Bone Marrow and Hematopoiesis

What are the 3 stages of hematopoiesis?

1. Mesoblastic phase

2. Hepatic phase

3. Myeloid (Medullary) phase

What happens during the mesoblastic (1st) stage of hematopoiesis?

• blood islands detected at 19-20 days after gestation

• some RBCs form primitive erythroblasts while others surround the cavity of the yolk sac and eventually form blood vessels

What are the 3 stages of hematopoiesis?

1. Mesoblastic phase

2. Hepatic phase

3. Myeloid (Medullary) phase

What happens during the mesoblastic (1st) stage of hematopoiesis?

• blood islands detected at 19-20 days after gestation

• some RBCs form primitive erythroblasts while others surround the cavity of the yolk sac and eventually form blood vessels

Why are yolk sac Erythrocytes important?

because they produce hemoglobin needed for delivery of oxygen to developing tissues

What happens during the Hepatic phase of hematopoiesis?

• at 5-6wks the liver starts producing blood

• lymphoid cells begin to appear

• Hematopoiesis during this phase occurs extra-vascularly with the liver remaining the major site of production during the second trimester

What happens during the Myeloid phase of hematopoiesis?

• before 5th month of gestation hematopoiesis being in the bone marrow

• occurs in the medulla (inner part) of the bone marrow

• Myeloid:Erythroid ratio gradually approaches 3:1 = adult levels

• by the end of 24wks gestation the bone marrow becomes the primary site of hematopoiesis

What is Erythropoiesis?

The production of red blood cells

What is Leukopoiesis?

the production of White blood cells

What is Megakaryopoiesis?

the production of megakaryocytes

What is Thrombopoiesis?

the production of platelets

What is Red marrow able to produce?

blood cells

What is Yellow marrow able to produce?

Fat cells

At what age is all bone marrow active red marrow?

0-4yrs

At what age does bone marrow start to change to fatty marrow - about 25%?

4-18yrs

At what age is 50% of marrow fatty?

18+ - adults

At what life stage is marrow 70% fatty?

Seniors/Elders

What % of body weight is bone marrow?

3.4-5.9%

How many blood cells does the bone marrow produce per day?

6 billion cells per kg/day

What is the term for the ratio of red marrow to yellow marrow?

marrow cellularity

What can yellow marrow do in cases of increased demand on the bone marrow such as excessive blood loss?

it can revert back to yellow marrow

What do Marrow Stromal Cells do?

• provide the hematopoietic microenvironment

• generates colony stimulating factors (CSF)

What happens if you have Idiopathic Myelofibrosis (IM)?

the marrow stoma cell begin to harden/fibrotic

What are some indications for bone marrow examination?

• neoplasia diagnosis

• unexplained pancytopenia

• monitoring tx

• unexplained anemia

Bone marrow collection consist of what 2 portions?

Aspirate and Core biopsy (trephine biopsy)

What is the most common bone marrow collection site?

Posterior superior iliac crest

What bone marrow collection site is used for an aspirate only?

Sternum

What bone marrow collection site is used for an aspirate, and only done on children under 2yrs?

Anterior medical surface of the tibia

What bone marrow collection site is rarely ever used?

Spinous processes of the vertebrae/ ribs

What are the advantages and disadvantages of the Marrow Aspirate Smear technique?

Advantages: fast, no decalcification, differential count

Disadvantages: not represent all cells, dry tap for fibrosis, does not represent architecture

What are the advantages and disadvantages for Marrow Core Biopsy?

Advantages: analyze cells and stoma, represents all cells

Disadvantages: slow, decalcification required, can perform differential count

What are bone marrow slides stained and fixed with?

fixed with methanol and stained with wrights Giemsa stain

What does the bone marrow evaluation in hematology include?

• cellularity of bone marrow

• Differential counts

• M:E ratio calculation

• Iron content of the marrow using a perls prussian blue stain

• Megakaryocyte evaluation

• presence of abnormal cells

What are some reasons to test bone marrow?

• diagnose disease

• determine stage/progression of a disease

• determine iron levels

• unexplained anemia

• investigate fever of unknown origin