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NBME 24 Answers

nbme24/Block 4/Question#35 (reveal difficulty score)
An investigator is conducting a study of a ...
Basal keratinocyte:suprabasal keratinocyte ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
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 +15  upvote downvote
submitted by โˆ—usmleuser007(464)
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After some research this is why the other answers are incorrect:

Basal keratinocyte & lamina lucida

  • Incorrect b/c lamina lucida is a component of the basement membrane which is found between the epithelium and underlying connective tissue (e.g., epidermis and dermis of the skin).
  • It is a roughly 40 nanometre wide electron-lucent zone between the plasma membrane of the basal cells and the (electron-dense) lamina densa of the basement membrane. (WIKI)
  • basal keratinocyte attaches to the basement membrane using hemidesmosome

Granular keratinocyte & stratum corneum

  • Stratum lucidum separates these two layers.
  • there are no desmosome that connect these two layers
  • Image for reference

Lamina lucida & Lamina densa -- click for image

  • both are part of the basement membrane and not the epidermis

Melanocyte & basal kertinocyte --- click for image

  • are both connected to eachoter via E-cadherins
  • it is probably the damage to this connection that
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azibird  The stratum lucidum is only present in the thick skin of the palms, soles, and digits. So the stratum granulosum and corneum do touch in most of the body. I guess they just aren't connected by desmosomes. https://opentextbc.ca/anatomyandphysiology/chapter/5-1-layers-of-the-skin/ +1
peridot  Wow if I'm understanding this correct, lamina lucida (basement membrane) is not the same as stratum lucidum (between stratum corneum and stratum granulosum). That def confused me about this question bc I simultaneously was like wait isn't this in the basement membrane but also recalled the picture in FA with all the layers. Thanks so much for the super detailed explanation of all the answer choices! +1
rena13  how do i unscramble to see the explanation? +1
drdoom  @rena13 -> https://nbmeanswers.com/membership +



 +13  upvote downvote
submitted by โˆ—fenestrated(32)
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Basically asking if you know Pemphigus Vulgaris. Separation of suprabasilar epidermis, intact basal keratinocytes vs Bollous pemphigoid--> includes separation of basal layer

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subclaviansteele  This how I thought of the question...Classic histology photo of the "tomb stone" row of basal cells and the lifted keratinocytes. +3



 +10  upvote downvote
submitted by โˆ—lsmarshall(465)
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"Desmosome (Macula adherens) - A cell-to-cell connection that provides structural support with intermediate filaments, particularly in tissues that undergo mechanical stress (e.g., skin, gastric tissue, bladder). Connects keratinocytes in the stratum spinosum of the epidermis." - AMBOSS

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sympathetikey  This is why I was looking for some answer indicating keratinocytes in the stratum spinosum...instead they just gave a bunch of bs choices. +31
roygbiv  I'm confused because I also know that S. aureus cleaves desmoglein in the stratum granulosum, so why is it specifically this answer? +4
duat98  desomosomes connects cells to cells. hemidesmosome connects cells to basement membrane. +4
medguru2295  I think what this is really asking is can you tell Pemphigus Vulgaris from Bullous Pemphigoid Vulgaris (question)- Attack on DESMOSOMES- this separates some keratinocytes from others (ie some in basal layer from ones above). Pemphigoid- attack on HEMIDESMOSOMES- this means separation of the keratinocytes from the basement membrane. +3



 +6  upvote downvote
submitted by โˆ—brethren_md(105)
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Stupid question, honestly just take your best guess and move on lol.

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seagull  โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–ˆโ–€โ–€โ–‘โ–‘โ–ˆโ–‘โ–‘โ–‘โ–‘โ–‘โ–‘ โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–„โ–€โ–€โ–€โ–€โ–‘โ–‘โ–‘โ–‘โ–‘โ–ˆโ–„โ–„โ–‘โ–‘โ–‘โ–‘ โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–ˆโ–‘โ–ˆโ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–โ–‘โ–‘โ–‘ โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–โ–โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–„โ–‘โ–โ–‘โ–‘โ–‘ โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–ˆโ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–„โ–€โ–€โ–‘โ–โ–‘โ–‘โ–‘ โ–‘โ–‘โ–‘โ–‘โ–„โ–€โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–โ–‘โ–„โ–„โ–€โ–‘โ–‘โ–‘โ–‘ โ–‘โ–‘โ–„โ–€โ–‘โ–‘โ–‘โ–โ–‘โ–‘โ–‘โ–‘โ–‘โ–ˆโ–„โ–€โ–‘โ–โ–‘โ–‘โ–‘โ–‘โ–‘ โ–‘โ–‘โ–ˆโ–‘โ–‘โ–‘โ–โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–„โ–‘โ–ˆโ–‘โ–‘โ–‘โ–‘โ–‘ โ–‘โ–‘โ–‘โ–ˆโ–„โ–‘โ–‘โ–€โ–„โ–‘โ–‘โ–‘โ–‘โ–„โ–€โ–โ–‘โ–ˆโ–‘โ–‘โ–‘โ–‘โ–‘ โ–‘โ–‘โ–‘โ–ˆโ–โ–€โ–€โ–€โ–‘โ–€โ–€โ–€โ–€โ–‘โ–‘โ–โ–‘โ–ˆโ–‘โ–‘โ–‘โ–‘โ–‘ โ–‘โ–‘โ–โ–ˆโ–โ–„โ–‘โ–‘โ–€โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–โ–‘โ–ˆโ–„โ–„โ–‘โ–‘โ–‘ โ–‘โ–‘โ–‘โ–€โ–€โ–„โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–„โ–โ–„โ–„โ–„โ–€โ–‘โ–‘โ–‘ THis Question โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘โ–‘ +3



 +4  upvote downvote
submitted by โˆ—usmleuser007(464)
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After some research this is why the other answers are incorrect:

  1. basal keratinocyte & lamina lucida
  2. Incorrect b/c lamina lucida is a component of the basement membrane which is found between the epithelium and underlying connective tissue (e.g., epidermis and dermis of the skin).
  3. It is a roughly 40 nanometre wide electron-lucent zone between the plasma membrane of the basal cells and the (electron-dense) lamina densa of the basement membrane. (WIKI)

  4. basal keratinocyte attaches to the basement membrane using hemidesmosome

  5. Granular keratinocyte & stratum corneum

  6. Stratum lucidum separates these two layers.
  7. there are no desmosome that connect these two layers

  8. Image for reference

  9. Lamina lucida & Lamina densa -- click for image

  10. both are part of the basement membrane and not the epidermis

  11. Melanocyte & basal kertinocyte --- click for image

  12. are both connected to eachoter via E-cadherins
  13. it is probably the damage to this connection that might lead to melanoma
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jbrito718  Loss of E-Cadherin!! +



 +2  upvote downvote
submitted by โˆ—osgoodschlatter10(41)
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Desomosmes by function interconnect keratinocytes in the stratum spinosum - startum spinosum is the suprabasal layer. Exclude option: a) Lucida is too high ; not in continuation with basal layer c) Corneum is even higher, Granulosum and Corneum aren't n continuation d) Lamina dens (BM) and lamina lucida not keratinocytes and not in continuation either e) Melanocyte are in the basal layer; it is not a keratinocyte

b) is the only option that makes sense based on histology and also the only option that speaks about inter-keratinocyte linkage

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 +1  upvote downvote
submitted by โˆ—misterdoctor69(70)
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How come melanocytes:basal keratinocytes don't also have a desmosomal connection (in addition to their E-cadherin link)?

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vivijujubebe  melanocyte is not part of the epidermal structure. they're at the epidermal-dermal junction and they produce melanin which is transported to the epidermal +1



 +1  upvote downvote
submitted by โˆ—osgoodschlatter10(41)
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Desomosmes by function interconnect keratinocytes in the stratum spinosum - startum spinosum is the suprabasal layer. Exclude option: a) Lucida is too high ; not in continuation with basal layer c) Corneum is even higher, Granulosum and Corneum aren't n continuation d) Lamina dens (BM) and lamina lucida not keratinocytes and not in continuation either e) Melanocyte are in the basal layer; it is not a keratinocyte

b) is the only option that makes sense based on histology and also the only option that speaks about inter-keratinocyte linkage

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 +0  upvote downvote
submitted by pygmymarmoset(1)
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So I thought about the "tombstone" picture on p.207 of Pathoma where the desmosomes are defective. The cells in the basal layer stay attached to the basement membrane, but the cells above get disconnected. So that made me think of breaking the connection between cells in the basal layer and cells above the basal layer (suprabasal).

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 +0  upvote downvote
submitted by jellyfish923(0)
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https://www.researchgate.net/profile/Mithun_Bhowmick5/publication/317179550/figure/fig1/AS:500004767715328@1496221834988/Cross-section-of-human-skin-Stratum-corneum-SC-and-epidermis-the-main-barrier-to.png maybe this picture can show where the desmosome exist

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 +0  upvote downvote
submitted by โˆ—usmleuser007(464)
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Blistering diseases such as pemphigus vulgaris (PV) and pemphigus foliaceus (PF) are autoimmune diseases in which auto-antibodies target desmogleins.

  • PV is caused by circulating autoantibodies (IgG) that target Dsg3 (Desmoglein 3) and sometimes Dsg1.
  • PV is manifested by suprabasal acantholysis, or blisters in the mucous membrane and blisters in the epidermis.
  • PF patients have autoantibodies that target Dsg1 with superficial blisters on the epidermis with no mucous membrane issues.
  • Both disease result in a loss of keratinocyte adhesion.
  • Pemphigus can also be caused by a bacterial infection: bullous impetigo is an infection caused by a staphylococcus bacterium that releases a toxin that cleaves the Dsg1 extracellular domain.
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 +0  upvote downvote
submitted by โˆ—madamestep(17)
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The key here is to know that desmosomes connect keratinocytes to other keratinocytes. Remember that in PV you get the "tombstone" look at the basement membrane.

I don't think they expect us to know all of these connections here, just where are desmosomes and where are hemidesmosomes.

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 +0  upvote downvote
submitted by โˆ—ankistruggles(18)
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Why is basal keratinocyte : suprabasal keratinocyte the cell junction thatโ€™s most likely to be affected? Is it because itโ€™s the only answer that lists a junction between two keratinocytes?

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sattanki  Not too sure on this one, but I interpreted the basal keartinocyte:suprabasal keratinocyte as the stratum spinosum region, which is known to have the most desmosomes. +



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