2 Introduction:Organs are body structurescomposed of two or more differenttissues.The skin and its accessory organsmake up the integumentarysystem.
3Skin and Its TissuesThe skin is a large organ responsible for: temperature regulation protection of underlying tissues Slowing the rate of water loss housing sensory receptors synthesizing certain chemicals excreting wastes
4The skin consists of an outer epidermis anda dermis, connected to underlying tissue bythe subcutaneous layer (hypodermis).
5EpidermisThe epidermis is made up of stratifiedsquamous epithelium and lacks bloodvessels.The layer of reproducing cells (the stratumbasale), which lies at the base of theepidermis, is well-nourished by bloodvessels from the deeper dermal layer.
6Cells are pushed outward as new cells areformed, and become keratinized as theydie.Layers of the Epidermis:Stratum corneumStratum lucidumStratum granulosumStratum spinosumstratum basale
7Skin ColorSpecialized cells in the epidermis calledmelanocytes produce melanin, a dark pigmentthat provides skin color.Differences in skin color result from differingamounts of melanin and in the size of melaningranules.The amount of melaninproduced is affected bygenetics andenvironmental factors.
8DermisThe dermis binds the epidermis to underlyingtissues.It consists of dense connective tissue with toughcollagen and elastic fibers within a gel-likeground substance.
9Dermal blood vesselscarry nutrients toupper layers of skinand help to regulatetemperature.The dermis alsocontains nerve fibers,sensory fibers, hairfollicles, sebaceousglands, and sweatglands.
10Subcutaneous LayerThe subcutaneous layer(hypodermis) is composedof loose connective tissueand insulating adiposetissue.It binds the skin tounderlying organs andcontains the major bloodvessels that supply theskin.
11Accessory Organs of the SkinHair FolliclesHair can be found in nearly all regions of the skin.Hairs develop from cells at the base of the hair follicle,an area of the lower epidermis that dips down into thedermis.As new cells are formed, old cells are pushed outward,become keratinized, and die forming the hair shaft.
12Hair color is determined by genetics; melanin frommelanocytes is responsible for most hair colors;red hair contains an additional pigment.A bundle of smooth muscle cells, called the arrectorpili muscle, attaches to each hair follicle. Thesemuscles cause goose bumps when cold orfrightened.
14Sebaceous GlandsAssociated with hair follicles and secrete an oilysubstance that waterproofs and moisturizesthe hair shafts.NailsNails consist of stratified squamous epithelialcells overlying the nail bed.As new cells are produced,older ones are pushedoutward and becomekeratinized.
15Sweat GlandsEach gland consists of a tiny tube that originatesas a ball shaped coil lined with sweat secretingepithelial cells.Cells respond to body temperature and stressModified Sweat GlandsModified sweat glands, called secrete wax in theear canal.Mammary glands, another modified type of sweatglands, secrete milk.
16Regulation of Body TemperatureThe skin plays a key role in the homeostatic mechanismthat regulates body temperature.Response to increased body temperature Heat from cellular metabolism or the environment istransferred to the blood and carried to thehypothalamus of the brain. The hypothalamus signals the dermal blood vessels todilate and sweat glands to secrete. Increased blood flow to the skin and evaporation ofsweat results in a release of heat from the body.
17Response to decreased body temperature Hypothalamus detects decrease in body temperature Hypothalamus stimulates dermal blood vessels toconstrict and sweat glands to remain inactive. Decreased blood flow to the skin and lack of sweatreduce amount of heat loss. Skeletal muscles may also be stimulated (shivering)which increases cellular metabolism and thus, heatproduction.
19Healing of Wounds and BurnsThe body’s initial response to skin trauma isinflammation.Inflammation-The dilation of blood vessels in affected areabecome more permeable, fluids leave the bloodvessels and enter the damaged tissues. Thisprovides the tissues with increased nutrientsand oxygen necessary for healing.
21Healing the woundShallow wounds are healed as epithelial cellsalong the margin of the wound divide morerapidly than usual and fill the gap.Wounds that affect the dermis &/or hypodermisresult in a blood clot and “scab” that cover andprotect the underlying tissues. Fibroblasts formcollagenous fibers that bind the edges of thewound together.
22Skin cancerSquamous cell carcinomaBasal cell carcinomaCommon, slow growing form of skin cancer,usually linked to over exposure to sun, usuallycurableMelanomadevelop in melanocytes, lesion becomesdangerous when it spreads downward into deeperlayers, survival rate low once this type of growthoccurs.