Hematopoiesis

Question 1

The marrow cavity houses the ….

Answer 1

developing blood cells

Question 2

What is the cellular composition of the bone marrow?

Answer 2

• composed of adipocytes and differentiating hematopoietic cells
  
  • present in varying proportions depending on age, during which cellularity declines
• also contains “stromal” cells = mesenchymal stem cells (MSCs)
  
  • thought of as specialized fibroblasts
  • contribute physical support for hematopoietic cells in the marrow
  • nurture marrow processes by secreting growth factors

Question 3

• What can MSCs differentiate into?
• What is their stem cell role?

Answer 3

• MSCs are multipotent stem cells and differentiate into:
  
  • endothelial cells
  • osteocytes
  • bone marrow adipose tissue
  • hematopoietic cells (controversial)
• In their stem cell role:
  
  • MSCs may enter the circulation
  • taking up residence as multipotent adult stem cells in organs to mediate regeneration

Question 4

1. In the early embryo, hematopoiesis occurs first in the blood islands of the ____ ___, followed by the ____
2. Blood production begins in the __________ of long and flat bones during the 5th month of prenatal life
3. By age 20, fat infiltration causes the marrow of long bones to be referred to as ____________

Answer 4

1. In the early embryo, hematopoiesis occurs first in the blood islands of the yolk sac, followed by the liver
2. Blood production begins in the “red marrow” of long and flat bones during the 5th month of prenatal life
3. By age 20, fat infiltration causes the marrow of long bones to be referred to as “yellow marrow”

Question 5

1. Where is blood production after the age of 20?
2. Where is a bone marrow biospy typically taken from?

Answer 5

1. Hematopoiesis after age 20 ⇒ flat bones
2. BMBx ⇒ posterior iliac crest

Question 6

1. How much of the body mass comes from blood cells?
2. What is the daily demand for:
   
   • Erythrocytes
   • Granulocytes
   • Platelets

Answer 6

1. 5% of total body mass
2. Daily demand:
   
   • Erythrocytes ⇒ 10¹¹ (100 billion)
   • Granulocytes ⇒ 10¹⁰ (10 billion)
   • Platelets ⇒ 10¹¹ (100 billion)

Question 7

A single, Go multipotent master stem cell in the bone marrow stroma gives rise to ….

Answer 7

• hematopoietic stem cells (HSCs; syn = hemocytoblast)
• endothelial progenitor cells (EPCs)
• mesenchymal stem cells (MSCs)

Question 8

HSCs comprise only about _:_____ marrow cells

Answer 8

1:10,000

Question 9

What is the hematopoeisis differentiation pathway?

Answer 9

Question 10

What is the CD for hemangioblasts?

Answer 10

CD34+

Question 11

What are the immunohisto markers for HSCs?

Answer 11

1. CD34+
2. c-kit+ (CD117)
3. Lin-

Question 12

What is the marker for endothelial cells?

Answer 12

CD34+

Question 13

• What comes from the lymphoid progenitor?
• What are the markers for these cells?

Answer 13

• B cell (CFU-B; CD45+)
• T cell (CFU-T; CD45+)

Question 14

Which blood cells do not have CD45?

Answer 14

erythrocytes and megakaryocytes (platelets)

Question 15

• What comes from the myeloid progenitor?
• What are the markers for these cells?

Answer 15

• erythroid (CFU-E; CD45-)
• granulocyte (CFU-G; CD45+)
• monocyte (CD45+)
• megakaryocyte (CFU-meg; CD45-)

Question 16

What is the technique used to type and isolate cluster differentiation (CD) markers?

Answer 16

fluorescent-activated cell sorter (FACS)

Question 17

Definition of myeloid:

1. “Pure” definition:
2. Definition for heme/lymph course:
3. M/E ratio:

Answer 17

1. “Pure” definition:
   
   • any cell arising from the bone marrow
2. Definition for heme/lymph course:
   
   • ​​cells arising from the granulocytic, monocytic, and megakaryocytic lineages
     
     • ​note that erythroid cells could be considered as well
3. M/E ratio (myeloid to erythroid ratio):
   
   • Myeloid = non-lymphoid leukocytes

Question 18

What are Colony Forming Units (CFUs) & Colony-Stimulating Factors (CSFs)?

Answer 18

• CFUs are progenitors, which undergo colonial expansion under the influence of one or more protein factors termed CSFs
• CSFs can be:
  
  • **unipotent **(induce 1 CFU)
  • mulitpotent (induce more than 1 CFU)

Question 19

• Pleuripotent CSFs ⇒
• **Unipotent CSFs ⇒ **

Answer 19

• Pluripotent CSFs ⇒
  
  • Stem cell factor (SCF; syn = steel factor)
• Unipotent CSFs ⇒
  
  • Erythropoietin (epo)
  • Thrombopoietin (tpo)
  • Granulocyte Colony-Stimulating Factor (G-CSF)
  • Macrophage or monocyte colony-stimulating factor (M-CSF)

Question 20

Erythropoietin

• What produces Epo?
• What is its function?
• What is its clincal use?

Answer 20

• secreted by kidney and liver cells
• induce the erythroid colony- forming unit (CFU-E)
• epo is used to treat many forms of anemia
  
  • most commonly in association with renal failure
• also used as a performance-enhancing drug (PED) by athletes

Question 21

Thrombopoeitin

• What is its function?
• What is its clinical use?

Answer 21

• induces the proliferation and differentiation of the colony-forming unit for megakaryocytes (CFU-meg),
  
  • increased platelet production.
• Recombinant forms are available for therapeutic use in patients with low platelet counts secondary to immune-mediated platelet destruction processes

Question 22

Granulocyte Colony-Stimulating Factor (G-CSF):

• What is its function?
• What is its clincal use?

Answer 22

• promotes differentiation of the neutrophil lineage (CFU-G)
• clinically used to mobilize the release of CFU-G into the peripheral circulation in patients who have low neutrophil counts secondary to infection or chemotherapy

Question 23

Macrophage or monocyte colony-stimulating factor (M-CSF or GM-CSF):

• What is its function?

Answer 23

• stimulates the production of approximately 10¹⁰ monocytes daily
• monocytes enter the tissue spaces and differentiate into macrophages
• M-CSF also induces macrophages to differentiate into osteoclasts, which are cells that degrade bone

Question 24

What do you look for when determining WBC differentiation?

Answer 24

1. Decreasing Cell Size
2. Changes in (Cytoplasmic) Color
3. Decreased Nuclear Size in Erythroid Cells
4. Changes in Nuclear Morphology in Granulocytes
5. Development of Specific Granules
6. Condensation of chromatin

Question 25

What happens to **cell size** during differentiation?

Answer 25

As differentiation ensues, the **cells become smaller**

Question 26

Why are **changes in cytoplasmic color** significant?

Answer 26

* Peripheral blood and bone marrow aspirate slides are stained with **Wright-Giemsa** * **Intense basophilia** (blue) in the cytoplasm of early differentiating: * **erythroid cells** – proerythroblasts and basophilic erythroblasts * indicative of **high nucleic acid concentration** (i.e. globin mRNA) in the cytoplasm * **As differentiation continues:** * **mRNA diminishes** * **protein** (hemoglobin) **accumulates** * causing the stain to become red (**eosinophilic**)

Question 27

What happens to the **nuclear size in erythroid cells**?

Answer 27

* Differentiation ensues, **nuclei become smaller** * Eventually, the **nucleus is extruded prior to release of RBCs to the peripheral circulation**

Question 28

What are the **changes in nuclear morphology in granulocytes** as differentiation progresses?

Answer 28

Nuclear changes is granulocytes: 1. Nuclei are **initially round** 2. Become progressively **segmented** * **kidney-shaped** (in **metamyelocytes**) ⇒ **deeply indented** (in **band cells**) 3. Ultimately turn into **multiple nuclear lobes** * held together by nuclear segments as seen in segmented neutrophils * poly-morpho-nuclear leukocytes (PMNs)

Question 29

Describe the morphologic **development of specific granules:**

Answer 29

* In the granulocytic series, **primary granules** (dark purple granules which are actually lysosomes) **are present at the promyelocyte stage** * As differentiation ensues, these **primary lysosomal granules become obscured by secondary** (**specific granules**) * **Specific granules present at the myelocyte stage** and beyond * Erythroid cells have no granules

Question 30

Describe the **condensation of chromatin****:**

Answer 30

* Nuclei in the most **immature cells** of the erythroid and granulocytic lineages have **euchromatic** (“open”) **chromatin** * **As these cells mature,** their chromatin becomes more condensed or heterochromatin (“closed”)

Question 31

Describe the general process of **granulopoeisis:**

Answer 31

Common myeloid progenitor ⇒ **myeloblast** ⇒ **promyelocyte** ⇒ **myelocyte** ⇒ **metamyelocyte** ⇒ **band cell** ⇒ **granulocyte**

Question 32

Describe the general process of **erythropoeisis:**

Answer 32

common myeloid progenitor ⇒ proerythroblast (**pronormoblast**) ⇒ basophilic erythroblast ⇒ polychromatic erythroblast ⇒ orthochromatic erythroblast (**normoblast**) ⇒ polychromatic erythrocyte (**reticulocyte**) ⇒ **erythrocyte**