Table of Contents
- What are Endothelial Cells?
- What is Endothelium?
- Endothelial Function
- Endothelial Dysfunction
- Lesson Summary
The definition of an endothelial cell is one that lines blood and lymphatic vessels within the body, surrounding the hollow space where liquid flows within these tubes (also known as the cavity or the lumen). These endothelial cells are only one layer thick. However, they are connected to each other using tight cell junctions to prevent anything from passing through them, and they bind to the connective tissue underneath them using an intermediate basement membrane. In a blood vessel like an artery, a thick layer of smooth muscle cells typically surrounds the endothelial cells in order to complete the structure of the blood vessel.
Another area that contains endothelial cells is the blood-brain barrier. Blood vessels in the brain are very thin, comprised of a single layer of endothelial cells and the surrounding basement membrane. This thin structure allows for needed substances (like nutrients, neurotransmitters, and hormones) to pass efficiently in and out of the brain. However, very tight junctions exist between endothelial cells at the blood-brain barrier which only allow for selective, controlled uptake and removal of these substances. This helps to prevent anything unwanted from entering the brain and altering or damaging delicate, essential neurological processes.
Epithelial cells are often confused for endothelial cells. These cells also act as lining, and can be found throughout the body in organs such as the skin, lungs, kidneys, and digestive tract. They allow for the absorption, excretion, and secretion of lubrication into and out of these organs. As it happens, endothelial cells are a specific subset of epithelial cell. However, endothelial cells are only found in the lining of cardiovascular and lymphatic systems.
In order to understand and remember the difference between these two types, consider the etymology of these words. Both end with -thelial, meaning a layer. However, epi- means on or over, while endo- means within. Endothelial cells are only found in structures within the body, whereas epithelial cells can be found in surface layers like the skin.
The endothelium refers to the entirety of the endothelial tissue structure that lines blood and lymphatic vessels. This consists of the embryonic mesoderm, the single layer of endothelial cells, and the surrounding basement membrane.
The endothelium in the blood vessels, made up of vascular endothelial cells, performs essential processes for the flow of blood.
The endothelial cells and the rest of the endothelium form the basic structure of these blood vessels and lymphatic vessels. In addition, endothelial cells are vital to maintaining the blood brain barrier, as well as performing specific tasks necessary for blood flow and regulation within a vessel.
Another function of the endothelium is to combat inflammation by producing substances that encourage anti-inflammatory activity in the body. This aids in blood clotting by regulating platelet adhesion and prompts the production of nitrous oxide, which acts directly on blood vessels in order to relax them. This allows for more blood flow and increases oxygen supply to organs when needed. These processes also helps in regulating blood pressure, as vessels can dilate or narrow to allow changes in blood pressure accordingly within the body as needed.
Lymphatic endothelial cells line all lymphatic vessels and sinuses throughout the body. Their main purpose is to aid in immune responses: they produce substances like chemokines, which signal immune cells to aggregate in lymph nodes. Ultimately, this signaling cascade results in a larger immune response against an infection or cancer. High endothelial venules are distinct post-capillary buddings with large endothelial cells. Their uncharacteristically large size allows for direct movement of lymphocytes from the blood into a nearby lymph node.
The endothelial cells and the endothelium, like all other cells and tissues in the body, can undergo breakdown in response to pathological triggers. Some triggers include:
There are two responses to these triggers that lead to breakdown: initial rapid response and slower phenotypical response. The initial rapid response involves changes in substances such as nitric oxide, while the slower phenotypical response causes actual breakdown of the physical structure of the endothelium and its cells, the basement membrane and surrounding muscle cells in the blood vessels and lymph vessels.
Many medical conditions can also cause breakdown of the endothelium, including hypertension, obesity, arthrosclerosis, or the deposition of plaque within the vessel wall. Cardiovascular diseases such as coronary heart disease and peripheral arterial disease can prompt this. Some infections that can also affect the endothelium include HSV (or Herpes Simplex Virus) and meningitis, which causes swelling of the protective membranes of the nervous system.
Endothelial cells are a specialized subset of epithelial cells that are only found in the cardiovascular system and the lymphatic system. They comprise the endothelium, which is made up of a single layer of endothelial cells tightly connected to each other and underlying basement membrane. While some vessels like capillaries are comprised only of that, larger vessels like vena cava and aorta also contain a very thick layer of smooth muscle cells around this. The thin structure of capillaries and vessels that form the blood-brain barrier allow for easy and rapid diffusion of substances across to and from the organs. The endothelium performs many crucial functions such as regulating blood clotting, vessel relaxation and tightening, combating infections and many more. However, in the presence of medical conditions and other pathogenic factors, the endothelium can also break down.
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The endothelium comprises the structure of the blood vessels and lymphatic vessels. It also allows for smooth vessel regulation, inflammation control, and initiation of immune response to pathogens.
The endothelium controls functions such as dilation and narrowing of blood vessels in order to help with blood pressure issues. It also secretes substances to alleviate inflammation and allow blood clotting when needed.
Endothelial dysfunction is caused by many factors such as low oxygen, inflammation, infections, and cardiac conditions like high blood pressure.
The 4 main functions of endothelial cells are filtration of fluids, blood vessel size regulation, hemostasis, and transport of various substances throughout the body.
Many factors can damage endothelial cells such as cardiovascular diseases, infections, inflammation, plaque deposition from increased fat intake, and turbulent and resistant blood flow.
The endothelial cells are located in the lining of the cardiovascular system (arteries, veins, and capillaries) and in the vessels of the lymphatic system.
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