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The Skin Facts about Skin • Receptor organ for tactile, heat, and pain sensations • Three layers: epidermis, dermis, hypodermis • Largest organ in the body – 7 % of body mass ANATOMY Hypodermis Blood vessels The Epidermis Consists of 4 layers of tissue – Stratum corneum • • • • What you see on the surface Waterproof Varies in thickness (ex. feet vs. ear) Flattened dead cells, which fall off the skin – Stratum granulosum – Stratum spinosum • Contains keratin-producing cells (protects skin vs. germs and wear and tear – Stratum basale • Cell division takes place and new skin cells are constantly made • Contains melanocytes which produce melanin – Melanin is responsible for skin tone – Melanin protects us from UV rays by absorbing them Epidermal layer Stratum Corneum Stratum Granulosum Stratum spinosum (keratin-producing cells) Stratum Basale Melanocyte Dermis • Middle layer of skin • Thickest layer • Contains blood vessels, sweat glands, hair follicles, sebaceous glands, arrector pili muscle, sensory neurons – Sebaceous glands secrete sebum to protect the hair follicles – The arrector pili muscle contracts and makes our hair stand up Hypodermis • Rich in adipose tissue (fat cells) – Various parts of the body contain more or less of this tissue – Ex. abdomen vs. eyelid PhysiologY Sensory Functions of the Skin • Turn light contacts and pressures into nerve impulses • 3 types of sensory neurons found in dermis that are stimulated by pain or temperature – Pacinian corpuscle (detects *new* pressure) – Ruffini corpuscle (heat, stretch, long touch) – Meissner’s corpuscle (superficial, light touch) Sensory neurons in the Skin Distribution of Sensory Receptors Homunculus – Somatosensory cortex Non-Sensory Function of the Skin • Protects the body (first line of defense) – Stratum corneum protects again bacteria – Sebum makes skin water proof – Melanin protects against UV rays • Regulates body temperature – In hot weather, blood vessels dilate which cause sweat glands to excrete sweat – In cold weather, blood vessels contract – Adipose tissue also keeps us warm • Excretion of certain substances (sweat, excess water and minerals) • Produces vitamin D when the rays of the sun interact with the cholesterol in the skin – Regulates proper calcium absorption which helps with proper bone development Nerve Impulse Pathway Role Pathway Tactile or Temperature Stimuli Receptor Skin Processor Sensory neurons (Pacinian, Ruffini, or Meissner corpuscles) Conductor Sensory Nerve Analyser Somatosensory cortex
