10 Pearls from the Basic Structure of Skin
Whitney A. High, MD, JD, MEng
Dr High provided the MauiDerm NP+PA Fall 2014 audience with a comprehensive presentation on the basic structure of skin. Here’s what you need to know…
1. The skin consists of “three layered cake.” The epidermis an outer protective outer layer. The dermis is a middle layer that provides “tensile” strength. The deeper subcutis is insulating fat.
2. The epidermis gets all its nutrition and sustenance from the dermis. The dermis contains all the “supportive” structures of the skin, such as blood vessels, nerves, and many “adnexal structures.”
3. The epidermis consists chiefly of keratinocytes (“skin cells”). These cells are arranged in layers to form a “maturing” protective layer that replaces itself every ~28 days:
- stratum basal = the germinative layer of the skin that divides to regenerate the epidermis
- stratum spinosum = names for the intraspinous properties that bind the keratinocytes
- straum granulosum = the granular layer where keratohyaline granules are produced
- stratum corneum = the “dead” outer layer the provides the most barrier function
4. The dermis is comprised of three main building blocks: collagen, elastic fibers, and “ground substance. Collagen is the material that provides the tensile strength to the skin. Elastic fibers provide skin resiliency. Ground substance facilitates the diffusion of nutrients and oxygen.
5. The “dermoepidermal junction” is where the epidermis attaches to the dermis. This is also the location of melanocytes that make protective melanin for the skin. The DEJ is where most nonmelanoma skin cancer invades the dermis, the place where nearly all melanoma originates, and the place where many bullous and “interface” diseases transpire.
6. When confronted with a skin disease, one must ask themselves, “where do I believe that that pathology is occurring?” For example, the pathologic process might be:
- epidermal – such as the spongiosis (intraepidermal edema) and weeping of dermatitis, or the yeast/hyphae of tinea versicolor/pityriasis versicolor growing in the stratum corneum
- dermal – such as the histiocytic/macrophagic infiltrate of granuloma annulare, or the neutrophilic inflammation of small blood vessels in leukocytoclastic vasculitis
- subcuticular – such as the panniculitis of erythema nodosum
7. Being able to predict where the likely pathology is occurring also facilitates the securing of a “representative” biopsy, which is always the responsibility of the clinician.
8. Adnexal structures may be the site of inflammatory pathologic processes (acne, hidradenitis), may be the site of neoplastic processes (sebaceous carcinoma), or these structures may simply behave in an undesired way (seborrhea, hyperhidrosis).
9. Uncontrolled and unchecked growth of certain components of the skin leads to cancer, such as basal cell carcinoma (from basilar keratinocytes), squamous cell carcinoma (also from keratinocytes) and melanoma (from melanocytes).
10. Skin structure and function changes with age, such as dyspigmentation and facial wrinkling, formation of “solar elastosis” (damaged elastic), and increased water loss to the environment.
