Skin Structure and Function I PDF

SKIN STRUCTURE AND FUNCTION I Dr. P. De Gabriele MD MMCFD DipWH(ICGP) SKIN Cutaneous membrane The integument An external body covering Pliable yet tough Is exposed to air and is a dry membrane. Keeps water and other important molecules in the body Keeps water out...

SKIN STRUCTURE AND FUNCTION I Dr. P. De Gabriele MD MMCFD DipWH(ICGP) SKIN Cutaneous membrane The integument An external body covering Pliable yet tough Is exposed to air and is a dry membrane. Keeps water and other important molecules in the body Keeps water out.  FUNCTIONS (i) Protects deeper tissues from – Mechanical damage Keratin Pressure receptors – Chemical damage The keratinized cells are relatively impermeable to foreign substances. Pain receptors – Bacterial damage Skin secretions are acidic and thus inhibit bacteria. The skin is an ‘unbroken surface’. Besides, phagocytes ingest foreign pathogens, preventing them from penetrating into deeper structures. FUNCTIONS (ii) Protects deeper tissues from – Ultraviolet radiation (damaging effects of sunlight) Melanin produced by melanocytes offers protection from UV damage. – Thermal damage Heat/cold/pain receptors respond to changes in the environment that can damage the skin. – Desiccation A waterproofing glycolipid Keratin FUNCTIONS (iii) Aids in body heat loss or heat retention – Sweat glands are activated and blood flushes into skin capillary beds. On this way, heat can be lost. – The reverse occurs to retain heat. FUNCTIONS (iv) Aids in excretion of urea and uric acid since these are present in perspiration secreted by the sweat glands. Synthesizes Vitamin D – Sunlight acts on modified cholesterol molecules that are converted to Vitamin D. SKIN STRUCTURE EPIDERMIS DERMIS HYPODERMIS – essentially adipose tissue – anchors the skin to underlying organs – acts as a shock absorber – insulates the deeper tissues from extreme temperature changes occurring outside the body. EPIDERMIS EPIDERMIS Stratum basale – The deepest layer of the epidermis and lies closest to the dermis – Epidermal cells receive their nutrients from the dermis. – The cells are undergoing continuous cell division. The daughter cells are pushed upwards to become part of the epidermal layers closer to the skin surface – the stratum spinosum and the stratum granulosum. The cells then become flatter, fill up with keratin and finally die forming the clear stratum lucidum. The outermost layer is the stratum corneum. It is 20 to 30 cell layers thick. This layer rubs and flakes off slowly and steadily and are replaced by cells produced by the division of the deeper stratum basale cells. DERMIS The papillary layer – the upper dermal region – uneven and has fingerlike projections called dermal papillae which indent the epidermis above. The reticular layer – the deepest skin layer – Blood vessels – Sweat and oil glands – Deep pressure receptors called Pacinian corpuscles – Phagocytes Collagen and elastic fibres are found throughout the dermis. Dermal Papillae These may contain: – Capillary loops – to furnish nutrients to the epidermis – Pain receptors (free nerve endings) – Touch receptors called Meissner’s corpuscles