• Saturday February 22,2020


Granulocytes are blood cells that belong to the series of leukocytes. With a share of about 50 to 70% of the total leukocyte count, they are even the most abundant fraction of this cell type.

What are granulocytes?

Basically, the granulocytes take over important tasks of the cellular immune system. They are divided once again into several subgroups. These result from the microscopic appearance of the individual cells and their respective staining behavior and correlate with their specific functions. Specifically, there are polymorphonuclear neutrophil granulocytes that are differentiated into rod-nucleated and segmented neutrophilic granulocytes, as well as eosinophilic and basophilic granulocytes.

All granulocytes are members of the innate immune response system. This is understood to mean non-specific control of fungi, bacteria and parasites. Partly, the granulocytes can even ingest phagocytic pests and render them harmless by destroying them. Their formation occurs in the adult in the bone marrow. This process is referred to in technical terms as granulocytopoiesis and begins with a multipotent hematopoietic stem cell, which undergoes various transformation steps and ultimately becomes the corresponding cell type.

Physiologically, the granulocyte in question is then released into the peripheral blood. If earlier maturation levels in the blood are detectable, this may be an indication of a serious illness.

Anatomy & Construction

The majority of the granulocytes make up about 55 to 65% of the polymorphonuclear neutrophilic granulocytes. They are about 15μm in size and have a cytoplasm that appears colorless to pale violet in microscopy. With dyes they are almost impossible to color. For this reason, they also bear the name "neutrophils" - they are neutral to colorations.

The nucleus of the neutrophils is further differentiated: if it is band-shaped and has only minor incisions, it is a rod-nucleated neutrophilic granulocyte. However, if incisions occur that make up more than two-thirds of the width of the cell nucleus, then there is a segmented neutrophilic granulocyte. These usually have cell nuclei consisting of two to five segments.

Eosinophils are rare, accounting for 2 to 4% of the total number of granulocytes. Their morphology is very similar to that of neutrophils, but their cytoplasm contains red-orange granules and their nucleus consists of only two segments. The basophils usually have only two core segments. Your cytoplasm contains numerous violet-colored granules. They account for 0 to 1% of granulocytes.

Function & Tasks

All types of granulocytes are in the service of the immune system. They fulfill specific functions depending on the subgroup.

The polymorphonuclear neutrophilic granulocytes are responsible for phagocytosis and the destruction of microbial pathogens. To make them readily available when needed, half of the neutrophils circulate in the blood while the other half sits on the walls of small blood vessels. When activated, they migrate into tissues and into exudates, where they do their job. To neutralize pathogens, their granules are very important: they contain peroxidases and esterases, which have a cytotoxic effect on bacteria and fungi. Eosinophilic granulocytes act as immune regulators.

They are used, for example, when foreign allergens acting as allergens enter the body. Furthermore, they take over the defense of parasites and the fibrin degradation, if in the context of inflammatory events a fibrin formation has taken place. Like the neutrophils, the eosinophilic granulocytes perform their tasks primarily in the tissue as well as in inflammatory exudates.

The basophilic granulocytes become active during the immediate allergic reaction. This is also referred to as Type I allergy and includes, for example, allergic rhinoconjunctivitis in hay fever. If the basophils are stimulated to activity, then their granules empty. These are usually filled with mediators such as histamine, heparin, serotonin, prostaglandins and leukotrienes, which mediate the immunological defense processes.


Changes in the granulocyte count as well as its appearance may have congenital and acquired causes. Since the granulocytes are so important for the immune defense, such variations sometimes cause drastic problems.

A pathological multiplication of neutrophilic granulocytes is called neutrophilia. Their absolute number is more than 8000 per microliter. Neutrophilia is primarily triggered by three pathomechanisms. On the one hand, there may be an increased mobilization of the neutrophilic granulocytes actually adhering to the vessel walls. This happens occasionally as a result of great stress. On the other hand, it may be that, for example, as a reaction of the body to acute infections more blood cells are released from the bone marrow. In addition, it is possible that the granulocyte formation is increased in the bone marrow per se.

If the number of neutrophils is less than 1500 / μl, neutropenia is present. If it is even below 500 / μl, there is a particularly critical condition called agranulocytosis. With a neutrophil count of less than 200 / μl, there is an acute danger to life, since then no efficient immune defense can take place. This can be caused by a bone marrow failure, allergies or autoimmune diseases.

Increased numbers of eosinophils and basophils, ie eosinophils or basophils, are usually caused by immune reactions. But they can also be based on a malignancy. Since eosinophils and basophils are already physiologically a very small proportion of the granulocyte count, reductions are difficult to diagnose. For the evaluation of granulocytes, therefore, the neutrophil count is the decisive factor. Overall, the granulocytes perform central tasks of the immune system, which is why deviations urgently require further clarification.

Typical & common blood disorders

  • Acute lymphocytic leukemia
  • Acute myeloid leukemia
  • Chronic lymphocytic leukemia
  • Chronic myeloid leukemia
  • blood poisoning

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