Methemoglobin and Blood Disorders

Methemoglobin Reductase

• Methemoglobin is a form of hemoglobin that is unable to bind to oxygen
• In methemoglobin, the iron atom in heme is in the ferric (Fe3+) state rather than the ferrous (Fe2+) state
• Methemoglobin reductase is an enzyme that reduces ferric (Fe3+) iron back to the ferrous (Fe2+) state
• This enzyme helps to maintain the normal function of hemoglobin

Heinz Bodies

• Heinz bodies are inclusions found within red blood cells
• They are precipitated denatured hemoglobin
• Heinz bodies are a result of oxidative damage to hemoglobin
• They are formed by the precipitation of denatured hemoglobin within the red blood cell
• The text mentions that Heinz bodies can decrease red blood cell survival

Sulfhemoglobin

• Sulfhemoglobin is a form of hemoglobin that is unable to bind to oxygen
• It is formed by the irreversible oxidation of hemoglobin
• It can be caused by exposure to certain drugs such to sulfonamides, phenacetin, acetanilide, and phenazopyridine
• It can also be caused by exposure to environmental pollutants, such as industrial pollutants and tobacco smoke
• Sulfhemoglobin has a lower affinity for oxygen than normal hemoglobin
• Individuals with high levels of sulfhemoglobin are more susceptible to hypoxia

Carbon Monoxide (CO)

• Carbon monoxide (CO) binds to hemoglobin with a much higher affinity than oxygen
• This prevents oxygen from binding to hemoglobin, leading to hypoxia
• COHb levels can be as high as 15% in smokers

Hemoglobin

• Hemoglobin is a protein found in red blood cells
• It is responsible for transporting oxygen throughout the body
• Oxygen binds to the heme component of hemoglobin

Iron Cycle and Transport

• Transferrin is a protein that transports iron throughout the body
• Iron is absorbed in the duodenum and jejunum
• Iron is transported to bone marrow for red blood cell production
• Iron is stored in the liver and spleen

Hepcidin

• Hepcidin is a hormone that regulates iron absorption
• It is produced by the liver
• Hepcidin binds to ferroportin, which is a protein that transports iron across cell membranes
• Hepcidin reduces the absorption of iron
• Hepcidin production is increased in high iron stores and decreased in low iron stores

Transferrin Receptors

• Transferrin receptors bind to transferrin, which is a protein that transports iron throughout the body
• Transferrin receptors are found on the surface of red blood cell precursors in the bone marrow

Ferritin

• Ferritin is a protein that stores iron in the body
• Ferritin can bind to ferric (Fe3+) iron
• Ferritin is found in the liver, spleen, and other tissues

Clinical Significance

• Rouleaux formation is a stacking of red blood cells
• It can be caused by increased levels of proteins in the blood, such as globulin and fibrinogen
• Rouleaux formation is often seen in hyperproteinemia and multiple myeloma
• When the text mentions "true rouleaux", it refers to rouleaux formation caused by increased levels of proteins in the blood
• When it mentions "artifactual rouleaux" it is caused by a technical issue with the blood smear.
• Autoagglutination is the clumping of red blood cells
• It can be caused by autoantibodies, which are antibodies that attack the individual's own body
• Autoagglutination is often seen in cold agglutinin disease, where red blood cells clump at cold temperatures

Red Blood Cell Morphology

• Red blood cells are normally biconcave discs (discocytes)
• This shape is optimal for gas transport
• Macrocytic red blood cells are larger than normal red blood cells
• Macrocytosis is often seen in megaloblastic anemia
• Microcytic red blood cells are smaller than normal red blood cells
• Microcytosis is often seen in iron deficiency anemia, thalassemia, and sideroblastic anemia
• Anisocytosis is the variation in red blood cell size
• Anisocytosis is often seen in iron deficiency anemia
• Oval macrocytes are oval-shaped red blood cells that are larger than normal red blood cells
• Oval macrocytes are often seen in megaloblastic anemia
• The text mentions that oval macrocytes have "markedly increased MCV"
• MCV is the mean corpuscular volume, which is a measure of the average size of red blood cells