Hematopoiesis

Vocabulary practice flashcards covering cell lineages, morphologic stages, regulatory cytokine networks, and physiological feedback mechanisms in hematopoiesis.

Hematopoiesis

The biological process of producing all cellular blood elements, including erythrocytes (RBCs), platelets, and all leukocytes.

Myelopoiesis

The production and development of non-lymphoid bone marrow or bone marrow-derived blood cells.

Erythropoiesis

The specific lineage process governing the production and maturation of erythrocytes (red blood cells).

Granulopoiesis

The production and maturation of granulocytes, specifically neutrophils, eosinophils, and basophils.

Thrombopoiesis (Megakaryocytopoiesis)

The developmental pathway responsible for the production of megakaryocytes and circulating platelets.

Lymphopoiesis

The production and differentiation of lymphocytes from lymphoid progenitors.

Hematopoietic Stem Cell (HSC)

An undifferentiated cell possessing extensive self-renewal capacity and full developmental potential to differentiate into all mature blood cell lineages.

Hematopoietic Progenitor Cell (HPC)

An immature hematopoietic cell with restricted lineage differentiation potential and limited self-renewal capacity, characterized by extensive proliferative ability and identified primarily by functional or molecular phenotypes rather than morphology.

Precursor Cell

A morphologically recognizable immature blood cell that lacks self-renewal capacity and proliferates and/or differentiates within a single hematopoietic lineage.

General Morphologic Trends of Precursor Maturation

Developmental features seen across bone marrow precursors (except the megakaryocytic lineage): reduction in overall cell and nuclear size, decreased nucleus-to-cytoplasm ($\text{N:C}$) ratio, disappearance of nucleoli, chromatin condensation, decreased cytoplasmic basophilia as RNA decreases, and accumulation of lineage-specific cytoplasmic contents.

Proliferative Pool (Erythropoiesis)

The mitotic bone marrow compartment capable of cell division during erythroid development, comprising rubriblasts, prorubricytes, basophilic rubricytes, and polychromatic rubricytes.

Maturative Pool (Erythropoiesis)

The post-mitotic bone marrow compartment undergoing non-dividing terminal maturation, comprising metarubricytes, reticulocytes (polychromic erythrocytes), and mature erythrocytes.

Prolyl Hydroxylase Domain 2 (PHD2)

An oxygen-dependent hydroxylating enzyme that hydroxylates HIF-$2\alpha$ during normoxia, targeting it for pVHL-complex ubiquitination and proteasomal degradation.

Hypoxia-Inducible Factor $2\alpha$ (HIF-$2\alpha$)

A transcription factor that is stabilized under hypoxic conditions when PHD2 activity drops, binding to the EPO gene promoter with HIF-$1\beta$ to induce erythropoietin transcription.

Erythropoietin (EPO)

A glycoprotein hormone synthesized primarily by renal cortical peritubular interstitial fibroblast-like cells (and secondarily by the liver) in response to hypoxia; stimulates erythroid progenitor proliferation, cellular maturation, hemoglobin synthesis, and reticulocyte release.

Erythroblastic Island

A specialized anatomic bone marrow niche consisting of a central macrophage ("nurse cell") surrounded by developing erythroid precursors that provides support and phagocytoses extruded nuclei.

Red Blood Cell Senescence

The aging process of circulating erythrocytes characterized by accumulated oxidative and membrane damage, vesiculation-mediated surface loss, and decreased deformability, ending in macrophage clearance within the splenic red pulp and liver.

Proliferative Pool (Granulopoiesis)

The division-capable granulocytic precursor compartment in the bone marrow, consisting of myeloblasts, progranulocytes, and myelocytes.

Maturative Pool (Granulopoiesis)

The non-dividing granulocytic compartment undergoing morphological nuclear shaping and functional maturation, comprising metamyelocytes, band neutrophils, and mature segmented neutrophils.

Granulocyte Colony-Stimulating Factor (G-CSF)

The primary glycoprotein cytokine regulating granulopoiesis during steady-state homeostasis and emergency inflammation; produced predominantly by endothelial cells, fibroblasts, and macrophages.

CXCL12-CXCR4 Signaling Axis

A chemokine-receptor interaction between stromal/endothelial CXCL12 and neutrophil CXCR4 that anchors and retains mature and developing neutrophils within the bone marrow.

CXCR2 Ligands

Chemokines including CXCL8 (IL-8), CXCL1, and CXCL2 that bind CXCR2 on neutrophils, counteracting retention signals and promoting neutrophil mobilization across the marrow sinusoid into blood.

Neutrophil Bone Marrow Storage Pool

The reservoir of mature segmented neutrophils stored in the bone marrow prior to vascular release; large in small animals (dogs and cats) and small in large animals (horses and cows).

IL-23 / IL-17 / G-CSF Axis

A negative-feedback regulatory loop of neutrophil production where macrophage efferocytosis of apoptotic neutrophils suppresses IL-23, subsequently reducing IL-17 production by lymphocytes and decreasing stromal/endothelial G-CSF secretion.

CFU-GM

A bipotent committed hematopoietic progenitor cell that serves as the common precursor yielding both neutrophil (CFU-G) and monocyte (CFU-M) lineages.

Monocytopoiesis

The developmental pathway producing monocytes (CFU-M $\rightarrow$ monoblast $\rightarrow$ promonocyte $\rightarrow$ monocyte); it lacks a bone marrow storage pool, meaning cells are released into the blood immediately after production before migrating to tissues as macrophages or histiocytes.

Thrombopoietin (TPO)

A hematopoietic growth factor constitutively synthesized by the liver and kidneys that stimulates megakaryocyte progenitor survival, expansion, and maturation; clearance occurs via binding to platelet and megakaryocyte receptors, creating an inverse relationship between free circulating TPO and platelet mass.

Endomitosis

A specialized cell cycle mechanism in megakaryocyte precursors (megakaryoblast to megakaryocyte) where chromosomal DNA replicates repeatedly without nuclear or cytoplasmic division, resulting in large, polypoid, multinucleated cells.

Proplatelet Extensions

Long cytoplasmic pseudopodia extended by mature megakaryocytes through sinusoidal endothelial apertures into marrow blood sinusoids, which shear under intravascular flow to release platelet fragments.

Thrombocytes (Non-Mammalian)

Small, functional, nucleated hemostatic cells possessing clear cytoplasm and occasional small granules that develop directly within bone marrow vessel sinusoids in birds, reptiles, amphibians, and fish.

Stem Cell Factor (SCF / KIT-Ligand)

A hematopoietic cytokine secreted by fibroblasts and endothelial cells that interacts with the c-KIT receptor on hematopoietic stem cells (HSCs) to promote survival, expansion, and multi-lineage hematopoiesis.

Interleukin-7 (IL-7)

A growth factor synthesized by bone marrow and thymic stromal cells that governs the survival, proliferation, and differentiation of common lymphoid progenitors (CLPs).

Interleukin-5 (IL-5)

A T-cell-derived cytokine that specifically induces the proliferation, differentiation, and survival of eosinophilic precursors during eosinophilopoiesis.