Erythrocytes: Erythrocytes, also known as red blood cells, are the most numerous blood cell component, and the hemoglobin in red blood cells makes our blood red. Microscopically, erythrocytes are 6-9.5 μm in diameter, with an average of 7.2 μm, and are biconcave and disc-shaped, with a thinner center (1.0 μm) and thicker circumference (2.0 μm), so they show lighter central staining and darker circumference in blood smear specimens, without nuclei. This morphology of red blood cells gives it a large surface area, thus maximizing its ability to adapt to its function DD carry O2 and CO2. fresh single red blood cells are yellow-green, a large number of red blood cells make the blood scarlet, and multiple red blood cells are often stacked together in a string of money, called red blood cell cord. Mature red blood cells do not have a nucleus. Mature red blood cells have no nucleus and no organelles, and the cytoplasm is filled with hemoglobin. Hemoglobin is an iron-containing protein that accounts for about 33% of the weight of red blood cells. When blood flows through the lungs, the partial pressure of O2 in the lungs is high and the partial pressure of CO2 is low, so hemoglobin releases CO2 and combines with O2; when blood flows through the tissues of other organs, because the partial pressure of CO2 is high and the partial pressure of O2 is low, red blood cells release O2 and combine with CO2. Because hemoglobin has this property, red blood cells can supply the O2 needed by tissues and cells throughout the body and carry away some of the CO2 produced. The average number of red blood cells per microliter of blood in a normal adult is about 4-5 million for men and 3.5-4.5 million for women. The hemoglobin content per 100 ml of blood is about 12-15 g for men and 10.5-13.5 g for women, and the total surface area of all red blood cells in the body is equivalent to 2000 times the surface area of the human body. The number of red blood cells and the content of hemoglobin can change physiologically, for example, babies are higher than adults, more often during exercise than in a quiet state, and residents of highland areas are mostly higher than residents of plain areas. In general, anemia is defined as a condition in which the number of red blood cells is less than 3 million/μ1 and the hemoglobin is less than 10g/100ml. This is often accompanied by changes in the diameter and morphology of red blood cells, such as an average diameter of red blood cells >9μm in macrocytic anemia and <6μm in microcytic anemia. in iron deficiency anemia, the central lightly stained area is significantly enlarged due to a significant decrease in the content of hemoglobin. The cell membrane of erythrocytes, in addition to the common characteristics of general cell membranes, has its own special features, such as the presence of ABO blood group antigens on the erythrocyte membrane. In addition to a large number of mature erythrocytes in the peripheral blood, there are a small number of not fully mature erythrocytes, called reticulocytes in adults about 0.5%-1.5% of the total number of red blood cells, more in newborns, up to 3%-6%. The diameter of reticulocytes is slightly larger than that of mature erythrocytes, and cannot be distinguished from mature erythrocytes in the routine staining of blood smears. In vitro staining with Brilliant Blue, the cytoplasm of reticulocytes can be seen to have a fine network or granules stained blue, which is the intracellular residual ribosomes. The presence of ribosomes indicates that reticulocytes still have some function of synthesizing hemoglobin. When the erythrocytes are fully mature, the ribosomes disappear and the amount of hemoglobin no longer increases. In anemic patients with good hematopoiesis, the percentage of reticulocytes in their blood is increased. Therefore, the count of reticulocytes has some clinical significance, and it is one of the indicators for diagnosis, efficacy judgment and estimation of prognosis of certain blood diseases such as anemia. The average life span of red blood cells is about 120 days. Although aging erythrocytes do not have morphological peculiarities, they have changes in their functional activities and physicochemical properties, such as reduced enzyme activity, hemoglobin degeneration, increased cell membrane fragility, and changes in surface charge, thus reducing their ability to bind oxygen and breaking easily. Senescent erythrocytes are mostly engulfed by macrophages in the spleen, bone marrow and liver, while the same number of erythrocytes are produced and released by the red bone marrow into the peripheral blood to maintain a relatively constant number of erythrocytes.