Integumentary System PDF

Integumentary System The Integumentary System The integument, or skin, is the largest organ in the body. ▫ 15-16% of body weight ▫ 1.5-2m2 in area (~21 ft2) ▫ ~11 miles blood vessels ▫ Thinnest: eyelids (.05mm) ▫ Thickest: soles (1.5mm)  The skin is a membrane – multiple tissues...

Integumentary System The Integumentary System The integument, or skin, is the largest organ in the body. ▫ 15-16% of body weight ▫ 1.5-2m2 in area (~21 ft2) ▫ ~11 miles blood vessels ▫ Thinnest: eyelids (.05mm) ▫ Thickest: soles (1.5mm)  The skin is a membrane – multiple tissues that serve as a boundary. ▫ Stratified squamous epithelium. ▫ Areolar Where do you find collagen? connective What does it do? tissue. ▫ Dense irregular connective tissue.  Skin also contains accessory structures, such as hair, nails, and glands. Functions of Skin The skin covers and protects from impacts, chemicals, infection, radiation, and prevents the escape of body fluid. Sodium hydroxide (NaOH) burn.  Skin helps in the homeostasis of body temperature by providing insulation during cold and sweating when hot. Thermal imaging before and after a workout.  The majority of the body’s energy storage is in adipose tissue directly under the skin.  The skin contains sensory receptors for touch, pressure, pain, and temperature stimuli.  Salts, water, organic wastes, and milk (in women) are all secreted by the skin.  Skin Layers There are three layers of skin: ▫ The epidermis  4-5 layers  Keratinized squamous  4 cell types ▫ The dermis  2 layers  Areolar and dense irregular CTs  Nerves, blood and lymph vessels ▫ The hypodermis (adipose) Epidermis The composition of the epidermis depends on the location in the body. Areas of thick skin contain five cell layers. ▫ Palms of hands, soles of feet. Areas of thin skin contain four cell layers. ▫ All other locations in the body. Life Cycle in the Epidermis Cells are created at the base (near the dermis) and gradually move upwards towards the outer surface. Each layer is called a stratum and represents a different stage in the life of a  Figure 5.2b The main structural features of the skin epidermis. Keratinocytes Stratum corneum Most superficial layer; 20–30 layers of dead cells, essentially flat membranous sacs filled with keratin. Glycolipids in extracellular space. Stratum granulosum Typically five layers of flattened cells, organelles deteriorating; cytoplasm full of lamellar granules (release lipids) and keratohyaline granules. Stratum spinosum Dendritic Several layers of keratinocytes unified by desmosomes. cell Cells contain thick bundles of intermediate filaments made of pre-keratin. Sensory Stratum basale Dermis nerve Deepest epidermal layer; one row of actively ending mitotic stem cells; some newly formed cells Melanin Tactile become part of the more superficial layers. granule (Merkel) cell See occasional melanocytes and dendritic Desmosomes Melanocyte cells. © 2013 Pearson Education, Inc.  The deepest layer of the epidermis is called the stratum basale (germinativum). ▫ Contains single layer of large stem cells that continuously divide. ▫ Cells are attached to each other through desmosomes. ▫ 25-45 days to surface  Cells of the Epidermis Keratinocytes ▫ Produce fibrous protein keratin ▫ Most cells of epidermis ▫ Tightly connected by desmosomes Melanocytes ▫ 10–25% of cells in deepest epidermis ▫ Produce pigment melanin – packaged into melanosomes  Protect apical surface of keratinocyte nucleus from UV damage Dendritic (Langerhans) cells ▫ Macrophages – key activators of immune system Tactile (Merkel) cells ▫ Sensory touch receptors © 2013 Pearson Education, Inc.  In the stratum spinosum, contains daughter cells produced by mitosis within the stratum basale. ▫ They continue to divide. ▫ Web-like system of prekeratin filaments attached to desmosomes In the stratum granulosum ▫ Cells die in this layer. ▫ Cell flatten, organelles disintegrate ▫ Keratinization (accumulation keratohyaline and lamellar granules)  Keratin is a durable, water-resistant protein found in skin, fingernails, and hair. Shridhar Chillal’s world record fingernails on a single hand (358in), grown from 1952-2014. Source:  The stratum lucidum is a layer of keratinized cells only found in thick skin. The stratum corneum is the outermost and exposed layer of skin. ▫ Made of 15-30 layers of dead, flattened, keratinized cells. ▫ ¾ of epidermal thickness ▫ ‘Hard’ barrier layer  Epidermal friction ridges are raised areas of dermis that increase the surface contact area with the dermis. ▫ The epidermis has no blood vessels, so all nutrients and oxygen diffuse from the dermis.  Epidermal ridges create the whorls and contours of prints. ▫ This is hypothesized to help increase grip when the hands are wet.  Cells take 7-10 days to reach the stratum corneum, then remain there for about two weeks until they are shed. ▫ These cells are a major component of dust. ▫ ~ 30-50k/minute Psoriasis Psoriasis is a skin disorder where the skin cells of the epidermis grow at an abnormally fast rate. ▫ Skin cells are replaced every 3-5 days instead of the usual 28-30 days. The rapid growth is trigged by cells in the immune system. ▫ These cells are triggered by a combination of genetic and environmental factors. Skin Color Ultraviolet light in small doses helps the body produce Vitamin D. ▫ Essential for the absorption of calcium and phosphorus by the intestines. ▫ A vitamin D deficiency causes rickets, a softening of the bones.  The stratum basale contains melanocytes; cells that produce the pigment melanin that colors the epidermis. ▫ This creates tanning, which helps to protect against UV damage from sun exposure. Human hand with uneven distribution of melanin. From wisegeek.org  Freckles are small, concentrated spots of melanin in light-skinned people.  Having a darker skin tone helps to protect against UV damage, but also reduces vitamin D production. ▫ Ethnicities from areas with less sun tend to be more fair- skinned. ▫ HHMI: Skin Color  The Dermis Layer underneath epidermis ▫ Papillary layer  Areolar tissue papillae  Most contain capillary loops  Some, Meissner’s (touch); some nociceptors (pain, “free nerve ending”)  Creates friction ridges  ▫Reticular layer contains dense irregular CT binding skin to deeper layers  ~80% dermal thickness  Some elastic fibers  Cleavage lines (mostly invisible on surface)  Flexure lines Striae, Blisters Color: melanins, carotene, hemoglobin  A bruise occurs when blood vessels in the dermis break and leak blood into the surrounding tissue. Tattoos Tattoos work by forcing small droplets of ink into the dermis. ▫ Since the cells of the dermis are more stable than the epidermis, the tattoo is permanent.  Laser treatment breaks up the ink droplets in tattoos enough that white blood cells can carry them away. Hypodermis The hypodermis contains layers of areolar and adipose tissue with many fat cells. ▫ Provides insulation, shock absorption, and an energy reserve.  Hair Shaft Stratum Corneum Stratum Basale Epidermis Nerve Sebaceous Gland Dermis Blood Vessels Merocrine Sweat Gland Hypodermis Arrector Pili Muscle Adipose Tissue Arrector Pili Muscle Hair Hair is a nonliving structure produced in hair follicles. ▫ Hair follicles project all the way into the hypodermis. ▫ No: palms, soles, lips, nipples, portions of external genitalia ▫ Functions:  Warn of insects  Protect against physical trauma, sunlight  Reduce heat loss  The hair papilla contains the hair’s capillaries and nerves. The hair matrix contains epithelial stem cells that divide, push towards the surface, and  The hair cells die about halfway between the papilla and surface. ▫ Below this point is the hair root/ matrix ▫ Above this point is the hair shaft. ▫ Under the root is the papilla, dermal blood supply  Hair provides insulation for the head and guards the entrances to the nose, ears, and eyes. Each hair has its own sensory nerve fiber, enhancing the sense of touch. Comes in 2 types: vellus/ terminal  A bundle of smooth muscle cells called the arrector pili can contract and pull on the follicle, causing the hair to stand up.  Hair color results from different amounts and types of melanin ▫ Pigment production decreases with age, either resulting in grey (decreased melanin) or white (air bubbles) hair. ▫ 2.25mm/ week ▫ Lose ~90 scalp hair/day Trichosederin  Male pattern baldness is a genetic trait caused by hair follicles overly sensitive to male sex hormone (DHT). ▫ Produces shorter, finer hairs. ▫ Can happen in females, but rare Alopecia  Figure 5.5b Skin appendages: Structure of a hair and hair follicle. Follicle wall Peripheral connective tissue (fibrous) sheath Glassy membrane Epithelial root sheath External root sheath Internal root sheath Hair Cuticle Cortex Medulla Photomicrograph of a cross section of a hair and hair follicle (100x) © 2013 Pearson Education, Inc.  Hair Cortex Hair Medulla Root Sheath Connective Tissue Sheath Sebaceous Gland Melanocyte Hair Papilla Sebaceous (Holocrine) Glands Sebaceous glands are exocrine glands that secrete an oil called sebum into hair and skin. ▫ Prevents drying out and is antibacterial. ▫ Sebum production increases with hormone secretion during puberty.  Acne is the formation of pimples due to the blockage of sebaceous gland pores. ▫ Whiteheads are infected; blackheads just contain oil and dirt. ▫ Pus is made up of dead white blood cells.  Sweat Glands Apocrine sweat glands secrete an oily fluid that acts as a pheromone. ▫ Only found in the axillary and anogenital areas ▫ Degraded by bacteria, resulting in body odor. ▫ Begin functioning at puberty ▫ Modified:  Ceruminous  Mammary  Eccrine sweat glands ▫ 99% water ▫ 1% electrolytes – salts Vit.C, antibodies, dermicidin, metabolic wastes ▫ Most numerous, esp. on palms, soles, forehead ▫ Ducts connect to pores Sweat, as it evaporates, carries  Figure 5.7b Photomicrograph of a sectioned eccrine gland (140x). Sebaceous gland Sweat pore Eccrine gland Duct Dermal connective tissue Secretory cells Photomicrograph of a sectioned eccrine gland (140x) © 2013 Pearson Education, Inc. Nails Nails are keratinized epidermal cells that protect the tips of the fingers and toes. ▫ Production of nails comes from the nail root. ▫ Blood vessels in the underlying nail bed give the nail its pink appearance. ▫ The cuticle is a layer of stratum corneum that overlaps part of the nail.  Nail Body Nail Bed Cuticle Nail Root Bone Hypodermis Skin Color Disorders Cyanosis is a bluing of the skin caused by poor circulation or inadequate oxygen in the blood. Jaundice is caused by a buildup of a product of red blood cell breakdown (bilirubin)in the blood. ▫ Usually a sign of liver disease. Skin Cancer All skin cancers are the result of cells in the epidermis dividing out of control. Basal cell carcinoma affects cells in the stratum basale. Squamous cell carcinoma occurs in the stratum spinosum.  Malignant melanoma is caused by out of control growth in melanocytes. ▫ The most dangerous form of skin cancer; can metastasize quickly to blood and lymph vessels. Malignant melanomas can be differentiated from normal moles with the ABCD(E) rule. ▫ Asymmetry, two sides of pigmented mole do not match ▫ Border irregularity, borders of mole are not smooth ▫ Color, different colors in pigmented area. ▫ Diameter, Spot is larger than 6 mm in diameter ▫ Evolving  The biggest risk factor for skin cancer is excessive UV exposure from the sun or tanning booths. Genetic Disorders of the Epidermis Harlequin ichthyosis is caused by a mutation in a protein that transports lipids in cells of the epidermis. ▫ Without this lipid, the skin dehydrates and cracks easily, making infections  Epidermolysis bullosa is caused by a genetic mutation that prevents the body from forming a specific type of collagen that binds the epidermis to the dermis. ▫ The two layers separate easily, resulting in painful widespread blistering, disfiguration, and high rates of infection. Repair of the Integument Healing requires a series of stages: Bleeding stage: Blood initially escapes the epidermis.  Hemostasis: Blood vessels constrict and a blood clot forms. ▫ When the clot dries, it is called a scab. Inflammation: Injured blood vessels leak fluid, causing swelling and redness.  Proliferation: New tissue is built as cells divide and new collagen and extracellular matrix is laid down. Remodeling: The tissue is remodeled to a form that closely resembles its original state. Scar tissue may remain.  Scar tissue has more collagen fibers, fewer blood vessels, and fewer accessory structures than undamaged skin. ▫ Collagen fibers travel in a single direction instead of the weaved pattern they usually have. Skin Burns First-degree burns ▫ Only epidermis is damaged ▫ Skin is red and swollen ▫ Sun burns Second-degree burns ▫ Epidermis and upper dermis are damaged ▫ Skin is red with blisters ▫ Boiling water burns Third-degree burns ▫ Destroys all layers, including nerves and blood vessels. ▫ Burn is gray-white or black, often no pain felt.  Rule of Nines © 2013 Pearson Education, Inc. Severity and Treatment of Burns Critical if ▫ >25% of body has second-degree burns ▫ >10% of body has third-degree burns ▫ OR face, hands, or feet bear third-degree burns Treatment includes ▫ Debridement (removal) of burned skin ▫ Antibiotics ▫ Temporary covering ▫ Skin grafts Effects of Aging The epidermis thins and stem cell (stratum basale) activity declines, resulting in more injury and infection. Vitamin D production declines, resulting in reduced bone strength. Less melanin is produced, so the skin becomes more sensitive to ultraviolet light. ▫ Hair becomes grey or white.  Gland activity declines, making the skin drier. Less hair, and finer hair is produced. The network of elastic fibers in the dermis becomes thinner, causing sagging and wrinkling. Wrinkling in Water After about 30 minutes in water, the skin wrinkles. ▫ Nerve cells cause blood vessels in the dermis to constrict, creating the wrinkling. Wrinkled fingers give better grip when wet. ▫ Similar to treads on a This individual has nerve damage in the middle finger, preventing wrinkling. wet tire. Botox Botox is a toxic substance produced by the bacteria Clostridium botulinium. Botox blocks a neurotransmitter that signals the contraction of muscles in the skin. ▫ This can diminish certain types of wrinkles (brow lines, frown lines) Skin Infections Most skin infections are spread by contact. Fungal infections include athelete’s foot, toenail fungus, ringworm. ▫ Only antifungal medications are effective  Bacterial infections, such as impetigo, boils, and staph, are all caused by a normally harmless species of bacteria (Staphylococcus aureus). ▫ Treated with antibiotics. ▫ Transmitted by contact. MRSA is a strain of staph that is resistant to many antibiotics.  Viruses cause chicken pox, warts, and cold sores. ▫ Infects epidermal cells, overgrowth and itching. ▫ Airborne and direct contact. Viral infections are difficult to treat but may be preventable through the use of vaccination. Irritation Itching is a response triggered by nerves that begin firing when an irritant lands on the skin surface and is rubbed into the dermis. ▫ Scratching is meant to remove the irritant with the nails.  Eczema, also known as dermatitis, is a group of diseases that causes itchiness, red skin, and a rash. ▫ Caused by the immune system overreacting to substances that are normally not harmful, such as dust mites.