Review and Self-Assessment
Which of the following statements regarding erythropoiesis is TRUE?
A. Hypoxia-inducible factor-1α is downregulated in response to hypoxia and results in increased production of erythropoietin.
B. In response to erythropoietin, red blood cell production can increase to by a maximum factor of 2 over a 3–6 day period.
C. Normal red blood cell production results in replacement of approximately 1% of all circulating red blood cells each week.
D. The erythroid precursor, the pronormoblast, can produce 16–32 mature red blood cells.
E. With increased erythropoietin, each progenitor cell is stimulated to produce additional red blood cells.
The answer is D. (Chap. 2) Normal erythropoiesis requires proper erythropoietin (EPO) production, proliferative capacity of the bone marrow, availability of iron and other cofactors, and effective maturation of red blood cell (RBC) precursors. The physiologic regulator of RBC production is EPO, a glycoprotein produced in the peritubular capillary lining cells of the kidney. EPO production and gene regulation is controlled by hypoxia inducible factor-1α, which is upregulated in response to hypoxia. EPO then stimulates the early progenitor cells in the bone marrow to increase in number and, in turn, to produce more RBCs. The first morphologically recognizable RBC precursor is the pronormoblast. This cell divides 4–5 times to generate a total of 16–32 mature RBCs. With EPO stimulation, red cell production increases markedly up to 4–5 fold, reaching maximum capacity within a 1–2 week period. In the absence of EPO, however, erythroid progenitor cells will undergo apoptosis or programmed cell death. Overall, normal red cell production and turnover result in the replacement of 0.8–1.0% of the red cell population on a daily basis.
A 36-year-old woman presents to your office complaining of easy fatigability. She is found to have anemia. On further questioning, she does report heavy menses and has been following a vegetarian diet. Her physical examination is normal with the exception of mildly pale conjunctiva. Her hemoglobin is 9.1 g/dL, hematocrit is 27.6%. The MCV is 65 fL, MCH is 24 pg, and MCHC is 26%. The red cell distribution width is 16.7%. The peripheral blood smear is shown in Figure 2.
FIGURE 2 (From RS Hillman et al: Hematology in Clinical Practice, 5th ed. New York, McGraw-Hill, 2010.)
Which of the following is present on the peripheral blood smear?