Blood carries various substances that must be brought to one part of the body or another. Red blood cells are an important element of blood. Their job is to transport oxygen to the body’s tissues in exchange for carbon dioxide, which is carried to and eliminated by the lungs.
Red blood cells are formed in the red bone marrow of bones. Stem cells in the red bone marrow called hemocytoblasts give rise to all of the formed elements in blood. If a hemocytoblast commits to becoming a cell called a proerythroblast, it will develop into a new red blood cell.
The formation of a red blood cell from hemocytoblast takes about 2 days. The body makes about two million red blood cells every second.
Blood is made up of both cellular and liquid components. If a sample of blood is spun in a centrifuge, the formed elements and fluid matrix of blood can be separated from each other. Blood consists of 45% red blood cells, less than 1% white blood cells and platelets, and 55% plasma.
Red blood cells (RBCs), also called erythrocytes, are the most common type of blood cell and the vertebrate organism's principal means of delivering oxygen (O2) to the body tissues—via blood flow through the circulatory system. RBCs take up oxygen in the lungs or gills and release it into tissues while squeezing through the body's capillaries.
The cytoplasm of erythrocytes is rich in hemoglobin, an iron-containing biomolecule that can bind oxygen and is responsible for the red color of the cells. The cell membrane is composed of proteins and lipids, and this structure provides properties essential for physiological cell function such as deformability and stability while traversing the circulatory system and specifically the capillary network.
In humans, mature red blood cells are flexible and oval biconcave disks. They lack a cell nucleus and most organelles, in order to accommodate maximum space for haemoglobin; they can be viewed as sacks of haemoglobin, with a plasma membrane as the sack. Approximately 2.4 million new erythrocytes are produced per second in human adults. The cells develop in the bone marrow and circulate for about 100–120 days in the body before their components are recycled by macrophages. Each circulation takes about 20 seconds. Approximately a quarter of the cells in the human body are red blood cells. Nearly half of the blood's volume (40% to 45%) is red blood cells.
Red blood cells are also known as RBCs, red cells, red blood corpuscles, haematids, erythroid cells or erythrocytes (from Greek erythros for "red" and kytos for "hollow vessel", with -cyte translated as "cell" in modern usage). Packed red blood cells (pRBC) are red blood cells that have been donated, processed, and stored in a blood bank for blood transfusion.
Erythropoiesis (from Greek 'erythro' meaning "red" and 'poiesis' meaning "to make") is the process which produces red blood cells (erythrocytes). In postnatal birds and mammals (including humans), this usually occurs within the red bone marrow. In the early fetus, erythropoiesis takes place in the mesodermal cells of the yolk sac. By the third or fourth month, erythropoiesis moves to the liver. After seven months, erythropoiesis occurs in the bone marrow. Increased level of physical activity can cause an increase in erythropoiesis. However, in humans with certain diseases and in some animals, erythropoiesis also occurs outside the bone marrow, within the spleen or liver. This is termed extramedullary erythropoiesis. Whole blood contains red cells, white cells, and platelets (~45% of volume) suspended in plasma (~55% of volume).
Red cells
Red cells, or erythrocytes, carry oxygen from the lungs to your body’s tissue and take carbon dioxide back to your lungs to be exhaled.
Platelets
Platelets, or thrombocytes, are small, colourless cell fragments in the blood whose main function is to interact with clotting proteins to stop or prevent bleeding.
Plasma
Plasma is a fluid, composed of about 92% water, 7% vital proteins such as albumin, gamma globulin, anti-hemophilic factor, and other clotting factors, and 1% mineral salts, sugars, fats, hormones and vitamins.
In the process of red blood corpuscle maturation, a cell undergoes a series of differentiations. The following stages of development all occur within the bone marrow: A Hemocytoblast, a multipotent hematopoietic stem cell, becomes
a common myeloid progenitor or a multipotent stem cell, and then
a unipotent stem cell, then
a pronormoblast, also commonly called an proerythroblast or a rubriblast.
This becomes a basophilic or early normoblast, also commonly called an erythroblast, then
a polychromatophilic or intermediate normoblast, then
an orthochromatic or late normoblast. At this stage the nucleus is expelled before the cell becomes
a reticulocyte.
