Why deoxygenated blood blue

Despite exceptions, the majority of blood from animals is red. There are many variations of hemoglobin present in different species, which allows scientists to distinguish blood samples from various animals.

Over time, spilled blood that starts out red turns darker and darker as it dries and its hemoglobin breaks down into a compound called methemoglobin. As time passes, dried blood continues to change, growing even darker thanks to another compound called hemichrome. This continual chemical and color change allows forensic scientists to determine the time a blood drop was left at a crime scene.

Then using computer modeling we can estimate the time since the blood was deposited to help investigators determine if a blood stain is relevant to a crime. If the blood is a year old, it might not be important to a crime committed yesterday. Edition: Available editions United Kingdom. Blood that has been oxygenated mostly flowing through the arteries is bright red and blood that has lost its oxygen mostly flowing through the veins is dark red.

Anyone who has donated blood or had their blood drawn by a nurse can attest that deoxygenated blood is dark red and not blue. The blood in your veins appears blue because you are looking at your veins through layers of skin and fat according to Alwin Kienle in his paper " Why do veins appear blue? A new look at an old question " published in the Journal of Applied Optics. An antigen is a substance that can cause an immune system response in the body. The two most common antigens are A and B.

For example, people with the blood type A have an A-antigen on their red blood cells, and people with type B blood have a B-antigen. Some people have both. People with O blood type do not have either A or B antigens on the red blood cells. Type O is the most common blood type in the world.

Another antigen is a protein called the Rhesus Rh factor. People with this protein are considered Rh-positive. If the blood lacks the protein, they are Rh-negative. It is more common to have Rh-positive blood than Rh-negative. If a person who is Rh-negative needs a transfusion, they should not receive Rh-positive blood.

For example, having blood type B is relatively common for people who are Asian or of Asian descent. Although A and B are the most common antigens, there are many other less common antigens that create rare blood types. Certain rare blood types are unique to specific racial and ethnic groups. If a person requires a blood transfusion, it is essential that the blood type they are given is a compatible type.

If a person receives an incompatible blood type, their immune system may reject it. This can be life-threatening. Most people can receive type O blood safely, regardless of their blood type.

This is why most blood donation clinics are in need of type O blood, as it can be used to help many people. Donating blood can save lives. For those who are unsure about donating blood, it is helpful to consider the facts below:. Blood is essential for the functioning of the human body, but many myths about the body persist. Having accurate information about blood or any other aspect of health is vital.

If someone is in doubt about a health issue, it is essential to talk to a doctor to get the most accurate information. Plasma is a component in blood, and donating it can help others combat serious illnesses.

Here, learn about the possible side effects and how to…. When do you need a blood transfusion? Is there a maximum number of blood transfusions a person can have? Find out in this article.