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Red blood cells (RBCs) or erythrocytes are the most common type of blood cell and the vertebrate organism's principal means of delivering oxygen (O2) to the body tissues - via blood flow through the circulatory system. RBCs take up oxygen in the lungs or gills and release it into tissues while squeezing through even smaller capillaries. The cytoplasm of erythrocytes is rich in hemoglobin, an iron-containing biomolecule that can bind oxygen. In humans, mature red cells are flexible and oval biconcave disks. They lack a nucleus and organelles; however, they have additional features such as their own ribosomes, mitochondria and golgi apparatus. They contain two and have a biconcave shape; this accommodates greater surface area to volume ratio with a thinner layer of cytoplasm in the center, thereby increasing their surface area for diffusion of oxygen from blood into tissue and by which deoxygenated blood returns from tissue to lungs. Red cells are about 7 to 8 micrometers (µm) in diameter. RBCs are produced through erythropoiesis in bone marrow, where they develop in interaction with the hematopoietic microenvironment. In mammals, mature red blood cells also called erythrocytes lack nuclei and organelles.

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Given all that is known about red blood cells, it should be easy for us to write at least a paragraph about them with good quality grammar and no plagiarism issues. But it's still worth going over some of the basic facts before we get started. Red blood cells are produced in bone marrow by stem cells as shown by images like these: [[Image:Bone_marrow1.jpg|left]].

Red blood cells have several functions such as delivering oxygen from the lungs or gills to tissues throughout the body, squeezing through even smaller capillaries, releasing O2 into tissue and bringing deoxygenated blood back to the lungs.

RBCs develop from stem cells in bone marrow, interacting with the hematopoietic microenvironment as shown by images like these. These cells are essential for delivering oxygen to tissues throughout the body and it’s important that we have good quality RBCs in our blood, so let's take a look at how to maintain them.

For more information on blood tests, you can read our comprehensive guide.

Of course, this is just a quick overview of red blood cells as they are an extremely complex subject with many more facts than what we could possibly cover here. But it should give us some idea of the kinds of things we can write about when thinking critically about these fascinating little cells.

In humans, mature red blood cells or erythrocytes lack nuclei and organelles. The red blood cells are about 7 to 8 micrometres or µm in diameter, each one being biconcave and disc-shaped with a thin layer of cytoplasm at the centre as shown by the image on the right here.

The shape of the erythrocytes is due to their older cellular structure which can be seen under a microscope, where it appears that there's no nucleus and little else in the way of organelles besides some small mitochondria and ribosomes. They also store 2 molecules called haemoglobin that bind with O2 in order to transport it throughout the body to specific tissues that need it. The red blood cells are flexible and biconcave disks, which means they can squeeze through even smaller capillaries.