Also known as… The SKIN! EPIDERMIS Pages

 Includes: ◦ Skin (cutaneous membrane) ◦ Skin derivatives/accessories:  Sweat glands  Oil glands  Hair  Nails © 2015 Pearson Education, Inc.

 Protection  Regulates loss of body heat ◦ as controlled by the nervous system  Aids in excretion of urea and uric acid  Synthesizes vitamin D  Sensory receptors detect: ◦ Touch ◦ Temperature ◦ Pressure ◦ Pain © 2015 Pearson Education, Inc.

 Protects deeper tissues from: ◦ Damage:  Mechanical damage (bumps)  Chemical damage (acids and bases) ◦ Pathogens/microbial threats ◦ Ultraviolet radiation (sunlight) ◦ Thermal damage (heat or cold) ◦ Desiccation (drying out)  Keratin protects the skin from water loss © 2015 Pearson Education, Inc.

 Epidermis—top/outer layer ◦ Stratified squamous epithelium ◦ Keratinized (cornified- hardened by keratin) to prevent water loss ◦ Avascular ◦ Most cells are keratinocytes  Dermis- lies below the epidermis ◦ Dense connective tissue © 2015 Pearson Education, Inc.

Dermal papillae Hair shaft Pore Appendages of skin Eccrine sweat gland Arrector pili muscle Sebaceous (oil) gland Hair follicle Hair root Cutaneous vascular plexus Adipose tissue Epidermis Dermis Papillary layer Reticular layer Hypodermis (subcutaneous tissue) Nervous structures Sensory nerve fiber Lamellar corpuscle Hair follicle receptor (root hair plexus)

 Hypodermis (subcutaneous tissue) lies underneath the dermis ◦ Not technically part of the skin ◦ Anchors skin to underlying organs ◦ Composed mostly of adipose tissue ◦ Functions:  shock absorber insulates deeper tissues © 2015 Pearson Education, Inc.

 composed of up to five layers  avascular  Most cells are keratinocytes ◦ Keratin is a fibrous protein that makes the epidermis tough ◦ Other cells include  Melanocytes (make melanin)  Sensory cells (Merkel cells)  Immune cells (Langerhans cells- phagocytes) © 2015 Pearson Education, Inc.

 From bottom to top (deep to superficial)  Stratum Basale  Stratum Spinosum  Stratum Granulosum  (Stratum Lucidum) –not always present  Stratum Corneum

Desmosomes Stratum corneum. Cells are dead; represented only by flat membranous sacs filled with keratin. Glycolipids in extracellular space. Stratum granulosum. Cells are flattened, organelles are deteriorating; cytoplasm full of granules. Stratum spinosum. Cells contain thick bundles of intermediate filaments made of pre-keratin. Stratum basale. Cells are actively dividing stem cells; some newly formed cells become part of the more superficial layers. Dermis Keratinocytes Epidermal dendritic cell Merkel cell MelanocytesMelanin granules Sensory nerve ending

 Also called stratum germinativum ◦ Deepest layer of epidermis ◦ Lies next to dermis ◦ Contains cells undergoing mitosis ◦ Daughter cells are pushed upward to become the more superficial layers © 2015 Pearson Education, Inc.

 Several cell layers thick  Contain bundles of intermediate filaments that serve to resist tension  House Langerhans cells ◦ your book calls these epidermal dendritic cells ◦ Macrophages that help activate the immune system ◦ Star-shaped cells

 thin; only 3-5 cell layers  Cells are flat  Thicker plasma membranes resist destruction  Contain granules that serve to: ◦ Form keratin in the upper layers ◦ Produce waterproofing glycolipids; control water loss © 2015 Pearson Education, Inc.

 Formed from dead cells of the deeper strata  Occurs only in thick, hairless skin ◦ palms of hands ◦ soles of feet

 Outermost (external and most superficial)layer of the epidermis ◦ cell layers thick  Shingle-like dead cells are completely filled with keratin ◦ This protective protein prevents water loss from skin ◦ Lysozomes consumed nuclei and organelles upon cell death ◦ This layer is called “cornified or horny” because the cells are now called “corneocytes”

Desmosomes Stratum corneum. Cells are dead; represented only by flat membranous sacs filled with keratin. Glycolipids in extracellular space. Stratum granulosum. Cells are flattened, organelles are deteriorating; cytoplasm full of granules. Stratum spinosum. Cells contain thick bundles of intermediate filaments made of pre-keratin. Stratum basale. Cells are actively dividing stem cells; some newly formed cells become part of the more superficial layers. Dermis Keratinocytes Epidermal dendritic cell Merkel cell MelanocytesMelanin granules Sensory nerve ending

 A pigment (melanin) produced by melanocytes ◦ Found mostly in the stratum basale  Melanin accumulates in membrane-bound granules called melanosomes  Color produced is yellow to brown to black ◦ More melanin = darker color  Amount of melanin depends upon: ◦ Genetics ◦ exposure to sunlight © 2015 Pearson Education, Inc.

 Epidermal dendritic cells ◦ Alert and activate immune cells to a threat from a pathogen such as a bacterial or viral invasion  Merkel cells- sensory receptors ◦ Serve as touch receptors called Merkel discs ◦ Found at the epidermal-dermal boundary © 2015 Pearson Education, Inc.

Desmosomes Stratum corneum. Cells are dead; represented only by flat membranous sacs filled with keratin. Glycolipids in extracellular space. Stratum granulosum. Cells are flattened, organelles are deteriorating; cytoplasm full of granules. Stratum spinosum. Cells contain thick bundles of intermediate filaments made of pre-keratin. Stratum basale. Cells are actively dividing stem cells; some newly formed cells become part of the more superficial layers. Dermis Keratinocytes Epidermal dendritic cell Merkel cell MelanocytesMelanin granules Sensory nerve ending