Bone marrow makes blood cells


What is the real color of blood? Is blood without oxygen really blue?
See http://scienceblogs.com/gregladen/2010/09/01/is-blood-ever-blue-science-tea-2/

If a person who says to themselves “Blood is blue in our veins” thinks either of the following:

… That blood is blue, like this:

… Or, that blood is “blue” in that you look at your veins and see blue, thus you are seeing your blue blood….

… Or, that you look at an anatomical chart and see the veins drawn in as blue, therefore the blood inside them is blue – then that person is laboring under a misconception.

If a person thinks that this “blue blood” is purple, then they may also be laboring under a misconception. The HTML Internet Purple looks like this:


(I know, it looks dark blue to me as well.) And Pantone purple looks like this:


(I’ve never seen blood that looks like this)

Pantone Dark Red looks like this:


… very close to my blog’s colors, but not very much like the darker shades of blood that I’ve seen.

Actual dark blood looks a little like this:


This color is 24% red, 2% green, 2% blue, but at a saturation of 92 with a color value of 24 and a hue of 0 degrees. Whatever that means.

(By the way if your computer’s video display is not set to a high value for number of colors shown, all of the above may look like only one or two colors. And, since all video screens are different, I might be seeing something different than you are…)


Why do veins appear to be blue?

( from http://scienceprojectideasforkids.com/2011/color-of-blood/ )

My skin lacks melanin (dark skin pigment), and thus is very pale. The veins near the surface of my skin are very blue. While my skin seems to be relatively transparent, it isn’t. If my skin were transparent, my veins would appear red due to the red blood flowing through them.

So, why do my veins look blue? The answer would be the same for –Why does the sky look blue? Everything that has a blue color reflects light energy with a wavelength that is perceived by your brain as some shade of blue.

When light, such as sunlight hits my skin, some of the light is absorbed and some is reflected. I can see my veins because they are close enough to the surface to absorb and reflect light. The light reflected by my skin and the veins enters my eyes where light sensors called cones send messages to my brain. My brain interprets the messages and sends back the message that the skin is pale, with some brown spots (freckles but mostly what are called age spots), and thin blue lines under the skin. Some of these lines have a very pale blue color, some medium blue, and a few with a slight purple shade.

The light striking my skin can slightly penetrate the skin. Most of this light is absorbed at or very near the skin’s surface. While all veins that are visible are reflecting light, the deeper veins receive very little light and not all of the the light these veins reflect exits the skin. The light from these veins barely stimulate the cones in your eyes, thus your brain reports that the veins are a very pale –even a blurred blue color. The opposite is true for veins close to the surface. The red light reflected from these veins plus the blue light from the skin above the veins is perceived as blue with a touch of purple.

With a bit of imagination, the diagram shows you a pink section representing pale skin with two types of blood vessels. The vessel with light-red blood is the vein, and the vessel with dark-red blood is an artery. A few red light rays are shown exiting the skin from the vein as well as blue light being reflected from the skin. The blue light basically masks the red, thus veins appear blue when viewing them through pale skin.


Different types of blood cells in other animals
( from http://www.compoundchem.com/2014/10/28/coloursofblood/ )

Most people will have learnt that human blood, as well as that of most other vertebrates, is red as a result of haemoglobin, a large protein found in red blood cells which contains iron atoms within its structure.

Haemoglobin is what’s known as a respiratory pigment, and it plays a vital role in the body, ferrying oxygen around the body to your cells and helping carbon dioxide back to the lungs where it can be exhaled. The large protein consists of four smaller units which themselves contain small sections called haems, each of which contains an iron atom. This can ‘bind’ to oxygen, giving red blood cells their oxygen transporting ability.

The iron atoms are also responsible for haemoglobin’s colour. The individual haems are conjugated molecules – they have lots of alternating double and single bonds between carbon atoms in their structure – and this conjugation causes them to absorb light wavelengths in the visible portion of the spectrum, leading to a coloured appearance. The presence of the iron atom modifies this absorption slightly, and as such haemoglobin is a red colour when oxygenated, and a slightly darker red when deoxygenated.

It’s a commonly believed myth that deoxygenated blood is blue – after all, if you look through your skin at any of your veins, which carry deoxygenated blood away from your body’s cells, they have a definite blue-grey hue. However, this appearance is in fact caused by the interaction of light with both the blood and the skin and tissue covering the veins.

BLUE blood is normal for for crustaceans, spiders, squid, octopuses, and some molluscs all have blue blood as a result of having a different respiratory pigment. Rather than haemoglobin, these creatures use a protein called haemocyanin to transport oxygen. The differing structure of the pigment, as well as the incorporation of copper atoms instead of iron, leads to the blood being colourless when deoxygenated, and blue when oxygenated. They also bind to oxygen in a different manner to haemoglobin, with two copper atoms binding to each oxygen molecule.

GREEN blood, too, is possible, in some species of worms and leeches. This is an interesting one, in that the individual units of chlorocruorin, the protein leading to a green blood colouration, are actually very similar in appearance to haemoglobin. In fact, they’re near identical – the only different is an aldehyde group in the place of a vinyl group in the chemical structure (although the name might suggest otherwise, chlorocruorin doesn’t contain any chlorine atoms).

Despite this minor difference, a noticeable colour change is the result – deoxygenated blood containing chlorocruorin is a light green colour, and a slightly darker green when oxygenated. Oddly, in concentrated solutions, it takes on a light red colour. A number of organisms that have chlorocruorin in their blood also have haemoglobin present as well, resulting in an overall red colouration.

Chlorocruorin isn’t always necessary for green blood, however, as the green-blooded skink lizard illustrates. This lizard is found in New Guinea, and despite its blood containing haemoglobin like other vertebrates, its blood is a distinctive green colour. The colour is due to a difference in how they recycle haemoglobin. Humans recycle haemoglobin in the liver, by breaking it down first into biliverdin, and then bilirubin. The lizards, however, aren’t capable of breaking down biliverdin any further, so it accumulates in their blood, giving a green colour intense enough to overpower the red colour of haemoglobin.

Finally, violet blood is also possible, albeit in a limited range of marine worms (including the rather unfortunately named penis worms). This colour is caused by yet another different respiratory pigment, this time one called haemorythrin. Haemorythrin contains individual units which themselves contain iron atoms; when deoxygenated, the blood is colourless, but when oxygenated it is a bright violet-pink. Like most of the other respiratory pigments, it’s a lot less efficient than haemoglobin, in some cases only having around a quarter of the oxygen carrying capacity.

Sample questions

Feb 2016 MCAS. Mature red blood cells in mammals contain the protein hemoglobin but do not contain a nucleus. The nucleus is lost as the red blood cell matures.
Which of the following can be concluded about mammalian red blood cells from this information?

A. The cells store their DNA in ribosomes.
B. The cells have no functionality once the nucleus is lost.
C. The cells divide by meiosis to produce more red blood cells.
D. The cells perform transcription and translation before the nucleus is lost.



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