Introduction to Clinical Dermatology

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Introduction to Clinical Dermatology
We’ll start with the basic structure of the skin, and as we probably know, the skin consists of two layers: dermis and epidermis. The epidermis has only one type of structures which are cells -no blood vessels, no lymphatics-, and the majority of those cells (about 85% of those cells) are called “keratinocytes”. The rest are called melanocytes, merkel cells, and langerhans cells. The cells in the epidermis are arranged into 4 layers:

* Basal layer: it is where we have mitosis, and then the cells will migrate to the layers above. * Prickle cell layer (spinous or squamous).
* Granular layer.
* Horney layer: it is the uppermost layer in the skin, and it is the layer that we see and touch on the surface of the skin, and it is composed of dead cells that had lost their nuclei. As you can see in the picture that the basophilic structures (the nuclei) are not present in this layer. Although the horney layer has dead cells, it is an important layer in the epidermis because it forms a physical barrier line to protect the internal environment. So problems and diseases affecting the horney layer will impair this protecting function leading to infections, allergies…

This is how the skin looks under the microscope. The bulk of the skin is dermis; 9/10th of the skin is dermis, and the bulk of dermis consists of collagen (mostly type 1 collagen). The blue things are the nuclei, and the horney layer is devoid of nuclei. And this is the normal basket-weave appearance of the skin. Epidermal cells:

* Keratinocytes: the majority.
* Melanocytes: they are the color-producing cells in the epidermis that produce melanin which is then transferred to keratinocytes. Melanin absorbs UV light and inactivates it, otherwise we have a risk of having cancer. So western communities that have a white skin color (low activity of melanocytes) are more prone to have skin cancers, and the most common type of cancer in the western community is skin cancer; in particular the basal cell carcinoma. * Langerhans cells: they are the macrophages of the skin, and the predominant antigen-presenting cells in epidermis and dermis. And as we know, macrophages have different names in different tissues; in the liver they are called kupffer cells, and in the brain they are called microglial cells. Their function is to take the antigens, process them, and then present them to T lymphocytes, and then they go to the lymph nodes where their action starts. * Merkel cells: they are modified transducers for fine touch.

The dermis:
The dermis consists of several components:
* Fibers (collagen and elastin).
* Ground substance (glycosaminoglycans) that hydrates the skin. * Several types of cells: Fibroblasts (they produce collagen and elastin), Lymphocytes, Macro, Mast cells… * And it has appendages; Glands like sebaceous glands that produce sebum that moisturizes the skin, Apocrine and Eccrine glands that produce sweat that has a function in the thermoregulation of the body; Hair follicles, and Nails. * Also we have supportive structures; nerves, lymphatics, vasculature, smooth muscles. So if a lesion bleeds, then we know that the pathology is in the dermis.

Now, how do we approach patients with a skin disease?
* Don’t be shy to introduce yourself as a medical student! Only few of your previous colleagues in the school could get into the medical school, so be proud to say to the patient that I’m a medical student :) * Believe it or not, you can establish a connection with the patient by breaking the ice with saying these few words. So it is important for you to identify yourself, so that the patient knows your name and sees your face to have a more personal relation. * Then you take the permission to touch the skin, this is the polite way! Some patients may reject that and say “NO”, so you should respect that and say “thank you”. * Also you should always maintain the patient’s...
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