hematology exam 1 - hematopoiesis and erythrocyte formation

ucsd extension

describe process of hematopoiesis

process of blood cell production

• occurs continuously and regulated

• cell renewal, proliferation, differentiation, and maturation

main centers of cell production (hematopoiesis) from fetal development until adulthood

1. mesoblastic phase

2. hepatic/liver phase

3. medullary phase

4. adult phase

1. mesoblastic phase

• starts around 19 days and occurs b/w 2-10 wks

• occurs in the vessels or intravascularly

• embryonic hemoglobin is produced

• primitive nucleated erythroblasts originate in the embryonic yolk sac lining, or mesoderm from mesenchymal stem cells

hepatic/liver phase

• starts at 5-7 wks, occurs between 1-9 months, peaking at 5 months, in between medullary and yolk sac phase until 1-2 wks after birth

• nucleated RBCs will migrate from yolk sac to the liver until the fetus reaches 7 months → changes to bone marrow

• + spleen (3-6 months), kidney, thymus, and lymph nodes

• recognizable cell clusters or blast being to arise

• megakaryocytes begin to be produced

• fetal hemoglobin (HbF) present, start of adult hemoglobin (HbA)

medullary phase:

• occurs in the bone marrow

• begins at 5 months, and by 6 months, bone marrow becomes primary site of hematopoiesis in the fetus

• liver and spleen cease hematopoiesis at birth

• active sites switch to bone marrow

• bone marrow produces all cell types

  • as well as lymph nodes, spleen, liver, and thymus

• provides stable, resourceful environment for proliferation and maturation of blood cells

• can find diff stages of maturation of all cell lines during this phase

adult phase (hematopoiesis)

contains cells that are developing: erythroid, myeloid, megakaryocytes, and lymphoid

• lymphoid cells will develop in the marrow, spleen, thymus, and lymph nodes

• occurs in the red bone marrow or extramedullary (outside of bone marrow)

• after age 18, hematopoiesis is primarily occurring in the sternum, ribs, pelvis, and vertebrae

hematopoiesis phases from fetal development to postnatal graph

what are each stages of erythrocyte formation, development, and differentiation

1. proerythroblast

2. basophilic erythroblast

3. polychromatic erythroblast

4. orthochromatic erythroblast

5. reticulocyte

6. mature red cell

proerythroblast

first step in erythrocyte formation (earliest morphologically distinguishable erythroid precursor)

• diameter: 20-25 micrometers

• nucleus takes up 80% of the cell (high nuclear to cytoplasm ratio); round

  • stains bluish-purple (basophilic due to RNA)

  • lacy chromatin

  • only 1 to 2 nucleoli present

• golgi complex may be visible

• chromatin is distinct and spread out

• ready to divide at 12 hrs

basophilic erythroblast (normoblast)

2nd stage of erythrocyte formation

• diameter: 16-18 micrometers (similar to pronormoblast but smaller)

• nucleus: 75% of cell

  • chromatin clumps and becomes coarse

  • heterochromatin is dark violet, euchromatin is lighter → forms a wheel with spokes appearance

• cytoplasm:

  • blue with pink, basophilic (higher number of ribosomes/RNA)

  • nucleus is deep purple

• require 20 hrs to develop

polychromatic erythroblast (normoblast)

3rd stage of erythrocyte formation

• diameter: 12-15 micrometers

  • ½ size of mother cell

• nucleus:

  • smaller nucleus and more cytoplasm (chromatin is being condensed)

  • irregular chromatin and coarsely clumped due to chromatin aggregation

  • nucleoli are NO LONGER visible

• cytoplasm:

  • abundant gray-blue/pink mixture from Hb and RNA

  • Hb is apparent in blue cytoplasm

• 30 hrs to mature

orthochromatic erythroblast (normoblast)

4th stage of erythrocyte formation

• diameter: 10-15 micrometers

• nucleus:

  • low nucleus:cell ratio

  • solid, blue-black nucleus that begins to degenerate that contains nonlinear clumped chromatin

  • nuclear chromatin is heavily condensed

  • at the end of this stage, nucleus is fragmented/structureless

  • phase contrast microscopy: can observe cytoplasmic projections protracting and retracting

    • preparing for nucleus ejection

• cytoplasm:

  • after final mitotic division, concentration of hemoglobin increases within → pink/salmon color, but slight tinge of blue

• not able to divide at this stage or moving forward bc the cell can’t perform DNA synthesis

• maturation time: 48 hrs

reticulocytes

5th stage of erythrocyte formation

• diameter: 7-10 micrometers

• cytoplasm:

  • blueish tint and slightly larger than RBCs

• contain residual RNA but no nucleus → bluish tinge w/ Romanowsky stains (supravital stains - new methylene blue-N)

• when nucleus is first ejected, the cell has irregular lobe shape

• when remaining 20% of cell’s Hb is made

• react w/ these stains to produce precipitation of RNA + mitochondria

  • supravital stains = purplish-blue inclusions spread out

  • new methylene blue N

  • brilliant cresyl blue

• released in 2-3 days and circulates for 1-2 before maturing

• ribosomes disappear as cell matures to carry more Hb

• granular filamentous ribosomes

mature red cell

6th stage of erythrocyte formation

• diameter: 7-8 micrometers

• volume: 80-100 fL

• bioconcave disc

• stains pink to orange bc of Hb (acidophilic)

• do NOT have cellular organelles and enzymes to synthesized new lipids/proteins

  • can’t be repaired

  • can’t synthesize Hb

• carries O2 from lungs and CO2 back

• flexible to allow for passage throughout the body