apocrine sweat glands dermatology dermis eccrine sweat glands eponychium hair inner root sheath integumentary system keratinocyte lamina densa lamina lucida nail plate outer root sheath panniculus adiposus panniculus carnosus papillary dermis paronychium sebaceous gland skin skin appendage stratum corneum stratum germinativum stratum granulosum stratum lucidum stratum spinosum subcutaneous tissue