Integumentary System: Skin Layers

• The skin and its accessory structures make up the integumentary system
• The skin is the largest organ by weight
• It consists of epithelial tissue overlying connective tissue
• The outer layer called the epidermis
• The inner layer called the dermis

Epidermis

• The epidermis is composed of stratified squamous epithelium
• It's the outer layer, composed of stratified squamous epithelium
• There is a basement membrane between the epidermis and dermis

Dermis

• The dermis is the inner layer and thicker than the epidermis
• It contains connective tissue, with collagenous and elastic fibers, muscle, blood, and nervous tissue

Subcutaneous layer (hypodermis)

• Located beneath the dermis and acts as an insulating layer
• Contains areolar and adipose connective tissue
• It is not considered part of the skin, contains blood vessels that supply the skin

Epidermis Details

• Consists of stratified squamous epithelium
• Lacks blood vessels
• The deepest layer is called the stratum basale, nourished by blood vessels in the dermis
• As cells grow, they migrate toward the free surface, away from the nutrient supply
• Older cells that are migrating are called keratinocytes, and they begin to flatten and die
• Keratinization occurs as epidermal cells migrate outward, hardening, dehydrating, and accumulating keratin
• Keratin is a tough, fibrous, and waterproof protein made and stored in the cells
• As cells reach the outer surface, they become tightly packed, developing desmosomes and forming the stratum corneum
• Stratum corneum cells are eventually shed from the skin surface
• Thickest on the palms and soles (0.8 through 1.4 mm)
• Most of the body has a thinner epidermis, 0.07 through 0.12 mm
• The functions protect against water loss, harmful chemicals, mechanical injury, and pathogens

Layers of the epidermis:

• Stratum corneum: Outermost layer with many layers of keratinized, dead epithelial cells that are flattened and non-nucleated
• Stratum lucidum: Between stratum corneum and granulosum on soles and palms; cells are clear and nuclei, organelles, and cell membranes are no longer visible
• Stratum granulosum: Beneath stratum corneum, with three to five layers of flattened granular cells containing shrunken fibers of keratin and shriveled nuclei
• Stratum spinosum: Beneath stratum granulosum, with many layers of cells containing centrally located, large, oval nuclei and developing fibers of keratin; cells becoming flattened
• Stratum basale: Deepest layer, with a single row of cuboidal or columnar cells that divide and grow; this layer also includes melanocytes

Special Cells of the Epidermis:

• Dendritic (Langerhans) Cells: Found in the stratum spinosum, they phagocytize and protect skin and underlying tissues from infection
• Tactile (Merkel) Cells: Found in the stratum basale, they are along with sensory nerve endings, for Tactile Discs in the dermis and act as sensory receptors for light touch
• Melanocytes: Found in stratum basale. Produce melanin pigment which absorbs UV light from sunlight and provides skin color. Melanin distributed to keratinocytes to protect against UV radiation

Skin Color is affected by:

• Melanin pigment where Eumelanin is the Brownish-black pigment of the epidermis and Pheomelanin is the Reddish-yellow pigment, found in certain areas
• Hereditary Factors where all people have same melanocytes except albinism, but vary in the amount of melanin produced
• Varying distribution and size of melanin granules
• Environmental Factors like Sunlight, UV light from sunlamps and X-rays
• Physiological Factors such as Oxygenation in blood of dermal blood vessels, Vasodilation/vasoconstriction of dermal blood vessels, Accumulation of carotene pigment from diet and Jaundice

Indoor Tanning and Skin Cancer

• Exposure to sunlight or a tanning bed causes melanocytes to produce more melanin, darkening the skin
• Tanning beds use UV radiation doses that can overwhelm the body's natural protective responses against skin cancer
• Basal cell carcinoma and squamous cell carcinoma arise from epithelial cells
• Melanomas arise from melanocytes
• Melanomas are least common skin cancers (4%) but cause 80% of skin cancer deaths.

Dermis Details

• The dermis is the inner layer of the skin
• It averages 1 to 2 mm thick
• The dermis contains projections called dermal papillae between epidermal ridges
• Binds the epidermis to underlying tissues
• It is a connective tissue layer, containing muscle fibers and nerve cell processes
• Dermal blood vessels supply nutrients to all skin cells
• Contains hair follicles, sweat, and sebaceous glands
• The dermis contains sensory receptors: Lamellated (Pacinian) corpuscles for pressure and Tactile (Meissner's) corpuscles for light touch

Layers of the Dermis:

• Papillary layer: Superficial layer with areolar connective tissue that is the thinner of the 2 layers. It's the location of dermal papillae and forms fingerprints
• Reticular layer: Deeper layer containing dense irregular connective tissue that is thicker than the papillary layer

Accessory structure details

• They originate from the epidermis and extend into dermis or hypodermis
• Hair follicles
• Nails
• Skin glands (sweat and sebaceous)
• Injured/burned dermis can regenerate if accessory structures remain intact

Nails details

• Nails are protective coverings on the ends of fingers and toes
• Made up of a Nail plate (body) which is the visible portion and consists of keratinized cells and overlies nail bad
• The nail bed is the surface of the skin, under nail plate
• The nail matrix is the active growth region, is not visible, at proximal end of nail bed with a Lunula (Pale, half-moon-shaped region over nail matrix)
• The cuticle is a fold at the proximal end of the nail which is Part of stratum corneum extends slightly over nail

Hair Follicles Details

• Hair is present on all skin surfaces, except palms, soles, lips, nipples, and parts of external reproductive organs,
• Hair follicle is the tube-like depression of an epidermal cell that extends into the dermis or the subcutaneous layer and which hair develops
• Parts of hair include
• Hair root which extends from skin surface to dermis or hypodermis
• Hair bulb which is the deepest part of the hair root and contains dividing cells of hair matrix
• Hair shaft which is the Portion of hair that extend beyond skin surface; composed of dead, epidermal cells
• Hair papilla contains blood vessels to nourish hair
• Arrector pili muscle that is Attached to hair follicle with contracts in response to cold or fear and causes goosebumps
• Hair color is due to the type and amount of melanin

Hair Loss

• Most common baldness is pattern baldness where the top of the head loses hair is called androgenic alopecia
• Associated with lowered testosterone (men) or estrogen (women)
• Progenitor cells are lacking in bald spots, but stem cells are present
• Alopecia areata is where the body attacks hair follicles, and is an autoimmune disorder

Sebaceous Glands

• Holocrine glands are usually associated with hair follicles
• Produce sebum, which consists of fatty material and cellular debris
• Sebum keeps hair and skin soft and waterproof, but excess can cause acne Located away from palms and soles.

Clinical Application 6.3

• Acne vulgaris is a disorder of sebaceous glands that is common at puberty because sebaceous glands are excessively responsive to androgens
• Sebaceous glands become clogged with extra sebum and epithelial cells and provide a good environment for anaerobic bacteria: resulting in infection and inflammation
• Affects 80% of people between 11 and 30 years of age
• Treated best with Vitamin A derivatives, systemic antibiotics, salicylic acid, benzoyl peroxide

Sweat Glands

• Sweat glands, also known as Sudoriferous glands are widespread on the skin
• Originate in the deeper dermis or hypodermis as ball-shaped coils
• Eccrine (merocrine) glands make up must abundant population which mainly consist of water, some salts, and waste and respond to elevated body temperature and the open to body surface through pores
• Apocrine sweat glands are located in the axillary and groin areas and open into hair follicles: called apocrine, secrete by exocytosis, and that respond to emotions, pain
• Specialized sweat glands include Ceruminous glands that produce ear wax and the Mammary glands which produce milk

Gland locations

• Sebaceous glands: groups of specialized epithelial cells that keeps hair soft, pliable, waterproof and is Located Near or connected to hair follicles (everywhere but on palms and soles)
• Merocrine: Abundant sweat glands that lowered body temperature, and the Originate in deep dermis or subcutaneous layer and opens to surface on forehead, neck, and back
• Apocrine: Less numerous glands located near hair follicles that wet skin during pain, and is Located in the in the armpit and groin
• Ceruminous & Mammary sweat glands: they are Modified that secrete ear wax and milk with Location of the ear and the breast respectively

Skin Functions

• Protective barrier: Protection against harmful substances, UV radiation, microorganisms, and water loss
• Sensation: Contains sensory receptors for touch, pressure, temperature changes, and pain
• Excretion of some wastes
• Production of Vitamin D: Starts in skin; when produced and activated, helps with calcium absorption
• Regulation of body temperature by Sweating and blood flow changes

Heat Production & Loss

• Important to regulate body temperature because a slight deviation can disrupt metabolic rates
• Set point is monitored by hypothalamus in brain
• Deep body temperature stays close to 37 degrees Celsius or 98.6 degrees Fahrenheit
• Skin plays a key role in the regulation of body temperature, a homeostatic mechanism
• Cellular metabolism produced heat, which is produced by active cells in liver, skeletal and cardiac muscle

Heat Loss

• Heat is the product of cellular metabolism. Its primary components include the Liver and active cells in the skeletal and cardiac muscles

• Convection: Heat is transfered to cooler objects

• Conduction: Heat loss from skin into circulating air currents

• Evaporation: Heat is lost through sweat as it carries heat away from the skin

Body Temperature Regulation Mechansims

• When body temperature rises, thermoreceptors signal the hypothalamus, causing vasodilation of dermal blood vessels, vasoconstriction of deep blood vessels, and activation of sweat glands

• When body temperature falls, thermoreceptors signal hypothalamus causing vasoconstriction of dermal blood vessels, vasodilation of deep blood vessels, sweat glands become inactive, and muscles contract involuntarily (shivering)

Heat is a Product of the Following

• Radiation: Primary method, infrared heat rays travel from warmer skin to the cooler environment.
• Conduction: Is caused by the contact between warmer and cooler objects
• Evaporation: Heat loss from skin by circulating air currents.

Hyperthermia & Hypothermia

• Hyperthermia is an abnormally high body temperature that can occur in hot, humid conditions and can lead to heat stroke

• Hypothermia is an abnormally low body temperature that can result in prolonged exposure to cold

• Hypothermia causes confusion, lethargy, loss of reflexes and consciousness

Elevated Body temperature

• Occurs when when temp is high, the body loses homeostasis and cant lower body temp. -Pyrogens are realeased to combat pathogens.

Inflammation Details

• Inflammation is a normal response to injury or stress and it is the Body's restrictions spread of infection
• Blood vessels affected in tissues dilate and become more permeable to allow fluids to leak into the damaged tissue
• Inflamed skin becomes:
• Reddened
• Swollen
• Warm
• Painful

Wounds

• A shallow cut affects only to the epidermis and a deep cut, reaching dermis or subcutaneous layer results in blood vessels breaking releasing blood to form a clot
• Clot of fibrin, blood cells, and platelets
• Forming scab, fibroblasts-secrete to collagen fibers-bind wound together
• Growth factors, increase the formation of new tissue.

Burns degree differences

• 1st Degree Burn: Are classified as (superficial, partial-thickness) which injures only the epidermis, like sunburn. Healing in days/weeks with no scaring
• 2nd Degree Burn: Are classified as (deep, partial-thickness) which destroys the epidermis and some of the dermis like a burn from hot liquid with healing dependent on the Burn intensity, some cell remains.
• 3rd Degree Burn: Are classified as (full-thickness)= epidermis and dermis, which accessory structures usually require the use of a Skin Graft

Rule of Nines

• Determines body estimate and replaces fluids, electrolyte. Divides into sections and estimates injured surface area

Explore the integumentary system, focusing on the skin's layers. Learn about the epidermis which is composed of stratified squamous epithelium, the dermis containing connective tissue, and the hypodermis for insulation. Understand their structures and functions.