Red blood cells are a type of blood cell. Blood contains three types of cells: white blood cells, platelets, and red blood cells. These red blood cells, also called erythrocytes, are the most common blood cell type, accounting for 40–45% of the blood’s volume. They contain hemoglobin, which is a protein that carries oxygen throughout the body.
Red blood cells have a diameter of about 6 micrometers, making them larger than platelets and smaller than white blood cells. Their small size allows them to squeeze through even the smallest human blood vessels.
The role of human red blood cells is twofold: to transport oxygen from the lungs to the body’s tissues for cells to use and to transport carbon dioxide from the body’s tissues to the lungs for expulsion.
A protein called hemoglobin inside red blood cells is the transport molecule that allows red blood cells to carry oxygen throughout the body. It also has a characteristic red pigment, giving blood its red color.
Red blood cells contain hemoglobin and are covered with a membrane composed of proteins and lipids. Hemoglobin—an iron-rich protein that gives blood its red color—enables red blood cells to transport oxygen and carbon dioxide. Red blood cells do not have nuclei, allowing for more room for hemoglobin.
The shape of red blood cells is a unique biconcave shape (round with a flat, indented center). Their lack of nuclei makes them so flexible that they can pass through extremely small blood vessels.
The red blood cells of adult humans are produced in the bone marrow, which is the soft fatty tissue inside bones. In human embryos, they originate in the yolk sac and liver. From the bone marrow, blood circulates through the human body via the veins and arteries.
In general, the production of red blood cells is controlled by erythropoietin, a hormone produced and released by the kidneys. Erythropoietin stimulates the production of red blood cells in the bone marrow.
The average adult human produces 2 to 3 million red blood cells every second, equating to about 200 billion red blood cells every day. Some conditions, such as a low oxygen content or red blood cell count, could trigger an increased production of erythropoietin.
All blood cells (white, red, and platelets) are produced from stem cells called hemocytoblasts located in bone marrow. It takes about 7 days for a stem cell to fully mature into a red blood cell that is prepared to be released into the bloodstream.
During this process, the stem cell becomes an immature red blood cell called an erythroblast. Then, the nucleus and mitochondria of the erythroblast disappear, and the immature cell is gradually filled with hemoglobin. At this point, the cell is called a reticulocyte. Finally, the cell becomes a full mature red blood cell and enters the blood, ready to transport oxygen throughout the body.
The life of a red blood cell is short due to its lack of nucleus; human red blood cells only survive for about 120 days. When red blood cells are old or damage, they are ready to be eliminated from the bloodstream.
Red blood cell removal is controlled by specialized cells called macrophages in the spleen (part of the lymphatic system) and the liver. The spleen disposes of worn-out red blood cells and controls the amount of blood cells at work in the body. Additionally, the liver recycles iron from damaged red blood cells. Together, the macrophages in the spleen and liver remove old red blood cells from the body.
A low quantity of red blood cells can be caused by a variety of factors:
Red blood cell count can also be reduced by certain drug interactions or nutritional deficiencies (iron, copper, vitamin B-6, vitamin B-12, or folate).
While some red blood cell diseases can be caused by illnesses or nutritional deficiencies, others are inherited.
Diseases involving red blood cells include anemia (low red blood cell count or low hemoglobin), thalassemia (inherited blood disorders), and polycythemia vera or other blood cancers. Bone marrow disease and hypoxia (low blood oxygen levels) are also possibilities.
A red blood cell isolation protocol is a critical part of preparing a blood sample for analysis. Centrifugal force is used to isolate a cell population from other cells or to separate the components of a blood sample. As a result, the particles create distinct layers, making it easier to obtain a cell type.
There are a few different approaches to red blood cell isolation.
One method is selection. Positive selection is when red blood cells are targeted by the removal mechanism and retained for downstream analysis. On the other hand, negative selection is when other cell types are removed to leave the red blood cells untouched.
Red blood cell depletion is another approach, where a single cell type—in this case, red blood cell—is removed from a biological sample.
No. DNA is encased in the nucleus of cells, and red blood cells do not have nuclei. However, white blood cells carry DNA in their nuclei.