Chapter 6 Integument PDF

Chapter 6 Integument – largest organ of the body (16% of total weight) Composed of: - skin - sweat glands - sebaceous glands - hair - nails Chapter 6  Chapter 6 Skin Functions: - protection (injury, bacterial invasion, desiccati...

Chapter 6 Integument – largest organ of the body (16% of total weight) Composed of: - skin - sweat glands - sebaceous glands - hair - nails Chapter 6  Chapter 6 Skin Functions: - protection (injury, bacterial invasion, desiccation) - regulation of body temperature (with circulatory system) - reception (environmental signals) - excretion (from sweat glands) - Absorption (UV light to synthesize vitamin D)  Chapter 6 Organization of the “skin”: 1. epidermis – composed of ectodermally derived tissue. (comprised of 5 layers). 2. dermis – dense, irregular collagenous connective tissue. Hypodermis (not part of skin) is the superficial fascia that covers the entire body just deep to the skin. Dermatoglyphs (fingerprints) – develop as a fetus and remain unchanged throughout life. Chapter 6  Chapter 6 Epidermis: - composed of stratified squamous keratinized epithelium - ranges from 0.07mm (thin skin) to 0.6 mm (thick skin) Thick skin: - exhibits all 5 layers of epidermis - lacks hair follicles, arrector pili muscles, sebaceous glands or sweat glands - locations – palms and soles Chapter 6  Chapter 6 Thin skin: - covers the remainder of the body - contains hair follicles, arrector pili muscles, sebaceous glands and sweat glands - lacks 1 of the 5 layers (lucidum and) Chapter 6  Chapter 6 Layers of the epidermis - Keratinocytes undergo cytomorphosis as they move from the basal to the apical surface of the epidermis and define 5 separate layers. - Basement membrane: 1. stratum basale (germinativum) 2. stratum spinosum 3. stratum granulosum 4. stratum lucidum 5. stratum corneum Chapter 6  Chapter 6 Stratum Basale: - aka stratum germinativum - single layer of cuboidal/columnar cells - lateral desmosomes and basal hemidesmosomes - mitotically active layer (only at night) - rests on a well developed basement membrane (separating it from the dermis). Chapter 6  Chapter 6 Stratum Spinosum: - thickest of the epidermal layers - keratinocytes “prickle cells” because of cell junctions - cells are mitotically active (in basal region) Chapter 6 Chapter 6  Chapter 6 Stratum granulosum: - most superficial layer with nuclei - other granules contain a lipid rich substance that when secreted generates a water-proof barrier. Chapter 6  Chapter 6 Stratum Lucidum - Present only in thick skin - Cells lack nuclei and organelles - Filled with keratin intermediate filaments Chapter 6  Chapter 6 Stratum Corneum - most superficial skin layer - several layers of dead cells (squames) that are filled with keratin. - Cells at the basal region of this layer retain desomsomes. Near the surface, they lose their adhesions and become desquamated (shed). Chapter 6  Chapter 6 Cells of the epidermis Keratinocytes: - largest population of cells in the epidermis - express and accumulate keratin intermediate filaments - life span of between 20-30 days. Chapter 6  Chapter 6 Langerhans cells - located in the stratum spinosum - 2-4% of all epidermal cells - Aka dendritic cells because of numerous long processes. - function as antigen presenting cells (APC) in the immune system.  Chapter 6 Merkel cells: - located in stratum basale - extend processes between keratinocytes - May function as mechanoreceptors Chapter 6 Chapter 6  Chapter 6 Melanocytes: - located in the stratum basale - processes extend into the stratum spinosum - Melanosomes are transferred to keratinocytes via cytocrine secretion and form a protective “umbrella” over the nucleus that is degraded slowly over several days. - Repeated exposure to UV radiation increases the number of melanocytes. Chapter 6 Chapter 6  Chapter 6 Dermis (corium) - region of skin immediately underlying the epidermis - composed of 2 layers: papillary layer reticular layer  Chapter 6 Papillary layer: - dermal papillae interdigitate with epidermal papillae forming an irregular boundary between the 2 layers (epi- and dermis) - the basement membrane separate the layers (epidermis and dermis) Chapter 6 Chapter 6  Chapter 6 Reticular layer: - dense irregular connective tissue - type I collagen fibers are abundant - thick elastic fibers are present. - Same cells as found in papillary layer plus adiopocytes (in deeper layers). - Sweat glands, sebaceous glands and hair follicles are present through the dermis. - Arrector pili muscles – smooth muscle bundles that attach to hair follicles to “raise” the hair on the body. Chapter 6  Chapter 6 Nerves: Dermis contains rich network of: a) sensory nerve fibers that collect information about our surroundings and send it to the brain (combined senses of touch composed of pain, pressure, heat, cold). b) motor nerve fibers (regulate blood flow and gland secretions)  Chapter 6 Dermal blood vessels Body temperature and blood pressure regulation Vasoconstriction - blood vessel Vasodilation - blood vessel diameters narrowed, blood is diameter increased allowing more shunted toward deeper blood close to the body surface. structures. Allows to lose heat. Allows to conserve heat.  Chapter 6 Hypodermis: not a part of the integument - areolar (Loose) connective tissue - abundant adipose tissue - Functions: protection, energy reserve and insulation. - Males: neck, upper arms, abdomen, lower back and buttocks - Females: breasts, buttocks, hips and thighs Chapter 6  Chapter 6 Glands of the skin I. Eccrine (aka. Exocrine) sweat gland: - Common sweat gland - function in thermoregulation - may form as much as 10L of sweat per day - merocrine secretion (via exocytosis)  Chapter 6 II. Apocrine sweat glands: located: axilla areola of nipple anal region - aprocrine type of secretion - odorless secretory product; after metabolism by bacteria, has a distinct odor. - Secretion is regulated by hormones and starts after puberty - Metabolic pathway similar to pheromone signals - May have evolved from sex attractants Chapter 6 Chapter 6  Chapter 6 Modified apocrine sweat glands: Ceruminous glands - Located only in the external ear canal - Secrete waterproof earwax, cerumen, that lubricates and helps to trap foreign material Mammary glands - Located in the breast, but are only activated in pregnant and lactating females in order to secrete milk.  Chapter 6 Hair: - filamentous keratinized structures that project from the epidermal surface. - 2 types of hair cover the human body: Vellus hair – (majority of human hair) soft, fine, short and pale hair (i.e., eyelashes) Terminal hair – hard, large, coarse, long pigmented hair (i.e, on scalp and eyebrows). - functions in tactile sensation (not so much for insulation in humans)  Chapter 6 Hair Follicles: - invaginations of the epidermis Three zones of a hair: 1. Shaft - portion of a hair above the skin surface. 2. Root - portion of a hair below the skin surface. 3. Hair bulb - swelling at the base. Contains: hair papilla (vessels and nerves) + hair matrix (actively dividing cells). Chapter 6  Chapter 6 Nails: nail plate – composed of highly compacted, keratinized epithelial cells that extended at a rate of approx. 0.5 mm/week nail bed – epidermis underlying the nail plate at the base of the nail, the epidermis overgrows the nail plate forming the proximal nail fold with the nail matrix (similar to the hair matrix) beneath in the area of the nail root. Chapter 6  Chapter 6 The Cuticle (eponychium) is that portion of the stratum corneum at the proximal nail fold. On the lateral borders, the lateral nail folds create the lateral nail grooves adjacent to the nail plate. Lunula – white crescent structure at the proximal end of the nail plate. Hyponychium – the collection of stratum corneum at the junction of the nail plate and the stratum corneum of the finger under the distal end of the nail plate.  Chapter 6 Integumentary system has an incredible ability to respond to stressors, trauma, and damage: a. In response to repetitive mechanical stress => mitosis stimulated in stratum basale => thickening of the epidermis => ↑protection  Chapter 6 Response to the damaged tissues can happen in two ways: 1. Regeneration - replacement of damaged cells with same cell type allowing to restore the organ function 2. Fibrosis - formation of scar tissue composed primarily of collagen produced by fibroblasts; functional activities are not restored (happens if organ is too damaged or cells lack ability to divide  Chapter 6 Cut blood Blood clot forms Blood vessels Epithelium vessels bleed as a temporary regrow, and regenerates and into the barrier, and granulation tissue connective tissue wound. leukocytes clean forms (vascular fibrosis occurs (hair the wound. connective tissue follicles, glands, that initially forms in nerves, and muscle the wound) cells are not repaired)  Chapter 6 Burns – Threat to life from fluid loss, infection, effects of burned tissue – First degree burns involve only epidermis First-degree burn immerse burned area in cool water – Second degree burns involve epidermis and part of dermis skin blistered and painful – Third-degree burns involve epidermis, dermis, and subcutaneous layer Second-degree burn require hospitalization treatment for dehydration and infection severe scarring may need debridement and skin graft from one part of body to another Third-degree burn  Chapter 6 Metabolic regulation of Vitamin D: Under UV lights, keratinocytes synthesize inactive vitamin D (cholecalciferol) Modified in the liver into another inactive form of vitamin D (calcidiol) Modified in the kidneys into the active form of vitamin D (calcitriol) Vitamin D ↑ absorption of Ca and P from small intestine into the blood, thus regulating blood levels of Ca and P.  Chapter 6 Clinical Correlations Langerhan’s cells - decrease in number after repeated exposure to UV radiation. Freckles - hyperpigmented area of the skin Warts - caused by papillomaviral infection of keratinocytes. Acne - most common disease seen by dermatologists. Involves sebaceous glands and hair follicles (obstructions) and bacterial involvement. Digestive systemChapter 6 Chapter 6 Chapter 6