Past Papers · SAQ
Blood Constituents — RBC Structure
2016B Q14
Exam questionDescribe the features of a red blood cell that facilitate oxygen transport.
CICMWrecks answer
Master answer
RED BLOOD CELL
Formation
Pluripotent haemopoetic stem cell → Colony Forming unit → Proerythroblast → Reticulocyte → Erythrocyte
Simplified – main steps.
Takes 7 days
- Proerythroblast propagates
- From proerythroblast to reticulocyte
- Concentration of haemoglobin increases
- Nucleus disappears
- Endoplasmic reticulum disappears
- Reticulocyte
- Ribosomes
- Mitochondria
- Reticulocyte released into circulation
- Matures to RBC in 1-2 days
EPO increases rate of differentiation
Produced in the kidney (in response to low PO2)
Structure
- Are 7.5μm in diameter
- Are 2um thick
- biconcave disc, contains haemoglobin A (Hb F in-utero), has a central Fe moiety and demonstrates positive cooperativity in binding oxygen
- Have a lifespan of 120 days
- make up 40-50% of the blood volume, usual value 4-5 x 1012/L
- Carry ~29pg of haemoglobin
| Structure | Function |
|---|---|
Biconcave disc shape | Maximises surface area (optimising gas transfer) |
| Flexible membrane with shape maintained by structural proteins | makes the cells flexible enough to pass through capillary beds (which are narrower than the cell). |
| No nucleus & other organelles | Maximises cell volume available for Hb. |
| No mitochondria (No oxygen utilization) | Cannot perform aerobic metabolism – all ATP is generated via glycolysis. 3 shunts that come off the anaerobic glycolytic pathway (RBC’s only means of ATP generation): i) the production of 2-3 DPG via the Rapoport-Luebering shunt ii) generation of NADPH by the hexose monophosphate shunt (protects RBC from oxidative damage) iii) reduction of metHb back to Hb by way of the NADH. Optimizes Oxygen carriage |
| No ribosomes | Incapable of producing protein |
| Haemoglobin Four globulin chains (2α + 2β) links to heme Heme: Porphyrin ring chelated to iron Formed in the mitochondria | High affinity for oxygen O2 in haemoglobin is Hb x SatO2 x 1.34, compared to 0.003 x PO2 dissolved in blood Haemoglobin is a good buffer |
| Contains carbonic anhydrase | CO2 + H2O → H2CO3 Enables transport of CO2 as bicarbonate |
JC / Mooney 2019
Past papers