Anatomy Review: Skin

00:01 Before we talk about each of those other items on our differential, behooves us to take a look at the skin layers themselves to make sure our anatomies is on point here.

00:10 So, as you can recall, the epidermis, which is all of those layers on the top there, is divided into 6 different layers, starting with the stratum corneum on the outside, which is essentially dead skin, the stratum lucidum, the stratum granulosum, the stratum spinosum, and the stratum basale.

00:29 It's the stratum basale, which is where new skin cells, new keratinocytes are being made, and they're gradually migrating out to those outer layers until at the outermost layer, it's basically just dead cells.

00:41 All the keratinocytes are connected to one another by individual desmosomes. That's what basically provides a nice link between each keratinocyte. In contrast, the epidermis is connected to the dermis at the stratum basale via hemidesmosomes. These are basically links that connect right at the base of those stratum basale cells connecting the basement membrane to the dermis.

01:07 Depending upon where an immune- mediated attack occurs, that's going to dictate how tense the bullae on the outside is.

01:15 So, if the lesion was within the keratinocytes in the epidermis, then the skin is going to be very thin, and it's unlikely that the blisters will stay intact.

01:27 Whereas, if the autoimmune attack is at the hemidesmosomes, at the junction between the epidermis and the dermis and the dermis, essentially, the epidermis is completely intact, and so, those bullae are going to be tense and are going to basically stay strong and intact, rather than falling apart. That principle, that idea about where this defect occurs, will help us to think about what the disease process that's affecting our patient may be. In this case, we know that our patient had very intact bullae, which tells us that the lesion is probably between the epidermis and the dermis, rather than within the epidermis itself.