Hematopoiesis, Blood Cells, and CBC Basics (Video Notes)

Key concepts from the lecture on how stem cells form blood cells, the different lineages, what each cell type does, and how CBC results are interpreted.

Stem cells

Cells produced in the bone marrow that differentiate into myeloid or lymphoid lineages.

Bone marrow

Primary site of hematopoiesis where stem cells are produced.

Myeloid lineage

Hematopoietic branch giving rise to erythrocytes, platelets, granulocytes, and monocytes.

Lymphoid lineage

Hematopoietic branch giving rise to T cells, B cells, and NK cells.

Erythrocyte (RBC)

Red blood cell; transports oxygen via hemoglobin and carries carbon dioxide from tissues to the lungs.

Hemoglobin

Oxygen-carrying protein in RBCs composed of heme (iron) and globin (protein).

Heme

Iron-containing component of hemoglobin essential for oxygen binding.

Globin

Protein part of hemoglobin that binds to the heme group.

Iron

Mineral required to synthesize heme and therefore hemoglobin.

Hematocrit

Percentage of blood volume occupied by red blood cells (in 100 mL of blood).

RBC count

Number of erythrocytes per volume of blood (usually millions per microliter).

Polycythemia

Excess red blood cells; can be genetic or due to high altitude/smoking; increases blood viscosity and clot risk.

Therapeutic phlebotomy

Regular removal of blood to decrease red blood cell mass in polycythemia.

Anemia

Low red blood cell count or hemoglobin; causes include blood loss, hemolysis, iron deficiency, or bone marrow suppression.

Platelet (thrombocyte)

Blood cell type essential for clotting and stopping bleeding.

Thrombocytopenia

Low platelet count; high bleeding risk; causes include bone marrow suppression and certain medications.

Petechiae

Small pinpoint skin hemorrhages seen with very low platelets or platelet dysfunction.

Leukocytes (White blood cells)

Cells of the immune system; produced in bone marrow and respond to infection and inflammation.

Leukocytosis

Elevated white blood cell count; often due to infection, inflammation, or cancer.

Leukopenia

Low white blood cell count; increases infection risk; neutropenia is a common example.

Neutrophil

Most abundant WBC; first responders to bacterial infection; part of CBC differential.

Eosinophil

WBC associated with allergic reactions and parasitic infections.

Basophil

Least common WBC; involved in allergic reactions and chronic inflammation; releases histamine.

Monocyte

Phagocytic WBC; elevated during certain bacterial infections and inflammation; can become macrophages.

Lymphocyte

WBCs (B cells, T cells, NK cells) central to adaptive immunity and antibody production.

CBC with differential

Complete blood count with breakdown of individual WBC types to identify specific infections or disorders.

Reference ranges

Lab-specific normal value ranges that vary by lab; used to interpret CBC results; often similar across labs.

Units (CBC values)

WBCs in thousands per microliter; RBCs typically reported in millions/µL; platelets in thousands/µL (often 150–400 thousand/µL).