Ch 4: Skin and Body Membranes Integumentary System P110

Skin Structure Figure 4.4

Integumentary System Skin (cutaneous membrane) Also called the integument Skin derivatives Sweat glands Oil glands Hairs Nails

Skin Functions Protects deeper tissues from: Mechanical damage (bumps) Chemical damage (acids & bases) Bacterial damage (from infection) Thermal damage (heat or cold) Ultraviolet radiation (effects of sunlight) Desiccation (drying out)

Skin Functions Aids in heat regulation Aids in excretion of urea and uric acid Synthesizes vitamin D

Skin Structure Figure 4.3

Skin Structure Epidermis – outer layer Stratified squamous epithelium Often keratinized (hardened by keratin) Dermis - inner layer Dense connective tissue Found underneath the epidermis Figure 4.3

Skin Structure Deep to dermis is the hypodermis Also called subcutaneous tissue Not part of the skin Anchors skin to underlying organs Composed mostly of adipose tissue

Skin Layers From outermost to inner most layer: Stratum Corneum Stratum Lucidum Stratum Granulosum Stratum Spinosum Stratum Basale (Germinativum)

Layer of Epidermis 1. Stratum basale 2. Stratum spinosum Also called stratum germinativum Stratum basale or germinativum is deepest layer Lies next to dermis Cells undergoing mitosis 2. Stratum spinosum 3. Stratum granulosum

Layer of Epidermis cont’d 4. Stratum lucidum Occurs only in thick skin 5. Stratum corneum Outermost layer of the epidermis Shingle-like dead cells Flakes off slowly and replaced by new cells

Epidermis Facts Avascular New epidermis every 35-45 days

Melanin Pigment (melanin) produced by melanocytes Color is yellow to brown to black Melanocytes are mostly in the stratum basale Amount of melanin produced depends upon genetics and exposure to sunlight Freckles and moles are found where melanin is concentrated to one spot CROSS OUT THE NEXT LINE

Dermis Two layers 1. Papillary layer Outermost layer of dermis Projections called dermal papillae Pain receptors Papillae are arranged in patterns that are genetically determined This is what allows you to leave fingerprints

Dermis 2. Reticular layer Blood vessels Glands Nerve receptors

Dermis Facts Vascular and helps maintain body temperature homeostasis Various fibers are found in the dermis Collagen fibers are responsible for the toughness and help keep skin hydrated Elastic fibers gives skin its elasticity Collagen & elastic fibers decrease as we age