The skin may be regarded as one of the most important organ of the human body due to its multiple indispensable functions. It protects a person from all challenges that may come from the environment and assists in the regulation of inner processes as well. This paper is dedicated to the examination of the skin, its gross and microscopic anatomy, functions, and the most common diseases.
Gross Anatomy
The skin is the largest vital organ in the human body. It covers the body’s entire external surface, forming a highly efficient initial protective barrier against mechanical injuries, pathogens, heat, UV light, chemicals, and other threats from the environment (Yousef et al., 2020). In general, the skin covers an area of 1.5 to 2 square meters and weighs between 3.5 and 10 kilograms depending on a person’s body mass and height (“How does skin work?” 2019). It is closely integrated “to the underlying fascial endoskeleton through retinacular ligaments, blood vessels, nerves. and lymphatics” (Wong et al., 2016, p. 92). Besides protection, the skin has other essential functions, including the regulation of body temperature and water release and gathering sensory information concerning environmental conditions. Moreover, it plays an ultimate role in the protection from diseases by the immune system and stores vitamin D, water, and fat.
The texture, thickness, and color of the skin differ over the body regions. In general, there are two major types of the skin on the basis of the thickness of the epidermal and dermal layers – thin hairy and thick hairless skin (Yousef et al., 2020). The first type is prevalent on the human body, while the second one is found in the hands’ palms and the feet’ soles as these parts endure excessive friction and are used heavily.
The skin consists of three layers that have completely different anatomy and functions – the epidermis, the dermis, and the hypodermis (Yousef et al., 2020). The epidermis, or the outer layer, is the primary protection of the whole body that contains melanocytes responsible for the production of melanin. The dermis contains sweat and oil glands, nerve endings, and hair follicles. The hypodermis, or the subcutis, is a subcutaneous tissue’s fatty layer.
Microscopic Anatomy
The first level of the skin, the epidermis, has several layers that include the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum (Yousef et al., 2020). Stratum basale, or stratum germinativum, is the skin’s deepest level separated by basal lamina, the basement membrane, from the dermis. At this level, cells are cuboidal to columnar mitotically active stem cells that produce keratinocytes (Yousef et al., 2020).
Stratum spinosum has 8-10 cell layers and contains irregular polyhedral and dendritic cells. Stratum granulosum with 3-5 cell layers contains keratohyalin and lamellar granules with keratin precursors and glycolipids in diamond-shaped cells. Stratum lucidum made from eleidin is presented in a hairless skin of soles and palms. Finally, the uppermost layer, stratum corneum, consisted of 20-30 cell layers and made up of anucleate squamous cells and keratin, participates in the body’s first immune defense.
The main cells that form the epidermis are melanocytes, keratinocytes, Merkel’s cells, and Langerhans’ cells (Yousef et al., 2020). Melanocytes produce melanin responsible for the skin’s pigment during tyrosine’s conversion to DOPA, and the secretion of melanin stimulated by UVB light protects against UV radiation (“How does skin work?” 2019). Keratinocytes are the epidermis’s predominant cell type that produces keratin and forms the epidermal water barrier through the secretion of lipids.
Merkel’s cells are the most populous in the palms, soles, fingertips, genital, and oral mucosa – they are functioning as mechanoreceptors and sensitive for light touch as their membranes are connected with the skin’s free nerve endings. In turn, Langerhans’ cells play a highly essential role in the body’s defense and antigen presentation. At the same time, the dermis consists of a thinner papillary layer and a thicker reticular layer merged together. The dermis houses hair, the sweat glands, muscles, hair follicles, blood vessels, and sensory neurons. The hypodermis, the deepest skin layer, contains adipose lobules and some skin appendages, including blood vessels, sensory neurons, and hair follicles as well.
Physiology/Functions
The human skin has multiple immeasurably essential functions, and every layer is responsible for particular ones.
Epidermis
It serves as a primary barrier to microorganisms, water, chemical and mechanical trauma, and damaging UV light. To be precise, it is melanin in the epidermis that defends the organism against ultraviolet radiation. In addition, Langerhans’ cells are involved in the immune system and protects the body against multiple infections. In addition, this layer’s turgor, color, and general appearance may indicate the body’s general health and the existence of particular diseases (“How does skin work?” 2019).
Dermis
The skin is responsible for the sensation of heat, cold, touch, and pain due to the nerve endings in the dermis. Moreover, this layer preserves homeostasis through the regulation of water loss and temperature with the help of sweat glands, hair follicles, and blood vessels. As a matter of fact, the skin is highly responsive to the changes in temperature and helps to regulate the body’s processes according to these changes. In addition, oil from the dermis’s sebaceous glands keep the skin moisturized and serves as a barrier to unknown external substances.
Hypodermis
As a fat layer, hypodermis protects the organism from extreme temperatures regulating its temperature as well, serves as the skin’s energy storage area, and provides protective padding.
Skin Diseases
In general, there are multiple types of skin diseases, and although the majority of them are non-fatal, they put a burden on almost 2 billion people worldwide (Liu et al., 2020). The most common ones include acne, rosacea, psoriasis, vitiligo, hives, ichthyosis, and eczema. In addition, the alteration of the skin may be a part of more serious general illnesses, such as measles or chickenpox, or the result of mechanical exposure, for instance, in the case of a blister. Temporary skin disorders include keratosis pilaris, the formation of small rough bumps, and contact dermatitis, the irritation of the skin due to contact with particular materials. In turn, psoriasis, rosacea, and vitiligo are among permanent, incurable skin diseases, the causes of which are still unknown.
References
How does skin work? (2019). Web.
Liu, Y., Jain, A., Eng, C., Way, D. H., Lee, K., Bui, P., Kanada, K., de Oliveira Marinho, G., Gallegos, J., Gabriele, S., Gupta, V., Singh, N., Natarajan, V., Hofmann-Wellenhof, R., Corrado, G. S., Peng, L. H., Webster, D. R., Ai, D., Huang, S. J.,…Coz, D. (2020). A deep learning system for differential diagnosis of skin diseases. Nature Medicine, 26, 900-908. Web.
Wong, R., Geyer, S., Weninger, W., Guimberteau, J. –C., & Wong, J. K. (2016). The dynamic anatomy and patterning of skin. Experimental Dermatology, 25(2), 92-98. Web.
Yousef, H., Alhajj, M., & Sharma, S. (2020). Anatomy, skin (integument), epidermis. NCBI. Web.