The Human Body

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Age-related Hematologic Changes

The percentage of marrow space occupied by hematopoietic tissue varies throughout iife, declining progressively from birth until about age 30, when it levels off.

After about age 70, it again declines progressively. Whether this second decline results from a real reduction in blood-forming elements or a relative reduction caused by an increase in bone marrow fat is not known.

The following age-related changes occur in marrow function:

(1) Marrow from older people can be maintained by serial transplantation in tissue culture just as long as marrow from younger people, but the number of stem cells in marrow decreases significantly with age.

(2) Incorporation of iron in marrow culture from older people is comparable to that from younger people, but it increases less with erythropoietin stimulation.

(3) Healthy older animals are unable to respond to bleeding or hypoxia as efficiently as younger animals because of in
effective erythropoietic, but whether the defect lies with the hematopoietic elements, a decrease in growth factors, or age-related architectural changes in the marrow is unclear.

(4) Although iron uptake from the intestines is normal in the elderly, slowed erythropoiesis reduces incorporation of iron into RBCs.

These changes in marrow function are not secondary to nutritional deficiencies since both total body and bone marrow iron increase with age, and both folate and vitamin B12 levels in healthy elderly people remain in the normal range.

Age-related changes in the peripheral blood include the following:
(I) Average values of hemoglobin and hematocrit decrease slightly with age but remain within the normal adult range.

(2) Mean corpuscular volume increases slightly with age, but RBC morphologic characteristics do not change significantly.

(3) RBC content of 2,3-diphospho-glycerate decreases with age.

(4) RBC osmotic fragility increases with age.

Factors that do not change with age include RBC life span, total blood volume, RBC volume, and platelet morphologic characteristics. Whether certain other factors change with age is uncertain: Lymphocyte and granulocyte counts have been reported as either normal or slightly decreased; platelet counts have been reported as either normal or slightly increased; and platelet function in healthy older people has been reported as normal, decreased, or increased.

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