Understanding The Function And Structure Of Red Blood Cells

Red blood cells, or erythrocytes, are a key part in the lives of life. From humans to birds and other animals, they play a key role in respiration and life.

Here, we are going to take a look at red blood cells, including what they are, what they do, characteristics, and how to count them.

Understanding The Function And Structure Of Red Blood Cells

No doubt we all learned about red blood cells in school, but there is so much more to discover. These cells are unique in many ways, and have a lot to teach us.

From their shapes and functions, to their viscoelastic behavior, these cells are more intriguing than you might originally think.

If you are interested in learning all about red blood cells, all you need to do is keep reading.

Understanding Red Blood Cells

Erythrocytes is the other name given to red blood cells. These are a type of blood cell that most of us will be familiar with.

Let’s take a look at what these cells are, and what they do in our bodies. Throughout this article, we will be using the term “red blood cells” and “erythrocytes” interchangeably.

What Are They?

As previously mentioned, red blood cells are also called erythrocytes. They are specialized cells in organisms that breathe oxygen.

Appearance-wise, these cells look similar to donuts without a hole, and are relatively flat and round. This shape allows them to carry out their functions within the body efficiently.

Their various characteristics, such as the fact that they have no nucleus, are important parts of these cells and allow them to be more efficient.

They are different to other types of blood cells, as they stay in the vascular network.

These cells get transported within this network to deliver oxygen and remove carbon dioxide from the system. As such, these cells are very important.

Overall, red blood cells make up around 45% of our total blood volume. White blood cells, or
Leukocytes make up only 1% and are responsible for fighting disease and infection.

Platelets, on the other hand, make up less than 1% of our blood and are responsible for forming blood clots and preventing bleeding.

The rest of our blood is made up of plasma. While each of these various parts of blood have a key function, we will be focusing on red blood cells in this post.

Their Function

The function of red blood cells is to carry oxygen from the lungs to the rest of the body.

This includes organs throughout the body as well as tissues.

These cells are restricted to the vascular network, as they do not have jobs in other parts of the body.

Red Blood Cell Structure And Adaptations

There are two primary structural characteristics that allow red blood cells to be so good at what they do.

Without these adaptations, they would encounter a number of difficulties while doing their job, and they would not be as effective as they are now.

Understanding the Function and Structure of Red Blood Cells

Let’s take a look at these two structural adaptations that make erythrocytes so incredible.

Biconcave Shape

The biconcave shape of the red blood cell is likely their most important characteristic. They are donut-shaped, but without the hole in the middle of them.

This shape ensures that the cells are perfectly suited for carrying oxygen molecules.

That isn’t all, though. These cells can also revert to a biconcave discoid shape if they are exposed to external forces, which can cause them to undergo deformations.

These red blood cells’ ability to go through these kinds of deformations, which can happen in vitro and vivo, is an important part of their overall structure.

Not only that, but it is important for their volume ratio, surface area, and mechanical properties.

These cells have very thin membranes that are made of lipid bilayer, which is attached to the cytoskeletal network.

This feature allows erythrocytes to survive forces that would cause deformities to happen.

The cells’ internal fluid matrix and composite membrane also adds to the viscoelastic behavior that red cells are known for.

This helps these cells be able to go through spaces smaller than you could imagine.

Their viscoelastic characteristics allow these red blood cells to squeeze through tiny capillaries to deliver oxygen and get rid of carbon dioxide within the body.

These cells’ incredible ability to revert to their biconcave shape has led to the conclusion that they have shape memory.

However, this is not only in regard to their shape, as the membrane elements have also been proven to return to the original position they had within the cell.

No Nucleus

The red blood cells on birds and fish are vastly different to those of humans and the majority of other animals.

The erythrocytes of birds and fish have inactive nuclei, whereas there are no nuclei or nucleus present in the red blood cells of other animals.

This characteristic enables the cells to carry more hemoglobin, which is needed for healthy bodily function.

Red blood cells are made of hemoglobin, which gives them their red coloring, and a globin protein.

The cells have four hemes, and each one is able to attach to one protein in order to form a polypeptide chain.

Transporting oxygen to other parts of the body and body cells is only possible because of this chain structure.

According to a Whitehead Institute study, mammalian red blood cells that approach maturity go through cell division.

This process is responsible for the nucleus being ejected from the erythrocyte.

The nucleus is pinched off the area of the cell by a ring of actin filament as it contracts.

When this part of the cell falls off, it is destroyed by macrophages (specialized cells that detect bacteria and various other organisms and destroy them).

By the cells not having a nucleus, they are made lighter. This allows them to be faster as they transport oxygen around the body.

Macrophages are thought to be involved in hematopoiesis, where they create signals. These signals trigger differentiation and reproduction of committed progenitors.

Red blood cells are removed after an average circulation of 120 days. This happens via macrophages from the liver and spleen.

As such, they play a pivotal role in the life and disposal of erythrocytes.

Though red cells are not capable of reproducing or cell division, it is estimated that around 2,000,000 are produced by the bone marrow every second.

This ensures that there is always a high number of these crucial cells. While they have long lifespans compared to other blood cells, they are only around for a few months.

In order to produce red blood cells, there needs to be an adequate amount of the following materials:

  • Amino acids
  • B vitamins
  • Copper
  • Lipids
  • Zinc
  • Iron

Rely On Anaerobic Respiration

Erythrocytes are pretty unique in the way that they do not have mitochondria. Because of this, they rely on anaerobic respiration in order to get the energy they need.

However, they also do not have endoplasmic reticulum (E.R). This means that they are not able to synthesize proteins like other cells can.

At first glance, this might sound like a disadvantage for red blood cells. However, this characteristic is actually an advantage when it comes to their function and the way they work.

This is because they do not need to use the oxygen that they carry around to the rest of the body. If they needed the oxygen too, then life in the body could be challenging.

Instead, they are able to use the energy they get from anaerobic respiration to supply the whole body with the oxygen it so desperately needs.

In other words, no oxygen is wasted in the whole process, and everything runs smoothly.

The lack of mitochondria also results in red blood cells not having oxidative enzymes that are needed for aerobic respiration.

Because of this, the Embden-Meyerhof pathway is instead used to process the glucose and obtain energy that way.

This process is the method used in anaerobic respiration in order to gain energy. Here, the process uses glycogen rather than glucose to produce the energy.

Red Blood Cells Transport Gasses

Most animals require oxygen in order to respire, and thus survive. In other words, oxygen is needed in order for energy to be created.

When this happens, carbon dioxide is also produced via anaerobic respiration, and has to be removed from the body.

If this carbon dioxide doesn’t get removed, it will begin to do damage to the organs within the body.

Red blood cells play a pivotal role in preventing this from happening.

_Red Blood Cells

Not only do they transport oxygen to where it needs to go, but it’s also specialized in the transport of carbon dioxide.

Red blood cells will transport gasses (e.g. oxygen) to the lungs and various tissues, but also transport gasses (e.g. carbon dioxide) from the lungs.

It is thought that around 1.5% of total oxygen gets dissolved in the blood plasma as it circulates through the body. A gas exchange occurs inside the lungs when oxygen is inhaled – this is known as diffusion.

The gasses are moved from the areas of high concentration to the areas where there is a lot concentration.

Since the blood in our bodies has a low oxygen concentration compared to areas like the lungs, that 1.5% of oxygen gets diffused in the blood because of the concentration gradient.

The oxygen then gets bound to the hemoglobin. As hemoglobin has four hemes, it can carry or transport four molecules of oxygen.

This means that every cell is able to carry four molecules of oxygen.

There is an average hemoglobin saturation between 95-99% in healthy individuals, which ensures that oxygen gets bound to almost all heme units.

When hemoglobin and oxygen come together, we get oxyhemoglobin. Blood that carries a lot of oxygen should appear to be bright when compared to deoxygenated blood.

However, since the binding of oxygen to hemoglobin is reversible, it is easy for oxygen to dissociate from hemoglobin because of partial pressure and diffusion.

Oxygen will move from the blood to tissues via diffusion because oxygen moves from high to low concentration.

As such, diffusion happens when the oxygenated blood moves from the lungs.

Unlike carbon dioxide, oxygen gets transported through the blood in high percentages.

For carbon dioxide, only around 20% of it is transported through the blood to the lungs. Carbon dioxide also doesn’t bind to hemoglobin like oxygen does.

Instead, it gets bound to amino acid moieties, which are present on carbaminohemoglobin’s globin.

The erythrocytes carrying carbon dioxide should appear a maroon color.

Like with oxygen, the partial pressure causes the binding and dissociation, and the gasses more from high to low concentration areas.

However, in the pulmonary capillaries, the partial pressure is higher than in the alveoli.

Because of this, the gas quickly dissociates from the red blood cells and diffuses via the respiratory membrane into the air.

Other methods of carbon dioxide transportation in blood include the following:

  • Bicarbonate Buffer – this refers to carbon dioxide that gets diffused into the capillaries and ultimately into the red blood cells. The carbon dioxide that does this is then subsequently transported as bicarbonate, and makes up roughly 70% of the total carbon dioxide that is transported in the blood.
  • In Blood Plasma – this refers to the carbon dioxide that gets dissolved in the blood plasma. This carbon dioxide makes up around 10% of the total carbon dioxide transported in blood.

Carbon dioxide does not easily separate from hemoglobin like carbon monoxide does.

Monoxide has a greater affinity for the hemoglobin compared to oxygen, resulting in it easily binding to hemoglobin when it comes into contact with it.

As such, the carbon monoxide prevents oxygen from being bound to red blood cells and transported to where it needs to go. This results in carbon monoxide poisoning, which can be deadly.

Red Blood Cell Count Tests

It’s important to know the red blood cell count in samples, as this is often related to health and medical conditions.

The red blood cell count tests allow us to do just that – count the number of red blood cells present in particular samples. These tests are frequently done during ordinary check-ups, as well as for specific checks.

These tests are incredibly important, as red blood cell counts can determine a number of health conditions, including things like internal bleeding and anemia.

One of the most popular ways of checking a red blood cell count is via use of the hemocytometer, though blood smear tests are also done.

The device, however, has been used for some time, and has proven to be an efficient and accurate method of finding out red blood cell counts in samples.


This is a manual way of counting red blood cells. In order to do this, the blood samples are diluted with normal saline (1:200). This reduces the number of red blood cells present, which makes counting them far easier.

What You Need

  • A pipette
  • A clean hemocytometer
  • Trypan blue/erythrosine B
  • A clean glass slide/coverslip
  • Ciliated blood- 4 percent w/v sodium ciliate with pH adjusted using citric acid

The Procedure

  1. Mix the blood sample with the chosen dye using a pipette. Make sure to do this at a 1:1 ratio. To do this, you can simply mix 10ul of the sample blood with 10ul of your dye of choice
  2. Place your clean glass slide or coverslip on the hemocytometer
  3. Get another clean pipette and carefully place the mixture into the gap between the coverslip and slide and hemocytometer. Be careful not to add too much liquid as to over fill the space.
  4. Gently place the hemocytometer under the microscope. You can now manually start counting the red blood cells in the central square’s smallest grid. To count, you must add the number of cells that are present in the central five squares of the device.

The formula to find out the number of red blood cells per microliter is as follows: Number of cells counted * dilution factor/number of counted squares * volume of a small square

Other Methods For Counting Red Blood Cells:

  • Cell Structure and Intensity Based Method – RGB images are converted to grayscale in this angular ring ration method.
  • Thresholding Based Method – red blood cell count is gained by producing a binary image.
  • Hough Transform-Based Methods – an automatic method used to get the red and white blood cell count by using computer vision. There are a number of automated methods that are used to get red blood cell counts that now use Hough Transform-Based Methods.
  • Watershed Transform Based Method – image processing techniques like spatial filtering, morphological operations, and segmentation using watershed transformation is used to find out the red blood cell count within a sample.


Microscopy is a popular method used by students and professionals, like to observe red blood cells.

This method is a good option to use when counting red blood cells, as well as diagnosing malaria in laboratories.

The process is relatively simple, and users can choose to use either wet mounts, or stains.

Stains allow for a better view of the cells, and the smears can be either thin or chick, depending on what the intended purpose is.

The most simple wet mount refers to a drop of blood being added to a clean glass slide, and one drop of distilled water on top of it.

The mount can then be easily viewed under the microscope to check for red blood cell counts or malaria.

What You Need

  • Giemsa (nucleic acid stain)
  • Blood sample
  • Distilled water
  • 95 percent methanol
  • Methanol (99 percent)
  • Compound microscope
  • Clean microscope slides

Thin Film Procedure

  1. Get all equipment and samples ready
  2. Place one drop of blood on the glass slide of the microscope
  3. Get another glass slide or use a coverslip and touch the blood drop to allow it to spread along the width of the glass.
  4. Gently push the slide forward at an angle. This should create a smooth, thin film along the glass slide you initially used

Thick Film Procedure

  1. Get all equipment and samples ready
  2. Place a drop of blood in the center of the glass slide of the microscope
  3. Using the edge of another slide (clean), or a wire loop, carefully spread the drop around the glass slide using a circular motion.
  4. Spread the drop of blood until it creates a smear that is around half an inch in diameter
  5. DO NOT fix the smear you have created

Staining Procedure

  1. Before you begin the straining, you will need to fix the film by using a 99% methanol for around five minutes
  2. Stain the front and back of the smear by using Giemsa. To do this, you need to dip the slide in the jar with stain in it for around 15 minutes.
  3. After 15 minutes, use distilled water to gently rinse the slide
  4. Lean the slide at an angle over a draining area to get rid of any excess water. You can also wipe the stain, then allow it to air dry completely.
  5. Place the slide under the microscope to view it. For the best results, start at around 10x magnification and work from there.

What You Should Observe

  • Wet mount – if you have a wet mount, the red blood cells should appear to be colorless and have a similar appearance to a donut.
  • Giemsa stained slide – if you have a slide that you stained with Giemsa, the red blood cells should appear to have a pink color under the microscope, and their central part should be bright.

If you are checking for malaria, you should keep an eye out for tiny blue rings inside the cells. The presence of these will indicate the presence of malaria in the blood.

To Summarize

Red blood cells or erythrocytes are incredible cells found in the bodies of animals. They are donut-shaped, but do not have a hole in the middle.

These cells transport oxygen throughout the body via the vascular system, and remove carbon dioxide. They do not require oxygen in order to live, instead relying on anaerobic respiration.

With a life cycle of only around 120 days in total, these cells are constantly dying off and being dealt with by macrophages.

However, thanks to bone marrow, roughly two million red blood cells are being produced every minute, ensuring that there is always a constant supply.

These erythrocyte cells are incredibly important to the function of animals, as the majority of animals require oxygen to live (aerobic respiration).

However, they are also the primary way to look for diseases such as malaria. Scientific procedures such as microscopy can be carried out in order to find out the red blood cell counts in samples.

These forms of testing, the hemocytometer includes, are imperative to understanding our health, as they can also determine the presence of anemia and even internal bleeding via erythrocyte counts.

Overall, these cells have a function in our bodies that keep us alive. Through the hard work of the red blood cells, our bodies and all the various parts, get the oxygen it needs to continue.

Jennifer Dawkins

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