Lec.2:Anemia

Destruction of Red Blood Cells
When red blood cells are delivered from the bone marrow into the circulatory system, they normally circulate an average of 120 days before being destroyed. Even though mature red cells do not have a nucleus, mitochondria, or endoplasmic reticulum, they do have cytoplasmic enzymes that are capable of metabolizing glucose and forming small amounts of adenosine triphosphate. These enzymes also:
(1) maintain pliability of the cell membrane.
(2) maintain membrane transport of ions.
(3) keep the iron of the cells’ hemoglobin in the ferrous form rather than ferric form
(Which causes the formation of methemoglobin that will not carry oxygen)
(4) prevent oxidation of the proteins in the red cells.

Even so, the metabolic systems of old red cells become progressively less active, and the cells become more and more fragile, presumably because their life processes wear out.Once the red cell membrane becomes fragile, the cell ruptures during passage through some tight spot of the circulation. Many of the red cells self-destruct in the spleen, where they squeeze through the red pulp of the spleen. There, the spaces between the structural trabeculae of the red pulp only 3 micrometers wide, in comparison with the 8-micrometer diameter of the red cell.

Destruction of Hemoglobin
When red blood cells burst and release their hemoglobin, the hemoglobin is phagocytized almost immediately by macrophages in many parts of the body, but especially by the Kupffer cells of the liver and macrophages of the spleen and bone marrow. During the next few hours to days, the macrophages release iron from the hemoglobin and pass it back into the blood, to be carried by transferring either to the bone marrow for the production of new red blood cells or to the liver and other tissues for storage in the form of ferritin (figure 1). The porphyrin portion of the hemoglobin molecule is converted by the macrophages, through a series of stages, into the bile pigment bilirubin, which is released into the blood and later removed from the body by secretion through the liver into the bile.