1. Definition of Erythropoiesis:
- Erythropoiesis is the
process of formation of red blood cells (RBCs).
- It occurs
mainly in the bone marrow and is regulated by the hormone erythropoietin
(EPO).
Mnemonic:
"Erythropoiesis = EPO + Bone Marrow = RBC Production"
2. Site of
Erythropoiesis:
|
Age |
Site of RBC Production |
|
Fetal life |
Yolk sac → Liver → Spleen |
|
After birth |
Red bone marrow (vertebrae, ribs, sternum) |
Mnemonic:
"In a fetus: Yolk Liver Spleen (YLS), After birth: Bone marrow
(BM)"
3. Regulation of
Erythropoiesis:
- Hormone:
Erythropoietin (EPO)
- Secreted
by the kidneys in response to low oxygen levels (hypoxia).
- Function
of EPO:
- Stimulates
red bone marrow to produce more RBCs.
Mnemonic:
"Kidneys Release EPO when O₂ is Low"
4. Stages of
Erythropoiesis:
Erythropoiesis involves the transformation of a hematopoietic stem
cell (HSC) into a fully mature RBC through various stages.
|
Stage |
Description |
Key Features |
|
1. Hematopoietic Stem Cell (HSC) |
The starting point, pluripotent stem cell. |
Can become any blood cell. |
|
2. Proerythroblast |
Precursor to RBCs, large, immature. |
High nuclear-to-cytoplasmic ratio, fine chromatin. |
|
3. Basophilic Erythroblast |
Start of hemoglobin synthesis. |
Cytoplasm turns blue (due to RNA). |
|
4. Polychromatic Erythroblast |
More hemoglobin, cytoplasm becomes purple. |
More hemoglobin and less RNA. |
|
5. Orthochromatic Erythroblast |
Nucleus is smaller, almost fully hemoglobinized. |
Pinkish cytoplasm (due to hemoglobin). |
|
6. Reticulocyte |
Immature RBC, leaves bone marrow. |
Still has some RNA, slightly larger. |
|
7. Erythrocyte |
Fully mature RBC, no nucleus, biconcave. |
Main function: Oxygen transport. |
Mnemonic:
"Help! Please Bring Purple Oranges Ready Every time"
(Hematopoietic → Proerythroblast → Basophilic → Polychromatic → Orthochromatic
→ Reticulocyte → Erythrocyte)
5. Duration of
Erythropoiesis:
- Takes
around 7 days from hematopoietic stem cell to mature RBC.
- Reticulocytes remain in
the blood for about 1–2 days before becoming fully mature RBCs.
Mnemonic:
"7 Days, 1–2 Days for Reticulocytes"
6. Components Involved
in Erythropoiesis:
- Iron (Fe) –
Essential for hemoglobin production.
- Vitamin
B12 and Folate – Vital for DNA synthesis and maturation of RBCs.
- Erythropoietin
(EPO) – Stimulates the bone marrow.
- Stem Cells –
Pluripotent stem cells give rise to erythroblasts.
Mnemonic:
“I Feel Extremely Safe”
(Iron, Folate, EPO, Stem Cells)
7. Summary of
Erythropoiesis Process:
- Stimulus: Hypoxia
(low oxygen in tissues)
- Signal: EPO from
kidneys
- Site: Red bone
marrow
- Stages:
Hematopoietic stem cells → Proerythroblasts → Basophilic → Polychromatic →
Orthochromatic → Reticulocytes → Erythrocytes
- Duration: ~7 days
for RBC formation
- Components
Needed: Iron, Vitamin B12, Folate, EPO, Stem Cells
Mnemonic:
“HP (Hypoxia) Signals EPO to Start the Stages, 7 Days Complete”
FAQs – Frequently Asked Questions
Q1. What is erythropoiesis?
Ans: Erythropoiesis is the process by which red blood cells (RBCs) are produced in the bone marrow.
Q2. Where does
erythropoiesis occur in adults?
Ans: In adult life, erythropoiesis occurs in the red bone marrow (vertebrae, ribs, sternum).
Q3. What is
erythropoietin (EPO)?
Ans: EPO is a hormone produced by the kidneys in response to low oxygen levels. It stimulates the bone marrow to produce RBCs.
Q4. How long does
erythropoiesis take?
Ans: Erythropoiesis takes about 7 days from the hematopoietic stem cell to the formation of a mature red blood cell.
Q5. What are the main
stages of erythropoiesis?
Ans: The main stages are:
- Hematopoietic stem cell → 2. Proerythroblast → 3. Basophilic erythroblast → 4. Polychromatic erythroblast → 5. Orthochromatic erythroblast → 6. Reticulocyte → 7. Mature erythrocyte.
Q6. What nutrients are
required for erythropoiesis?
Ans: Key nutrients include Iron (Fe), Vitamin B12, and Folate.
Q7. What is a
reticulocyte?
Ans: A reticulocyte is an immature RBC that still contains some RNA. It is released from the bone marrow into the bloodstream before becoming a fully mature RBC.
