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Structure And Function Of Red Blood Cells

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Erythrocyte Definition And Examples

Red blood cells, also called erythrocytes, a cellular component of blood, of which there are millions in the bloodstream of vertebrates that give the blood its characteristic color and carry oxygen from the lungs to the tissues. Mature human red blood cells are small, round, and bispherical; it appears dumbbell-shaped in profile. The cell is flexible and takes on a bell shape as it passes through very small blood vessels. It is covered by a membrane composed of lipids and proteins, lacks a nucleus, and contains hemoglobin—a red iron-rich protein that binds oxygen.

Observe how red blood cells travel from the heart to the lungs and other body tissues to exchange oxygen and carbon dioxide

The role of red blood cells and its hemoglobin is to transport oxygen from the lungs or gills to all body tissues and transport carbon dioxide, a waste product of metabolism, to the lungs where it is excreted. In invertebrates, oxygen-carrying pigment is transported freely in the plasma; its concentration in red blood cells in vertebrates, so that oxygen and carbon dioxide are exchanged as gases, is more efficient and represents an important evolutionary development. The mammalian erythrocyte is further adapted by lacking a nucleus – the amount of oxygen the cell needs for its own metabolism is therefore very small, and most of the oxygen transported into the tissues can be released. The bispherical shape of the cell allows oxygen exchange at a constant rate over the largest possible area.

The red cell develops in the bone marrow in several stages: from a hematopoietic cell, a pluripotent cell in the mesenchyme, it becomes an erythroblast (normoblast); during two to five days of development, the erythrocyte gradually fills with hemoglobin and its nucleus and mitochondria (particles in the cytoplasm that provide the cell with energy) disappear. Late, the cell is called a reticulocyte, which eventually becomes a mature erythrocyte. The average human erythrocyte lives 100–120 days; there are about 5.2 million red blood cells per cubic millimeter of blood in adult humans.

Red Blood Cell

Although erythrocytes are usually round, a small percentage are oval in a normal person, and in certain inherited diseases a higher percentage may be oval. Some diseases also show abnormally shaped erythrocytes – e.g. oval in pernicious anemia, crescentic in sickle cell anemia, and with thorny projections in the inherited disorder acanthocytosis. The number of red blood cells and the amount of hemoglobin varies from person to person and under different conditions; the number is higher, for example, in persons living at high altitudes and in the disease polycythemia. At birth, the red blood cell count is high; it falls shortly after birth and gradually rises to adult levels at puberty. The erythrocyte, commonly known as a red blood cell (or erythrocyte), is by far the most common component: a single drop of blood contains millions of erythrocytes and only thousands of leukocytes (Figure 18.3.1). Specifically, men have about 5.4 million erythrocytes per microliter (

L. In fact, erythrocytes are estimated to make up about 25 percent of the body’s total cells. These are small cells, with an average diameter of 7-8 micrometers (

M). The main function of erythrocytes is to absorb oxygen from the lungs and transport it to the tissues of the body and to absorb carbon dioxide in the tissues and transport it to the lungs. Although leukocytes normally leave the vasculature to carry out their defense functions, the movement of erythrocytes from the vasculature is abnormal.

As an erythrocyte matures in the red bone marrow, it pushes out its nucleus and most other organelles. During the first day or two in circulation, an immature red blood cell, known as a reticulocyte, will still usually contain remnants of organelles. Reticulocytes should be approximately 1–2 percent of the erythrocyte count and provide a rough estimate of the rate of erythrocyte production. Abnormally low or high levels of reticulocytes indicate abnormalities in the production of these red blood cells. These organelles are quickly shed, so circulating erythrocytes have few internal cellular structural components. They lack endoplasmic reticulum and do not synthesize protein.

Red Blood Cell Membranes: Structure, Function, Clinical Implications

The role of erythrocytes in transporting blood gases is enhanced by their structure, such as the lack of organelles, especially mitochondria, their bilobed shape, and the presence of a flexible cytoskeletal protein component called spectrophotons. Since erythrocytes lack mitochondria and must rely on anaerobic metabolism, they use none of the oxygen they transport when returning it to the tissues. Erythrocytes are bispherical discs; that is, they are thick at their edges and very thin in the middle (Figure 18.3.2). Since they lack most organelles, there is more internal space for the presence of the hemoglobin molecules which, as you will soon see, transport gases. The bispherical shape also provides a larger surface area over which gas exchange can occur, relative to its volume; a sphere of similar diameter would have a lower surface-to-volume ratio. In the capillaries, the oxygen carried by the erythrocytes can diffuse into the blood and then through the capillary walls to reach the cells, while some of the carbon dioxide produced by the cells as waste products diffuses into the capillaries to be taken up by the erythrocytes. The capillary beds are very narrow, slowing the passage of red blood cells and providing more opportunity for gas exchange to occur. However, the space within the capillaries can be so small that, despite their small size, red blood cells travel in single file, sometimes collapsing to pass through. Fortunately, their structural proteins like spectrin are flexible, allowing them to fold and then spring back as they move into wider vessels.

Figure 18.3.2 – Shape of red blood cells: Erythrocytes are bispherical discs with a very shallow center. This shape maximizes the surface-to-volume ratio, which facilitates gas exchange. It also allows them to fold as they pass through narrow blood vessels.

Hemoglobin is a large molecule composed of proteins and iron. It consists of four folded chains of the globin protein, called alpha 1 and 2, and beta 1 and 2 (Figure 18.3.3a). Each of these globin molecules is bound to a red pigment molecule called heme, which contains an iron ion (Fe)

Figure 18.3.3 – Hemoglobin: (a) A hemoglobin molecule contains four globin proteins each bound to one molecule of the iron-containing pigment heme. (b) One erythrocyte can contain 300 million hemoglobin molecules and thus more than 1 billion oxygen molecules.

Types Of White Blood Cells And Their Functions

Each iron ion in the heme can bind to one oxygen molecule, therefore each hemoglobin molecule can carry four oxygen molecules. A single red blood cell can contain about 300 million hemoglobin molecules and can bind and transport up to 1.2 billion oxygen molecules.

In the lungs, hemoglobin takes up oxygen, which binds to the iron ions and forms oxyhemoglobin. The bright red, oxygenated hemoglobin travels to the capillaries of the body tissues, where it releases some of its oxygen molecules and becomes the darker red deoxyhemoglobin. Oxygen release depends on the oxygen demand of the surrounding tissues, so hemoglobin rarely leaves all of its oxygen behind. At that time, carbon dioxide (CO

Is bicarbonate ion. About 23–24 percent of it binds to the amino acids in hemoglobin and forms a molecule called carbaminohemoglobin. From the capillaries, hemoglobin carries CO

Changes in the amount of red blood cells can significantly affect the body’s ability to effectively deliver oxygen to the tissues. Overproduction of red blood cells causes a condition called polycythemia. The main drawback of polycythemia is not not delivering enough oxygen to the tissues, but the increased viscosity of the blood, which makes it harder for the heart to circulate the blood. Inefficient hematopoietic hematopoiesis results in an insufficient number of red blood cells and causes one of several forms of anemia. In patients with insufficient hemoglobin, the tissues cannot receive enough oxygen, leading to another form of anemia.

Rna Technology For New Parents: Turning On Fetal Hemoglobin

In determining tissue oxygen consumption, the value of greatest interest in healthcare is relative saturation; it is the percentage of hemoglobin that takes up oxygen in the patient’s blood. Clinically, this value is usually simply called “percent sat.” Percent saturation is usually monitored using a device called a pulse oximeter, which is placed on a thin part of the body, usually the patient’s fingertip. The device works by sending two different wavelengths of light (one red, the other infrared) through the finger and

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