What Is Function Of Red Blood Cells – The erythrocyte, commonly known as a red blood cell (or RBC), is by far the most common formed element: a single drop of blood contains millions of erythrocytes and only thousands of leukocytes. Specifically, men have about 5.4 million erythrocytes per microliter (
L. In fact, erythrocytes are estimated to make up about 25 percent of all cells in the body. As you can imagine, these are quite small cells, with an average diameter of only about 7-8 micrometers (
What Is Function Of Red Blood Cells
M) (Figure 1). The main task of erythrocytes is to collect inhaled oxygen from the lungs and transport it to the tissues of the body, and to collect part (about 24 percent) of carbon dioxide waste from the tissues and transport them to the lungs for exhalation. Erythrocytes remain in the network of blood vessels. Although leukocytes normally leave the blood vessels to perform their protective functions, the movement of erythrocytes out of the blood vessels is abnormal.
The Immunological Functions Of Red Blood Cells
As an erythrocyte matures in the red bone marrow, it expels its nucleus and most of its other organelles. During the first day or two that it is in the bloodstream, an immature erythrocyte, known as a reticulocyte, usually still contains remnants of organelles. Reticulocytes should make up about 1 to 2 percent of the erythrocyte count and provide a rough estimate of the rate of erythrocyte production, with an abnormally low or high rate indicating abnormalities in the production of these cells. However, these remnants, mainly from the ribosome networks (reticulum), are rapidly detached and mature circulating erythrocytes have few intracellular structural components. For example, in the absence of mitochondria, they rely on anaerobic respiration. This means they don’t use transportable oxygen, so they can deliver it all to the tissues. They also lack endoplasmic reticulum and do not synthesize proteins. However, erythrocytes contain some structural proteins that help blood cells maintain their unique structure and allow them to change their shape to squeeze through capillaries. This includes the protein spectrin, a protein element of the cytoskeleton.
Figure 2. Shape of red blood cells Erythrocytes are biconcave discs with very shallow centers. This shape optimizes the surface-to-volume ratio, facilitating gas exchange. It also allows them to fold as they move through narrow blood vessels.
Erythrocytes are biconcave discs; that is, they are plump at their periphery and very thin in the middle (Figure 2). Because they lack most organelles, there is more room for hemoglobin molecules, which, as we will soon see, transport gases. The biconcave shape also provides a larger surface area over which gas exchange can occur relative to its volume; a sphere with a similar diameter would have a lower surface area to volume ratio. In the capillaries, the oxygen carried by the erythrocytes can diffuse into the plasma and then through the capillary walls to reach the cells, while some of the carbon dioxide produced as a waste product in the cells diffuses into the capillaries, where it is taken up by the cells. erythrocytes. Capillary beds are extremely narrow, slowing down the passage of erythrocytes and providing a longer opportunity for gas exchange. However, the capillary space can be so small that, despite their small size, erythrocytes can pack themselves to pass through. Fortunately, their structural proteins, such as spectrin, are flexible, allowing them to bend into place to a surprising degree, only to spring back up again as they enter a wider container. In wider blood vessels, erythrocytes can pile up like a roll of coins, forming a grid, from the French word for “roll”.
Hemoglobin is a large molecule composed of proteins and iron. It consists of four folded protein chains called globins, designated as alpha 1 and 2 and beta 1 and 2 (Figure 3a). Each of these globin molecules is bound to a red pigment molecule called heme, which contains an iron ion (Fe
Blood: Function, What It Is & Why We Need It
Figure 3. (a) The hemoglobin molecule contains four globin proteins, each bound to one molecule of iron-containing pigment heme. (b) A single erythrocyte can contain 300 million molecules of hemoglobin and thus more than 1 billion molecules of oxygen.
Each heme iron ion can bind to one oxygen molecule; therefore, each hemoglobin molecule can transport four oxygen molecules. A single erythrocyte can contain about 300 million hemoglobin molecules and therefore can bind and transport up to 1.2 billion oxygen molecules (see Figure 3b).
In the lungs, hemoglobin picks up oxygen, which binds to iron ions to form oxyhemoglobin. The bright red oxygenated hemoglobin travels to the body’s tissues, where it releases some of its oxygen molecules, becoming the darker red deoxyhemoglobin, sometimes called reduced hemoglobin. The release of oxygen depends on the oxygen demand of the surrounding tissues, so hemoglobin rarely, if ever, gives up all the oxygen. In the capillaries, carbon dioxide enters the bloodstream. About 76 percent dissolves in plasma, some of it remains as dissolved CO
And the rest form the bicarbonate ion. About 23 to 24 percent of this binds to the amino acids of hemoglobin to form a molecule known as carbaminohemoglobin. From the capillaries, hemoglobin carries carbon dioxide back to the lungs, where it releases it for oxygen exchange.
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Changes in red blood cell levels can significantly affect the body’s ability to effectively deliver oxygen to tissues. Inefficient hematopoiesis causes an insufficient number of red blood cells and causes one of several forms of anemia. An overproduction of red blood cells causes a condition called polycythemia. The primary disadvantage of polycythemia is not the inability to deliver enough oxygen directly to the tissues, but rather the increased viscosity of the blood, which makes it difficult for the heart to circulate blood.
In patients with insufficient hemoglobin, tissues may not receive enough oxygen, resulting in another form of anemia. When determining tissue oxygen content, the most interesting value in healthcare is the saturation percentage; it means the percentage of oxygenated hemoglobin points in the patient’s blood. Clinically, this value is usually simply referred to as “percent sitting”.
Percentage saturation is usually monitored with a device known as a pulse oximeter, which is worn on a thin part of the body, usually the patient’s fingertip. The device works by sending two different wavelengths of light (one red, one infrared) through the finger and measuring the light as it exits with a photodetector. Hemoglobin absorbs light differently depending on its oxygen saturation. The machine calibrates the amount of light received by the photodetector and the amount absorbed by the partially oxygenated hemoglobin and reports the data as a percentage of saturation. Normal pulse oximeter readings are between 95 and 100 percent. Lower percentages indicate hypoxemia, or low blood oxygen. The term hypoxia is more general and simply refers to low oxygen levels. Oxygen levels are also monitored directly from the free oxygen in the plasma, usually after the arterial stick. When applying this method, the amount of oxygen present is expressed as the partial pressure of oxygen, or simply pO
The kidneys filter about 180 liters (~380 pints) of blood each day in the average adult, or about 20 percent of the total resting volume, and are thus ideal sites for receptors that determine oxygen saturation. In response to hypoxemia, less oxygen leaves the blood vessels supplying the kidneys, resulting in hypoxia (low oxygen concentration) in the renal tissue fluid, where the oxygen concentration is actually monitored. Interstitial fibroblasts in the kidney secrete EPO, thereby increasing red blood cell production and restoring oxygen levels. In a classic negative feedback loop, as oxygen saturation increases, EPO secretion decreases and vice versa, thereby maintaining homeostasis. Populations living at high altitudes, where the oxygen content of the atmosphere is inherently lower, naturally maintain a higher hematocrit than people living at sea level. Consequently, people traveling to high altitudes may experience symptoms of hypoxemia, such as fatigue, headache, and shortness of breath, within days of arrival. In response to hypoxemia, the kidneys secrete EPO to boost erythrocyte production until homeostasis is restored. To avoid symptoms of hypoxemia or altitude sickness, climbers usually rest for several days to a week or more at camps at progressively higher altitudes to allow EPO levels and, consequently, erythrocyte counts to rise. When climbing the highest peaks, such as Everest and K2 in the Himalayas, many climbers rely on bottled oxygen near the summit.
Blood Components (9.6.1)
The production of erythrocytes in the bone marrow occurs at an astonishing rate of over 2 million cells per second. For such production to take place, there must be a sufficient amount of raw materials. These include the same nutrients that are essential for the production and maintenance of any cell, such as glucose, lipids, and amino acids. However, the production of erythrocytes also requires several trace elements:
Erythrocytes live in the bloodstream for up to 120 days, after which the spent cells are removed by a type of myeloid phagocyte.
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