Dermatology

Can you tell that I'm going through my different subject blocks and catching my readers up on those things in vet school that I think are cool are think you might want to know?

Today's post comes courtesy of the Dermatology block, which was the 2 weeks of class before my Christmas break started.

As I looked at more and more derm pics of really unhappy animals with miserable skin diseases, I was more and more convinced that repro and research is my calling.


Did you know that horses have sweat glands in their frogs? (thought they might function in trail marking!).

Did you know that the entire horse hoof is a derm structure? I think most of us are probably familiar with the inside and outside of a hoof from both working with our horses' feet and from various magazine articles on laminitis etc. but never before have I had such a whole picture view of the horses foot and thus such an appreciation for the beauty of its structure. Considering i go on and on about the incredible hoof, thats quite a statement, so I want to share with you the wonder of the hoof through understanding. Thus I introduce, Mel's dermatology short course (and of course the horse hoof is on the only important part of dermatology as far as I'm concerned....).

Using histo images from Colored Atlas of Veterinary Histology, 3rd Edition (highly recommend as a vet histo text book!). The cross section image is from Zachary's vet path text book. White board stuff is mine and the other pictures is stuff from off the internet.

Here's a picture of "normal"skin --> note the layers. 4 is the different layers of the epidermis (outerportion of the skin). Underneath 4 is the dermis. The dermis and epidermis interlock like little fingers in non-haired areas. This example comes from the pad of a dog (I think).

Here's a picture of a hoof epidermis. This entire thing is epidermis!!!!




Here is a picture of hoof dermis, which fits inside the epidermis hoof capsule. Do you see how the epidermis takes on the shape of the underlying dermis? It's hard to see in the picture above, but the epidermis capsule has little ridges in it on the inside.

Do you see how the epidermis and dermis might velcro together? The epidermis and dermis of the hoof have little fingers that tie it together just like in the first histo picture.

The hoof has folds because the dermis and epidermis must slide past eachother as the epidermis grows down to the ground and gets worn down, BUT the dermis and epidermis must stick together well enough that the force and concussion from the ground doesn't tear it apart. The more surface area that is in contact with 2 surfaces, the harder it is to slide past eachother. The function of the folds is to increase surface area. In addition to the folds are many itty bitty tiny projections, like velcro, that increase the surface area EVEN MORE, but doesn't interfere with the hoof epidermis being able to slide past the dermis.

Here's the hoof in a histo image. Can you see the same layers as the first picture? The epidermis looks a little different because instead of having a cell layer that flakes off the top, the epidermis has little tubes running through the "horn" of the epidermis that provide strength and flexibility to the epidermis much like rebar in concrete. But the layers and structures are still there!


In this picture below --> #3 is dermis, everything on top of that to the left is epidermis. 

In this picture below, number 6/8/7 is epidermis.  5 is dermis.





In this pic, 9/8 is epidermis


What's underneath the dermis? Fat, tendons, and bone. There's not much dermis in a horse hoof. Do you see how thin the epidermis is compared to the dermis? The arrows are showing the interface between one section of the dermis and epidermis.



Do you see the fat that is between the epidermis/dermis and the bone at the bottom/sole portion of the foot. That's a pad! It cushions the bone and tendons inside of the hoof capsule. I asked the professor whether that atrophies on a shod horse since the physiology rule is use it or lose and and a shod horse does not use their sole like a barefoot and she said although she hadn't seen any research on that specifically, that it was likely.

BTW - they covered just a few points about propery shoeing in the hoof portion of dermatology and made some points that I thought were really interesting --> mostly because I hadn't heard this in any of the shoeing articles I had read prior to going booted. If I could find a farrier that would shoe my horse with the following points, I probably wouldn't worry about going barefoot as much!

1. The nails shouldn't extend so far behind the toe/quarter that the heel and quarters can't expand --> the back part of the shoe that is in contact with the bottom of the hoof near the heel/quarters should be polished shiny by the movement/expansion of the hoof on top of the shoe.

2. The frog should have contact with the ground.

Unfortunately if there's a farrier out there that can do that, I haven't found them in my area, so I guess I'm barefoot in my renegades! (and honestly, the boots are easier than sticking to a regular shoeing schedule).

Not to mention, I have a strong suscepision that some of the soreness we see in horses that have just had their shoes pulled is from the atrophy of that internal cushion, which takes time to rebuild perhaps? Would love to see some studies on this......

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