1. The Integumentary System Chapter 5

2. Functions of the Integumentary System Protection – chemical, physical, and mechanical barrier Body temperature regulation Body temperature regulation is accomplished by: o Dilation (cooling) and constriction (warming) of dermal vessels o Increasing sweat gland secretions to cool the body Cutaneous sensation – exoreceptors sense touch and pain Metabolic functions – synthesis of vitamin D in dermal blood vessels Blood reservoir – skin blood vessels store up to 5% of the body’s blood volume Excretion – limited amounts of nitrogenous wastes are eliminated from the body in sweat

4. Skin (Integument) Consists of three major regions o Epidermis – outermost superficial region o Dermis – middle region o Hypodermis (superficial fascia) – deepest region Back to dermis Back to Accessory

5. Skin (Integument) Back to dermis

7. Epidermis Outer portion of skin exposed to the external environment & functions in protection Composed of keratinized stratified squamous epithelium Cell types o Melanocytes – produce the brown pigment melaninMelanocytes o Keratinocytes – produce the fibrous protein keratin o Langerhans’ cells –epidermal macrophages o Merkel cells –touch receptors associated with sensory nerve endings

8. Layers of the Epidermis: Stratum Basale (Basal Layer) o Deepest epidermal layer firmly attached to the dermis o Consists of a single row of the youngest keratinocytes o Cells undergo rapid division, alternate name stratum germinativum Stratum Spinosum (Prickly Layer) o Cells contain weblike system of intermediate filaments attached to desmosomes o Melanin granules and Langerhans’ cells are abundant in this layer Stratum Granulosum – (Granular Layer) o Thin; three to five cell layers in which drastic changes in keratinocyte appearance o Keratohyaline and lamellated granules accumulate in the cells of this layer Keratinized – skin on body suface Nonkeratinized – moist skin In mouth Thick skin Thick skin – palms and solespalms Thick skin Thick skin – palms and solespalms

9. Layers of the Epidermis Layers of the Epidermis (cont.) o Functions include:  Waterproofing  Protection from abrasion and penetration  Rendering the body relatively insensitive to biological, chemical, and physical assaults Stratum Corneum -(Horny Layer) o Outermost layer of keratinized cells o Accounts for three quarters of the epidermal thickness Stratum Lucidum -(Clear Layer)Lucidum o Thin, transparent band superficial to the stratum granulosum o Consists of a few rows of flat, dead keratinocytes o Present only in thick skin thick

10. Layers of the Dermis: Hypodermis o Subcutaneous layer deep to the skin o Composed of adipose and areolar connective tissue Dermis mainly connective tissue (pink collagen); binds epidermis to underlying tissues Papillary layer – note the capillaries and nerve endings in the dermal papillae oAoAreolar connective tissue with collagen and elastic fibers Reticular layer- irregular dense connective tissue which contains hair follicles, glands, blood vessels, arrector pili muscle, nerve fibers and nerve receptors. oAoAccounts for approximately 80% of the thickness of the skin oCoCollagen fibers in this layer add strength and resiliency to skin oEoElastin fibers provide stretch-recoil properties Pacinian corpuscles

11. Accessory OrgansAccessory Organs of the Skin Epidermal Derivatives – note the basal layer around the following structures: Sweat Glands - prevent overheating of the body; secrete cerumen and milkSweat Glands o Eccrine sweat glands – found in palms, soles of the feet, and forehead o Apocrine sweat glands – found in axillary and anogenital areas o Ceruminous glands – modified apocrine in ear canal that secrete cerumen o Mammary glands – specialized sweat glands that secrete milk Sebaceous Glands o Simple alveolar glands found all over the body o Soften skin when stimulated by hormones o Secrete an oily secretion called sebum Nail Nail -Scalelike modification of the epidermis on the distal, dorsal surface of fingers and toes Details health

12. Accessory Organs of the Skin (cont.) Hair o Filamentous strands of dead keratinized cells produced by hair follicles o Contains hard keratin which is tougher more durable than soft keratin of skin Hair Follicle o Root sheath extending from the epidermal surface into the dermis o Deep end is expanded forming a hair bulb o A knot of sensory nerve endings (root hair plexus) wraps around each hair bulb o Made up of the shaft projecting from the skin, and the root embedded in the skin o Consists of a core called the medulla, a cortex, and an outermost cuticle o Pigmented by melanocytes at the base of the hair

13. More on Hair Functions of hair include: o Helping to maintain warmth o Alerting the body to presence of insects on skin o Guarding the scalp against physical trauma, heat loss, and sunlight Hair is distributed over entire skin surface except o Palms, soles, and lips o Nipples and portions of the external genitalia Types of Hair o Vellus – pale, fine body hair found in children and the adult female o Terminal – coarse, long hair of eyebrows, scalp, axillary, & pubic regions Hair Thinning and Baldness o Alopecia – hair thinning in both sexes o True, or frank, baldness  Genetically determined and sex-influenced condition  Male pattern baldness – caused by follicular response to DHT (dihydrotestosterone)DHT (dihydrotestosterone)

14. Skin Cancer Most skin tumors are benign and do not metastasize Crucial risk factor for nonmelanoma skin cancers is disabling of the p53 gene The three major types of skin cancer are: o Basal cell carcinoma Basal cell carcinoma  Least malignant and most common skin cancer  Stratum basale cells proliferate and invade dermis and hypodermis  Slow growing and do not often metastasize  Can be cured by surgical excision in 99% of the cases o Squamous cell carcinoma Squamous cell carcinoma  Arises from keratinocytes of stratum spinosum  Arise most often on scalp, ears, and lower lip  Grows rapidly and metastasizes if not removed  Treated by radiation therapy or removed surgically o Melanoma (next page)

15. Melanoma Melanomas have the following characteristics (ABCD rule) o A: Asymmetry; the two sides of the pigmented area do not match o B: Border is irregular and exhibits indentations o C: Color (pigmented area) is black, brown, tan, and sometimes red or blue o D: Diameter is larger than 6 mm (size of a pencil eraser) Treated by wide surgical excision accompanied by immunotherapy Chance of survival is poor if the lesion is over 4 mm thick Melanoma - Cancer of melanocytes is the most dangerous type of skin cancer because it is: o Highly metastatic o Resistant to chemotherapy

16. Burns Rule of Nines - Estimates the severity of burns o Burns considered critical if:  Over 25% of the body has second-degree burns  Over 10% of the body has third-degree burns  There are third-degree burns on face, hands, or feet First-degree – only the epidermis is damagedFirst-degree o Symptoms include localized redness, swelling, and pain Second-degree – epidermis and upper regions of dermis are damaged o Symptoms mimic first degree burns, but blisters also appear Third-degree – entire thickness of the skin is damaged o Burned area appears gray-white, cherry red, or black; there is no initial edema or pain Lund and Browder

22. Developmental Aspects of the Integument Fetal o Epidermis develops from ectoderm o Dermis and hypodermis develop from mesoderm o Lanugo – downy coat of delicate hairs covering the fetus o Vernix caseosa – substance produced by sebaceous glands that protects the skin of the fetus in the amnion Adolescent to Adult o Skin and hair become oilier and acne may appear o Skin shows effects of cumulative environmental assaults around age 30 o Scaling and dermatitis become more common Old Age o Epidermal replacement of cells slows and skin becomes thinner o Skin becomes dry and itchy o Subcutaneous fat layer diminishes, leading to intolerance of cold o Decreased elasticity and loss of subcutaneous tissue leads to wrinkleselasticitywrinkles o Decreased numbers of melanocytes and Langerhans’ cells increase the risk of skin cancer

23. Homeostatic Imbalances of the Skin o Stretch marks, blisters, calluses, bed sores (Decubitus Ulcers) Erythema, pallor, jaundice, cyanosis, black and blue marksErythemapallorjaundice cyanosisblack and blue marks o largely hormonally induced o androgens stimulate sebum productionsebum o treatments include antibiotics, topical creams, birth control pills Terms - intradermal injection; hypodermic (subcutaneous injection; intramuscular injection) Acne Vulgaris o most common skin disorder o sebum and epithelial cells clog glandsclog o produces whiteheads and blackheads (comedones)comedones o anaerobic bacteria trigger inflammation (pimple)