Chapter 6: Integumentary System- 6.1: Skin and Subcutaneous Tissueo The skin is the body’s largest and heaviest organ 15% of the body weight Stratified squamous epithelium (epidermis) and connective tissue(dermis) 1-2mm thick Thick Skin: covers palms, soles, and corresponding surfaces of thefinders and toes- It’s epidermis is .5 mm thick because of the stratum corneum- Has sweat glands, but no hair follicles or sebaceous glands Thin Skin: epidermis of .1 mm- Thin stratum corneum- Possess hair follicles, sebaceous glands, and sweat glandso Functions of the Skin  Resistance to Trauma and Infections: suffers most physical injuries, but resists and recovers from trauma better than any other organ- Keratin: tough protein in the skin that gives it its durability - Linked by desmosomes- Slight acidity (pH 4-6) is a defense mechanism (acid mantle)- Dry and flaky  Other Barrier Functions: barrier to water- Prevents from absorbing too much and losing too much water- Barrier to UV rays and potential chemicals Vitamin D Synthesis: reacts to heat, cold, touch, texture, pressure, vibrations, and tissue injury- Abundant in face, palms, fingers, soles, nipples, and genitals Thermoregulations: Monitor the body surface temperature- Thermo-receptors: cutaneous nerve endings Nonverbal Communication: expressive faces- Appearance of hair, skin, and nails- Birth marks and scarso The Epidermis: a keratinized stratified squamous epithelium that’s surface consists of dead cells that lacks blood vessels so it depends on diffusion of nutrients from the underlying connective tissue  Cells of the Epidermis- Stem Cells: undifferentiated cells that divide and give rise to the keratinocytes o Found in stratum basale- Keratinocytes: the great majority of epidermal cells o Synthesize keratin - Melanocytes: only occur in the stratum basale amid to the stems cells and deepest to the keratinocyteso Synthesize brown/black pigments melanino Constantly shedding melanin-containing fragments o Accumulate on sunny side of nucleus- Tactile Cells: receptors for touch o Basal layer and dermal nerve fiberso Tactile disc- Dendritic Cells: found in the spinosum and granulosum o Immune cells that originate in the bone marrow but migrate to the epidermis of the oral cavity, esophagus, and vaginao Stand guard against toxins, microbes, and other pathogens  Layers of the Epidermis- Stratum Basale: consists mainly of single layers of cuboidal to low columnar stem cells and keratinocytes resting on the basement membrane- Stratum Spinosum: several layers of keratinocytes makes this the thickest stratumo Only the first layer can divide- Stratum Granulosum: three to five layers of flat keratinocytes - Stratum Lucidum: thin zone only in thick skin o Densely packed with a clear protein called “eleidin”- Stratum Corneum: 30 layers of dead, scaly, keratinized cells that form a durable surface layero Resistant to abrasion, penetration, and water loss Life History of a Keratinocyte- Produced deep in the epidermis by the mitosis of stem cells in the basale- As they form they push older ones toward the surfaceo Become flatted the closer they get to the surfaceo Produce more keratin filaments and lipid filled membrane-coating vesicleso Granulosum: 4 important developments  Keratohyalin granules release a protein calledfilaggrin that binds cytoskeletal keratin filaments together into coarse, tough bundles Cells produce a tough layer of envelope proteins just beneath the plasma membraneresulting in a nearly indestructible protein sac around the keratin bundles Membrane-coating vesicles release a lipid mixture that spreads out over the cells surface and waterproofs it  Barriers cut keratinocytes off from the supplyof nutrients from below, their organelles degenerate and the cells die, leaving just the tough waterproof sac enclosing coarse bundles of keratin- Results in epidermal water barriero Corneum: compact layers of dead keratinocytes and fragments Exfoliate into dander Thickening of the corneum causes it to wrinkle - Why our hands and feet pruneo Dermis: connective tissue layer that ranges from .2 mm to 4 mm thick  Composed mainly of collagen but also contains elastin and reticular fibers, fibroblasts, and other fibrous connective tissues Well supplied with blood vessels, cutaneous glands, and nerve endings Dermal papillae: upward waves are finger like extensions of the dermis- Produce finger prints Epidermal ridges: downward waves- Interlock Papillary Layer: a thin zone of areolar tissue in and near the dermal papillae- Loosely organized allows for mobility of white blood cells - Rich in small blood vessels Reticular Layer: deeper and much thicker- Dense irregular connective tissue - Collagen forms thinker bundles with less room for ground substance - Where stretch marks are madeo Tear the collageno Hypodermis: also known as subcutaneous tissue is beneath the skin Lot of areolar and adipose tissue  Pads the body and binds the tissues Highly vascular Subcutaneous Fat: composed of predominantly adipose- Serves as an energy reservoir and thermal insulationso Skin Color: determined by melanin Melanin: produced by the melanocytes but accumulates in the keratinocytes of the stratum basa;e and spinosum - Eumelanin: a brownish-black pigment- Pheomelanin: a reddish-yellow sulfur containing pigment  Usually same number of melanocytes, but in darker skin they produce greater quantities of melanin  UV increases melanin production Hemoglobin: red pigment of blood, imparts reddish to pinkish hues as blood vessels show through the skin - Capillaries come closer to the skin and hemoglobin shows through more vividlyo Lips Carotene: yellow pigment acquired from egg yolks and yellow and orange vegetables  Abnormal Colors:- Cyanosis: blueness resulting from deficiency of oxygen in the circulating blood o Changes hemoglobin to a violet coloro Lack of oxygen or cold weather - Erythema: abnormal redness o Exercise, hot weather, sunburn, anger, and embarrassment o Increased blood flow - Pallor: pale or ashen color that occurs when there is so little blood flow through the skin that the white of the dermal collagen shows through o Emotional stress, low blood pressure, circulatory shock, cold, severe anemia- Albinism: a genetic lack of melanin that usually results in milky white hair and skin and blue-gray eyeso Amino acid tyrosine is nonfunctional-