Skin
Skin

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skin (integument) functions: - temperature modulation - protection - sensation - vitamin D activation - excretion (H 2 O, Na + Cl - ) - temperature modulation - from heat - perspiration - from cold - hair and subcutaneous fat - protection - from blunt or sharp trauma - from ultraviolet radiation - melanin pigment in epidermis is prod uced by melanocytes (of neural crest origin) , which transfer melanin pigment granules to the epidermal cells (keratinocytes) - UV radiation damages DNA, increasing risk of skin cancer - UV radiation breaks down folic acid , increasing daily requirement - UV radiation activates vitamin D, supporting calcification of the bones - sensation - epidermal (receptors in epidermis) - pain and temperature = ‘injury’ receptors (nociceptors ) = free nerve endings → nerve fibers penetrating among the lower layers of skin epidermal cells, concentrated in skin of the face, hands, feet, and genitals - fine touch (discriminative, high resolution) → nerve fibers adjacent to the basal lamina of skin send neural processes which synapse with Merkel cells (neural crest origin), scattered in basal layer of skin - dermal (receptors in dermis) - light touch → nerve endings in Meissner corpuscles in dermal ridges - stretch → nerve endings in Ruffini corpuscles in reticular dermis - pressure → nerve endings in Pacinian corpuscles in deep dermis - Pacinian corpuscles occur in face (lips), palmar hands, plantar feet, and genitals - hair movement → p eritrichial (perifollicular) nerve endings - vitamin D activation - primary activation of vitamin D in blood is by solar ultraviolet rays via skin capillaries - secondary activation of vitamin D (to calcitriol) occurs in the kidney (vitamin D deficiency: child = rickets; adult = osteomalacia) - excretion - water and salt (perspiration) ©