Red blood cells life span

The symptoms of vitamin E deficiency produced by artificial diets high in unsaturated fatty acids or observed in patients unable to absorb fat (sprue, fibrocystic disease of the pancreas) include low blood and tissue tocopherol levels, increased red blood cell fragility and shortened red blood cell life-span, and increased urinary excretion of creatine (the latter is indicative of muscle damage). Marked improvement in these conditions is noted following administration of alpha-tocopherol. 

The life span of the normal red blood cell is 120 days this means that slightly less than 1% of the population of red cells (200 billion cells, or 2 million per second) is replaced daily. The new red cells that appear in the circulation still contain ribosomes and elements of the endoplasmic reticulum. The RNA of the ribosomes can be detected by suitable stains (such as cresyl blue), and cells containing it are termed reticulocytes they normally number about 1% of the total red blood cell count. The life span of the red blood cell can be dramatically shortened in a variety of hemolytic anemias. The number of reticulocytes is markedly increased in these conditions, as the bone marrow attempts to compensate for rapid breakdown of red blood cells by increasing the amount of new, young red cells in the circulation. 

The cellular elements of the blood have a short life span and must be continuously replaced. The formation of red blood cells, white blood cells, and platelets, collectively, is referred to as hematopoiesis. This process takes place in the red bone marrow. In adults, red bone marrow is found in the pelvis, ribs, and sternum. 

After an erythropoietic agent is initiated, hemoglobin response is typically delayed. Steady-state hemoglobin levels do not occur until after the life span of a red blood cell (mean 2 months range 1 to 4 months). To avoid... 

If the average life span of a human red blood cell is 120 days, how many red blood cells are produced in an average 70-kg person every second ... 

In 1969, McCord and Fridovich discovered that a copper-containing protein, erythrocuprein, isolated from red blood cells, catalyzed the dismutation of superoxide O - [17]. This enzyme was renamed superoxide dismutase (SOD). A striking positive correlation is now known to exist between the life-span potential of mammal species and the ratio of SOD activity and specific metabolic rate of their tissues [18]. The ubiquitous vitaminE, glutathione peroxidases and superoxide dismutases provide a primary protective barrier against the toxicity of free radicals and peroxides in mammalian cells. 

After red blood cells, which contain hemoglobin, reach their life span of about 120 days, they are phagocytized by cells of the reticuloendothelial system. Globin is released and converted to amino acids. Heme is degraded to bilirubin, which is excreted in the bile. 

D. A pyruvate kinase deficiency would slow glycolysis in red blood cells and cause ATP production to decrease and NADH to increase. Intermediates of glycolysis before the blocked step would accumulate, and glucose 6-phosphate would inhibit hexokinase. The life span of the cells would decrease. Fatty acids cannot serve as a source of energy because these cells lack mitochondria. 

Exposure to lead in adults has been associated with hypertension, nephropathy, decreased hearing acuity, anemia, peripheral neuropathy, and encephalopathy. Onset of symptoms may be slow with chronic exposure. Anemia, common in chronically exposed adults and children, tends to be more severe in children. The life span of red blood cells decreases when lead concentrations in blood increase. In the past, the morphology of various blood cells was used to diagnose lead poisoning. Zero content is allowed in food (Food and Drug Administration). 

A number of these enzymes are expressed in other tissues as well but cause a notable deficiency predominantly in red blood cells because of the life span of the erythrocyte after the loss of protein synthesis. Once an enzyme is degraded or otherwise becomes nonfunctional, it cannot be replaced by new or other compensating proteins because of the lack of nucleus, mitochondria, ribosomes, and other cell organelles in mature red cells. Disorders have been described in the EMP, HMP, Rapoport-Luebering cycle, the glutathione pathway (Figure 21-9), purine-pyrimidine metabolism and methemoglobin reduction. 

Normal red blood cells are deformable biconcave disks. Their shape is determined by the external environment of the cell, the metabolic activity of the cell, the nature of hemoglobin, the membrane skeleton (see below), and the age of the cell. A normal human red blood cell has a life span of about 120 days and travels a distance of about 175 miles. Much of this travel occurs in capillary channels of the microcirculation, where flow rates are very slow. Here, particularly at branch points, the shape of the cell undergoes striking deformations and can squeeze through openings as small as one-twentieth the cell diameter. Thus, the primary determinant of blood flow and viscosity is... 

The intricate interactions of the spectrin-protein 4.1-actin complex may be of central importance in maintaining the structural integrity of the red cell membrane. Two genetic disorders affecting the red cell membrane skeleton are hereditary spherocytosis and hereditary elliptocytosis. The former, the most common congenital form of hemolytic anemia in persons of northern European descent, exhibits an autosomal dominant inheritance pattern. The red blood cells are spherical, osmotically fragile, and considerably reduced in life span. They undergo... 

Removal of senescent red blood cells from the circulation has been attributed to desialylation of the membrane glycoproteins. In vitro removal of sialic acid from human red blood cells and introduction of the modified cells into the circulatory system result in drastic shortening of their life span. However, aging and removal of red blood... 

Under steady-state conditions, the average red blood cell takes approximately 5 days to develop from a committed stem cell, through the various stages of development from the early proerythroblast to the relatively mature reticulocyte and, finally, to the mature red cell seen in the peripheral blood. Its average life-span is 120 days if there are no abnormal extraneous circumstances, such as bleeding. Approximately 3 x 109 reticulocytes are delivered in to the blood every day, representing approximately 1 % of the circulating red cell pool. 

Sickle cell anemia is a hereditary disease in which abnormally shaped red blood cells restrict the flow of blood to vital organs in the human body, causing swelling, severe pain, and in many cases a shortened life span. There is currently no cure for this condition, but its painful symptoms are known to be caused by a defect in hemoglobin, the oxygen-carrying protein in red blood cells. 

A characteristic of the early cells in the model is that they remain in the blood stream only 3 days. In the original model normal red blood cells were assumed to have a life span of 20 days (I). To account for normal variability in life span, cells were removed from the circulation according to a normal distribution centered at 20 days with a standard deviation of approximately 1 day. 

The finite life span of most mature blood cells requires their continuous replacement, a process termed hematopoiesis. New cell production must respond to basal needs and states of increased demand. Red blood cell production can increase >20-fold in response to anemia or hypoxemia, white blood cell production increases dramatically in response to a systemic infection, and platelet production can increase 10-20-fold when platelet consumption results in thrombocytopenia. 

Mammalian hemoglobin free in the plasma would be expected to have a half-life of about 40 minutes and would easily be lost through the kidneys and the reticuloendothelial system [3]. Having evolved to travel in a cell that acts simultaneously as a protective environment and a vehicle, the life expectancy of hemoglobin increased to the life expectancy of the red blood cell itself. Hemoglobin occupies approximately a quarter of the volume of an erythrocyte s internal space. A mature mammalian erythrocyte has lost its capacity to synthesize proteins, and consequently its repair ability and probably the capacity to maintain its disc shape, thus becoming a cell with a limited life span. In man, this is about 120-140 days. 

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