Your endothelium is a large organ that plays a key role in keeping your blood moving smoothly through your body. It’s made up of over a trillion endothelial cells, which release substances that aid in blood flow. Damage to your endothelium puts you at risk for a range of health problems like atherosclerosis and related heart diseases.


What is the endothelium?

Your endothelium is a single layer of cells, called endothelial cells, which line all your blood vessels and lymphatic vessels. These include your:

Your endothelium provides a space for your blood and tissues to interact. So, your endothelium is vital to the functioning of all your organs and tissues.

Your endothelium actively performs many jobs to support your blood flow and keep your body in a stable state. That’s why scientists consider your endothelium an endocrine organ, and in fact, it’s one of the largest organs in your body.

When something goes wrong with your endothelial cells, there can be severe consequences in your body. That’s because these tiny cells play a huge role in keeping your body healthy and strong. It’s important to learn about your endothelium and its functions so you can do whatever possible to prevent endothelial damage.

Vascular endothelium vs. lymphatic endothelium

These two terms both refer to a lining of endothelial cells. The main difference is where they’re found:

  • Your vascular endothelium lines your blood vessels.
  • Your lymphatic endothelium lines your lymphatic vessels. Your lymphatic vessels are a network of tubes and lymph capillaries that transport extra fluid (lymph) away from your tissues.

So, your vascular endothelium helps with blood flow. And your lymphatic endothelium helps with lymph flow. Both play a role in your cardiovascular health.


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What is the function of the endothelium?

Endothelial cells have many different jobs depending on where they’re located in your body. Below are some of the key functions of your vascular endothelium.

Controls the contraction (vasoconstriction) and relaxation (vasodilation) of your blood vessels

When they’re healthy, your endothelial cells keep your blood vessels relaxed and open enough that blood can easily flow through. They also adjust to internal and external stimuli. These include the pressure of your blood against the vessel walls, changes in your stress level and various medications you’re taking.

They also react to changes in temperature. For example, in cold weather, your blood vessels in your extremities (arms and legs) constrict to keep blood in your core. In warm weather, they dilate to help circulate blood and cool off. During exercise, the blood vessels of your muscles dilate to help deliver blood and oxygen.

So, your endothelium helps blood reach all your body’s organs and tissues no matter what you’re doing.

Manages how much fluid travels from your blood into your tissues

In a healthy state, your endothelium is permeable enough to allow fluids to travel in between its cells to reach your tissues. But it’s still tight enough to form an adequate barrier and protect your blood from toxins and other substances that shouldn’t be there. In various states of illness, such as infection/sepsis, your endothelium becomes more permeable to allow infection-fighting cells to enter your tissues and help healing.

Prevents thrombosis

Thrombosis is the formation of blood clots that could block your blood flow and cause serious complications. Your endothelium produces substances called nitric oxide and prostacyclin. These keep your blood fluid and prevent it from clotting when it shouldn’t. In some disease states, these substances are not produced appropriately, thus increasing your risk of clotting.


Where is the endothelium in your body?

Your endothelium extends throughout your whole body. Your vascular endothelium supports about 60,000 miles of blood vessels. To show someone the location of your heart, you’d point to your chest. To show them the location of your brain, you’d point to your head. To show them your endothelium, you could point to anywhere on your body. This distributed aspect of the endothelium makes it unique compared to many of your other organs.

Your endothelial cells make up the lining of your blood vessels. They’re the cells that come into direct contact with your blood. They’re attached to a structure called your basal lamina. Together, your endothelium and your basal lamina form the innermost layer of your blood vessel wall (the tunica intima). The tunica intima provides a smooth surface for your blood to flow.


How big is the endothelium?

Your endothelium is one of your largest organs. In terms of surface area, it covers 3,000 to 6,000 square meters of a typical person’s body. And it includes at least 1 trillion endothelial cells, which are made of epithelial tissue.

How big are endothelial cells?

You can only see endothelial cells through a microscope. Their dimensions are typically:

  • About 30 to 50 micrometers (microns) long.
  • About 10 to 30 micrometers wide.
  • About .1 to 10 micrometers thick.

To get a sense of an endothelial cell’s size, imagine one strand of hair. A single strand is about 100 micrometers in diameter. So, even at its longest, an endothelial cell’s length of 50 micrometers is just one-half the diameter of a strand of hair. That explains why your body can hold over 1 trillion of these specialized cells.


What is the difference between the endothelium and the epithelium?

Your endothelium lines fully internal pathways that don’t interact with your outside environment. These include your blood vessels and lymphatic vessels.

Your epithelium, on the other hand, lines pathways that may come into contact with your outside environment. These include your digestive system and respiratory tract.

The endothelium and epithelium are both specialized for their jobs best. The epithelium is usually more protective and functions as a barrier to the outside world. Your endothelium is specialized in delivering blood and other substances to your body.

Conditions and Disorders

What is endothelial dysfunction?

Endothelial dysfunction means your endothelium can’t perform its usual duties as well as it should. Endothelial dysfunction happens when something damages your endothelial cells. A wide range of medical conditions and lifestyle factors can cause endothelium dysfunction. These include:

Atherosclerosis is one of the key consequences of endothelial dysfunction. Atherosclerosis is the gradual buildup of plaque in your arteries over time. Scientists know that damage to your endothelium is the first stage of atherosclerosis. Usually, the culprit is too much LDL (bad cholesterol) circulating in your bloodstream, tobacco use or long-term high blood pressure.

When your endothelium becomes damaged, your body’s immune response kicks in. Your immune system sends white blood cells called monocytes to the injured part of your artery wall. These monocytes cluster together in that spot and trigger inflammation within your artery. Some cellular changes happen that ultimately lead to the formation of a “fatty streak.” This is the start of plaque formation.

Over time, the plaque grows and narrows your artery so less blood can flow through them. Plus, the plaque raises your risk of blood clots that can block blood flow. That’s why people with a damaged endothelium face a higher risk of:

Endothelial damage also raises your risk of:


How can I keep my endothelium healthy?

You can help keep your endothelial cells healthy by reducing the number of free radicals in your body. Free radicals are unstable atoms that latch onto your body’s healthy atoms and harm them. Antioxidants are substances that protect your body (especially your endothelium) from free radicals. So, it’s important to eat foods rich in antioxidants. These include:

  • Brown rice.
  • Citrus fruits and juices.
  • Dark green vegetables.
  • Oatmeal.
  • Red and yellow bell peppers.
  • Sweet potatoes.
  • Tomatoes and tomato juice.
  • Whole grains.

Ask your provider what changes you can make in your diet to help you consume more antioxidants. Your provider may also refer you to a dietitian who can help you start with small, simple changes that feel manageable to you. For example, your dietitian may recommend you follow a Mediterranean diet to support the health of your heart and blood vessels.

Certain medical conditions, lifestyle factors and toxins can cause you to have more free radicals in your body. These include:

  • Air pollution.
  • Certain drugs, pesticides and industrial cleaners.
  • Eating too much sugar.
  • Not getting enough sleep.
  • Obesity.
  • Smoke from tobacco products.

Talk with your provider about how you can combat free radicals and protect your body from their harmful effects.

It’s also important to visit your healthcare provider for yearly check-ups and take your medications as prescribed. You should also talk to your provider about a healthy exercise regimen to maximize your health. Doing so can help you keep your heart and circulatory system functioning at their best, in turn keeping your endothelium healthy, too.

A note from Cleveland Clinic

Nearly everyone has risk factors for endothelial damage at some point in their lives. But it’s within your power to lower your risks as much as possible by making healthy lifestyle changes and managing your medical conditions. Talk with your provider about how you can support the health of your endothelium and your entire body.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 07/10/2022.

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