The function of red blood cells turns out to be like this

The red blood cell count is one of the values ​​that people are most concerned about during blood tests, but most people do not fully understand what the role of red blood cells is. In fact, the main function of red blood cells is to transport oxygen and carbon dioxide, so the value of red blood cells is directly related to whether our human body can function normally.

1. The shape and number of red blood cells

Red blood cells are very small, with a diameter of only 7 to 8 μm. They are disc-shaped, concave in the middle and thicker at the edges. It is elastic and plastic, and can change its shape when passing through capillaries with a smaller diameter than itself, and return to its original shape after passing through. The normal morphology of red blood cells is shown in the figure.

Normal mature red blood cells do not have a nucleus, nor do they have organelles such as the Golgi complex and mitochondria, but they still have metabolic functions. Red blood cells are filled with abundant hemoglobin, which accounts for about 32% of the cell weight, water accounts for 64%, and the remaining 4% is lipids, sugars and various dielectrics.

Red blood cells are the most numerous blood cells in the blood, with an average of 5 million/mm3 in adult males and 4.2 million/mm3 in adult females. The number of red blood cells may change with external conditions and age. The rate in plateau residents and newborns can reach over 6 million/mm3. People who engage in sports and exercise regularly also have a higher red blood cell count. The hemoglobin content is 12-15g/100ml for men and 11-13g/100ml for women.

2. Physiological functions of red blood cells

The main function of red blood cells is to transport O2 and CO2. In addition, they also play a certain buffering role in acid-base balance. Both of these functions are accomplished by hemoglobin in red blood cells. If the red blood cells rupture, hemoglobin is released and dissolved in the plasma, thus losing the above functions.

Hemoglobin (Hb) is composed of globin and heme. Blood appears red because it contains heme. When the oxygen partial pressure is high, the Fe2+ in this molecule combines with oxygen to form oxygenated hemoglobin (HbO2); when the oxygen partial pressure is low, it dissociates from oxygen, releasing O2 to become reduced hemoglobin, thereby achieving the function of transporting oxygen (see the respiration chapter). If Fe2+ in hemoglobin is oxidized into Fe3+, it is called methemoglobin, and it loses the ability to carry O2. The affinity of hemoglobin for CO is 210 times greater than that for oxygen. When the concentration of CO in the air increases, hemoglobin combines with CO and loses the ability to transport O2, which can be life-threatening. This is called CO (or coal gas) poisoning. Hemoglobin also plays an important role in the transport of CO2.

3. Physiological characteristics of red blood cells

1. Osmotic fragility (abbreviated as fragility) Under normal conditions, the osmotic pressure inside red blood cells is roughly equal to the osmotic pressure of plasma, which is very important for maintaining the morphology of red blood cells. When the body's red blood cells are placed in an isotonic solution (NaCl/0.9%), they can maintain their normal size and shape. However, if red blood cells are placed in a hypertonic NaCl solution, water will escape from the cells and the red blood cells will shrink due to water loss. On the contrary, if red blood cells are placed in a hypotonic NaCl solution, water enters the cells, the red blood cells swell and become spherical, and may even swell and burst, and hemoglobin is released into the solution, which is called hemolysis.

Normal human red blood cells were placed in solutions of different concentrations (from 0.85%, 0.8%...0.3% NaCl solution). In the 0.45% solution, some of the red blood cells began to rupture, that is, the upper liquid appeared slightly red. When the red blood cells were in 0.35% or lower NaCl solution, all of them ruptured. Clinically, 0.45% NaCl to 0.3% NaCl solution is considered to be the normal range of human red blood cell fragility (also known as resistance). If red blood cells rupture when placed in a solution with a concentration higher than 0.45%, it indicates that the red blood cells are very fragile and have low resistance. On the contrary, if they rupture when placed in a solution with a concentration lower than 0.45%, it indicates that they are less fragile and have high resistance.

2. Suspension stability Suspension stability refers to the property of red blood cells to remain suspended in plasma and not easily sink. Place the blood mixed with the anticoagulant in an erythrocyte sedimentation tube and let it stand vertically. After a certain period of time, the red blood cells will gradually sink due to their specific gravity. The distance that the red blood cells sediment per unit time is called the erythrocyte sedimentation rate (ESR for short). The speed of erythrocyte sedimentation rate is used as a measure of the stability of red blood cell suspension. At the end of the first hour, the ESR of a normal man should not exceed 3mm, and that of a normal woman should not exceed 10mm. ESR may be accelerated during pregnancy, active tuberculosis, rheumatic fever, and in patients with malignant tumors. Clinical examination of erythrocyte sedimentation rate is helpful for the diagnosis and prognosis of diseases.

Regarding the reason for maintaining the stability of red blood cell suspension, some people believe that it is because the surface of red blood cells carries a negative charge. Because like charges repel each other, red blood cells are not easy to aggregate, thus showing better suspension stability. If the positively charged proteins in plasma increase, they will be adsorbed by red blood cells, reducing their surface charge. This will promote the aggregation and stacking of red blood cells, reduce the ratio of total surface area to volume, reduce friction, and accelerate erythrocyte sedimentation rate. The speed of erythrocyte sedimentation rate is mainly related to the type and content of plasma protein.