Integumentary System Chapter 6 PDF

The Integumentary system BSC 1085C Dr. Lovell  Overview of skin Largest organ (15% of body weight) Epidermis keratinized stratified squamous epithelium Dermis connective tissue layer Hypodermis Thickness variable, normally 1-2 mm dermis may thicken, up to 6 mm...

The Integumentary system BSC 1085C Dr. Lovell  Overview of skin Largest organ (15% of body weight) Epidermis keratinized stratified squamous epithelium Dermis connective tissue layer Hypodermis Thickness variable, normally 1-2 mm dermis may thicken, up to 6 mm stratum corneum layer increased calluses on hands and feet  Functions of the Skin Resistance to trauma and infection packed with keratin and linked by desmosomes acid mantle (pH 4-6) Barrier to ultraviolet light (UV damages DNA) Vitamin D synthesis Sensory receptors Thermoregulation through sweating Nonverbal communication Structure of the Skin Cells of the Epidermis Stem cells undifferentiated cells in deepest layers Keratinocytes – most of the skin cells Melanocytes synthesize pigment that shield UV Tactile (merkel) cells receptor cells associated with nerve fibers Dendritic (langerhans) cells macrophages guard against pathogens  Layers of the epidermis The epidermis has 4 distinct layers, each composed of different cells Stratum corneum Stratum granulosum Stratum spinosum Stratum basale Stratum Basale Single layer of cells on basement membrane Cell types in this layer Stem cells undergo mitosis to replace epidermis melanocytes distribute melanin through cell processes melanin picked up by keratinocytes merkel (tactile) cells Cell + nerve ending = tactile disk Stratum Spinosum Several layers of keratinocytes Dendritic (Langerhans) cells macrophages from bone marrow that migrate to the epidermis 800 cells/millimeter2 help protect body against pathogens Stratum Granulosum 3 to 5 layers of flat keratinocytes Contain keratinohyalin granules combine with filaments of cytoskeleton to form keratin Produce lipid-filled vesicles that release a glycolipid by exocytosis to waterproof the skin Stratum Corneum Corneum Up to 30 layers of dead, scaly, keratinized cells surface cells flake off (exfoliate)  Dermis Thickness = 0.6mm to 3mm Composition (connective tissue!) collagen, elastic and reticular fibers, fibrocytes Dermal papillae - extensions of the dermis into the epidermis forming the ridges of the fingerprints Layers papillary layer reticular layer is deeper part of dermis Hypodermis Subcutaneous tissue/ superficial fascia Mostly adipose Functions energy reservoir thermal insulation highly vascular Therefore, good site for hypodermic injections….WHY? Characteristics of Human Hair Hair (composed of hard keratin) disulfide bridges between molecules Hair found almost everywhere on body differences between sexes or individuals is difference in texture and color of hair 3 different body hair types lanugo -- fine, unpigmented fetal hair vellus -- fine, unpigmented hair of children and women terminal hair -- coarse, long, pigmented hair of scalp Structure of Hair Follicle Epithelial root sheath Connective tissue root sheath Hair receptors (sensory) entwine each follicle Piloerector muscle goose bumps  Functions of Hair Body hair (too thin to provide warmth) alert us to parasites crawling on skin Scalp hair heat retention and sunburn cover Beard, pubic and axillary hair indicate sexual maturity and help distribute sexual scents Guard hairs and eyelashes prevent foreign objects from getting into nostrils, ear canals or eyes Expression of emotions with eyebrows Cutaneous Glands  Sweat Glands Sweat: Filtrate of blood plasma 500 ml of insensible perspiration/day sweating with visible wetness is diaphoresis Eccrine (Merocrine) glands are simple tubular glands millions of them help cool the body Apocrine glands produce sweat containing fatty acids found only near hair follicles and respond to stress and sex bromhidrosis is body odor produced by bacterial action on fatty acids  Sebaceous Glands Oily secretion called sebum that contains broken-down cells lanolin in skin cream is sheep sebum Flask-shaped gland with duct that opens into hair follicle  Skin Cancer Induced by UV rays of the sun basal cell carcinoma (least dangerous) arises from stratum basale and invades dermis squamous cell carcinoma arises from keratinocytes in stratum spinosum metastasis to the lymph nodes can be lethal malignant melanoma (most deadly) arises from melanocytes of a preexisting mole ABCD--asymmetry, border irregular, color mixed and diameter over 6 mm Result of oncogene BRAF in men