Red blood cell facts for kids
Quick facts for kids Red blood cell |
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| Scanning electron micrograph of human red blood cells (ca. 6–8 μm in diameter) |
Red blood cells (also known as RBCs, red blood corpuscles or erythrocytes) are cells in the blood which transport oxygen. In women, there are about 4.8 million red blood cells per microliter of blood. In men, there are 5.4 million red blood cells per microliter of blood. Red blood cells are red because they have hemoglobin in them.
Human
A typical human red blood cell has a disk diameter of approximately 6.2–8.2 µm and a thickness at the thickest point of 2–2.5 µm and a minimum thickness in the centre of 0.8–1 µm, being much smaller than most other human cells. These cells have an average volume of about 90 fL with a surface area of about 136 μm2, and can swell up to a sphere shape containing 150 fL, without membrane distension.
Adult humans have roughly 20–30 trillion red blood cells at any given time, constituting approximately 70% of all cells by number. Women have about 4–5 million red blood cells per microliter (cubic millimeter) of blood and men about 5–6 million; people living at high altitudes with low oxygen tension will have more. Red blood cells are thus much more common than the other blood particles: there are about 4,000–11,000 white blood cells and about 150,000–400,000 platelets per microliter.
Human red blood cells take on average 60 seconds to complete one cycle of circulation.
The blood's red color is due to the spectral properties of the hemic iron ions in hemoglobin. Each hemoglobin molecule carries four heme groups; hemoglobin constitutes about a third of the total cell volume. Hemoglobin is responsible for the transport of more than 98% of the oxygen in the body (the remaining oxygen is carried dissolved in the blood plasma). The red blood cells of an average adult human male store collectively about 2.5 grams of iron, representing about 65% of the total iron contained in the body.
Life cycle
Human red blood cells are produced through a process named erythropoiesis, developing in the red bone marrow of large bones in about 7 days. When matured, in a healthy individual these cells live in blood circulation for about 100 to 120 days (and 80 to 90 days in a full term infant). At the end of their lifespan, they are removed from circulation. In many chronic diseases, the lifespan of the red blood cells is reduced.
Function
The most important function of red blood cells is the transport of oxygen (O2) to the tissues. The hemoglobin absorbs oxygen in the lungs. Then it travels through blood vessels and brings oxygen to all other cells via the heart. The blood cells go through the lungs (to collect oxygen), through the heart (to give all cells oxygen). They go back to the heart to be re-pumped to the lungs (to again collect oxygen), so the blood in your body travels in a double circuit, going through your heart twice before it completes one full circulation of the body.
A fact which makes mammalian red blood cells different to all other cells is that, when they are mature, red blood cells do not have a nucleus. All other vertebrates have red cells with nuclei.
Red blood cells are doughnut-shaped, but without the hole. This shape is called a bi-concave disc. However, hereditary diseases such as sickle-cell disease can cause them to change shapes and stop blood flow in capillaries and veins. Plasma is got from whole blood. To prevent clotting, an anticoagulant (such as citrate) is added to the blood immediately after it is taken.
Transport of CO2 in the blood
Carbon dioxide (CO2) is carried in blood in three different ways. The exact percentages vary depending whether it is arterial or venous blood.
- Most of it (about 68% to 83%) is converted to bicarbonate ions HCO−
3 by the enzyme carbonic anhydrase in the red blood cells. by the reaction CO2 + H2O → H2CO3 → H+ + HCO−
3. - 5% – 10% is dissolved in the blood plasma.
- 5% – 10% is bound to haemoglobin as carbamino compounds.
Images for kids
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Typical mammalian red blood cells: (a) seen from surface; (b) in profile, forming rouleaux; (c) rendered spherical by water; (d) rendered crenate (shrunken and spiky) by salt. (c) and (d) do not normally occur in the body. The last two shapes are due to water being transported into, and out of, the cells, by osmosis.
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Scanning electron micrograph of blood cells. From left to right: human red blood cell, thrombocyte (platelet), leukocyte.
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Two drops of blood are shown with a bright red oxygenated drop on the left and a deoxygenated drop on the right.
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Animation of a typical human red blood cell cycle in the circulatory system. This animation occurs at a faster rate (~20 seconds of the average 60-second cycle) and shows the red blood cell deforming as it enters capillaries, as well as the bars changing color as the cell alternates in states of oxygenation along the circulatory system.
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The most common red blood cell membrane lipids, schematically disposed as they are distributed on the bilayer. Relative abundances are not at scale.
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Red blood cell membrane proteins separated by SDS-PAGE and silverstained
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Red blood cell membrane major proteins
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Affected by Sickle-cell disease, red blood cells alter shape and threaten to damage internal organs.
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Variations of red blood cell shape, overall termed poikilocytosis.
See also
In Spanish: Eritrocito para niños
