hema lec rbc production prelim

Erythrocyte

The mature red blood cell; carries oxygen from lungs to tissues (primary function) and returns carbon dioxide to the lungs while buffering blood pH (secondary function).

Erythroblasts

The formal term for any nucleated erythroid precursor located in the bone marrow.

Normoblasts

Developing nucleated erythroid precursors in the bone marrow that exhibit a normal morphological appearance.

BFU-E

The earliest committed erythroid progenitor stage; takes exactly 1 week to mature to the CFU-E stage.

CFU-E

The late erythroid progenitor stage; takes 1 week to mature to a pronormoblast and completes 3 to 5 divisions before maturing further.

Pronormoblast

The earliest morphologically recognizable nucleated erythroid precursor; expresses the Fas death receptor.

Basophilic Normoblast

The second normoblastic maturation stage; characterized by active hemoglobin synthesis and intensely basophilic cytoplasm.

Polychromatophilic Normoblast

The third normoblastic maturation stage; the cytoplasm begins showing a gray-pink color as hemoglobin production increases.

Orthochromic Normoblast

The fourth normoblastic maturation stage; the stage at which enucleation (nuclear expulsion) occurs.

Reticulocyte

A young, non-nucleated erythrocyte containing residual RNA and protein production machinery, giving it a bluish tinge on Romanowsky stains.

Erythron

The total collection of all erythrocyte stages throughout the body, including developing marrow precursors and circulating mature cells in peripheral blood and organs.

Erythropoietin

The major stimulatory cytokine and true hormone produced by renal peritubular interstitial cells in response to tissue hypoxia.

Fas

The death receptor expressed on early, immature erythroid precursors that triggers apoptosis when EPO levels are low.

FasL

The death receptor ligand expressed on older, more mature erythroid precursors that cross-links with Fas-bearing younger precursors to trigger apoptosis.

EPO Rescue

The protective mechanism where EPO binds to receptors on young precursors to activate antiapoptotic molecules, allowing them to survive and mature.

Shift Reticulocytes

Larger, bluish-tinged reticulocytes released early from the marrow that skip a division and achieve hemoglobin concentration in 2 instead of 3 divisions.

20% reduction

The cell-cycle shortening effect (equivalent to 1 day) exerted by erythropoietin on marrow transit time.

5 to 30 mU/mL

The normal reference range for plasma erythropoietin concentration.

Testosterone

The hormone that directly stimulates and increases erythropoiesis.

Thyroid hormone

A hormone whose reduction slows down metabolism and decreases the overall rate of erythropoiesis.

Marrow microenvironment

The specialized anatomical area close to the venous sinuses where erythroid precursors grow and mature.

Erythroid Islands

Specialized bone marrow niches close to venous sinuses consisting of central macrophages surrounded by developing erythroid precursors.

"Suckling pig" phenomenon

The characteristic physical arrangement of an erythroid island featuring a central macrophage acting as an anchor surrounded by precursors.

Anchoring system

The bone marrow apparatus keeping precursors in place, consisting of a stable matrix of stromal cells, bridging molecules, and membrane receptors.

Stable matrix of stromal cells

The first component of the marrow anchoring system to which developing normoblasts attach.

Bridging molecules

The second component of the marrow anchoring system that physically links normoblasts to the matrix.

Receptors on the erythrocyte membrane

The third component of the marrow anchoring system located on the outer surface of the precursor cell.

Macrophage

The central cell in an erythroid island that acts as both the major physical and biochemical anchor for developing red blood cells.

Fibronectin

The major bridging or adhesive molecule responsible for anchoring developing normoblasts to the marrow matrix.

Receptor downregulation

The process by which mature RBCs cease production of adhesive membrane receptors so they can detach from fibronectin and exit the bone marrow.

Venous sinuses

The specialized blood vessels in the bone marrow through which mature RBCs pass to enter peripheral circulation.