What is hematopoiesis (def)? Characteristics?
Process of formation, development and differentiation of formed elements of blood
- Very dynamic process
- Highly regulated to maintain normal function
- Hierarchal system
Three basic hematopoietic organs? Time frame?
Yolk sac: 16 days (blood islands)
Liver: 6 weeks (also placenta)
Bone marrow: 5 months
What organ(s) is/are responsible for postnatal hematopoiesis?
- Bone marrow
What organ is responsible for T-cell development?
At what age does this start?
Thymus: 7-8 weeks
When does aortogonadomesonephros form?
Developmental hematopoiesis process (figure)?
What is the basic hierarchy of hematopoietic stem cells (HSCs)?
Hematopoietic stem cell
- Lymphoid progenitors -> T cells, B cells, NK cells, dendritic cells
- Myeloid progenitors -> RBCs, Megakaryocytes/platelets, Monocytes/macrophages, Granulocytes
Hematopoiesis chart (figure)
What are hematopoietic stem cells (HSCs) broadly? Cell markers?
Rare cells that are indistinguishable morphologically from lymphocytes
- Express certain cell markers, such as CD34 and have other characteristics that identify/separate them
Characteristics of HSCs?
- Multipotential; giving rise to all other hematopoietic cells
- Self-renewal: thereby able to maintain HSC numbers
- Quiescent: only dividing every few months (thought to be promoted by niche factors within bone marrow; protective against transformation and cancer development)
What are hematopoietic progenitor cells?
Especially in regard to HSCs?
More differentiated than HSCs
- Not multipotent
- No capacity for self-renewal
Have increased proliferative capacity
Have surface expression of specific receptors for hematopoietic growth factors
Divided into common myeloid progenitors and common lymphoid progenitors
What is myelopoiesis?
Refers to production of myeloid elements
Controlled by several growth factors, some of which affect multi-lineage, while others are restricted to one line:
- Erythropoeisis: Erythropoietin
- Platelet production: thrombopoietin
- Granulocyte production: granulocyte colony stimulating factor
Growth factors are used in many clinical settings
What is Lymphopoiesis: B cell differentiation (chart)?
What is Lymphopoiesis: T cell differentiation (chart)?
[typo in pic- should have opposite CD markers)
Where does hematopoiesis occur?
Special micro-environment of the bone marrow stroma
- Matrix includes: endothelial cells, adipose cells, macrophages, fibroblasts, and ECM proteins
Where/how does stem cell trafficking occur?
Out of (mobilization) or into (homing) the matrix under influences of specific cytokines