Target cell (codocyte)
Encyclopedia
Codocytes, also known as target cells or Mexican hat cells, are red blood cells that have the appearance of a shooting target with a bullseye
. The cells have a dark center (a central, hemoglobinized area) surrounded by a white ring (an area of relative palor), followed by dark outer (peripheral) second ring containing a band of hemoglobin.
These cells are characterised by a disproportional increase in the ratio of surface membrane
area to volume. This is also described as a "relative membrane excess." It is due to either increased red cell surface area (increased beyond normal), or else a decreased intracellular hemoglobin content (which may cause an abnormal decrease in cell volume without affecting the amount of membrane area). The increase in the surface area to volume ratio also gives the cell decreased osmotic fragility, as it allows it to take up more water for a given amount of osmotic stress.
In vivo (within the blood vessel), the codocyte is a bell-shaped cell. It assumes a "target" configuration only when processed to obtain a blood film. In the film these cells appear thinner than normal, primarily due to their pallor (by which thickness is judged on microscopy).
Cells may appear in association with the following conditions:
In patients with obstructive liver disease, lecithin cholesterol acetyltransferase activity is depressed, which increases the cholesterol-to-phospholipid ratio and produces an absolute increase in the surface area of the red cell membrane. In contrast, membrane excess is only relative in patients with iron-deficiency anemia and thalassemia because of the reduced quantity of intracellular hemoglobin.
Bullseye (target)
The bullseye, or bull's-eye, is the centre of a target , and by extension the name given to any shot that hits the bullseye...
. The cells have a dark center (a central, hemoglobinized area) surrounded by a white ring (an area of relative palor), followed by dark outer (peripheral) second ring containing a band of hemoglobin.
These cells are characterised by a disproportional increase in the ratio of surface membrane
Biological membrane
A biological membrane or biomembrane is an enclosing or separatingmembrane that acts as a selective barrier, within or around a cell. It consists of a lipid bilayer with embedded proteins that may constitute close to 50% of membrane content...
area to volume. This is also described as a "relative membrane excess." It is due to either increased red cell surface area (increased beyond normal), or else a decreased intracellular hemoglobin content (which may cause an abnormal decrease in cell volume without affecting the amount of membrane area). The increase in the surface area to volume ratio also gives the cell decreased osmotic fragility, as it allows it to take up more water for a given amount of osmotic stress.
In vivo (within the blood vessel), the codocyte is a bell-shaped cell. It assumes a "target" configuration only when processed to obtain a blood film. In the film these cells appear thinner than normal, primarily due to their pallor (by which thickness is judged on microscopy).
Causes
Cells may appear in association with the following conditions:
- Liver diseaseLiver diseaseLiver disease is a broad term describing any single number of diseases affecting the liver.-Diseases:* Hepatitis, inflammation of the liver, caused mainly by various viruses but also by some poisons , autoimmunity or hereditary conditions...
: Lecithin cholesterol acyltransferase (LCAT) activity may be decreased in obstructive liver disease. Decreased enzymatic activity increases the cholesterol to phospholipid ratio, producing an absolute increase in surface area of the red blood cell membranes. - Iron deficiencyIron deficiency (medicine)Iron deficiency is one of the most common of the nutritional deficiencies. Iron is present in all cells in the human body, and has several vital functions...
: Decrease in hemoglobin content relative to surface area is probably the reason for the appearance of target cells. This is also seen in Thalassemias, Hemoglobin C disease, etc. - Alpha-thalassemiaAlpha-thalassemiaAlpha-thalassemia is a form of thalassemia involving the genes HBA1 and HBA2. Alpha-thalassemia is due to impaired production of 1,2,3, or 4 alpha globin chains, leading to a relative excess of beta globin chains...
and beta-thalassemiaBeta-thalassemiaBeta-thalassemias are a group of inherited blood disorders caused by reduced or absent synthesis of the beta chains of hemoglobin resulting in variable phenotypes ranging from severe anemia to clinically asymptomatic individuals. The total annual incidence of symptomatic individuals is estimated...
(hemoglobinopathy) - Hemoglobin CHemoglobin CHemoglobin C is an abnormal hemoglobin with substitution of a lysine residue for a glutamic acid residue at the 6th position of the β-globin chain.-Clinical significance:...
Disease - Post-splenectomySplenectomyA splenectomy is a surgical procedure that partially or completely removes the spleen.-Indications:The spleen, similar in structure to a large lymph node, acts as a blood filter. Current knowledge of its purpose includes the removal of old red blood cells and platelets, and the detection and fight...
: A major function of the spleen is the clearance of opsonizedOpsoninAn opsonin is any molecule that targets an antigen for an immune response. However, the term is usually used in reference to molecules that act as a binding enhancer for the process of phagocytosis, especially antibodies, which coat the negatively-charged molecules on the membrane. Molecules that...
, deformed, and damaged erythrocytes by splenic macrophageMacrophageMacrophages are cells produced by the differentiation of monocytes in tissues. Human macrophages are about in diameter. Monocytes and macrophages are phagocytes. Macrophages function in both non-specific defense as well as help initiate specific defense mechanisms of vertebrate animals...
s. If splenic macrophage function is abnormal or absent because of splenectomy, altered erythrocytes will not be removed from the circulation efficiently. Therefore, increased numbers of target cells may be observed. - AutosplenectomyAutosplenectomyAn autosplenectomy occurs when a disease damages the spleen to such an extent that it ends up shrunk.-Consequences:...
caused by sickle cell anemia
In patients with obstructive liver disease, lecithin cholesterol acetyltransferase activity is depressed, which increases the cholesterol-to-phospholipid ratio and produces an absolute increase in the surface area of the red cell membrane. In contrast, membrane excess is only relative in patients with iron-deficiency anemia and thalassemia because of the reduced quantity of intracellular hemoglobin.
External links
- http://arbl.cvmbs.colostate.edu
- http://biomedx.com/microscopes/training/LB2.html
- http://www.ornl.gov