Erythropoiesis

Question 1

What is erythropoiesis

Answer 1

It is the process of production of red cells.

Question 2

Life span of RBCs

Answer 2

120 days

Question 3

Normal red cell mass

Answer 3

Males - 26-32 ml/kg of body wt

Females - 23-29 ml/kg of body wt

Question 4

What are the stages of erythropoiesis

Answer 4

Mesoblastic
Hepatic
Medullary

Question 5

Mesoblastic erythropoiesis

Answer 5

During IUL erythropoiesis first takes place in the mesoderm of yolk sac and body . During this stage erythropoiesis is intravascular.

Question 6

Hepatic stage

Answer 6

From the 5th week of gestation erythropoiesis takes place in the liver and spleen.

Question 7

Medullary stage

Answer 7

From 5th month of IUL the bone marrow starts forming red cells. Erythropoiesis os very slow in 2nd trimester .

Medullary erythropoiesis becomes more effective towards end of the third trimester. After birth bine marrow becomes the sole site of erythropoiesis.

Till adolescence marrow cavity of all bines is involved in erythropoiesis . After which it regresses in the limb bones.

After the age of 20-30 erythropoiesis is mostly limited to sternum , ribs , vertebrae , skull , pelvic and pectoral girdles.

Extramedullary erythropoiesis after birth is abnormal.

Question 8

What are the 4 major cell stages of erythropoiesis ?

Answer 8

Stem cells
Progenitor cells
Precursor cells
Mature cells

Question 9

Where are red cells formed from ?

Answer 9

They’re formed from pluripotent hemopoietic stem cells

Question 10

What are the cellular changes taking place during erythropoiesis ?

Answer 10

Cell size reduces progressively

Size of nucleus and number of nucleoli decreases , chromatin material condenses and finally nucleus disappears.

Staining reactikn of cytoplasm changes from basophilic to polychromatophilic to acidophilic due to the geadual decrease in quantitiy of nucleus

Question 11

What are pleuripotent stem cells ?

Answer 11

They are the mother stem cells that form the stem cells for different cell lines.

Question 12

Functions of pleuripotent cells

Answer 12

They have 2 functions -
Self renewal
Differentiation

They constantly renew themselves, thus the bone marrows is never depleted of stem cells.

They also have the capacity to differentiate into different stem cells

Question 13

Committed stem cells

Answer 13

Formed from pleuripotent cells.
2 series are present myeloid and lymphoid series .

The myeloid series produces the erythroid series ,megakaryoid series , monocytic series and granulocytic series.

The erythroid series gives rise to the progenitor cells.

Question 14

Types of progenitor cells

Answer 14

BFU-E : burst forming unit - erythroid progenitor cells

CFU-E : colony forming unit - erythroid progenitor cells

Question 15

Short note on progenitor cells

Answer 15

The BFU-E cells forms large no. of CFU-E cells which then forms a moderate no. of blast cells (erythroblasts)

Question 16

Precursor cells

Answer 16

Erythroblasts are the first identifiable cells in the bone marrow hence they are the precursors of RBCs .

Erythroblasts are also called normoblasts. Normoblasts arise from pronormoblasts .

Question 17

Types of normoblasts cells

Answer 17

Early
Intermediate
Late

Question 18

What are pronormoblasts

Answer 18

They are the firsr identifiable blast cell in the erythroid series. First cells to appear in the bone marrow.

Question 19

Characteristics of pronormoblast cells

Answer 19

Less cytoplasm (only 20% of cell)
Increased amounts of polyribosomes makes the cell basophilic
Large cell with irregular edges oval in shape (15-20 microm)
RNA content is high — high protein synthesis
Mitosis is present
Hb production hasnt started
Nucleus is large (80% of the cell) contains many nucleoli.

Question 20

What are early normoblast cells

Answer 20

They are the first appearing erythroblast cells

Question 21

Features of early normoblast cells

Answer 21

Diameter , 12-18 microns

Cytoplasm is scanty and basophiloc hence they’re also called basophilic erythroblasts .

The nucleus is large (occupies 3/4th of the cell). Contains dark violet stained heterochromatin and pink stained euchromatin . These are linked by linear chains giving the nucleus a wheel spoke appearance.

Hb production starts at this stage

Question 22

Intermediate normoblast

Answer 22

Formed due to the mitosis of early normoblast.

Question 23

Characteristics of intermediate normoblasts ?

Answer 23

Smaller in size , radius is 10-15 microns
The cytoplasm changes from blue to pink as Hb content increases and polyribosome content gets diluted.

Nucleus is small and occupies half of the cell. The heterochromatin clumps in the nucleus gives a checkerboard appearance. There are no nucleoli .

The presence of RNA makes the cell eosinophilic .

Hence the cell is polychromatic in nature.

Mitosis activity is reduced

Question 24

Late normoblast

Answer 24

Produced by last mitosis in the erythropoietic series

Question 25

Characteristics of late normoblast

Answer 25

Smallest in size (7-12 microns)
Orthochromatic cells since cytoplasm is eosinophilic in nature
Hb synthesis almost completes at this stage
Nucleus is pyknotic and small. The chromatin material is
arranged in dark cartwheel like appearance

Question 26

Characteristics of reticulocytes

Answer 26

Slightly larger than red cells

Has a network of reticular nuclear material. These nuclear materials are the remnants of organelles especially that of the nucleus.

The reticulum is stained by supravital stain

The hn production continues in some reticulocytes . The count is 0-1% of adult erythrocyte

Question 27

Erythrocytes

Answer 27

Final cell in erythropoiesis
Diameter- 7.5 microns
Biconcave discs

Question 28

Duration of erythropoiesis

Answer 28

A total of 7-9 days
5-7 for the progenitor cells to become reticulocytes
And 2 days for reticulocytes to become red cells