Psoriasis Vulgaris: A Literature Review

The skin is a major component of the integumentary system and forms a defensive barrier that protects the internal environment against external forces (Seeley, 2008). Studies carried out by Lowes, Suárez-Fariñas, and Krueger (2013), Cargill et al. (2007) and Tsoi et al. (2012) show that psoriasis vulgaris is a homeostatic disorder of the skin that interrupts the normal proliferation, differentiation and maturation of epithelial cells in the stratum corneum. The focul site of psoriasis vulgaris, called psoriatic, lesions contain higher than normal levels of T Cells, leading to the conclusion that psoriasis vulgaris is a T Cell mediated response to external triggers of either the skin or the immune system (Roberson & Bowcock, 2010; Sabat & Wolk, 2011) The integumentary system provides a protective barrier between the internal and external environments, provides insulation, support, and can detect sensations (Seeley, 2008). Skin is the most visually obvious component of the integumentary system and is categorised into three major layers; the epidermis, the dermis and the hypodermis. The skin houses the integumentary systems accessory structures; the nails, hair, glands and the sensory receptors. The dermis is situated deep to the epidermis and is made up of mainly collagenous connective tissue as well as containing sensory receptors, hair follicles, glands and blood vessels. The deepest layer of the skin is the hypodermis and contains subcutaneous tissue (Seeley, 2008). The epidermis is avascular and has five distinguishable strata; stratum germinativum, stratum spinosum, stratum grainulosum, stratum lucidium and the stratum corneum. The stratum corneum is the most superficial layer of the epidermis and forms a barrier that protects and prevents excess absorption and loss of bodily fluids in a terrestrial environment in addition to hindering the entry of pathogens into the body (Scheuplein RJ, 1971). Elias (2005), explains that keratinocytes make up ~90% of the stratum corneum along with lipids located in the extracellular space. The stratum corneum also contains populations of immune cells, or T Cells, that assist in the homeostatic maintenance and repair of the skins barrier by detecting areas of irritation, pathogens and creating areas of inflammation in a process known as wound-healing (Ghadially, Reed, & Elias, 1996; Seeley, 2008). Homeostasis involves the cooperation of all body systems to maintain a relatively constant internal environment. There and various types of homeostatic functions such as temperature regulation, mineral regulation, cell proliferation, differentiation and repair mechanisms (Van Keymeulen & Blanpain, 2012). The ongoing maintenance and repair of the skins barrier is an important part of the homeostatic functioning of the integumentary system. In normal homeostatic skin barrier functioning there is a determined rate of proliferation of keratinocytes from stem cells located in the basal layer of the stratum corneum, also known as the dermal-epidermal bridge (Van Keymeulen & Blanpain, 2012). Keratinocytes produce keratin, a strong protein that provides protection and support for the …show more content…
The lesions may diminish in-time however psoriasis vulgaris is classified by a re-emergence and ongoing flare-ups (Griffiths & Barker, 2007). There are several recognised forms of psoriasis such as sebhorric psoriasis, nail psoriasis, inverse psoriasis, guttate psoriasis and pustular psoriasis; however psoriasis vulgaris is the most common form of the skin disorder with 90% of cases reportedly of psoriasis vulgaris (Parisi, Symmons, Griffiths, & Ashcroft, …show more content…
The abnormal T Cell mediated response results in a hyper-proliferation of epithelial cells and as a result the keratinocyte is not able to follow the normal process of differentiation and maturation (Nograles, Davidovici, & Krueger, 2010; Sabat & Wolk, 2011). The cells reaching the superficial layers of the stratum corneum in psoriatic skin have not yet fully matured into corneocytes. The layers of immature cells accumulate on the surface of the skin to form psoriatic lesions which contain higher than normal levels of T Cells (Ghadially et al., 1996; Lowes et al., 2008; Lowes et al., 2013; Nograles et al., 2010).
Psoriasis vulgaris is said by Lowes et al. (2013) to be “…a disease mediated by activated T Cells that are present in focal skin regions…” (Lowes, M., Suárez-Fariñas, M., Krueger, J., 2013, Immunology of Psoriasis Annual Review of Immunology; 32: 227–255). But it is unclear whether the genetic foundation for the abnormality is of the skin itself or the immune system (Roberson & Bowcock, 2010). It is generally agreed up that the normal homeostatic repair of the skin’s barrier, in psoriatic skin, is malfunctioning and there is a defective immune response to irritation (Lowes et al., 2008; Sabat & Wolk,