Question 1
Paper 2Hard16 marksHistology technicians are testing whether vessel type can be identified from transverse micrographs. Specimen A has been independently identified as an artery and specimen B as a vein. Wall thickness and lumen diameter were measured in three micrographs of each specimen.
| Specimen | Wall thickness / mm (micrographs 1, 2, 3) | Lumen diameter / mm (micrographs 1, 2, 3) |
|---|---|---|
| A | 0.48, 0.50, 0.52 | 3.0, 3.1, 3.2 |
| B | 0.38, 0.40, 0.42 | 6.0, 6.2, 6.4 |
The relative wall thickness index is calculated as:
Calculate the relative wall thickness index for specimens A and B. Give each answer to one decimal place and show your working.
Describe the structural difference between specimen A and specimen B indicated by your results.
A further unknown specimen, C, is examined in three transverse micrographs. Its wall thickness measurements are 0.58, 0.60 and 0.62 mm; its lumen diameters are 7.8, 8.0 and 8.2 mm.
Calculate the relative wall thickness index for specimen C, giving your answer to one decimal place.
Identify specimen C as an artery or a vein. Explain why comparing only its absolute wall thickness with that of specimen A could lead to a different conclusion.
A colleague proposes using a universal cutoff of 10.0%: any vessel with an index above 10.0% is an artery and any vessel with an index below 10.0% is a vein. Evaluate this proposal using the results for A, B and C, and suggest one way to test the cutoff before using it to identify further micrographs.