Principles of skin

===Lecture Details===
Paul McMenamin; Week 1 MED1011; Anatomy
===Lecture Content===
Skin is a critical barrier especially to dehydration, is the largest sensory organ in the body, important for thermoregulation and has important metabolic and immune functions. The layers are epidermis, dermis, subcutaneous tissue (or hypodermis) with fat and deep fascia. Fibrous septum can connect the dermis and the deep fascia.
Thin skin is found everywhere except the palms and soles of the feet. There are 5 layers of the epidermis- stratum basale, which contains stem cells, melanocytes and Merkel discs; stratum spinosum which contains Langerhans cells, stratum granulosum which contains granular keratinocytes, stratum lucidum which contains clear keratinocytes, and stratum corneum which is the outer layer that is continually sloughed off. Stratum corneum and lucidum may be difficult to tell apart in thin skin.
Dermis has papillary layer and reticular layer. Papillary layer is where dermis interdigitates with the epidermis, forming papillae. Some Meissner corpuscles are in the papillary layer. Reticular layer lies beneath the papillary layer but is constituently identical. Sweat glands, sebaceous glands and hair follicles are contained in the dermis.
Skin tension lines are known as Langer lines. Determined by alignment of dermal connective tissue and effect of underlying muscle. Langerhans cells, mast cells and macrophages all exist in the skin, act as defences for the body. Melanin influences the colour of the skin. There are 5 modalities of sensation- temperature, vibration, light touch, temperature and pain. Preaxial border is the cranial side of outstretched dermatomes, post axial the caudal. A distinct line separates the two. Females generally have lighter skin, possibly due to vitamin D3 requirements during pregnancy and lactation.
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