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Series 1: The Skin · Episode 3

The Dermis

Where Your Scars Are Written

23 minutes. 16 references, each checked at source.

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A skin graft shrinks the moment you lift it, and the thicker the graft, the more it shrinks. Which sits very awkwardly beside the thing everyone is taught, that thicker grafts contract less. Both are true. They are two different contractions, running in opposite directions, and separating them is the difference between a full answer and half of one.

Episode 3 of The Anatomy Purist. Dev takes you into the dermis. Two zones, two collagen types, and a set of lines that Karl Langer mapped on cadavers in 1861 that still determine whether your incision scars or disappears.

Covering the papillary and reticular dermis, Langer's lines, the biology of collagen remodelling, solar elastosis, and why full thickness grafts contract less than split thickness.

Themes from this episode

Practice what you just heard

Two questions on the themes of this episode, free, marked as you go. Then one from the Vault on the same ground.

Question 1 · Applied

Which statement about collagen distribution in the dermis is correct?

Answer to see the explanation and the source.

Question 2 · Foundation

What provides the tensile strength of skin?

Answer to see the explanation and the source.

From the Vault, on the same theme

Synoptic: The Operating Theatre Across Regions · Purist Locked

On the face, elective incisions are laid along the relaxed skin tension lines; on the digits, no incision may cross a flexor crease at a right angle. Which single property of scar tissue do both rules exist to manage?

  • AA scar does not regain the full strength of the skin around it, so it must lie where tension is least
  • BA scar cannot lengthen, so its axis must not lie along a direction the skin has to stretch
  • CA scar contracts only during its first months, after which splintage ceases to matter
  • DA scar recovers its elasticity as elastin returns during remodelling, provided tension is avoided
  • ECollagen in a scar aligns with the underlying muscle fibres, whatever the incision’s direction

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References

  1. Standring S, editor. Gray's Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. Elsevier; 2020.
  2. Langer K. Zur Anatomie und Physiologie der Haut. I. Über die Spaltbarkeit der Cutis. Sitzungsber Akad Wiss Wien. 1861;44:19-46. *(Historical source; predates PubMed indexing.)*
  3. Borges AF, Alexander JE. Relaxed skin tension lines, Z-plasties on scars, and fusiform excision of lesions. Br J Plast Surg. 1962;15:242-254. PMID: 13871292.
  4. Borges AF. Relaxed skin tension lines (RSTL) versus other skin lines. Plast Reconstr Surg. 1984;73(1):144-150. PMID: 6691065.
  5. Meigel WN, Gay S, Weber L. Dermal architecture and collagen type distribution. Arch Dermatol Res. 1977;259(1):1-10. PMID: 71020.
  6. Lovell CR, Smolenski KA, Duance VC, Light ND, Young S, Dyson M. Type I and III collagen content and fibre distribution in normal human skin during ageing. Br J Dermatol. 1987;117(4):419-428. PMID: 3676091.
  7. Lee Y, Hwang K. Skin thickness of Korean adults. Surg Radiol Anat. 2002;24(3-4):183-189. PMID: 12375070.
  8. Silver FH, Freeman JW, DeVore D. Viscoelastic properties of human skin and processed dermis. Skin Res Technol. 2001;7(1):18-23. PMID: 11301636.
  9. Gurtner GC, Werner S, Barrandon Y, Longaker MT. Wound repair and regeneration. Nature. 2008;453(7193):314-321. PMID: 18480812.
  10. Goslen JB. Wound healing for the dermatologic surgeon. J Dermatol Surg Oncol. 1988;14(9):959-972. PMID: 3045181.
  11. Mutsaers SE, Bishop JE, McGrouther G, Laurent GJ. Mechanisms of tissue repair: from wound healing to fibrosis. Int J Biochem Cell Biol. 1997;29(1):5-17. PMID: 9076937.
  12. Rudolph R. Contraction and the control of contraction. World J Surg. 1980;4(3):279-287. PMID: 6998140.
  13. Fisher GJ, Wang ZQ, Datta SC, Varani J, Kang S, Voorhees JJ. Pathophysiology of premature skin aging induced by ultraviolet light. N Engl J Med. 1997;337(20):1419-1428. PMID: 9358139.
  14. Uitto J, Bernstein EF. Molecular mechanisms of cutaneous aging: connective tissue alterations in the dermis. J Investig Dermatol Symp Proc. 1998;3(1):41-44. PMID: 9732056.
  15. Braza ME, Fahrenkopf MP. Split-Thickness Skin Grafts. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2023. Bookshelf ID: NBK551561. *(Source for the primary/secondary contraction distinction; StatPearls is not assigned PMIDs.)*
  16. Reilly DM, Lozano J. Skin collagen through the lifestages. Plast Aesthet Res. 2021;8:2. *(Source for the 1, 1.5% per year decline in dermal collagen production. This journal is not indexed in PubMed; the figure is voiced in the script as an approximation.)*
Episode 2: Langer's LinesEpisode 4: Blood Supply
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