intro

• made up of skin, sweat + oil glands, hair and nails

• around 7% of body weight

• role: protection from pathogens and dehydration

• varies in thickness from 1.5-4.0 mm

• 3 layers: epidermis, dermis and hypodermis/superficial fascia

epidermis: outermost layer

• composed of mainly keratinized stratified squamous epithelium

• 4 distinct cell types and 4-5 layers

cells of epidermis

• keratinocytes: produce keratin (protein), connected by desmosomes

  • surface is dead

• melanocytes: synthesize melanin, located at deepest level of epidermis

  • melanin → to keratinocytes, protects against uv damage

• langerhans cells: arise from bone marrow, act as microphages that activate immune system

• merkel cell: present at junction for epidermis and dermis, associated with sensory receptors

layers of the epidermis

• thick skin (palms, fingertips and soles) have 5 strata

• thin skin has 4 (missing stratum basale)

• stratum basale: deepest layer, where mitosis takes place

  • also called stratum germinativum

• stratum spinosum: several layers thick, has intermediate filaments, reduces tension

• stratum granulosum: 3-5 layers thick, flattened keratinocytes

• stratum lucidum: thin layer of dead keratinocytes, only in thick skin

• stratum corneum: outermost layer, 20-30 layers thick, cornified cells, very tough

dermis: made up of connective tissue, rich innervated and vascularized

• contains hair follicles, sweat and oil glands and much more

2 layers

• papillary layer: areolar connective tissue, heavily vascularized

• reticular layer: dense irregular connective tissue

skin appendages

• sweat glands: more than 2.5 mil per person

  • eccrine sweat glands: cells in dermis, duct leads to pore on superficial surface

  • apocrine sweat glands: empty into hair follicles, no ducts

• ceruminous glands: secrete earwax

• mammary glands: secrete milk

• sebaceous glands: oil glands, everywhere except palms

hair