Red blood cell production

Introduction

Red blood cell (RBC) production (erythropoiesis) takes place in the bone marrow under the control of the hormone erythropoietin (EPO), which is produce primarily in the kidney.

Red blood cells starts as immature cells in the bone marrow and after approximately seven days of maturation are released into the blood stream. Unlike many other cells, red blood cells have no nucleus and can easily change shape, helping them fit through the various blood vessels in the body. However while the lack of a nucleus makes a red blood cells move flexible, it also limits the life of the cell as its travels through the smallest blood vessels, damaging the cells membrane and depleting its energy supplies. The red blood cells have a life span of 120 days. It contains a special protein called haemoglobin, which helps carry oxygen from the lungs to the rest of the body and then returns carbondioxide from the body to the lungs so it can be exhaled. Blood appears red because of the large number of red blood cells, which get their colour from the haemoglobin.

The percentage of whole blood volume that is made up of red blood cells is called the hematocrit and is a common measure of red blood cell levels. Red blood cells are the most common type of blood cell and the veterbrate organism principal means of delivering oxygen (O2) to the body tissue via blood flow through the circulating system. Red blood cell take up oxygen in the lungs or gills and release it into the tissue while squeezing through the body capillary.

Red blood cell are also known as red blood corpuscles, hematids, erythoid cells or erythrocytes (from Greek erythros for red  and kytos for hollow vessel with cyte as cell. Erythrocyte consist mainly of hemoglobin, a complex metalloprotein containing heme groups whose iron atoms temporarily bind to oxygen molecule (O₂) in the lungs or gills and release them throughout the body. Oxygen can easily diffuse through the red cell membrane. Hemoglobin in the erythrocyte also carries some of the waste product carbondioxide back from the tissue (Abayomi, 2007).

Life cycle of the erythrocyte

Red blood cells are manufacture from the hemopoietic stem cells, in the bone marrow. These cells are known as erythropoietic bone marrow cells and are partially differentiated. When red blood cell have to be manufactured, these cells go through the various phase of development until the mature red blood cell can be released into the blood stream.

The final stage of maturation requires two important vitamins – vitamin B12 and folic acid. This process of developing from erythropoietic bone marrow cells to mature red blood cells take about 7 days. The stimulus for producing red blood cells is hypoxia (low oxygen) however, hypoxia alone will not be sufficient to trigger the production of new red blood cells unless the hormone erythropoietin is circulating in the blood stream. The hormone is primarily produce by the kidneys.

Structure of red blood cells

Red blood cells are small and biconcave in shape as they lack a nucleus and other organelles. This means the cell can be packed with haemoglobin, the oxygen carrying pigment. The red blood cells are flexible so they can squeeze through the small capillaries (Ochei, 2007).

 Size of the red blood cell

A red blood cell measures about 6-8 micrometers in diameter (average = 7.8um) with an average thickness of 2micrometer (2.5μm at the thickness point and less than 1um at the center)

Though a red blood cell is wider than some capillaries, its flexibility allows it to become distorted as it squeezes through narrow passages and then restore to its original shape.

 Function of the red blood cell

Apart from carrying oxygen, which is the main function of the red blood cell, it can also  conduct the following function.

1. Release the enzyme carbonic anhydrase which allows water in the blood to carry carbondioxide to the lungs where it is expelled.
2. Control the PH of the blood and by acting as an acid-base buffer (Ochei, 2007).

Erythrocyte differentiation

In the process of red blood carpasel maturation, a cell undergoes a series of differentiations. The following stages of development all occur within the bone marrow.

1. Hemocytoblast – stem cells in the bone marrow from which all blood cells form.
2. Proerythroblasts – are produced by the division and differentiation of stems cells.
3. Basophilic (Early) Erythroblast – during this stage in erythpoiesis hemoglobin synthesis begins.
4. Intermediate erythroblasts – at this time we see the accumulation of hemoglobin due to its continued synthesis.
5. Late erythroblasts – during this stage the nucleus is extruded from the cell.
6. Reticulocyte – these cells exhibit a net-like appearance or reticulum in their cytoplasm when stained. A small number of reticulocytes (only 1 to 3%) of the circulating red cells are found in the circulation.
7. Mature erythrocytes – at this final stage of maturation there is a loss of ribosomes these cells enter the circulation (Ochei, 2007).

Factors stimulating red blood cell production

The common factor is blood hypoxia due to a reduced oxygen carrying capacity. We have other factors such as

1. Hemorrhage
2. Damage to bone marrow
3. Exposure to high altitude
4. Exercise
5. Hemolytic disease
6. Low hemoglobin levels

Basic mechanism of red blood cell production

1. Hypoxia in blood, specifically stimulates the juxtaglomerular apparatus within the nephron of the kidney to produce and release erythropoietin.
2. Erythropoietin stimulates the red marrow of the bones to form increase numbers of proerythoblasts. It also shortens the time period for the maturation of erythrocytes.
3. The increase in red blood cell production leads to an increased oxygen carrying capacity of the blood. This increased capacity reduces the stress of hypoxia and in turn produces a negative feedback control on red blood cell production.

Breakdown of red blood cells

A typical matured erythrocytes lives for about 120days in the circulation, since these cells lacks nucleus, they cannot divide or synthesize new cellular components. As a result, the cells degenerate due to damage. The damage RBCs are removed from the circulation in the following ways.

1. 90% are removed from the circulation by the phagocytic activities of macrophages in the liver, spleen and lymph nodes
2. 10% of the old cells hemolysed in the circulation. The fragments of these cells are then engulfed by macrophages.
3. The chemical components of the RBCs are broken down within vacuoles of the macrophages due to the action of lysosomal enzymes (Ochei, 2007)

Characteristics seen in erythrocyte during erythopoiesis

As they mature a number of erythrocytes characteristic changes occurs. The size of the cell is reduced and the cytoplasmic matrix increase in amount, and the staining reaction of the cytoplasm changes from blue to pinkish red because of the decrease in the amount of RNA and DNA. Initially, the nucleus is large in size and contains open chromatin. But as the red blood cells mature the size of the nucleus decreases and finally disappears with the condensation of the chromatin material.

The regulation of erythropoiesis

A feedback loop involving erythropoietin helps to regulate the process of erythopoiesis so that in non-disease states, the production of red blood cells is equal to the destruction of red blood cells and the red blood number is sufficient to sustain adequate tissue oxygen levels but not so high as to cause sludging, thrombosis or stroke. Erythropoietin is produce in the kidney and liver in response to low oxygen levels. In addition, erythropoietin is bound by circulating red blood cells ; low circulating numbers lead to a relatively high level of unbound erythropoietin, which stimulates production in the bone marrow (Monica, 2000).

Quantity of red blood cell in the human body

The average male adult has 5million red blood cells per cubic millimeter of blood, while the average female adult has about 4.5 million red blood cells per cubic millimeter of blood

This may vary by about 300,000 to 500,000 red blood cells. It may also vary depending on the geographical location, a person who lives in high altitude will have more red blood cells (Turgeon, 2009).

Abnormalities in erythrocyte

Alterations in the morphology of erythrocytes are associated with many diseases. The most significant of these conditions is anemia, in which the oxygen carrying capacity of blood is decreased. The causes of anemia are varied and most of them are expressed as changes in RBC morphology. Therefore morphological examination of red cells is very helpful in evaluating and determining the causes of anemia.

Normal red blood cells stained with a Romanowsky stain are nearly uniform in size, shape and colour. Each cell appears as a pink, disc about 7.2microns in diameter, with a rim of haemoglobin and a clear central area called central pallor. The central area generally occupies less than one-third of the cells. The red cells having normal size and normal colour are said to be normocytic and normochromic.

During the examination of the peripheral blood smear, the following characteristics in the red cell morphology should be observed (Ochei, 2007).

1. Colour
2. Size
3. Shape
4. Nucleated red cells
5. Inclusions etc.

Variation in colour of erythrocyte

A red cell showing a normal staining reaction is described normochromic and represent a haemoglobin content within the normal range.

1. Hypochromic cells: Stains very pale and show an increased area of central pallor. Hypochromasia is a result of reduced hemoglobin content, most commonly observed in non-deficiency anemia.
2. Hyperchromic cells: are not seen very commonly these cells stain deeply appearing over saturated with hemoglobin example is spherocytosis.
3. Polychromatic cells: show a mixed staining reaction and appear blue-orange in colour. They contain residual ribonucleic acid (RNA) which is basophilic in addition to haemoglobin.

Variation in size of erythrocyte

Variation in size called anisocytosis is a common and important erythrocyte morphological feature. The term describes any large variation in size of a normal erythrocyte. A red cell within the normal range of diameter is called normocyte.

1. Macrocytosis: it is a condition in which red blood cells have a diameter greater than 7.8 microns and mcv usually greater than 100 cu. Mmicron (femtoliter, FL). Macrocytic cells are seen in megaloblastic anemia due to VitB12 or folic acid deficiencies.
2. Microcytosis: it is a condition in which red blood cells have a diameter less than 6.5 microns and mcv less than 80 cu microns (FL). Microcytic cells frequently have less haemoglobin than normal cells and are seen in iron deficiency anemia, spherocytes anemia etc.

Variation in shape of erythrocyte

A normal red cell is a circular, biconcave disc. Any alteration in this shape is been observed.

1. Poikilocytosis: the term described a condition in which there are major variation in the shape of the erythrocyte. The most common of these variations is a tear drop shape which are found in various anemia.
2. Spherocytes: it is a red cell whose average thickness has increased, usually with a reduced diameter. The spherical shape results when a normal cell volume is enclosed within a reduced surface area. A spherocyte has a 14days life span as compared to 120 days and a normal blood cell.
3. Target cells: These cells have a central area of haemoglobin within the area of central pallor, making them look like targets. This is as a result of having excessive cell membrane compared to the amount of haemoglobin. They occur in various types of anemia, liver disease etc.
4. Sickle cells: These are elongated erythrocytes with crescentic shapes and occasionally U, S or L shapes are formed after exposure to reduced oxygen tension. This variation occurs if the red blood cell contains the abnormal haemoglobin S. This is a hereditary disorder which may appear in two forms. The sickle cell trait or sickle cell disease.
5. Elliptocytes: these are red blood cells which are oval or egg- shape, sometimes almost cylindrical. They do not show the central pallor. Large elliptocytes may been seen in megaloblastic anemia.
6. Schistocytes: these are fragmented portion of red cells which appear in various shapes e.g helment cells. Their presence indicates a very serious pathological condition e.g mechanical fracture of cell during circulation in condition such as a defective heart valve and glomerula filtration (Ochei, 2007).

Abnormal inclusions in erythrocyte.

A normal red cells does not contain any inclusion. Various types may indicate disorders or disease conditions.

1. Basophilic stippling: the red cells may show fine or coarse dark blue granules dispersed throughout the cell. This is known as basophilic stippling and results from the precipitation of ribosomal RNA. The stippling may occur due to abnormal red cell formation in the bone marrow and is seen in heavy metal poisoning (lead, mercury etc) thalassamia and megaloblastic anemia (Brady,2007)
2. Howell-jolly bodies: these are round dense purple granules less than 1micron in size appearing eccentrically located in some red cells. If present, not more than two Howell-jolly bodies are seen in a single red cell. They are remnants of the nuclear material and indicate incomplete expulsion of the nucleus from the red cell through the spleen.
3. Heinz bodies: Heinz bodies are oxidize denatured hemoglobin. They can be demonstrated only by supravital staining with brilliant cresyl blue. Heinz bodies may appear in the peripheral blood smear after removal of the spleen or in haemolytic anemias such as that of due to G6PD deficiency.
4. Siderocytes: the red cells containing small, dense, blue-purple granules are called siderocytes. They resemble Howell-jolly bodies in appearance, but they are granules of free iron, uncombined with haemoglobin, instead of fragments of DNA. They are seen in the peripheral blood after the removal of the spleen.
5. Cabot’s rings: these are rare inclusions appearing as threadlike strands in the form of a ring or figure of 8, reddish-violet in colour. Their origin is not clearly understood, but may be the result of an abnormality in mitosis. They appear in cases of megaloblastic anemia or lead poisoning.
6. Parasites: various stages of the malaria parasites may be seen in the red cells of patients suffering from malaria. Their appearance depends on the developmental stage (e.g ring form, amoeboid, trophoziote, schizont, gametocyte) and the infecting species of the genus plasmodium e.g Plasmodium vivax, Plasmodium falciparium. Other parasite such as trypanosome and microfilaria may also be seen in a peripheral blood smear (Ochei, 2007)

Alteration in the distribution pattern of red blood cells

1. Rouleaux formation: sometimes red cells stick together in row looking like stacks of coins, this is called rouleaux formation. They may appear in the thick portion of the smear of healthy individuals however, their presence in the thinner “examination area” of the smear indicates increased levels of plasma globulin or fibrinogen e.g. in multiple myeloma.
2. Agglutination: agglutination is irregular clumping, if agglutination is observed in blood samples stored in the refrigerator, it may be due to the presence of cold agglutinins, which are autoantibodies indicating an auto-immune haemolytic state or anemia (Bunn,2011).

Erythroblastic reaction

The peripheral blood of a healthy individual does not show the presence of nucleated red cells. Their appearance in the peripheral blood indicates intense stimulation of the bone marrow releasing red cell precursors in the peripheral blood. This occurs in acute blood cells megaloblastic and haemolytic anaemias.

Artifacts in red blood cells

Platelets on top of a red cell, punched-out red cell morphology. They should not be confused with or stain deposit may appear as variation in red cell abnormalities.

 Causes of abnormal result of red blood cell

1. Higher than normal numbers of RBCs may be due to:
2. Problem with heart structure and function that is present at birth (congenital heart disease)
3. Failure of the right side of the heart (corpulmonale)
4. Kidney tumor (renal cell carcinoma)
5. Dehydration (such as from severe diarrhea)
6. Low blood oxygen level (hypoxia)
7. Bone marrow disease that causes abnormal increase in RBCs (polycythemia vera)

Lower the normal numbers of RBCs may be due to:

• Anaemia
• Bleeding
• Bone marrow failure ( for example from radiation, toxins or tumors)
• Deficiency of a hormone called erythropoietin (caused by kidney disease)
• RBC destruction (haemolysis) due to transfusion, blood vessel injury, or other cause.
• Leukamia
• Malnutrition
• Bone marrow cancer called multiple myeloma (Brady, 2007).

Method of estimating red blood cell count

Red blood cell count is the estimation of the number of red blood cells per liter of blood. Abnormally low numbers of red blood cells may indicate anemia as a result of blood loss, bone marrow failure, malnutrition such as iron deficiency, over hydration or mechanical damage to red blood cells.  Abnormally high numbers of red blood cells may indicate congenital heart disease, some lungs disease dehydration, kidney disease or polycythemia.

Red blood cell can be counted using the:

1. Traditional method (manual)
2. Automated method

1. Traditional method (manual): The red blood cell count can be performed using the hemocytometer. This precision instrument possesses a platform with microscopic grid scoring. The most common diluents used for the manual red cell count is a solution of formal citrate prepared by mixing 10ml of formalin (40% formaldehyde) with 1liter of 31.3g/l trisodium citrate solution.

Method:

• 4ml of formal citrate is pipette into a clean test tube
• 20um (0.2ml) of well mixed anticoagulated blood is added
• A clean coverslip is placed on the chamber
• The diluted sample is re-mix properly and loaded into the chamber avoiding air bubbles
• The cells are allow to settle for 20mins on a moist Petri dish
• The cells are counted microscopically using x10, x40 objective, count the cell lying on 5 of the 0.04mm² areas

2. Automated cell count: These are used to perform complete blood counts, erythrocyte sedimentation rates (ESR) or coagulation test. The automated red cell counters sample the blood and quantify, classify and describe the cell population using both electrical and optical techniques. Electrical technique involve passing a dilute solution of the blood through an aperture across which an electric current is flowing. Optical detection may be utilized to gain a differential count of the population of white cell types (Ochei, 2007).

Value of estimating red blood cell

A red blood cell (RBC) count is typically ordered as part of a complete blood count (CBC) and may be used as part of a health check up to screen for a variety of conditions. This test may also be used to help diagnose and/or monitor a number of diseases that affect the production of lifespan of red blood cells, especially if the RBCs are deformed due to an inherited or acquired defect or abnormality. If RBCs are lost or destroyed faster than they can be replaced, if bone marrow production is disrupted or if the RBCs produced do not function normally, then a person will become anemic, which affect the amount of oxygen reaching tissues. If too many RBCs are produced and released then a person can develop polycythemia. This can cause decreased blood flow and related problems (Turgeon, 2009)

Prevention and treatment of abnormal red cell count

A health practitioner must determine the cause of someone’s abnormal red blood cell count so that appropriate treatment can be prescribed. For some anemias treatment may include a dietary supplement or a change in diet to include nutritional foods. In some instances it may only require a change in the person’s current medication. For severe cases, treatment may involve transfusion with blood from a donor. For some, prescribing a drug to stimulate the red cell production in the bone marrow may be required. Eat a well-balanced diet, you can also prevent anemia, due to a lack of iron, vitamin B12 or folate in the food you eat. However the most common cause of vitamin B12 deficiency is malabsorption and the most common cause of iron deficiency is bleeding. These conditions and other RBCs problem that are caused by disease other than nutritional deficiencies will not be corrected by diet (Turgeon, 2009).

Some signs and symptoms observed in low rbcs count

Fatigue and weakness may indicate a low RBC count. Fainting, pallor, shortness of breath, dizziness and/or altered mental status can also indicate a low RBC count.

High RBCs count

Disturbed vision, headache and flushing may be present with an increased numbers of RBCs (Turgeon, 2009)   

 Conclusion

Since Red blood cell plays an important function in the body, which take place in the bone marrow under the control of the hormone erythropoietin produced primarily by the kidneys, and it’s disorder leads to condition such as anemia of various types and polycythemia. Therefore it is concluded that each individuals should check and know their RBC level from time to time in order to keep it within the normal range

 Recommendation

Since Red blood cell plays an important role in the body, it is therefore recommended that individuals should know their red blood cell value and make sure that it is at the normal reference range and moreover trying to prevent anaemia by eating the required dietary supplements.

References

Abayomi, A. (2007). Erythrocyte (Red blood count), In: A text book for      Medical laboratory Practices (2^nd Ed). Lagos: Edoson Book center. PP. 187-207.

Brady, P.G. (2007). “Iron deficiency anemia”. A call for” South: Med. J. 100 (10): 966-967

Bun, H.F. (2011). Approach to the anaemias. In: Goldman L, Schafer. AL, eds. Goldman’s Cecil Medicine. 24^th ed. Philadelphia, Pa: Elsevier Saunders. PP 161

Monica, C. (2000): Erythropoiesis. In: A text book for District Laboratory Practices in tropical countries. United Kingdom: Cambridge University Press PP. 340-349.

Ochei, J. and Kolhatkar, A. (2007): Erythrocyte. In: A text book of Medical Laboratory science, Theory and Practical. New Delhi: Tata McGraw-Hill publisher. PP. 99-110

Turgeon, M. (2009). Red Blood Cell. “8” Clinical Hematology Theory and Procedures (4^th ed). Philadelphia: Lippincott Williams and Wilkins. PP.117.