Overview
This lecture explains hematopoiesis, the process of blood cell formation in the bone marrow, and the differentiation pathways of blood cells from hematopoietic stem cells into myeloid and lymphoid lineages.
Hematopoiesis Basics
- Hematopoiesis is the formation of new blood cells in the body.
- All blood cells are produced in the bone marrow, not in the bloodstream.
- The bone marrow contains red, spongy tissue inside bones, known as the site of hematopoiesis.
Origin of Blood Cells
- Blood cells originate from a single type of cell, the hematopoietic stem cell.
- Hematopoietic stem cells differentiate into two main lineages: myeloid and lymphoid.
Lymphoid Lineage
- The lymphoid lineage produces T-lymphocytes (T cells) and B-lymphocytes (B cells).
- Both T and B cells have large nuclei with minimal surrounding cytoplasm.
Myeloid Lineage
- The myeloid lineage produces several cell types:
- Erythrocytes (red blood cells), which have no nucleus and a pale center due to their biconcave shape.
- Megakaryocytes, large cells that create platelets through cytoplasmic blebbing.
- Monocytes, white blood cells with kidney-shaped nuclei that ingest pathogens by engulfment.
- Neutrophils, characterized by multi-segmented nuclei, and are the major component of pus.
- Basophils, identified by bright blue granules in their cytoplasm.
- Eosinophils, known for bright red granules and often a two-lobed nucleus.
Cell Development and Nomenclature
- Immature forms of blood cells are named with the suffix "blast" (e.g., erythroblast, lymphoblast).
- Mature cells use the suffix "cyte" (e.g., erythrocyte, lymphocyte, megakaryocyte).
- Neutrophils, basophils, and eosinophils all develop from a common myeloblast precursor.
Key Terms & Definitions
- Hematopoiesis — the process of forming new blood cells.
- Hematopoietic stem cell — the common ancestor cell for all blood cell types.
- Myeloid lineage — stem cell pathway giving rise to erythrocytes, megakaryocytes, monocytes, neutrophils, basophils, and eosinophils.
- Lymphoid lineage — stem cell pathway giving rise to T-lymphocytes and B-lymphocytes.
- Blast — term for an immature precursor cell.
- Cyte — term for a mature cell form.
- Erythrocyte — red blood cell.
- Megakaryocyte — cell that produces platelets.
- Monocyte — a type of white blood cell that engulfs pathogens.
- Neutrophil/Basophil/Eosinophil — types of white blood cells with distinct staining and nuclear features.
Action Items / Next Steps
- Review diagrams of blood cell differentiation and stages.
- Study the next lesson on hemoglobin for further understanding.