Human red blood cells do not have a nucleus like most other cells. Red blood cells in most mammals and reptiles have a nucleus. A few species of reptiles have red blood cells that do not contain a nucleus.
1. What Are Red Blood Cells?
Most biologists consider the loss of the nucleus in human red blood cells to be an adaptation that allows the cells to pass freely through the small spaces in the capillaries. If a red blood cell had a nucleus the nucleus would be damaged and the cell would not function due to the extreme constriction of the red blood cells as they pass through the capillaries.
Red blood cells do not have mitochondria or any of the organelles that are seen in the majority of other cells in the body. Red blood cells do not contain RNA or DNA like most other cells in the body.
The advantage of not having a nucleus or organelles means that red blood cells do not use energy to transport oxygen to the cells of the body. Not having DNA or RNA prevents any virus from being able to attack red blood cells directly.
When red blood cells are first manufactured in the bone marrow, the red blood cells have a nucleus. The nucleus is eliminated in the early stages of cell development.
3. Role They Play
Red blood cells release energy when the cells pass through the capillaries. The shear that is placed on the red blood cell and the blood vessel when a red blood cell passes through a small space causes a release of adenosine triphosphate from the red blood cell and the blood vessel. This compound produces energy. The energy helps the blood vessels expand to allow the flow of red blood cells and also keeps the body temperature stable.
Red blood cells transport other gases besides oxygen. These gasses promote vascular health and help the blood transport system work properly.
The tone of blood vessels is maintained by the release of nitrous oxide by red blood cells. The shear that red blood cells experience passing through small blood vessels produces a chemical transformation of an enzyme in the red blood cells that produces nitrous oxide.
Red blood cells also release hydrogen sulfide. Hydrogen sulfide acts to relax the blood vessel walls and allow red blood cells to pass through narrow spaces.
4. Lifecycle of Red Blood Cells
Most red blood cells last for about 120 days. The average adult manufactures about 2.5 million new red blood cells every second. The dead red blood cells are decomposed in the liver. Some of the components like hemoglobin are recycled and some become waste.
Red blood cells can bind carbon monoxide more strongly than oxygen to the hemoglobin molecule in the red blood cells. This is the reason that people die from carbon monoxide poisoning. The red blood cells do not get oxygen to carry to the cells in the body.
Red blood cells are red when they leave the lungs with oxygen bound to hemoglobin. Red blood cells are blue after the cells deliver oxygen to body cells. This is why a person’s veins look blue. The color difference is a change in the frequency of light absorbed and reflected by the red blood cells.