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Endothelial Cells: Function & Explanation

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  • 0:00 What Are Endothelial Cells?
  • 0:43 Main Function
  • 1:42 Other Specialized Functions
  • 3:12 When Endothelial Cells…
  • 4:07 Lesson Summary
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Lesson Transcript
Instructor: Marta Toran

Marta has taught high school and middle school Science and has a Master's degree in Science Education.

Endothelial cells account for about 1 kilogram of an adult human body, which is on par with the liver. They line the inside of all blood vessels - from large arteries to tiny capillaries. This lesson covers their basic functions, as well as more specialized ones, like keeping bacteria out of our brain.

What Are Endothelial Cells?

Endothelial cells line the inside of every blood vessel in the body. They form a one-cell-thick layer called the endothelium, which is also found on the inner walls of the heart chambers and lymphatic vessels, which carry excess blood plasma around the body. The endothelium is very extensive. If all the endothelium tissue in an adult body were to be spread out, it would take up the area of eight tennis courts!

In the larger vessels, such as the veins and arteries, the endothelium forms the blood vessel wall along with much thicker layers of muscle cells and elastic fibers. In the capillaries, however, the endothelium makes up the entirety of the blood vessel wall (see video).

Main Function

The main job of endothelial cells is to provide a barrier between the blood and the rest of the body tissues. Blood must be contained inside the transporting vessels, but substances need to move in and out of it in a controlled manner. The endothelium provides this selectively permeable layer across which chemicals and white blood cells move according to where they are needed.

The role of the endothelium as a barrier is particularly critical around the brain. The endothelial cells are part of the blood-brain barrier (BBB), a layer that separates the blood flowing through vessels surrounding the brain from the brain tissue itself. The endothelial cells act like a sieve, restricting the passage of large molecules, toxic substances, and bacteria into the brain tissue while allowing necessary molecules like oxygen, enzymes, and hormones to go through. They also allow waste substances like carbon dioxide produced by neurons to diffuse out of the brain and back into the blood.

Other Specialized Functions

Endothelial cells also have several other specialized functions, including the following:

Produce Nitric Oxide (NO): NO has several roles, including making blood vessels dilate to increase blood flow, preventing platelets from sticking to vessel walls, and bringing down inflammation.

Blood Vessel Formation: Endothelial cells help in the production of new blood vessels not only by dividing into more endothelial cells, but because they can differentiate into other cells that make up the blood vessel walls.

Inflammation: The body responds to pathogens, or germs, by causing the site of infection to become swollen, red, and hot. The epithelium helps this along by increasing blood flow and allowing white blood cells to move through to the infected tissue.

Blood Clotting: By making different proteins for the job, endothelial cells both prevent blood clotting from happening inside the blood vessel blocking it, and help in blood clotting by releasing clotting proteins like factor VIII at the source of the bleed.

Blood Pressure: Endothelial cells produce substances that make blood vessels dilate and contract, thus playing an important role in controlling blood flow.

Water Regulation: Endothelial cells in the glomeruli (bundles of blood capillaries in the kidneys) control the concentration of urine by regulating how much water is reabsorbed into the blood and which substances are in excess in the blood and must be excreted in the urine.

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