Blood Constituents — RBC Lifecycle

Current · V5 (2025) → N1.ii Historical · V4 (2023) → Q1.i 2 exam appearances

2025A Q06

Exam question

(a) With respect to red blood cell production, outline the following: (i) the site (10% of marks). (ii) the stimuli (5% of marks). (iii) the process (15% of marks). (b) With respect to red cell breakdown, outline the following; (i) the usual lifespan in neonates and adults (10% of marks). (ii) the process of red cell aging, degradation and clearance (40% of marks). (iii) the process of haemoglobin breakdown (20% of marks).

CICMWrecks answer

Master answer

RBC

Role

Oxygen transport
Carbon dioxide transport
- Bound to N-terminal of globin → carbamino-Hb
Buffering function
- Imidazole group on Hb Histadine residues
Iron storage
- 65-70% of total iron stores

Normal Values

40-50% of the blood volume
Usual value 4-5 x 10¹²/L

RBC Production

3-4w embryionic → Mesenchymal stem cells in yolk sac
6w-7mo
- → Liver (and spleen to lesser extent)
- continues until birth
7mo onwards:
- Bone marrow
- Proximal ends of femur/humerus
  - fat replacement of long bone marrow occurs by age 18-20 y.o.
- Central skeleton (vertebrae, pelvis, ribs, sternum and skull)

Diagram used in Blood constituents — Master Answer — Legacy CICMWrecks figure · Source verification pending.

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)

RBC Destruction

Globin chains → aa’s

Haem → Biliverdin + Fe + CO

Biliverdin
- Haeme + Haem oxygenase → biliverdin
- Biliverdin + biliverdin reductase → bilirubin
- Free bilirubin + albumin → transported to hepatocytes
- Conjugated with glucuronide to ↑ water solubility
- Excreted to bile canniliculus
- Secreted to gut at D2 (duodenum)
- Intestinal flora hydrolyse and reduce → urobilinogen
- 3 fates:
  - 1) Gut bacteria form the dark pigment stercobilin, which is egested in the faeces
  - 2) Urobilinogen reabsorbed unchanged by the portal system and recycled by the liver
  - 3) Remainder is reabsorbed by the portal system and then excreted in the urine
Fe²⁺ → oxidised to Fe³⁺ → recycled
CO (only endogenous source of CO)

Gladwin 2016

Answer by Gladwin

Past papers

Exam appearances

2 appearances

Exam	Exact exam wording	Candidate success
2025A Q06	(a) With respect to red blood cell production, outline the following: (i) the site (10% of marks). (ii) the stimuli (5% of marks). (iii) the process (15% of marks). (b) With respect to red cell breakdown, outline the following; (i) the usual lifespan in neonates and adults (10% of marks). (ii) the process of red cell aging, degradation and clearance (40% of marks). (iii) the process of haemoglobin breakdown (20% of marks).	72%
2012A Q15	Briefly outline the production and fate of Red Blood Cells (RBC) (40% of marks). Describe the breakdown of haemoglobin (Hb) (60% of marks).	60%