Blood-WBC

1. Types of White Blood Cells
White blood cells are also referred to as WBCs or
leukocytes. They are the cells that make up the majority of the immune system,
which is the part of the body that protects itself against foreign substances and
various types of infections. Leukocytes are made in the bone marrow from
multipotent cells called hematopoietic stem cells. Leukocytes exist in all parts of
the body, including the connective tissue, lymph system, and the bloodstream.
There are five different types of white blood cells, each of which has a different
funtions in the immune system.
Five Types of White Blood Cells and Their Functions
There are two different types of white blood cells and each looks different from one
another under the microscope. These include granulocytes and agranulocytes.
 ŸGranulocytes have visible granules or grains inside the cells that have different
cell functions. Types of granulocytes include basophils, neutrophils, and
eosinophils.
 ŸAgranulocytes are free of visible grains under the microscope and include
lymphocytes and monocytes.
Together, they coordinate with one another to fight off things like cancer, cellular
damage, and infectious diseases. Below, detailed information about each type will
be discussed.
1. Neutrophils
Neutrophils are the most common type of white blood cell in the body with levels of
between 2000 to 7500 cells per mm3
in the bloodstream. Neutrophils are medium-
sized white blood cells with irregular nuclei and many granules that perform
various functions within the cell.

2. Function: Neutrophils function by attaching to the walls of the blood vessels,
blocking the passageway of germs that try to gain access to the blood through a
cut or infectious area. Neutrophils are the first cells to reach an area where a
breach in the body has been made. They kill germs by means of a process known
as phagocytosis or “cell-eating”. Besides eating bacteria one-by-one, they also
release a burst of super oxides that have the ability to kill many bacteria at the
same time.
2. Lymphocytes
Lymphocytes are small, round cells that have a large nucleus within a small
amount of cytoplasm. They have an important function in the immune system,
being major players in the humoral immune system, which is the part of the
immune system that relates to antibody production. Lymphocytes tend to take up
residence in lymphatic tissues, including the spleen, tonsils, and lymph nodes.
There are about 1300 to 4000 lymphocytes per mm3
of blood.
Function: B lymphocytes make antibodies, which is one of the final steps in
disease resistance. When B lymphocytes make antibodies, they prime pathogens
for destruction and then make memory cells ready that can go into action at any
time, remembering a previous infection with a specific pathogen. T lymphocytes
are another type of lymphocyte, differentiated in the thymus and important in cell-
mediated immunity.
3. Monocytes
Monocytes are the largest of the types of white blood cells. There are only about
200-800 monocytes per mm3
of blood. Monocytes are agranulocytes, meaning
they have few granules in the cytoplasm when seen under the microscope.
Monocytes turn into macrophages when they exit the bloodstream.
Function: As macrophages, monocytes do the job of phagocytosis (cell-eating) of
any type of dead cell in the body, whether it is a somatic cell or a dead neutrophil.
Because of their large size, they have the ability to digest large foreign particles in
a wound unlike other types of white blood cells.
4. Eosinophils
There aren’t that many eosinophils in the bloodstream—only about 40-400 cells
per mm3
of blood. They have large granules that help in cellular functions.
Eosinophils are especially important when it comes to allergies and worm
infestations.
Function: Eosinophils work by releasing toxins from their granules to kill
pathogens. The main pathogens eosinophils act against are parasites and worms.
High eosinophil counts are associated with allergic reactions.
5. Basophils
Basophils are the least frequent type of white blood cell, with only 0-100 cells per
mm3
of blood. Basophils have large granules that perform functions that are not

3. well known. They are very colorful when stained and looked at under the
microscope, making them easy to identify.
Function: Basophils have the ability to secrete anticoagulants and antibodies that
have function against hypersensitivity reactions in the bloodstream. They act
immediately as part of the immune system’s action against foreign invaders.
Basophils contain histamine, which dilates the vessels to bring more immune cells
to the area of injury.
What are White Blood Cells?
Our bodies are constantly under siege. If we could see into the world of tiny microorganisms,
we would observe the constant attack of viruses and bacteria upon us. These potentially harmful
intruders enter through any nook or cranny, be it our mouth and nose or an open cut. Sometimes
we succumb to infection. However, fortunately for us, we are protected by an equally tough
microscopic army within our own body.
A Lymphocyte, One Type of White Blood Cell
Welcome to the world of white blood cells. These tiny organisms serve as the armed forces of
our body, fighting off intruders, patrolling for invaders, and even cleaning up. Also known as
leukocytes, white blood cells represent our immune system. If not for these fighters, we may
have succumbed to tiny potential killers long ago. There are five different types of white blood
cells, each performing specific jobs to keep us healthy and alive. In this lesson, learn more about
these cells and how they work for our body.
Where do White Blood Cells Come From?
Although there are several different types of white blood cells, they all come from the same
place. White blood cells originate from stem cells in our bone marrow.The bone marrowis
essentially a blood cell producing factory, pumping out billions of new cells every day. These
freshly made white blood cells have the ability to move on their own. Once produced, they leave
the marrow and enter the bloodstream.
However, it may surprise you to know that most white blood cells do not actually reside in the
bloodstream. The majority of leukocytes are found outside the blood, in tissues and interstitial
fluid. The ones that are found within the blood are typically just utilizing the bloodstream as a
vehicle to get to another location. Like soldiers in charge of certain posts, white blood cells have
specific areas and tissues in the body for which they are responsible.
The Five Types of White Blood Cells

4. Let's take a look at the first type of white blood cell, the basophil. This is the least numerous of
all the white blood cells. But it plays an important part in the inflammatory response of the body.
For example, have you ever found yourself in a sneezing fit after walking through a field of
flowers? This allergic reaction is due to the inflammatory response of the body as it attempts to
get rid of the pesky pollen in your nose. A substance called histamine is released, causing your
allergic reaction. Basophils produce and store the histamine that is used at a time like this.