Observing Monocytes With The Microscope 

Microscopes allow us to study microorganisms in the closest possible detail. Whether it’s intrigue that sparks an interest in observing different organisms or scientific research, there’s no doubt that getting up close and personal with different organisms is fascinating.

Observing Monocytes With The Microscope

Also studied under the lens of a microscope are blood cells. One particular type is Monocytes. These are a white blood cell, also referred to as leukocyte.

Monocytes are a type of white blood cell (leukocyte) that are made from pluripotent stem cells present in bone marrow. They are created in  bone marrow, but only for a very small period.

On average, they are produced in less than 24 hours. After this, they migrate to the marginating pool and circulatory system.

Once they arrive in these environments, monocytes stay for around two to three days until they eventually travel to different tissues. Here, they will transform into macrophages. 

Monocytes are only responsible for making up around five percent of all the leukocytes in blood circulation. This is quite surprising as they are the largest of all white blood cells.

Nevertheless, it’s when an infection appears that monocytes grow in numbers. When protozoa or bacteria invade bodily tissues, inflammation may occur. This is when monocytes start to build an army and fight back.

As you can see, monocytes are extremely important for the normal functioning of the body. Continue reading as we discuss the observation of monocytes under a microscope.

Monocytes Under The Microscope

Leukocytes are next to impossible when trying to identify them when unstained. But, if you stain a small blood smear with stains, such as Wright-Giemsa, the contrast can improve.

In this instance, you will stand a better chance of finding the differences between the various types of white blood cells. 

Below is a tried and tested technique for identifying monocytes. Before you start, however, there are a few items and instruments you will require:

  • A compound light microscope
  • Immersion oil
  • Sterilized/unused picking needles
  • Microscope glass slides
  • A drying rack
  • A cotton swab
  • Alcohol 
  • A PAP stain/Wright-Giemsa

Steps – Blood Smear

The first step in this procedure is the blood smear

Quick Tip: We suggest that you add some acetone-free methanol to the thin slide before you stain it with any blood. Then, allow it to dry completely.

Take a cotton swab and dab this in alcohol. Then, clean the tip of your ring or middle finger to prevent the risk of any infection forming.

Now, prick the tip of the finger with a clean, sterilized, unused laboratory picking needle. Once pricked, wipe away the initial drop of blood with another cotton swab dampened with alcohol.

Once the first drop of blood has been removed, very gently press the finger. Then, make a round smear on one of the glass slides (the thick film). Press the tip of the finger very gently and allow one or two drops of blood to fall onto the center of another sterilized, clean slide.

Using another clean cotton swab, dabbed in alcohol, press it against the pricked finger. This will help prevent further bleeding and any risk of infection. 

Now, get another clean glass slide and place it at an angle to the glass slide. Place one or two drops of blood on here to create a thin film of blood. 

Gently place the two glass slides, the one with a thick blood film and the other with a thin blood film, on to the drying rack. Now, wait and allow the blood to completely dry. 


Now, we move onto staining the slide. You need to stain your slide with a modified Wright-Giemsa stain.

But, make sure that this stain has been sufficiently buffered with methanol (pH 6.8). This essentially involves submerging the slides in a beaker or jar that hold the stain for approximately 30 minutes. 

Take the slide from the jar or beaker and place it on a rack. Here, wait for it to dry completely. Now, place your slide on the microscope stage.

Here, you can start observing your specimen with low power. When you reach 1000x, you can add a small drop of immersion oil in order to view the slide properly. 

Observing Monocytes With The Microscope

Observing Monocytes

When observed under a microscope with high power, you should notice many red blood cells with what seems to be spaces in the middle.

You will also be able to observe multiple monocytes. These will have bean-shaped or spherical appearances with a darkened material inside them. 

When you compare monocytes to other types of leukocytes, you will notice that they are much larger. Therefore, you can easily distinguish them from others under the microscope.

What Do Monocytes Do?

Essentially, monocytes are the superheroes and firefighters of your cells. Their life begins in your bone marrow. This is where they grow, become stronger, and train to protect your body against infections and diseases.

Once monocytes mature, they will enter the bloodstream and tissues. Here, they will begin in their quest to defend your body against any foreign invaders, such as germs and unwanted bacteria. 

Why do we compare monocytes to firefighters? Well, germs can be considered as fires when they enter the body.

And, fires need to be put out before they cause too much damage. When germs enter body tissues, monocytes are alerted and are called into action to fight the germ (fire). 

Altogether, there are two types of these cellular saviors:

  • Dendritic cells – These inform other cells in the immune system of dangerous germs and ask them for backup.
  • Macrophages – These monocytes defend the body against germs and other foreign invaders. 

To put it simply, monocytes help to defend our bodies against germs and foreign entities that can be harmful to our health and immune system.

Common Disorders That Can Affect Monocytes 

The number of monocytes in your blood are determined by the overall conditions. An individual’s monocyte count can either be too high or too low if the body is fighting a disease or an infection. 

Some common disorders that can affect the monocyte count are:

  • Monocytosis
  • Monocytopenia

Monocytosis develops when the monocyte count is too high. This disorder is usually linked to a disease or chronic infection that the body is trying to fight off. However, there are a number of causes of monocytosis, such as:

  • Certain blood disorders
  • Autoimmune diseases, such as rheumatoid arthritis, and lupus
  • Cancer, such as lymphoma and leukemia
  • Infections, such as mononucleosis
  • Cardiovascular disease
  • Inflammatory disorders, such as sarcoidosis

Another disorder is monocytopenia. This develops when the monocyte count is too low. Monocytopenia tends to occur when the white blood cell count decreases, but there are a few common causes of this condition:

  • Blood infections
  • Aplastic anemia
  • HIV
  • Injuries from burns
  • Certain reactions from chemotherapy 

Closer observation can help determine the count of monotypes in your body.

In Summary

Monocytes play an integral role in helping eliminate different foreign materials, microorganisms, and tumorous cells in the body. This is achieved through a process known as phagocytosis. 

With the use of a microscope, you can study these largest of the white blood cells in great detail and, therefore, gain a deeper understanding of their importance in the human body.

Jennifer Dawkins

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