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. Iron deficiency anemia is the most common type and results when the amount of available iron is insufficient to allow production of sufficient heme. This condition can occur in individuals with a deficiency of iron in the diet and is especially common in teens and children as well as in vegans and vegetarians.
Additionally, iron deficiency anemia may be caused by either an inability to absorb and transport iron or slow, chronic bleeding. Vitamin-deficient anemias generally involve insufficient vitamin B12 and folate. Lack of meat or a viable alternate source, and overcooking or eating insufficient amounts of vegetables may lead to a lack of folate.
Pregnancies, some medications, excessive alcohol consumption, and some diseases such as celiac disease are also associated with vitamin deficiencies. It is essential to provide sufficient folic acid during the early stages of pregnancy to reduce the risk of neurological defects, including spina bifida, a failure of the neural tube to close.
Assorted disease processes can also interfere with the production and formation of RBCs and hemoglobin. If myeloid stem cells are defective or replaced by cancer cells, there will be insufficient quantities of RBCs produced. Aplastic anemia is the condition in which there are deficient numbers of RBC stem cells. Aplastic anemia is often inherited, or it may be triggered by radiation, medication, chemotherapy, or infection. Thalassemia is an inherited condition typically occurring in individuals from the Middle East, the Mediterranean, African, and Southeast Asia, in which maturation of the RBCs does not proceed normally.
Lead exposure from industrial sources or even dust from paint chips of iron-containing paints or pottery that has not been properly glazed may also lead to destruction of the red marrow.
Various disease processes also can lead to anemias. These include chronic kidney diseases often associated with a decreased production of EPO, hypothyroidism, some forms of cancer, lupus, and rheumatoid arthritis.
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.
The breakdown products are recycled or removed as wastes: Globin is broken down into amino acids for synthesis of new proteins; iron is stored in the liver or spleen or used by the bone marrow for production of new erythrocytes; and the remnants of heme are converted into bilirubin, or other waste products that are taken up by the liver and excreted in the bile or removed by the kidneys.
Which of the following statements about mature, circulating erythrocytes is true? A patient has been suffering for 2 months with a chronic, watery diarrhea. A young woman has been experiencing unusually heavy menstrual bleeding for several years. She follows a strict vegan diet no animal foods. She is at risk for what disorder, and why? She is at risk for anemia, because her unusually heavy menstrual bleeding results in excessive loss of erythrocytes each month.
At the same time, her vegan diet means that she does not have dietary sources of heme iron. The non-heme iron she consumes in plant foods is not as well absorbed as heme iron. A patient has thalassemia, a genetic disorder characterized by abnormal synthesis of globin proteins and excessive destruction of erythrocytes. This patient is jaundiced and is found to have an excessive level of bilirubin in his blood.
Explain the connection. Bilirubin is a breakdown product of the non-iron component of heme, which is cleaved from globin when erythrocytes are degraded. Excessive erythrocyte destruction would deposit excessive bilirubin in the blood. Bilirubin is a yellowish pigment, and high blood levels can manifest as yellowed skin. Skip to content The Cardiovascular System: Blood. Learning Objectives By the end of this section, you will be able to: Describe the anatomy of erythrocytes Discuss the various steps in the lifecycle of an erythrocyte Explain the composition and function of hemoglobin.
Summary of Formed Elements in Blood. Erythrocytes are biconcave discs with very shallow centers. This shape optimizes the ratio of surface area to volume, facilitating gas exchange. It also enables them to fold up as they move through narrow blood vessels. Lifecycle of Erythrocytes Production of erythrocytes in the marrow occurs at the staggering rate of more than 2 million cells per second.
However, erythrocyte production also requires several trace elements: Iron. We have said that each heme group in a hemoglobin molecule contains an ion of the trace mineral iron. On average, less than 20 percent of the iron we consume is absorbed.
Heme iron, from animal foods such as meat, poultry, and fish, is absorbed more efficiently than non-heme iron from plant foods. The bone marrow, liver, and spleen can store iron in the protein compounds ferritin and hemosiderin. Ferroportin transports the iron across the intestinal cell plasma membranes and from its storage sites into tissue fluid where it enters the blood.
When EPO stimulates the production of erythrocytes, iron is released from storage, bound to transferrin, and carried to the red marrow where it attaches to erythrocyte precursors. A trace mineral, copper is a component of two plasma proteins, hephaestin and ceruloplasmin. Without these, hemoglobin could not be adequately produced. Located in intestinal villi, hephaestin enables iron to be absorbed by intestinal cells.
Ceruloplasmin transports copper. In a state of copper deficiency, the transport of iron for heme synthesis decreases, and iron can accumulate in tissues, where it can eventually lead to organ damage. The trace mineral zinc functions as a co-enzyme that facilitates the synthesis of the heme portion of hemoglobin.
B vitamins. Thus, both are critical for the synthesis of new cells, including erythrocytes. Hemoglobin that is not phagocytized is broken down in the circulation, releasing alpha and beta chains that are removed from circulation by the kidneys.
The iron contained in the heme portion of hemoglobin may be stored in the liver or spleen, primarily in the form of ferritin or hemosiderin, or carried through the bloodstream by transferrin to the red bone marrow for recycling into new erythrocytes. The non-iron portion of heme is degraded into the waste product biliverdin , a green pigment, and then into another waste product, bilirubin , a yellow pigment. Bilirubin binds to albumin and travels in the blood to the liver, which uses it in the manufacture of bile, a compound released into the intestines to help emulsify dietary fats.
In the large intestine, bacteria breaks the bilirubin apart from the bile and converts it to urobilinogen and then into stercobilin. It is then eliminated from the body in the feces. Broad-spectrum antibiotics typically eliminate these bacteria as well and may alter the color of feces.
The kidneys also remove any circulating bilirubin and other related metabolic byproducts such as urobilins and secrete them into the urine. Erythrocyte Lifecycle. 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. A characteristic change in the shape of erythrocytes is seen in sickle cell disease also referred to as sickle cell anemia. A genetic disorder, it is caused by production of an abnormal type of hemoglobin, called hemoglobin S, which delivers less oxygen to tissues and causes erythrocytes to assume a sickle or crescent shape, especially at low oxygen concentrations Figure.
These abnormally shaped cells can then become lodged in narrow capillaries because they are unable to fold in on themselves to squeeze through, blocking blood flow to tissues and causing a variety of serious problems from painful joints to delayed growth and even blindness and cerebrovascular accidents strokes.
Sickle cell anemia is a genetic condition particularly found in individuals of African descent. Sickle Cells. Sickle cell anemia is caused by a mutation in one of the hemoglobin genes. This reaction is reversible by the same enzyme. Carbonic anhydrase also removes water from carbonic acid to turn it back into carbon dioxide and water.
This process is essential so carbon dioxide can exist as a gas during gas exchange in the alveolar capillaries. As carbon dioxide is converted from its dissolved acid form and exhaled through the lungs, blood pH becomes less acidic. This reaction can occur without the presence of RBCs or carbonic anhydrase, but at a much slower rate. With the catalyst activity of carbonic anhydrase, this reaction is one of the fastest in the human body. Hemoglobin can also bind to carbon dioxide, which creates carbamino-hemoglobin.
However, because of allosteric effects on the hemoglobin molecule, the binding of carbon dioxide decreases the amount of oxygen bound for a given partial pressure of oxygen. Conversely, when the carbon dioxide levels in the blood decrease i.
A reduction in the total binding capacity of hemoglobin to oxygen i. Human erythrocytes are produced through a process called erythropoiesis. They take about seven days to mature. Human erythrocytes are produced through a process called erythropoiesis, developing from committed stem cells to mature erythrocytes in about seven days. When matured, these cells circulate in the blood for about to days, performing their normal function of molecule transport.
At the end of their lifespan, they degrade and are removed from circulation. Scanning electron micrograph of blood cells : Shown on the left, the erythrocyte, or red blood cell, has a round, donut-like shape. Erythropoiesis is the process in which new erythrocytes are produced, which takes about seven days. Erythrocytes are continuously produced in the red bone marrow of large bones at a rate of about 2 million cells per second in a healthy adult.
Erythrocytes differentiate from erythrotropietic bone marrow cells, a type of hemopoietic stem cell found in bone marrow. Unlike mature RBCs, bone marrow cells contain a nucleus. In the embryo, the liver is the main site of red blood cell production and bears similar types of stem cells at this stage of development. Erythropoiesis can be stimulated by the hormone erythropoietin, which is synthesized by the kidney in response to hypoxia systemic oxygen deficiency.
These dietary nutrients that are necessary for proper synthesis of hemoglobin iron and normal RBC development B12 and folic acid.
Just before and after leaving the bone marrow, the developing cells are known as reticulocytes. These immature RBCs that have shed their nuclei following initial differentiation. After 24 hours in the bloodstream, reticulocytes mature into functional RBCs.
Eryptosis, a form of apoptosis programmed cell death , is the aging and death of mature RBCs. As an RBC ages, it undergoes changes in its plasma membrane that make it susceptible to selective recognition by macrophages and subsequent phagocytosis in the reticuloendothelial system spleen, liver, and bone marrow.
This process removes old and defective cells and continually purges the blood. Eryptosis normally occurs at the same rate as erythropoiesis, keeping the total circulating red blood cell count in a state of equilibrium.
Many diseases that involve damage to RBCs hemolytic anemias, sepsis, malaria, pernicious or nutritional anemias or normal cellular processes that cause cellular damage oxidative stress may increase the rate of eryptosis.
Conversely, erythropotein and nitric oxide a vasodilator will inhibit eryptosis. Following eryptosis, the hemoglobin content within the RBC is broken down and recirculated throughout the body. The heme components of hemoglobin are broken down into iron ions and a green bile pigment called biliverdin. The biliverdin is reduced to the yellow bile pigment bilirubin, which is released into the plasma and recirculated to the liver, then bound to albumin and stored in the gallbladder.
The bilirubin is excreted through the digestive system in the form of bile, while some of the iron is released into the plasma to be recirculated back into the bone marrow by a carrier protein called transferrin. This iron is then reused for erythropoiesis, but additional dietary iron is needed to support healthy RBC life cycles. Privacy Policy. Skip to main content. Cardiovascular System: Blood. Search for:. Red Blood Cells. RBC Anatomy Red blood cells lack nuclei and have a biconcave shape. It also facilitates oxygen transport.
Red blood cells are considered cells, but they lack a nucleus, DNA, and organelles like the endoplasmic reticulum or mitochondria. Red blood cells cannot divide or replicate like other bodily cells. They cannot independently synthesize proteins. Each human red blood cell contains approximately million hemoglobin biomolecules, each carrying four heme groups to which oxygen binds.
Key Terms iron : A metallic chemical element with atomic number 26 and symbol Fe. Iron-containing enzymes and proteins, often containing heme prosthetic groups, participate in many biological oxidations and in transport. It consists of a protein globulin and haem a porphyrin ring with an atom of iron at its center.
RBC Physiology The primary functions of red blood cells RBCs include carrying oxygen to all parts of the body, binding to hemoglobin, and removing carbon dioxide. Learning Objectives Discuss the primary function of erythrocytes red blood cells.
Key Takeaways Key Points Red blood cells contain hemoglobin,which contains four iron-binding heme groups. Oxygen binds the heme groups of hemoglobin.
Each hemoglobin molecule can bind four oxygen molecules. The binding affinity of hemoglobin for oxygen is cooperative. It is increased by the oxygen saturation of the molecule.
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