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Series 1: The Skin · Episode 7, not yet released

Regional Variation

Why Every Site Operates Differently

19 minutes. 13 references, each checked at source.

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A cut artery retracts and closes itself, everywhere in the body except the scalp, where the fibrous septa hold it open and a child can bleed to death from a laceration you could cover with a thumb.

That is where Episode 7 of The Anatomy Purist starts, and the rest of the episode is the same argument in six other regions. Eyelid thickness as Hwang actually measured it, 320 microns at the lash margin and 1127 just below the brow, it triples across one lid. Why the lower lid everts, which has nothing whatever to do with orbicularis. The five SCALP layers, and the subgaleal plane that is only *relatively* avascular, because emissary veins run through it into the dural sinuses. Why palm and sole are follicle-free but not reservoir-free. What a full-thickness glabrous graft really delivers, and the one thing it never does. And what buccal mucosa actually displaced in urethroplasty, it was not scrotal skin.

Tiered Foundation to Purist. Every reference verified. Episode 7.

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

Why do scalp wounds gape so dramatically?

Answer to see the explanation and the source.

Question 2 · Foundation

What do the five layers of the SCALP mnemonic stand for?

Answer to see the explanation and the source.

From the Vault, on the same theme

General Principles: Fascia, Compartments & Tissue Planes · Purist Locked

A student dissecting notes that the limbs are ensheathed in a strong investing fascia, while beneath the skin of the face there is no such layer, the muscles lying within the subcutaneous tissue itself. What functional rule explains where the body omits its investing sheet?

  • AInvesting fascia is absent where muscles must move the skin itself
  • BInvesting fascia forms only where muscles attach to underlying bone
  • CInvesting fascia develops only in regions built for weight-bearing
  • DInvesting fascia is lacking wherever fat must glide freely over muscle
  • EInvesting fascia is absent wherever the skin itself is thin

Unlock to see the answer

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References

  1. Standring S, editor. Gray's Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. London: Elsevier; 2020. [Textbook, no PMID.]
  2. McCarthy JG, editor. Plastic Surgery. Vol. 1. Philadelphia: WB Saunders; 1990. [Textbook, no PMID.]
  3. Sherris DA, Larrabee WF Jr. Principles of Facial Reconstruction: A Subunit Approach to Cutaneous Repair. 2nd ed. New York: Thieme; 2010. [Textbook, no PMID.]
  4. Wei FC, Mardini S, editors. Flaps and Reconstructive Surgery. 2nd ed. Philadelphia: Elsevier; 2017. [Textbook, no PMID.]
  5. Tolhurst DE, Carstens MH, Greco RJ, Hurwitz DJ. The surgical anatomy of the scalp. Plast Reconstr Surg. 1991;87(4):603-12. PMID: 2008459.
  6. Carstens MH, Greco RJ, Hurwitz DJ, Tolhurst DE. Clinical applications of the subgaleal fascia. Plast Reconstr Surg. 1991;87(4):615-26. PMID: 2008460. doi:10.1097/00006534-199104000-00003
  7. Rittié L, Sachs DL, Orringer JS, Voorhees JJ, Fisher GJ. Eccrine sweat glands are major contributors to reepithelialization of human wounds. Am J Pathol. 2013;182(1):163-71. Epub 2012 Nov 14. PMID: 23159944. doi:10.1016/j.ajpath.2012.09.019
  8. Bhargava S, Chapple CR. Buccal mucosal urethroplasty: is it the new gold standard? BJU Int. 2004;93(9):1191-3. PMID: 15180603. doi:10.1111/j.1464-410X.2003.04860.x
  9. Chapple C, Andrich D, Atala A, et al. SIU/ICUD Consultation on Urethral Strictures: the management of anterior urethral stricture disease using substitution urethroplasty. Urology. 2014;83(3 Suppl):S31-47. PMID: 24411214. doi:10.1016/j.urology.2013.09.012
  10. Hwang K, Kim DJ, Hwang SH. Thickness of Korean upper eyelid skin at different levels. J Craniofac Surg. 2006;17(1):54-6. PMID: 16432408. doi:10.1097/01.scs.0000188347.06365.a0
  11. Chopra K, Calva D, Sosin M, et al. A comprehensive examination of topographic thickness of skin in the human face. Aesthet Surg J. 2015;35(8):1007-13. PMID: 26508650. doi:10.1093/asj/sjv079
  12. Ha RY, Nojima K, Adams WP, Brown SA. Analysis of facial skin thickness: defining the relative thickness index. Plast Reconstr Surg. 2005;115(6):1769-73. PMID: 15861089. doi:10.1097/01.prs.0000161682.63535.9b
  13. Patel BC, Malhotra R. Anatomy, head and neck: eyelid. In: StatPearls. Treasure Island (FL): StatPearls Publishing. NCBI Bookshelf ID: NBK482304.
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