Integumentary System

Transcription

1 Integumentary System Overview Skin is the largest organ in the body Accounts for about 7% of total body weight in adult Aka, Integument = covering Composed of two distinct regions: epidermis and dermis o Each region of epidermis consists of several layers; each layer is called a stratum (i.e., strata (plural)). Epidermis Outer part of skin Composed of four to five strata depending on location (i.e., thickness of skin) o Stratum Corneum (Horny Layer) topmost stratum Composed of dead cells that have flattened out; cells with remain there for two to four weeks until they are lost or washed off. Varying ages of cells are found in this layer with oldest near the surface and youngest closest to the following layer below. These cells are held together by very strong cellular connections called tight junctions and desmosomes. This is why they can peel off in sheets when you get sunburned. Keratin-a tough, durable protein that is secreted and fills this stratum for protection; holds up to lots of wear-and-tear and waterproofs the body. o Stratum Lucidum (Clear Layer) next stratum underneath the Stratum Corneum on palms and soles Protects soles of feet and palms of hands from abrasion Contains no pigment; why the soles and palms of dark skinned people appear lighter than the rest of their bodies. o Stratum Granulosum (Granular Layer) underneath Stratum Corneum Here is where keratin production occurs; stratum gets its name from granules of keratin found there. The protein granules of keratin produced in this layer are the actual protective mechanism in the epidermis. o Stratum Spinosum (Prickly Layer) below the Stratum Granulosum Here cells start to round up like little balls; cells change shape, dehydrate, and protrude into the other layers from here hence the name from the spiny architecture of this layer. o Stratum Basale (aka, Stratum Germinativum) (Basal Layer) last layer of epidermis In this layer the cells of the epidermis germinate or are formed. Located at the junction between the epidermis and dermis. Dermis The inner subdivision of skin Serves several functions o Makes Sweat (Sudoriferous Glands) o Secretes Oils (Sebaceous Glands) o Gives rise to Hair & Nails o Contains many sensory receptors and blood vessels

2 o Contains two types of connective tissue fibers Collagen Gives skin strength and resistance to stretching Elastin Allows your skin to stretch and then recoil back to normal length Consists of Two Layers o Papillary Layer forms projections into the epidermis Contains sweat and oil glands, hair follicles, blood vessels, lymph vessels, and the sensory nerves that sense changes on the surface of the epidermis o Reticular Layer innermost layer of dermis This layer contains the network of collagen and elastic fibers that gives skin its properties of strength and flexibility. This network of protein fibers provides support and attaches the dermis to the epidermis. Most of the accessory structures, such as the hair, nails, and glands, arise from within the dermis. Hypodermis Subcutaneous tissue just deep to the skin; aka, superficial fascia Strictly speaking, this is not part of the skin, but it shares some of the skin s protective functions. Consists mostly of adipose tissue Besides storing fat, the hypodermis anchors skin to the underlying structures (mostly muscles). Skin Color Determined by the amount of melanin produced; darker skin = more melanin production Melanocytes produce melanin; these cells are located between the epidermis and dermis. Brown pigment serves two important purposes o Primary way skin gets its color o Protects from harmful UV rays Glands Associated with Skin Exocrine Glands = glands that secrete through a tube/duct onto the surface; generally, have a local effect. o Sweat (Sudoriferous) Glands Sweat is composed mostly of water (99%); 1% = potassium ions, lactic acid, ammonia, and sodium chloride (making sweat taste salty) Two types of sweat glands Merocrine o Most numerous on the skin o Produce watery perspiration that cools your body temperature and aids in excretion. o Most abundant on the soles, palms, and forehead. o On average, you will sweat five hundred milliliters per day without realizing it. With heavy exercise, you could lose up to one liter of sweat per hour. Apocrine o Associated with hair follicles, where they secrete their products. o Help reduce friction between the hair follicle and the surrounding skin.

3 o Sebaceous (oil) Glands o Found in the anal region, groin, armpits, and areola. They also occur in the beard region of men. o Produce the scents associated with body odor. They become particularly active with stress and sexual stimulation. o Fresh secretions are odorless. But stale sweat gets trapped in clothing and is degraded into fatty acids by bacteria, producing a rancid odor. Produce an oily secretion called sebum. Sebum keeps the skin and hair supple and prevents it from becoming dry, brittle, and scaly. Acne is a condition in which the sebaceous glands ducts become blocked, their secretions accumulate, and a bacterium colonizes the area. The condition can be exacerbated in individuals with a genetic predisposition, or by hormone fluctuations, like the ones that occur at puberty. o Ceruminous glands Produce earwax o Mammary Glands Produce milk during lactation Hair One hair is called a pilus; many hairs are called pili Hair is made out of a slender filament of keratinized cells that grow out of a tube in the skin called the hair follicle. The keratin that makes up the hair shaft is called hard keratin. It is more compact than the keratin in your skin and reinforced by many cross-linkages between the keratin molecules, so it doesn't break easily. Hair originates in the dermis of the skin at the bulb. Composed of three layers o Innermost layer = medulla; contains loosely arranged cells and air spaces o Middle layer = cortex; layer of keratinized cells o Outermost layer = cuticle; comprised of a layer of scaly cells that overlap each other like roofing shingles, but all pointing upward Texture: o When we examine the different types of hairs in cross-section, we see why they differ in texture and color. In a cross-section: Curly hair is flat Straight hair is round Wavy hair is oval People can change the texture of their hair by changing the chemical bonds between keratin molecules. When getting a permanent, the chemicals used cause more disulfide bonds to form, allowing the hair to curl. Coloring infiltrates the dead keratin cells of the hair shaft. However, only the portion that has already grown out of the scalp is affected.

4 Naturally curly hair is caused by hydrogen bonds between the keratin proteins that make up your hair. These bonds are weak and can be enhanced by water, which is why your hair gets curlier when you've been out in the rain. Conditioners can straighten or relax curly hair by coating your hair strands with oils that keep moisture from penetrating the hair strands. That's also why your hair feels especially soft and smooth after using these products. Color: o Hair color comes from melanocytes located at the base of the hair follicle. o Melanocytes secrete various proportions of melanin of different colors, such as yellow, brown, and black. The pigments produced are transferred to the cells of the cortex. Red hair also has an iron-containing pigment called trichosiderin. Gray or white hair As people get older, their hair cells are not as active and produce less melanin. This decrease or absence of color in the cortex as well as the presence of additional air in the medulla causes the hair to turn gray or white. Nails Scale-like modification of the epidermis Forms a clear protective covering Changes in nail appearance may help diagnose certain conditions o Yellow-tinged nails = respiratory or thyroid gland disorders o Yellow-tinged and thickened nails = fungal infection o Outwardly concave nail (spoon nail) = iron deficiency o Horizontal lines (Beau s Lines) = malnutrition Functions of Integumentary System Protection o Chemical Barriers Skin secretions low ph (aka, acid mantle); natural antibiotics Melanin barrier preventing UV damage o Physical/Mechanical Barriers Continuity of skin Keratinized cells hard, shell-like barrier o Biological Barriers Immune cells in both epidermis and dermis; i.e., dendritic cells in epidermis, macrophages in dermis Body Temperature Regulation o Body Temperature Rises Nervous system stimulates dermal blood vessels to dilate Sweat glands are stimulated into vigorous secretory activity Visible output of seat is called sensible perspiration o Body Temperature Falls Dermal blood vessels constrict Warm blood bypasses skin temporarily

5 Skin temperature drops to external environment temperature Passive heat loss from body is slowed, conserving body heat Cutaneous Sensation o Receptors part of the nervous system located in skin that respond to stimuli arising outside the body Metabolic Functions o Vitamin D production when exposed to UV from the sun o Keratinocyte enzymes can disarm many cancer-causing chemicals that penetrate epidermis Blood Reservoir o Dermal vascular supply can hold about 5% of the body s entire blood volume Excretion o Nitrogen-containing wastes (i.e., ammonia, urea, and uric acid) are eliminated from the body in sweat