The Integumentary System Includes the membranous covering, sweat and oil glands, hair and nails 3.2 “integumentary” comes from the Latin word that means covering

FunctionsMechanisms protectionTough keratin protects against mechanical injury and chemical damage. Melanocytes produce melanin to protect against UV ray damage. Acidic sweat protects against bacterial infections. Water barrierKeratin and oils in the skin reduce water loss through evaporation and form a barrier against water infusion. Temperature regulationCapillaries dilate to dissipate heat and constrict to conserve heat. Sweat evaporation provides a cooling effect. Vitamin D productionSunlight converts modified cholesterol molecules to vitamin D, which is essential for bone health. Sensory perceptionReceptor cells transmit information about touch, pressure, vibration, pain, and temperature to the central nervous system.

Anatomy of the Skin Outer layer-epidermis Underlying layer –dermis Hypodermis (subcutaneous fascia)—connects the skin to the underlying tissue, also provides cushioning and insulation against extreme external temperatures; is a fat storage area of lipocytes (fat cells)

Epidermis Has 5 layers 1. stratum corneum – Consist of dead cells completely filled with keratin and are continuously shed. – Is completely replaced every days Stratum lucidum – Clear layer of thick skin only found on the palms of the hands, fingers, soles of the feet, and toes Stratum granulosum Stratum spinosum Stratum basale – absorbs nutrients from the underlying dermis – Constantly producing new cells – Contains melanocytes None contain blood vessels. As the cells move upward they become flatter and more filled with keratin making them tougher and more water resistant

Epidermis cells Epidermal dendritic cells – Associated with the immune and nervous system – Over 800 of these per square millimeter of skin – Initiate an immune response to bring in other specialized cells to attack the foreign invaders Merkel cells – In the stratum basale layer – Function as touch receptors by forming junctions with sensory nerve endings

Dermis “true skin” Most outer layer –papillary layer – Same have capillaries – Some have nerve endings – Form ridged patterns of “prints” Reticular layer – Have collagen and elastic fibers in an irregular arrangement – Includes blood and lymphatic vessels, sweat and oil glands, involuntary muscles, hair follicles, and nerve endings

Appendages of the Skin Sudoriferous (sweat) glands – Each person has 2-3 million sweat glands – in the dermis all over the body, big concentration in the axilla, palms of hands, soles of feet, and on forehead Sebaceous (oil) glands – Located everywhere except palms, soles; produce sebum, an oily substance that helps keep the skin and hair soft and kills bacteria; empty into hair follicles or directly onto skin Hair Nails

2 types of Sudoriferous (sweat) glands Eccrine glands-major sweat glands; secrete clear, acidic fluid that is 99% water, the other 1% is urea, uric acid, slats, vitamin C; ducts open directly onto skin; sweat is odorless but bacteria chemically change it an make an odor; nerve endings in the sweat glands cause the body to form sweat when the body temp is elevated. As much as 1 liter of sweat can be lost in one hour. Apocrine glands-begin to function during puberty; located in the genital and axilla areas; large sweat glands and secrete a milky fluid of sweat, fatty acids, and proteins; empty into hair follicles.

Hair The hair is produced by the hair follicle in the dermis The bottom of the follicle has connective tissue that has capillaries to give the hair nourishment. The growth zone, matrix, has specialize cells that make living hair cells but as the cells move up to the scalp they become filled with keratin and die so most of the shaft is nonliving. “goose bumps” are made when we are cold or scared. The arrector pili muscle is connected to the hair follicle to the epidermis and contracts pulling the hair upright which traps a layer of air close to the skin to add insulation and warmth. Melanocytes produce a pigment that gives hair a particular color. As a person ages less pigment is produced which results in gray or white hair. The shape of a hair follicle determines the hair shape: – Round follicle=straight hair – Oval follicle = wavy hair – Flat shaped follicle= curly hair

Nails The nail bed is part of the stratum basale under the nail. The proximal end of it is the thickened nail matrix where the nail grows. The cells quickly become keratinized and die. Nails are transparent but look pinkinsh because of the capillary supply. The lunule is positioned over the thickened nail bed.