Bone Marrow and Hematopoiesis

Bone Marrow

Soft, specialized connective tissue in interior of bones

Type of Connective Tissue in Bone Marrow

Reticular CT with very fine collagen fibers

Bone Marrow Types

Red marrow

Yellow marrow

Red Marrow

Hematopoietic tissue

Yellow Marrow

Mostly adipocytes

Red Marrow Predominates In

Fetus and neonates, replaced by yellow marrow through life

Red Marrow Components

Siusoids

Megakaryocytes

Macrophages

Adipocytes

Hematopoietic cells

Megakaryocytes

Very large cells in red marrow that produce platelets

Hematopoiesis

Blood cell formation

Hematopoietic Stem Cells

Precursor for all blood cells

Hematopoietic Stem Cells Renewal

Self-regenerates

Hematopoietic Signals

Stem Cell Factor

Thrombopoietin

Erythropoietin

M-CSF

G-CSF

Interleukins

Thrombopoeitin

Stimulates platelet production

Erythropoietin

Stimulates RBC production

M-CSF

Stimulates monocyte production

G-CSF

Stimulates granulocyte production

Interleukins

Regulation of lymphoid system

Hematopoiesis Locations

Yolk sac first

Liver takes over

Small boost from spleen

Bone marrow takes over

Myeloid Progenitor

Gives rise to platelets, erythrocytes, mast cells, granulocytes, and monocytes

Lymphoid Progenitor

Gives rise to lymphocytes

Bone Marrow vs Blood

Bone marrow has many more nucleated cells

Erythrocyte Developmental Stages

Hematopoietic stem cell -> prorubricyte -> Rubricyte -> Metarubricyte -> Reticulocyte -> Erythrocyte

Erythrocyte

Red blood cell

Rubricyte Appearance

Large nucleus with blue (basophilic) cytoplasm

Nucleus off to side

Metarubricyte Appearance

Smaller, dense nucleus

Cytoplasm starting to get more eosinophilic

Accentric nucleus

Reticulocyte Appearance

No nucleus

Speckled eosinophilic cytoplasm

No biconcave shape but irregular

Granuloctye Developmental Stages

Hematopoietic Stem Cell -> Myeloblast -> Promyelocyte -> Myelocyte -> Metamyelocyte -> Band Cell -> Granulocyte

Granulocytes

Neutrophils, eosinophils, basophils

Myelocyte Appearance

Specific granules, mix between eosinophilic and basophilic

Round to slightly dented nucleus

Metamyelocyte Appearance

Specific granules to granulocyte

Clear indentation of nucleus but less than 50% dented

Band Cell Apperance

Specific granules

Nucleus more than 50% dented, not completely segmented

Regenerative Anemia

Loss of RBC and increased response from bone marrow

Regenerative Anemia Diagnosis

Anemia with increased reticulocytes in circulation

MCV increased, MCHC decreased

Mean Corpuscular Volume (MCV)

How big a RBC is

Mean Corpuscular Hemoglobin Concentration (MCHC)

Average concentration of hemoglobin in RBC

Reticulocytes in Regenerative Anemia

Big and decreased hemoglobin concentration

Regenerative Anemia Caused by

Blood loss

Hemolysis

Hemolysis

Destruction of RBC

Non-regenerative Anemia

Loss of ability of bone marrow to produce enough erythrocytes

Reticuloctye

Step before mature RBC (erythrocyte)

Non-regenerative Anemia Diagnosis

Anemia without an increase in reticulocytes, could see a reduction

Non-regenerative Anemia Caused by

Endocrine failure (loss of EPO)

Iron deficiency

Bone marrow disorders

Chronic blood loss

EPO

Signal for RBC development

GM-CSF

Signal for granulocyte development

Neutrophil Under Normal Conditions

Balanced by neutrophil diapedesis leading to a steady state concentration in the blood

Neutrophils During Early Acute Infections

Increased production, will see more band cells in the blood

Neutrophilia

Neutrophils During Chronic Infection

Increased production is balanced by increased diapedesis, may see more band cells

Neutrophils During Severe Infection

Increased diapedesis overwhelms production leading to neutropenia

May also see band cells