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[[Image:LH Monocyte Histology.jpg|right|thumb|150px|<p>'''Monocyte'''</p>^{©RVC 2008}]]

[[Image:LH Monocyte Histology.jpg|right|thumb|150px|<p>'''Monocyte'''</p>^{©RVC 2008}]]

<p>Monocytes are the largest [[Leukocytes - WikiBlood|leukocytes]]. They have a large indented nucleus, few granules and constitute about 5% of circulating [[Leukocytes - WikiBlood|leukocytes]]. Monocytes are precursors to a number of cells that make up the [[Lymphoreticular System - Anatomy & Physiology|mononuclear phagocytic system]]. Developing in the [[Bone Marrow - Anatomy & Physiology|bone marrow]], monocytes migrate into the circulation where, after approximately three days, they migrate into tissues and differentiate.</p>

Monocytes are the largest [[Leukocytes|leukocytes]]. They have a large indented nucleus, few granules and constitute about 5% of circulating leukocytes. Monocytes are precursors to a number of cells that make up the [[Lymphoreticular System - Anatomy & Physiology|mononuclear phagocytic system]]. Developing in the [[Bone Marrow - Anatomy & Physiology|bone marrow]], monocytes migrate into the circulation where, after approximately three days, they migrate into tissues and differentiate.

 

==Development==

==Development==

<p>Monocytes develop from the bi-potential [[Overview of Haematopoiesis - WikiBlood#Colony Forming Units|CFU-GM]] stem cell. Further details of this process ([[Leukopoiesis - WikiBlood|leukopoiesis]]) can be found [[Leukopoiesis - WikiBlood#Monocyte development|here]].</p>

<p>Monocytes develop from the bi-potential [[Haematopoiesis - Overview#Colony Forming Units|CFU-GM]] stem cell during [[Leukopoiesis|leukopoiesis]].</p>

<p>When monocytes leave the blood stream they then differentiate into a number of cells (all are [[Macrophages|macrophages]]):

<p>When monocytes leave the blood stream they then differentiate into a number of cells (all are classified as [[Macrophages|macrophages]]):

* Connective tissue histiocyte

* Connective tissue histiocyte

* [[Respiratory System General Introduction - Pathology#Alveolar macrophages|Alveolar macrophage]]

* [[Respiratory System General Introduction - Pathology#Alveolar macrophages|Alveolar macrophage]]

* Peritoneal macrophage

* Peritoneal macrophage

* Kupffer cell of [[Liver - Anatomy & Physiology|liver]]

* Liver Kupffer cell  

* Melanophage of skin

* Melanophage of skin

* Lipophage

* Lipophage

* [[Bones - Anatomy & Physiology#Osteoclasts|Osteoclasts]] in bone

* [[Bones - Anatomy & Physiology#Osteoclasts|Osteoclasts]] in bone

* Microglial cell in bone & brain

* [[Neurons_- Anatomy & Physiology#Microglial_Cells|Microglial cell]] in bone & brain

* Specialised histiocytes

* Specialised histiocytes

** Epithelioid cell

** Epithelioid cell

* Histiocytic giant cell

* Histiocytic giant cell

** Langhan’s cell

** Langerhans cell

** Touton giant cell</p>

** Touton</p>

[[Image:Monocyte Picture.jpg|thumb|right|150px|Monocyte Picture - Copyright Prof Dirk Werling DrMedVet PhD MRCVS]]

[[Image:Monocyte Picture.jpg|thumb|right|150px|Monocyte Picture - Copyright Prof Dirk Werling DrMedVet PhD MRCVS]]

<p>Monocytes can live for months to years in the circulation.</p>

<p>Monocytes can live for months to years in the circulation.</p>

<p>Monocytes are referred to as macrophages once they enter a tissue by '''diapedesis'''.</p>

<p>Monocytes are referred to as macrophages once they enter a tissue by '''diapedesis'''.</p>

<p>Monocytes/macrophages act as phagocytes, removing particular antigens. They also act as antigen presenting cells to take up, process and present antigen to [[Lymphocytes#T cells|T cells]].</p>

<p>Monocytes/macrophages act as phagocytes, removing particular antigens. They also act as antigen presenting cells to take up, process and present antigen to [[T cells]].</p>

===In pathology===

==Monocytosis==

*[[Changes in Inflammatory Cells Circulating in Blood - Pathology#Monocytosis|Monocytosis]]

An increase in the number of monocytes (haematogenous macrophages) in the blood is known as a [[Monocytosis|monocytosis]]. It occurs in conjunction with other changes inidicative of a [[Stress Leucogram|stress leucogram]] or it may occur independently. Monocytes in the blood represent a brief transitional stage as they quickly move into tissues and differentiate further to tissue macrophages; they rarely perform any notable functions whilst in the bloodstream but they have been found to phagocytose red blood cells in cases of immune-mediated haemolytic anaemia. The major causes of monocytosis are:

*Stress leucogram mediated by the production or administration of glucocorticoids (plus a neutrophilia, eosinopenia and lymphopenia).

*Chronic inflammatory processes, including chronic bacterial infections and chronic inflammatory diseases of the liver (chronic hepatitis and cholangitis) and pancreas (chronic pancreatitis).

<center><b><sup>Blood cells: [[Erythrocytes - WikiBlood|Erythrocytes]] |

*Granulomatous disease results in monocytosis as monocytes are recruited to contain certain types of bacteria (namely Mycobacteria spp., Nocardia spp., Actinomyces and Rhodococcus equi) or foreign bodies.

[[Basophils|Basophils]], [[Eosinophils|Eosinophils]], [[Lymphocytes|Lymphocytes]], [[Macrophages|Macrophages]], [[Mast Cells|Mast cells]], [[Monocytes|Monocytes]] & [[Neutrophils|Neutrophils]] |  [[Thrombocytes|Thrombocytes]] & [[Thrombopoiesis - WikiBlood#Megakaryocyte|Megakaryocytes]]</sup></b></center>

 

[[Category:WikiBlood]]

[[Category:Blood_Cells]] [[Category:Kate English reviewing]]