 Includes your entire outer layer of skin (16% of your total body weight), accessory organs like hair, nails, and glands.  Consists of two major parts:  (1) Cutaneous membrane  (2) Accessory structures

 Made up of two layers:  (1) Epidermis (superficial epithelium), and Dermis (underlying connective tissue)  (2) Accessory structures – Including hair, nail, exocrine glands. Located mostly in the dermis and protrude into the epidermal layer  (3) Subcutaneous layer deep to the dermis is known as the hypodermis; often not considered part of the integumentary system, but because its fibers extend into the dermis, we will include it here

 (1) Protection of underlying tissues and organs against shocks, abrasion, and chemicals  (2) Excretion of salts, water, and organic wastes  (3) Maintenance of normal body temperature via insulation or evaporative cooling (sweating)  (4) Synthesis of vitamin D3  (5) Storage of nutrients – including lipids/adipose  (6) Detection of touch, pressure pain, and temperature stimuli and relaying information to the control center (brain)

 Recall epidermis composed of stratified squamous cells for the purpose of protection  Most abundant epithelial cells are called keratinocytes

 Keratinocytes make up five layers of thick skin, and four layers in thin skin  Thick skin is found in the palms of your hands and soles of your feet  Thin skin is found everywhere else in your body  Thick and thin refer to the thickness of the epidermal layer

Top layer of skin Bottom layer of skin

 Stratum germinativum, also known as stratum basale, is the bottom most layer of skin  Epidermal ridges are found here, and they extend into the dermis.  Projections called dermal papillae creates an interlocking arrangement that increases the strength of the bond between the dermal and epidermal layers

 The contours of the skin surface follow the ridge patterns  Ridges on the palms and soles of feet increase the skin’s surface area and friction, helping to maintain grip  Ridge shapes are genetically determined, unique to you, and do not change throughout your life  Ridge prints located on your fingers are called fingerprints

 Basal cells dominate this layer. Basal cells are stem cells whose divisions replace skin cells lost to shedding at the skin’s surface  Merkel cells are also found in this layer. Merkel cells are sensitive to touch. Basal Cell

 Melanocytes are pigment cells that give skin its color; they are also found in this layer

 Means “spiny layer”  Contains Langerhans cells, which are part of the immune system  Langerhans cells are responsible for stimulating a defense against:  (1) microorganisms that penetrate the epidermis  (2) superficial cancer cells

 Known as the “grainy layer”  By the time the cells reach this layer, they have stopped dividing and now begin to make lots of the protein keratin  Keratin makes up our hair and nails

 Present only in thick skin  “Clear layer” filled with keratin

 Top layer of epidermis; consists of layers of cells  Keratinization or cornification, is the formation of protective, superficial layers of cells made of keratin  Dead layers of cells so tightly connected that when they slough off they separate as sheets of cells

 Takes days for epithelial cells to move from stratum basale/germinativum to the stratum corneum  They stay in the stratum corneum for about two weeks before being washed/shed

 A dry layer, so few microorganisms can survive here  Layer is water resistant, but not waterproof. Water from inside the body slowly penetrates to the surface where it is evaporated. We lose ~500mL (1 pint) of water/day  This process is called insensible perspiration  If this layer is damaged or lost (as in burns), the rate of water loss dramatically increases and you are at risk of dehydration

 Recall from biology that freshwater will move into cells, causing them to SWELL  This is why when you take a bath your hands swell and look like raisins  Likewise, water will leave cells if placed in highly concentrated solutions, like oceanwater  Although the process occurs slowly, it will accelerate the dehydration process in shipwreck survivors After 51 hours of exposure to seawater and wearing gloves