Wednesday, July 6

That red blood cells are red matters more than it seems

We feel bad. Let’s go to the doctor. And it doesn’t fail: whatever our symptoms may be, and whatever the doctor’s suspicion may be, he asks us for a blood test that includes a red blood cell count.

Search, search your analytics reports and you will almost always find them. With this name or with any of its aliases: red blood cells, red blood cells, RBC (for Red Blood Cells) or erythrocytes.

Why? What is so special about these cells that they are in all the tests? Why is it necessary to know how many we have and in what state?

This big question is actually a mixture of several issues. On the one hand, what function do red blood cells have and how do they carry it out. But also how they manage to access all corners of the body. And what interests us the most with regard to blood tests: how its functioning is assessed through the results of the laboratory.

The important mission of red blood cells

Our blood is a watery fluid with an essential function: transportation. There are many goods that it transports, but one of the most important –if not the most important– is oxygen.

Animals are biological machines that work is not exactly free. In fact, we spend our lives paying with energy molecules of ATP (adenosine triphosphate), which we could consider our biomoney. Although there are several different metabolic pathways to obtain it, aerobic beings (like us) normally oxidize immediate principles. Basically glucose. This oxidation is obviously done with oxygen.

Oxygen, therefore, has to reach our cells so that ATP is generated inside them and they stay alive.

And that is exactly what red blood cells do: ensure the supply of oxygen to each and every cell in our body. Its absence would inevitably mean tissue ischemia and its consequent necrosis. That is, death by anoxia.

How do red blood cells transport oxygen?

Oxygen is transported back and forth within the red blood cells. The more free space they have, the more oxygen will fit. That is why it is convenient that the red blood cells are practically hollow cells. To achieve this goal, during their maturation process (erythropoiesis) from the bone marrow (where they are generated) to the peripheral blood (where they will carry out their transcendental mission), they “throw the house out the window”. And they do it literally, that is, they expel most of their cellular content, leaving practically no organelles. So much so that they are the only mammalian cells that even lack a nucleus.

What do they get with it? Well, transform into perfect containers. In millions of trillions of thousands of ships ready to transport the most precious of goods through our bodies: oxygen.

But oxygen is a gas, and gases diffuse across biological membranes, including those of the red blood cell. How do they manage, then, to retain it? They just chemically bind it. Hemoglobin, the protein that fills erythrocytes, takes care of that. Thanks to the iron atom present in each of its four heme groups (which, by the way, are what give blood that characteristic metallic taste), it binds covalently and reversibly to oxygen.

When blood reaches the lungs through the pulmonary artery, hemoglobin is highly oxidized, reaching a saturation rate of 98% and being called oxyhemoglobin. Red blood cells, at this time, live up to their name by wearing the spectacular and brilliant scarlet red of arterial blood.

Thus, with their best blush, they begin their journey throughout the body. The different cells receive them with joy and capture their coveted oxygen. Hemoglobin then progressively loses its saturation (up to a rate of 32%), transforms into deoxyhemoglobin and red blood cells darken. Therefore, poorly oxygenated tissues show that unhealthy cyanotic color.

Contortionists who reach every corner

Arteries don’t work like sprinklers watering the lawn. In fact, the blood never leaves the pipes (the blood vessels) in animals that have a closed circulatory system. The vessels branch more and more to end up being very fine capillaries that access our most remote corners where the oxygen will be released, will cross the membranes of the red blood cell and the capillary, and will be captured by the receptor cell.

But there is a problem. Sometimes the caliber of the capillary is less than the width of the red blood cell itself. What happens then? Does a plug form? Do we suffer a thrombosis?

The answer is as wonderful as it is incredible and simple. As if it were the bus from Harry Potter and the Prisoner of Azkaban, the red blood cell deforms.

Originally, the red blood cell is discoidal, flattened and biconcave in shape. This is possible thanks to a very special membrane, composed of cholesterol and phospholipids, and linked to an elastic network of skeletal proteins (with ankyrin and 4.1R complexes). This molecular organization endows the globule with a biological material with a unique behavior that allows it to:

-Be highly elastic (100 times more than a latex membrane of comparable thickness).

-Respond quickly to the stresses of the applied fluids.

-Be stronger, in terms of structural strength, than steel itself.

Image of the spatial organization of proteins involved in the elasticity of the erythrocyte plasma membrane (taken from the article by Mohandas et al. in J. Clin. Invest., doi: 10.1172/JCI109888)

We are facing a prodigious membrane that makes the erythrocyte a contortionist capable of withstanding linear deformations of up to 250% without disheveled.

Thus, in this amazing way, and as if they were postmen from before the digital age, red blood cells travel the most tortuous paths to ensure the supply to each and every one of our cells, to each and every one of our tissues, to each and every one of our organs, devices and systems.

These luxury delivery men guarantee us life.

Interpreting a blood test

The first thing we have to check in an analysis is if there are enough delivery vehicles, that is, if the number of red blood cells is within normal limits.

Subsequently, it will be necessary to verify if they are well loaded with hemoglobin. In case there is a deficiency in the concentration of this protein, the red blood cells will not be such, they will be rather pale and their efficiency will leave much to be desired.

Third, its shape and size must be just right. Otherwise, they will be indicating that their plasticity and elasticity may be affected and their access to the different tissues compromised.

For this reason, within the red series of its analysis, so many different parameters are reported (RBC, HCT, HgB, MCV, HCM, MCHC,…) . And also, for the same reason, the evaluation of its operation will not depend on the isolated quantification of a parameter but rather it will be necessary to consider and study them globally.

I hope that from now on you will take care of your red blood cells. What circulates through his veins is truly a prodigy of nature.

Example of a red series in a blood test: Red blood cells (RBC): It is the number of red blood cells per unit volume (microliter) of blood. Hemoglobin (Hgb): It is the concentration of the oxygen transporting protein that the blood sample has. Hematocrit (Hct): It is the proportion of blood volume occupied by red blood cells. Mean Corpuscular Volume (MCV): It is the mean volume of the red blood cells in the sample. Mean Corpuscular Hemoglobin (MCH): It is the amount of hemoglobin that, on average, each erythrocyte of this sample contains. Mean Corpuscular Hemoglobin Concentration (MCHC): It is the concentration of hemoglobin that, on average, each erythrocyte presents.

This article has been published in
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