Lecture 2 1/22/24 Flashcards
What is hematopoiesis?
the formation of blood cellular components
Which components are involved in hematopoiesis?
-stem cells
-cytokines
Where does hematopoiesis primarily occur in mammals?
bone marrow
What is extramedullary hematopoiesis?
hematopoiesis occurring outside the bone marrow (liver, spleen, lymph nodes) when there is an increased need for cellular blood components
What are the characteristics of hematopoietic stem cells?
-mononuclear cells
-long-term self-renewal
-differentiate/commit to cell lines
What are the two types of hematopoietic stem cell lines?
-lymphoid
-myeloid
Which cell types arise from the lymphoid lineage?
-B cells
-T cells
-NK cells
What is the erythron?
total amount of RBCs in the body
What are the three pools that make up the erythron?
-marrow
-blood
-spleen
What are the cellular steps of RBC maturation?
-rubriblast
-prorubricyte
-rubricyte
-metarubricyte
-reticulocyte
-erythrocyte
What happens during RBC maturation?
-decrease in cell size
-decrease in nucleus size
-compaction of chromatin
-cytoplasmic color change
How are old erythrocytes removed from circulation?
phagocytosis via macrophages
During which step of RBC maturation is the nucleus extruded?
metarubricyte to reticulocyte
Which cell type is the best indicator of regeneration?
reticulocytes
Which species does not have reticulocytes?
horses
What is the cycle involving erythropoietin?
-renal hypoxia stimulates the kidneys to produce erythropoietin
-increased erythropoietin levels stimulate increased RBC production
-result is erythroid hyperplasia
What are the three causes of renal hypoxia?
-anemia
-poor oxygenation of blood
-poor renal perfusion
How are RBCs broken down extravascularly?
-macrophages phagocytose old RBCs
-RBCs are broken down in the lysosome to produce heme, amino acids, and porphyrin
What are the potential fates of heme?
-storage via hemosiderin
-transfer to the bone marrow for erythropoiesis via apotransferrin and transferrin
What is the fate of porphyrin?
-converted into biliverdin and eventually unconjugated bilirubin
-sent to the liver for conjugation and bile formation
What happens to bile/conjugated bilirubin?
-excreted into the intestine
-converted into urobilinogen
What are the fates of urobilinogen?
-excreted in urine
-recirculated to the liver
-converted to stercobilinogen
What are the characteristics of thrombopoiesis?
-formation of platelets from megakaryocytes
-platelets delivered into circulation
-mediated by thrombopoietin
Which tissues constantly produce thrombopoietin (TPO)?
-hepatocytes
-renal epithelium
-stromal cells in bone marrow
