The Erythrocytes "Chapter 5"

List and describe the stages of erythrocyte maturation in the marrow from youngest to most mature cells

Precursor cells in BM that are morphologically identifiable

• Erythroblasts

- Includes all nucleated RBC precursors in BM

- If the maturation sequence is normal, the cells are

often called normoblasts

• Reticulocytes (polychromatophilic R BCs)

- Young RBCs that do not have a nucleus but have

residual RNA

Explain the maturation process of reticulocytes and the cellular changes that take place.

The reticulocyte has an irregular lobulated or puckered shape

following nuclear extrusion

• The cell is remodeled

- Eliminating excess membrane

- Gradually acquires a biconcave disc shape

• Cytoplasm has a bluish tinge

- Due to residual RNA and mitochondria

- Called a polychromatophilic RBC or diffusely basophilic RBC

on Wright's stain

- Remaining 20% of hemoglobin is made during the

reticulocyte stage

Identify the reference interval for reticulocytes.

Explain the function of erythropoietin and include the origin of production, bone marrow effects, and normal values.

•Only cytokine important in regulating the final stages of erythroid maturation

•Androgens have some effect on maturation

-Can stimulate EPO production

-Can directly affect the erythropoietic marrow

•Other hormones

-Thyroid hormone, adrenal cortical hormones, growth hormone, have varying effects on erythropoiesis

Describe the function of the erythrocyte membrane.

•Is essential for erythrocyte development and function

•Erythroblast membrane has receptors for:

-EPO and transferrin (iron transport protein)

•Selectively sequesters vital components

•Allows escape of metabolic waste products

•Regulates metabolism

-Reversibly binding and inactivating many glycolytic enzyme

Define and differentiate intravascular and extravascular red cell destruction.

•Intravascular destruction

-RBC trauma damages red blood cell membrane

▪Results in cell lysis

▪Release of hemoglobin directly into circulation

-10% of RBC destruction

-Plasma proteins, haptoglobin and hemopexin, bind to free hemoglobin and transport to liver for catabolism

•Extravascular destruction

-RBC removal by spleen, bone marrow, and liver

-90% of aged RBC destruction

-Efficient method of cell removal, conserving, and recycling amino acids and iron (essential RBC components)

-Occurs in macrophages of spleen

▪Hypoxic, hypoglycemic environment

-Occurs in macrophages of liver

▪Liver lacks ability to detect minimal defects of RBCs

▪More efficient than spleen in removing RBCs due to more RBC circulation throughput

Summarize the mechanisms involved in the regulation of erythrocyte production

•Body can regulate the number of circulating RBCs by changing the:

-Rate of cell production in the marrow

-Rate of cell release from the marrow

•Rate of RBC release to circulation is balanced to the rate of RBC destruction

•An increase in EPO release occurs

-Impaired O2 delivery to tissues

Low intracellular O2 tension (PO2)