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Question 316
Physiology → Haematology
Classification
Question
SSBAQuestion Header
A circulating erythrocyte approximately 7 micrometres in diameter enters a capillary approximately 5 micrometres in diameter. Which mechanism permits its passage?
Question Stem
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Options
A
Fragmentation into platelet-sized particles
B
Permanent reduction in erythrocyte diameter
C
Development of pseudopodia
D
Deformation into a bullet-shaped configuration
E
Loss of haemoglobin from the cell
Explanation
erythrocytes as approximately 7 micrometres in diameter but capable of passing through capillaries approximately 5 micrometres wide by deforming and becoming bullet-shaped.
Option Validity
A) Platelets are separate non-nucleated fragments derived from megakaryocytes. Erythrocytes do not normally fragment into platelets to traverse small capillaries.
B) reversible deformation rather than permanent reduction in erythrocyte size. The cell changes shape to pass through the narrower capillary.
C) Pseudopodia are described in activated platelets following collagen exposure. The erythrocyte instead deforms into a bullet-shaped configuration.
E) Haemoglobin loss is not the mechanism described for passage through a narrow capillary. The relevant property is erythrocyte deformability.
Further Reading
Saxena. Textbook for MRCOG-1. Physiology - Haematology - Red Blood Cells, p.67.