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This figure shows how leukocytes respond to chemical signals from injured cells. The top panel shows chemical signals sent out by the injured cells. The middle panel shows leukocytes migrating to the injured cells. The bottom panel shows macrophages phagocytosing the pathogens.
Leukocytes exit the blood vessel and then move through the connective tissue of the dermis toward the site of a wound. Some leukocytes, such as the eosinophil and neutrophil, are characterized as granular leukocytes. They release chemicals from their granules that destroy pathogens; they are also capable of phagocytosis. The monocyte, an agranular leukocyte, differentiates into a macrophage that then phagocytizes the pathogens.

Classification of leukocytes

When scientists first began to observe stained blood slides, it quickly became evident that leukocytes could be divided into two groups, according to whether their cytoplasm contained highly visible granules:

  • Granular leukocytes contain abundant granules within the cytoplasm. They include neutrophils, eosinophils, and basophils (you can view their lineage from myeloid stem cells in [link] ).
  • While granules are not totally lacking in agranular leukocytes    , they are far fewer and less obvious. Agranular leukocytes include monocytes, which mature into macrophages that are phagocytic, and lymphocytes, which arise from the lymphoid stem cell line.

Granular leukocytes

We will consider the granular leukocytes in order from most common to least common. All of these are produced in the red bone marrow and have a short lifespan of hours to days. They typically have a lobed nucleus and are classified according to which type of stain best highlights their granules ( [link] ).

Granular leukocytes

The  left image shows a neutrophil, the middle image shows an eosinophil, and the right image shows a basophil.
A neutrophil has small granules that stain light lilac and a nucleus with two to five lobes. An eosinophil’s granules are slightly larger and stain reddish-orange, and its nucleus has two to three lobes. A basophil has large granules that stain dark blue to purple and a two-lobed nucleus.

The most common of all the leukocytes, neutrophils    will normally comprise 50–70 percent of total leukocyte count. They are 10–12 µ m in diameter, significantly larger than erythrocytes. They are called neutrophils because their granules show up most clearly with stains that are chemically neutral (neither acidic nor basic). The granules are numerous but quite fine and normally appear light lilac. The nucleus has a distinct lobed appearance and may have two to five lobes, the number increasing with the age of the cell. Older neutrophils have increasing numbers of lobes and are often referred to as polymorphonuclear    (a nucleus with many forms), or simply “polys.” Younger and immature neutrophils begin to develop lobes and are known as “bands.”

Neutrophils are rapid responders to the site of infection and are efficient phagocytes with a preference for bacteria. Their granules include lysozyme    , an enzyme capable of lysing, or breaking down, bacterial cell walls; oxidants such as hydrogen peroxide; and defensins    , proteins that bind to and puncture bacterial and fungal plasma membranes, so that the cell contents leak out. Abnormally high counts of neutrophils indicate infection and/or inflammation, particularly triggered by bacteria, but are also found in burn patients and others experiencing unusual stress. A burn injury increases the proliferation of neutrophils in order to fight off infection that can result from the destruction of the barrier of the skin. Low counts may be caused by drug toxicity and other disorders, and may increase an individual’s susceptibility to infection.

Questions & Answers

) Which of the following best describes the human body's defense mechanism against environmental bacteria?
what is an inflammation
Lodrick Reply
it's a reaction from a body tissue
is the body own mechanism of fighting against disease especially infections or injuries.
which cells are responsible for bone formation?
Richard Reply
which muscles are innervated by the lateral plantar nerve?
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let ask u aquiz where bones live in a body
Lowyer Reply
306 bones in a human body
Netope Reply
206 bones in a human body
there are 206 bones in human body and a baby's body has about 300 bones at birth
what is anatomy?
Nuwagaba Reply
anatomy is the study of the internal structure of a living organism
can be define as the Scientific Study Of internal structure of the body Some of this Structures are Very tiny they can only be seen by The assistance of a microscope, While other structures can be seen manipulated and Weighted
Anatomy is the scientific study of the body and the physical relationship between systems
gross anatomy is the study of the internal structure of a living organism at a visible or macroscopic level
Favour Reply
homeostasis is the steady maintenance of the internal system
study of the structure of cells,tissue using a microscope
is the study of how the human body works and relates
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where are bones lived
name of all the bones and eg
Shantal Reply
treatment for hereditary diseases
With gene therapy, the treatment or elimination of inherited diseases or physical conditions due to these mutations could become a reality. Gene therapy involves the manipulation of genes to fight or prevent diseases. Put simply, it introduces a "good" gene into a person who has a disease caused by
Why do cardiac muscle demonstrate autorhythmicity
Olemogile Reply
cardiac muscle tissue has autorhythmicity, the unique ability to initiate a cardiac action potential at a fixed rate. spreading the impulse rapidly from cell to cell to trigger the contraction of the entire heart.
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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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