8.1.5—Plan diagrams of arteries and veins

A plan diagram is a simplified record of the visible organisation of a specimen. It preserves the vessel outline, lumen and relative wall layers without copying every cell or adding structures that the section does not show.

1. Read the evidence first: identify transverse section (TS) or longitudinal section (LS), note the field of view, and record magnification or a scale bar when supplied. Keep orientation and scale consistent.
2. Trace the overall outline: lightly locate the vessel boundary and lumen, then draw a large, clear outline using continuous unbroken lines. Preserve the specimen’s relative proportions rather than inventing a circular or symmetrical shape.
3. Add the visible arrangement: show the wall as the major layers or regions that can be distinguished, including relative thickness and the lumen position. In a longitudinal section, show the lengthwise arrangement rather than forcing a cross-section view.
4. Simplify deliberately: use clean lines and omit individual cells, shading, colour and microscopic texture. A plan diagram communicates pattern and proportions, not every cell boundary.
5. Label only evidence: add ruled, non-crossing labels for visible structures such as lumen, wall layers or a valve if present. Do not label a feature inferred only from oxygen content or from an unseen part of the vessel.
6. Check before finishing: compare lumen-to-wall proportions with the source, make sure lines are continuous and labels are unambiguous, and state any scale or section limitation that affects the interpretation.

Diagram boundary: a plan diagram is not a detailed histological drawing; its value is a faithful, labelled summary of the structures and relative arrangement that are actually visible.

Do not draw every cell, add unobserved layers or use decorative shading. Staff-only visual brief: paired TS/LS plan-diagram examples with continuous outlines, lumen, wall-layer labels and a scale/orientation cue; do not generate or bind an image.