Why is venous blood blue?

Have you ever wondered why venous blood appears blue? Maybe during a zoom call, while checking out your veins on the back of your hand. Don’t worry; you’re not alone! This age-old question has puzzled scientists, philosophers and people like us for centuries.

You might be surprised to learn that deoxygenated blood appearing blue is nothing more than an optical illusion – let me explain!

Busting Common Myths

It’s essential to start by debunking some common misconceptions about the colour of venous blood.

Myth 1: Deoxygenated Blood Is Blue

Many people believe that venous blood in our bodies is always blue rather than red. But have we seen blue-coloured drops come out when we bleed or scratches ourselves?! Of course NOT!

The fact of the matter is, whether oxygen-rich or poor, all human blood has a similar deep red colour.

Myth 2: Oxygen In The Air Makes Our Blood Bright Red

Another popular thought regarding deoxygenation explains falsely that oxygen present in air causes our hemoglobin molecules to light up bright red as air enters into the lungs.

However, if this claim were accurate, then it stands to reason that other animals also would have their arterial blood become brilliant crimson on breathing fresh clean air. Yet everyone knows it does not happen so much-so with fish who use gills-based respiratory system where they filter dissolved oxygen from water -and still their arterial found (of various marine species) are usually bluish-greenish mixed colours due essentially because heated coloured pigments photodecay- meaning organism-wise just small process within gases exchange could turn up into completely different color-hence making things quite cyclical and confusing aren’t we?!

Are these facts blowing your mind already? Do you want even further explanation? Let’s dive deeper!


Quick Recap: Despite many myths surrounding the colour of our blood that claim otherwise, human venous blood is always red- not blue. Oxygen present in air does NOT make our hemoglobin molecules light up brilliant crimson but instead goes through a more complicated process to deliver oxygenation.


How Does The Blood Deliver Oxygen?

The importance of transferring oxygen throughout the body cannot be overstated as it forms the cornerstone of all living events. So let’s dig into how this essential molecule gets transported from one cell to another every moment.

Our Red Blood Cells (RBCs) carry four iron atoms associated with haemoglobin hormone, which bind onto incoming gaseous molecules – both carbon dioxide and oxygen included- to communicate well-being throughout our system.

But when we take a closer look at these red-blooded cells through visible light spectrum microscopy (‘spectral decomposition’), it indeed looks bluish-greenish! This distinction is because simple sunlight can only penetrate skin tissues over topmost layers before being spectroscopically absorbed by other components such as collagen fibres while less penetrating shorter wavelengths are preferably scattered once striking larger RBC organelles like mitochondria or nuclei complexes within them allowing absorbance trends between green yellow giving blue/green hues since it’s edge limits mostly active within those colours area; thus, experience color changes even though no difference in actual amount received per organ!

Amazing right?! Have you ever seen something so small operating on this scale? It truly gives new meaning to “tiny-but-mighty”!!


Quick Recap: Red Blood Cells work very hard carrying around much-needed energy supply – aka Oxygen -, delivering trace elements, nutrients and expelling waste buildup while making sure your internal organs do their job fighting pathogens or doing whatever they are meant for based on your body design overall-health plan. Their inner workings appear bluish-greenish under microscopic observation lending shiny tubes underneath dermis with fascinating opulence!


Why Does Venous Blood Look Blue?

A lot of this confusion cascades down to us being unsure about the actual colour we’re trying to identify. So let’s try and examine our train of thoughts in asking why de-oxygenated blood (venous) looks blue.

You see, when we look at a vein beneath your skin, it may very well appear faintly blue or greenish tinge since shorter wavelengths are selective scatterers within RBC which makes them flexible to pick up different hues that suddenly refract through dermis cells while longer more penetrating rays could be completely comprised by tissues pigments like HemeOxidases making it manifest as red- thus again some variants settle as deep green with mirror-like absorption process!


Quick Recap: When viewing Venous blood under our skin surface, specialised light scattering select-all filter makes for various colours visible via absorptions not usually seen conventionally! With such systems comes limitations and ‘refraction’ and transformation intricacies that result in biological variations whilst letting us view mesmerising sights.


Indeed what seemed straightforward has turned into somewhat complicated scientific phenomena through human eyes! Nevertheless, you should now be comfortable explaining the myth-busting concept behind venous blood appearing blue.

So next time someone quizzes you on why your veins resemble a roadmap highlighted in blues n greens, you can break out all these facts with surprising confidence!!

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