Lecture 3 - RBC Development and Morphology

Question 1

Erythropoiesis

Answer 1

Process that results in the production of RBC
It is a subclass of haematopoiesis
It occurs in specialised anatomical sites
It encompasses many morphologically identifiable stages of RBC development
- serial (sequential) FBC
- a biopsy of bone marrow

Question 2

Sites of Erythropoiesis

Answer 2

Embryo - yolk sac
Foetus - Liver
Immature - bone marrow
Mature - bone marrow

Question 3

Erythropoietin

Answer 3

Erythropoiesis is largely influence by erythropoietin (EPO)
EPO is produced by cells in the kidney (~80%) and liver
It is a 166 amino acid peptide
Circulates in plasma with a half-life of 7-8h
Binds to high-affinity receptors present in relatively small numbers (1000/cell) on the surface of erythroid progenitor cells in the bone marrow
Hypoxic induction of EPO depends on the transcription factor hypoxia inducible factor 1 (HIF)
HIF is activated in virtually all cells by exposure to hypoxia

Question 4

What does underproduction and overproduction of EPO lead to?

Answer 4

Underproduction
- develop overt anaemia
Overproduction
- develop erythrocytosis
- commonly due to anoxia
- occasional mutations in oxygen sensing/HIF
- neoplasms producing EPO e.g. kidney, liver, cerebellum

Question 5

Erythropoiesis in the Bone Marrow

Answer 5

Occurs in erythroblastic islands
Mediated by macrophages
Results in two cells
- reticulocyte (anucleated)
- pyrenocyte (nucleus with small amount of cytoplasm), rapidly phagocytosed by macrophages

Question 6

Nucleated RBC (nRBC) in Peripheral Blood

Answer 6

nRBC usually found in bone marrow but can be seen in peripheral blood
Commonly orthochromic normoblast (metarubricyte) or polychromatophilic normoblast (rubricyte)
Round nucleus, dense dark chromatin
Basophilic, amphophilic or eosinophilic cytoplasm depending on stage

Question 7

Polychromatophilic RBC in Peripheral Blood

Answer 7

Second to last stage of erythroid development
Anucleated 
Bluish cytoplasm 
- contains residual RNA/ribosomes
Can only be seen on a Romanowsky

Question 8

The difference between polychromatic RBC and a reticulocyte?

Answer 8

They are the same cell just stained differently
Polychromatic RBC
- Romanowsky stain
- dried, fixed blood films then stained
- bluish cell
Reticulocyte
- Supravital stain
- incubate living cells with stain then make film
- aggregates of RNA (=reticulum)
- blue chips in the cells

Question 9

Indications of Erythropoiesis

Answer 9

Increased concentration of reticulocytes indicates active/increased erythropoiesis
Increased polychromatophilic RBC on blood film

Question 10

RBC Structure

Answer 10

RBC cell membrane
- lipid bilayer
- glycophorins (glycosylated proteins)
- channels that actively uses energy to maintain electrolyte balance so that intraRBC K+ > plasma K+
RBC cell cytoskeleton
- several components:
- band 3
- spectrin 
- ankyrin
- others
- these maintain cell shape as biconcave disc
RBC contents
- haemoglobin
- carbonic anhydrase
- others

Question 11

Variant Morphology - Spherocyte

Answer 11

Decreased surface area to volume
Spherical shape
No/little central pallor
May be congenital or acquired

Question 12

Variant Morphology - Echinocyte

Answer 12

Decreased volume to surface area
Dehydrated or 'crenated'
'Folding' of membrane results in 'spikes' in the membrane
May be formed in 
- artefact (type 1)
- physiological
- pathological

Question 13

Variant Morphology - Acanthocyte

Answer 13

Formed by increased membrane area
Irregular ‘out-foldings’ of membrane
Typically due to abnormal lipid content of membrane
May be congenital or acquired

Question 14

Variant Morphology - Elliptocyte

Answer 14

Altered membrane composition -> altered cell shape (cylinder looking)
Hb usually concentrated at poles -> central pallor
Congenital

Question 15

Variant Morphology - Target Cell

Answer 15

A.k.a codocyte
Altered membrane lipid composition -> increased surface area to volume
Pale areas contain less [Hb]
Looks like a bullseye

Question 16

Consequences of Variant Morphology

Answer 16

May effect function
- e.g. decreased efficiency of oxygen transfer
May decrease lifespan of cell
- e.g. lack deformability which leads to them being removed from circulation by macrophages
Some variants can be used to identify pathophysiological processes
- e.g. spherocytes immune haemolytic anaemia

Question 17

RBC Size and Volume

Answer 17

Size of RBC may vary with pathophysiological influences
Often assess as volume (e.g. MCV)
Increase in size - macrocyte
Decrease in size - microcyte
Normal - normocytes
Assessed via
- MCV
- blood film