RED BLOOD CELLS

 

RED BLOOD CELLS

Red blood cell are also called red blood corpuscles,  haematids, erythroid cells or erythrocytes .It is the most abundant cellular component of blood which helps to carry oxygen from the lungs to the tissues. The mature human red blood cell is small, round and biconcave. It appears dumbbell-shaped. The cell is flexible and assumes a bell shape as it passes through extremely small blood vessels. It is covered with a membrane composed of lipids and proteins and contains hemoglobin—a red iron-rich protein. The cells develop in the bone marrow and circulate for about 100–120 days in the body before their components are recycled by macrophages. Red cells contain a special protein called hemoglobin, which helps carry oxygen from the lungs to the rest of the body and then returns carbon dioxide from the body to the lungs so it can be exhaled. Blood appears red because of the large number of red blood cells, which get their color from the hemoglobin. Mature red blood cells do not contain a nucleus, mitochondria, or ribosome’s. The absence of these cell structures leaves a space for the millions of hemoglobin molecules found in red blood cells. A mutation in the hemoglobin gene can result in the development of sickle-shaped cells and lead to sickle cell disorder.

 

FUNCTIONS OF RED BLOOD CELLS-

*Transport hemoglobin (Hb), the oxygen carrier from lungs to tissues.

*Consist of the enzyme carbonic anhydrase which catalyzes the reaction CO2 + H20= H2CO3. This catalytic effect is essential for the transport of CO2 in the form of HCO3- (bicarbonate ion) in the blood, which is taken from tissues to lungs where it is reconverted by alveolar carbonic anhydrase to CO2 that will be excreted.

*Hemoglobin gives RBCs a strong acid-base buffer (responsible for most of buffering power in blood – HHb).

*RBCs give blood its viscosity.

 Red Blood Cell Production

Red blood cells are derived from stem cells in red bone marrow. New red blood cell production, also called erythropoiesis, is triggered by low levels of oxygen in the blood. Low oxygen levels can occur for various reasons including blood loss, presence in high altitude, exercise, bone marrow damage, and low hemoglobin levels.

When the kidneys detect low oxygen levels, they produce and release a hormone called erythropoietin. Erythropoietin stimulates the production of red blood cells by red bone marrow. As more red blood cells enter blood circulation, oxygen levels in the blood and tissues increase. When the kidneys sense the increase in oxygen levels in the blood, they slow the release of erythropoietin. As a result, red blood cell production decreases.

Life cycle of erythrocytes

Erythropoiesis

The life cycle of erythrocytes involves three stages; production, maturity and destruction. Production of erythrocytes (erythropoiesis) is one of the sub-processes of hematopoiesis, happening in red bone marrow. 

In Early phases of hematopoiesis result in the creation of an erythroid stem cell, called CFU-E (Colony Forming Unit - Erythroid). This is the beginning of erythropoiesis, a process driven forward by the hormone erythropoietin. CFU-E cells are found within erythroid cell in the bone marrow, where they replicate and differentiate towards mature erythrocytes. The differentiation process produces several generations of cells; proerythroblasts, erythroblasts, reticulocytes and erythrocytes.

Erythrocyte destruction

 The cell membrane of erythrocytes gets damaged. Macrophages recognize this morphological blueprint of an old or unfeasible erythrocyte and phagocytose it. The primary site of erythrocyte clearance, called eryptosis, is the spleen. In a healthy organism, eryptosis is in balance with erythropoiesis, ensuring a physiological amount of RBCs.

Disorder of erythrocytes

Erythrocytes disorder includes anemia and polycythemia.

Types of Anemia

Iron-deficiency anemia

To make red blood cells, iron is required. However a low intake of iron and a substantial loss of blood can cause iron-deficiency anemia; where the body isn’t making enough red blood cells.

This is the most common type of anemia especially as there are more people controlling what they eat so could be starving the body of iron.

 Sickle cell anemia

 Sickle Cell is an inherited disease where the red blood cells are shaped like Cs instead of their normal circular shape. This makes the cells sticky and causes blood flow problems, which can result in blockages. Furthermore, the blockages can then lead on to chronic pain and organ damage. The sickle cells also have a shorter lifespan than normal red blood cells surviving only 10 to 20 days rather than 120 days, this then causes a shortage of blood cells overall.

 Normocytic anemia

 Your body needs to produce enough red blood cells for the body to function normally, if the body is not producing enough cells this is known as Normocytic Anemia.

This type of anemia is usually caused by long-term conditions such as kidney disease, rheumatoid arthritis and cancer.

 Haemolytic anemia

 In some cases, the body can destroy red blood cells due to an abnormality, this means the body does not have enough red blood cells to function and the bone marrow can’t keep up with the demand for more cells.

 Fanconi anemia

 Another inherited disorder, this type of Aplastic anemia is when the bone marrow cannot make red blood cells. In children this can be very dangerous as it stunts growth and can lead to serious conditions such as leukemia.

 Pernicious anemia

 Also known as B12 deficiency, is when the body is not absorbing enough B12 vitamins. This can be caused by a weakened stomach lining or by an autoimmune condition. If not managed Pernicious anemia can result in nerve damage.

 Thalassemia

Another genetic forms of anemia, but mainly affects those of Mediterranean, South Asian and Middle Eastern descent. This condition causes the body to produce little to no haemoglobin, which is needed by red blood cells to carry oxygen.