- Consists of three major regions
- Epidermis - outermost superficial region
- Dermis - middle region
- Hypodermis (superficial fascia) - deepest region
- Outer portion of the skin is exposed to the external environment and functions in protection
- Composed of keratinized stratified squamous epithelium, consisting of four distinct cell types and four or five layers
- Cell types
- Keratinocytes - produce the fibrous protein keratin
- Melanocytes - produce the brown pigment melanin
- Langerhans' cells - epidermal macrophages that help activate the immune system
- Merkel cells - function as touch receptors associated with sensory nerve endings
- Layers of the Epidermis:
- Stratum Basale (Basal Layer)
- Deepest epidermal layer firmly attached to the dermis
- Consists of a single row of the youngest keratinocytes
- Cells undergo rapid division, alternate name stratum germinativum
- Stratum Spinosum (Prickly Layer)
- Cells contain weblike system of intermediate filaments attached to desmosomes
- Melanin granules and Langerhans' cells are abundant in this layer
- Stratum Granulosum - (Granular Layer)
- Thin; three to five cell layers in which drastic changes in keratinocyte appearance
- Keratohyaline and lamellated granules accumulate in the cells of this layer
- Stratum Lucidum -(Clear Layer)
- Thin, transparent band superficial to the stratum granulosum
- Consists of a few rows of flat, dead keratinocytes
- Present only in thick skin
- Stratum Corneum -(Horny Layer)
- Outermost layer of keratinized cells
- Accounts for three quarters of the epidermal thickness
- Functions include:
- Waterproofing
- Protection from abrasion and penetration
- Rendering the body relatively insensitive to biological, chemical, and physical assaults
- Psoriasis is a chronic skin disorder characterized by a more rapid division and movement of keratinocytes through the epidermal strata .
- cells shed in 7 to 10 days as flaky silvery scales
- abnormal keratin produced
- Mainly connective tissue (pink collagen); binds epidermis to underlying tissues
- Layers of the Dermis
- Papillary layer - note the capillaries and nerve endings in the dermal papillae
- Areolar connective tissue with collagen and elastic fibers
- Reticular layer - made up of irregular dense connective tissue which contains hair follicles, glands, blood vessels, arrector pili muscle, and nerve fibers and nerve receptors.
- Accounts for approximately 80% of the thickness of the skin
- Collagen fibers in this layer add strength and resiliency to skin
- Elastin fibers provide stretch-recoil properties
HYPODERMIS
- Subcutaneous layer deep to the skin
- Composed of adipose and areolar connective tissue
Accessory Organs of the Skin (Epidermal Derivatives) - note the basal layer around the following structures:
- Sweat Glands (Sudoriferous) - prevent overheating of the body; secrete cerumen and milk
- Eccrine sweat glands - found in palms, soles of the feet, and forehead
- Apocrine sweat glands - found in axillary and anogenital areas
- Ceruminous glands - modified apocrine in ear canal that secrete cerumen
- Mammary glands - specialized sweat glands that secrete milk
- Sebaceous Glands
- Simple alveolar glands found all over the body
- Soften skin when stimulated by hormones
- Secrete an oily secretion called sebum
- Nail - Scalelike modification of the epidermis on the distal, dorsal surface of fingers and toes
- Details health
- Note the following:
- Stratum Germinativum
- Nail bed
- Nail Matrix
- Eponychium
- Lunula
- Hair Follicle
- Root sheath extending from the epidermal surface into the dermis
- Deep end is expanded forming a hair bulb
- A knot of sensory nerve endings (a root hair plexus) wraps around each hair bulb
- Arrector pilli muscle attached
- Hair
- Filamentous strands of dead keratinized cells produced by hair follicles
- Contains hard keratin which is tougher and more durable than soft keratin of the skin
- Made up of the shaft projecting from the skin, and the root embedded in the skin
- Consists of a core called the medulla, a cortex, and an outermost cuticle
- Pigmented by melanocytes at the base of the hair
- Review Structures
- Functions of hair include:
- Helping to maintain warmth
- Alerting the body to presence of insects on the skin
- Guarding the scalp against physical trauma, heat loss, and sunlight
- Hair is distributed over the entire skin surface except
- Palms, soles, and lips
- Nipples and portions of the external genitalia
- Types of Hair
- Vellus - pale, fine body hair found in children and the adult female
- Terminal - coarse, long hair of eyebrows, scalp, axillary, & pubic regions
- Hair Thinning and Baldness
- Alopecia - hair thinning in both sexes
- True, or frank, baldness
- Genetically determined and sex-influenced condition
- Male pattern baldness - caused by follicular response to DHT
Functions of the Integumentary System
- Protection - chemical (melanin), physical, and mechanical barrier
- Body temperature regulation is accomplished by:
- Dilation (cooling) and constriction (warming) of dermal vessels
- Increasing sweat gland secretions to cool the body
- Cutaneous sensation - exoreceptors sense touch and pain
- Metabolic functions - Vitamin D synthesis 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
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:
- 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
- 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
- Melanoma
Cancer of melanocytes is the most dangerous type of skin cancer because it is:
- Highly metastatic
- Resistant to chemotherapy
- Melanomas have the following characteristics (ABCD rule)
- A: Asymmetry; the two sides of the pigmented area do not match
- B: Border is irregular and exhibits indentations
- C: Color (pigmented area) is black, brown, tan, and sometimes red or blue
- 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
BURNS
- First-degree - only the epidermis is damaged
- Symptoms include localized redness, swelling, and pain
- Second-degree - epidermis and upper regions of dermis are damaged
- Symptoms mimic first degree burns, but blisters also appear
- Third-degree - entire thickness of the skin is damaged
- Burned area appears gray-white, cherry red, or black; there is no initial edema or pain
- Rule of Nines
- Estimates the severity of burns Lund and Browder
- 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
- Skin Grafts - New skin can not regenerate if stratum basale and its stem cells are destroyed
- autograft: covering of wound with piece of healthy skin from self
- isograft is from twin
- autologous skin
- transplantation of patient's skin after it has grown in culture
Developmental Aspects of the Integument
- Fetal
- Epidermis develops from ectoderm
- Dermis and hypodermis develop from mesoderm
- Lanugo - downy coat of delicate hairs covering the fetus
- Vernix caseosa - substance produced by sebaceous glands that protects the skin of the fetus in the amnion
- Adolescent to Adult
- Skin and hair become oilier and acne may appear
- Skin shows effects of cumulative environmental assaults around age 30
- Scaling and dermatitis become more common
- Old Age
- Epidermal replacement of cells slows and skin becomes thinner
- Skin becomes dry and itchy
- Subcutaneous fat layer diminishes, leading to intolerance of cold
- Decreased elasticity and loss of subcutaneous tissue leads to wrinkles
- Decreased numbers of melanocytes and Langerhans' cells increase the risk of skin cancer
Homeostatic imbalances of the skin
- Bed sores (Decubitus Ulcers)
- caused by a constant deficiency of blood to tissues overlying a bony projection that has been subjected to prolonged pressure
- typically occur between bony projection and hard object such as a bed, cast, or splint
- the deficiency of blood flow results in tissue ulceration.
- Preventable with proper care
- Stretch marks, blisters, calluses,
- Erythema, pallor,
jaundice, cyanosis,
black and blue marks
- Acne Vulgaris
- most common skin disorder
- sebum and epithelial cells clog glands
- produces whiteheads and blackheads (comedones)
- anaerobic bacteria trigger inflammation (pimple)
- largely hormonally induced
- . androgens stimulate sebum production
- treatments include antibiotics, topical creams, birth control pills
Terms - intradermal injection; hypodermic (subcutaneous injection; intramuscular injection)
Deep Wound Healing
- When an injury extends to tissues deep to the epidermis, the repair process is more complex than epidermal healing, and scar formation results.
- Healing occurs in 4 phases
- inflammatory phase has clot unite wound edges and WBCs arrive from dilated and more permeable blood vessels
- migratory phase begins the regrowth of epithelial cells and the formation of scar tissue by the fibroblasts
- proliferative phase is a completion of tissue formation
- maturation phase sees the scab fall off
- Scar formation
- hypertrophic scar remains within the boundaries of the original wound
- keloid scar extends into previously normal tissue
- collagen fibers are very dense and fewer blood vessels are present so the tissue is lighter in color
- Phases of Deep Wound Healing
- During the inflammatory phase, a blood clot unites the wound edges, epithelial cells migrate across the wound, vasodilatation and increased permeability of blood vessels deliver phagocytes, and fibroblasts form
- During the migratory phase, epithelial cells beneath the scab bridge the wound, fibroblasts begin scar tissue, and damaged blood
vessels begin to grow. During this phase, tissue filling the wound is called granulation tissue.
- During the proliferative phase, the events of the migratory phase intensify.
- During the maturation phase, the scab sloughs off, the epidermis is restored to normal thickness, collagen fibers become more organized, fibroblasts begin to disappear, and blood vessels are restored to normal
- Scar tissue formation (fibrosis) can occur in deep wound healing.
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