Other components, such as the heme groups, are broken down into bilirubin, transported to the liver, and secreted with the bile into the intestine for eventual elimination from the body. Hemoglobin deficiency may be a result of structural abnormality in the hemoglobin molecules themselves.
In sickle cell disease , this structural abnormality creates malformed red blood cells which clog blood vessels, severely restricting the supply of blood flowing to body tissues. The Columbia Electronic Encyclopedia, 6th ed. All rights reserved.
These include the same nutrients that are essential to the production and maintenance of any cell, such as glucose, lipids, and amino acids. However, erythrocyte production also requires several trace elements:.
Erythrocytes live up to days in the circulation, after which the worn-out cells are removed by a type of myeloid phagocytic cell called a macrophage , located primarily within the bone marrow, liver, and spleen. The breakdown pigments formed from the destruction of hemoglobin can be seen in a variety of situations. At the site of an injury, biliverdin from damaged RBCs produces some of the dramatic colors associated with bruising. With a failing liver, bilirubin cannot be removed effectively from circulation and causes the body to assume a yellowish tinge associated with jaundice.
Stercobilins within the feces produce the typical brown color associated with this waste. And the yellow of urine is associated with the urobilins. Figure 4. Erythrocytes are produced in the bone marrow and sent into the circulation. At the end of their lifecycle, they are destroyed by macrophages, and their components are recycled. When the number of RBCs or hemoglobin is deficient, the general condition is called anemia.
There are more than types of anemia and more than 3. Anemia can be broken down into three major groups: those caused by blood loss, those caused by faulty or decreased RBC production, and those caused by excessive destruction of RBCs. Clinicians often use two groupings in diagnosis: The kinetic approach focuses on evaluating the production, destruction, and removal of RBCs, whereas the morphological approach examines the RBCs themselves, paying particular emphasis to their size.
A common test is the mean corpuscle volume MCV , which measures size. Normal-sized cells are referred to as normocytic, smaller-than-normal cells are referred to as microcytic, and larger-than-normal cells are referred to as macrocytic. Reticulocyte counts are also important and may reveal inadequate production of RBCs.
The effects of the various anemias are widespread, because reduced numbers of RBCs or hemoglobin will result in lower levels of oxygen being delivered to body tissues. Since oxygen is required for tissue functioning, anemia produces fatigue, lethargy, and an increased risk for infection. An oxygen deficit in the brain impairs the ability to think clearly, and may prompt headaches and irritability.
Lack of oxygen leaves the patient short of breath, even as the heart and lungs work harder in response to the deficit. Blood loss anemias are fairly straightforward. In addition to bleeding from wounds or other lesions, these forms of anemia may be due to ulcers, hemorrhoids, inflammation of the stomach gastritis , and some cancers of the gastrointestinal tract.
The excessive use of aspirin or other nonsteroidal anti-inflammatory drugs such as ibuprofen can trigger ulceration and gastritis. Excessive menstruation and loss of blood during childbirth are also potential causes. Anemias caused by faulty or decreased RBC production include sickle cell anemia, iron deficiency anemia, vitamin deficiency anemia, and diseases of the bone marrow and stem cells. Figure 5. Sickle Cells Sickle cell anemia is caused by a mutation in one of the hemoglobin genes.
Erythrocytes produce an abnormal type of hemoglobin, which causes the cell to take on a sickle or crescent shape. It can occur transiently in a person who is dehydrated; when water intake is inadequate or water losses are excessive, the plasma volume falls.
As a result, the hematocrit rises. For reasons mentioned earlier, a mild form of polycythemia is chronic but normal in people living at high altitudes. Some elite athletes train at high elevations specifically to induce this phenomenon. Polycythemia vera can dangerously elevate the viscosity of blood, raising blood pressure and making it more difficult for the heart to pump blood throughout the body.
It is a relatively rare disease that occurs more often in men than women, and is more likely to be present in elderly patients those over 60 years of age. The most abundant formed elements in blood, erythrocytes are red, biconcave disks packed with an oxygen-carrying compound called hemoglobin.
The hemoglobin molecule contains four globin proteins bound to a pigment molecule called heme, which contains an ion of iron. In the bloodstream, iron picks up oxygen in the lungs and drops it off in the tissues; the amino acids in hemoglobin then transport carbon dioxide from the tissues back to the lungs.
Erythrocytes live only days on average, and thus must be continually replaced. Worn-out erythrocytes are phagocytized by macrophages and their hemoglobin is broken down. Gas Exchange 5. Homeostasis Higher Level 7: Nucleic Acids 1.
DNA Structure 2. Transcription 3. Translation 8: Metabolism 1. Metabolism 2. Cell Respiration 3. Photosynthesis 9: Plant Biology 1.
Xylem Transport 2. Phloem Transport 3. Plant Growth 4. Plant Reproduction Genetics 1. Meiosis 2. Inheritance 3. Speciation Animal Physiology 1. Antibody Production 2. Movement 3.
0コメント