Effects of Aging on the Blood

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Chapter: Anatomy and Physiology for Health Professionals: Blood

Blood cells form early in fetal development in the yolk sac, spleen, liver, and many other sites.


Effects of Aging on the Blood

Blood cells form early in fetal development in the yolk sac, spleen, liver, and many other sites. By the seventh month, the red marrow is the main hematopoietic area, unless there is serious illness and it will remain throughout life. When the need for blood cell produc-tion is severe, the spleen and liver can resume their fetal blood-formation activities. When needed, the inactive yellow bone marrow, which is basically fatty tissue, can convert back into active red marrow. Blood cells normally develop from mesenchymal “blood islands,” which are cells from the mesoderm germ layer. Fetal hemoglobin F has a higher oxygen affinity than adult hemoglobin A. Per globin molecule, hemoglobin F hastwo alpha and two gamma polypeptide chains, instead of the paired alpha and beta chains of hemoglobin A. Following birth, the liver quickly destroys the eryth-rocytes that carry hemoglobin F, and the erythroblasts start to produce hemoglobin A.

Aging can cause a variety of changes to the blood, including decreased hematocrit levels, increased risk of thrombi, and pooling of blood in the legs. A thrombus is a stationary blood clot that can detach, pass through the heart, and lodge in a small artery. This usually occurs in the lungs, causing a pulmonary embolism. When blood pools in the legs, it is usu-ally because the valves of the leg veins are no longer working normally. The most common blood diseases linked to aging are anemias, clotting disorders, and chronic leukemias. However, most age-related blood disorders are caused by disorders of the blood vessels, heart, or immune system. Increased likelihood of leu-kemia in old age is linked to reduce immune system function. Atherosclerosis is responsible for the forma-tion of abnormal thrombi and emboli.

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