

So, we've talked a lot about epithelial tissue. You can probably imagine how important this tissue is in our bodies, and how many different jobs it performs. From protecting our skin, to absorbing food, excreting waste, and even helping us smell, this epithelial tissue helps us.

Sometimes a doctor may use the word "epithelium" when telling you about a test or a type of cancer. Some of the words in the medical field can be a little complicated and strange. If a doctor says a word you never understand, don't be afraid to ask what it means. It's very important to be informed about your health.

So, I hope this information was useful to you. Stay healthy!

Epithelium , Epithelial cells, Body Tissues, Cell structure, Skin health, Digestive system, Respiratory system