TOB Integument (12)

• 1. protective, waterproof barrier (keratin, hair, sebum)
• 2. maintains body temperature through capillary dilation/contraction & production of sweat (thermoregulation)
• 3. major sensory input for pain, pressure, heat & cold
• 4. performs important metabolic functions (eg. site of vitamin D synthesis)
• 5. immunological (contains langerhan's cells [DC], wandering lymphocytes)
• (6. absorption: nicotine, steroid hormones)

• 1. epidermis: SSKE (stratified squamous, keratinizing epithelium)
• 2. dermis

• outer layer of the integument firmly attached to the underlying dermis
• made up of distinct layers
• this region is enriched with nerve endings, is AVASCULAR & has a stratified squamous keratinizing epithelium
• epidermis keratinocyte layers exterior --> inward (apical --> basal)
• 1. Stratum Corneum
• 2. Stratum Lucidum
• 3. Stratum Granulosum
• 4. Stratum Spinosum
• 5. Stratum Basale (Germinativum)
• (Come Let's Get Sun Burned)

• outermost region contains many layers of flattened, cornified, dead cells whose cytoplasms are packed with TONOFIBRILS
• number of cell layers varies with the thickness of the skin (more layers in thick skin like palms & soles of the feet)

thin translucent layer apparent in some sections of thick skin, but not always present (possibly an artifact)

• contains 2-3 layers of flattened squamous epithelial cells whose cytoplasms are filled with coarse basophilic (keratohyalin) granules
• granules contain filaggrin (binds tonofilaments into tonofibrils) and loracrin (thickens/stiffens the outer surface of cells)
• last layer before the cells "die"

• THICKEST of the living layers of the epidermis
• cells connected by abundant desomosomes
• have a spiny appearance
• 
• 

• innermost layer of cells rest on basement membrane & are single layer of cuboidal cells
• these cells divide regularly meaning a high number of mitotic figures are visible
• they move upward & replenish cells lost at the surface during epidermal turnover

cells of the epidermis that contain abundant water insoluble keratin assembled into 7-8 nm tonofilaments inside their cytoplasm

• finger like projections of the dermis into the epidermis which enhance the attachment of the epidermis to the underlying dermis
• these structures generate an enormous surface area for strong epidermal-dermal interaction
• stem cells are located near the tips of the dermal papilla

• 
• primary ridge: encompassing single ridge over two dermal papilla

connective tissue layer that lies deep to the epidermis and consists of a highly vascularized connective tissue with different types of glands, hairs and sensory structures

• lies deep to the dermis, but is not technically a part of the skin
• several structures associated with the true skin (eg. hair follicles, sensory receptors) may be found in this region
• hypodermis contains adipose tissue & may contain skeletal muscle

• 1. Keratinocytes
• 2. Melanocytes
• 3. Langerhan's Cells
• 4. Merkel Cells

• pigment producing cells derived from the neural crest found in the basal layer
• have long processes containing melanosomes that extend among the keratinocytes
• melanosomes = membrane-bound organelles that make pigments (melanin and phaeomelanin)

• NO, melanocytes do
• keratinocytes phagocytose the pigment-containing cytoplasm of the melanocyte and ACQUIRE pigment

exposure to UV light as well as by melanocyte stimulating hormone (MSH)

• dendritic cells, functionally related to the monocyte-macrophage group (and thus derived from the bone marrow) found particularly in the upper layers of the stratum spinosum
• present antigen to lymphocytes

• cells involved in sensory (mechano) reception & contain granules similar to those found in the cells of adrenal medulla
• occur in small numbers in the basal part of the epidermis

• caused by pathological changes that lead to over-proliferation of the stratum basale layer
• can lead to basal cell carcinoma (most common form of skin cancer) if the changes are neoplastic

• a much more aggressive form of skin cancer caused by neoplastic changes in the melanocytes
• responsible for the majority of skin cancer deaths
• Initial diagnoses are usually made based upon visual appearance w/ mnemonic ABCDE:
• A - asymmetry
• B - Border (irregular)
• C - Color (usually multiple)
• D - diameter (> 6mm)
• E - enlarging
• good prognosis w/ excision of early identified tumors

• 1. papillary
• 2. reticular

• layer just deep to the epidermis composed of finger-like papilla that project toward the surface, forcing epidermis to acquire an undulating morphology
• this greatly increases the surface area for epidermal-dermal adhesion

because they bring the dermis as close to the outside world as possible, an ideal location for two such entities

• constitutes the bulk of the dermis & contains large bundles of type I collagen fibrils [Langer lines] + elastic fibers
• reticular dermis contains sensory receptors, hairs & several types of glands

• 1. Eccrine Sweat Glands
• 2. Apocrine Sweat Glands
• 3. Sebaceous Glands

• a basal coil from which a duct leads through the dermis into the epidermis assists in maintaining a normal body temperature
• secretory portions of eccrine sweat glands pump Na+ ions into the lumen to generate an osmotic gradient; water follows by osmosis. In addition to water, several protein components (e.g. dermcidin) and other waste products (urea) are added to the fluid
• ductal cells actively resorb sodium & passively reabsorb chloride; the final product to reach the surface is mostly water & a small amount of protein/sodium
• are found over most of the body but most concentrated in the forehead, axilla & palms of the hand

stratified cuboidal epithelial cells rich in mitochondria

• patients have compromised removal of salts by eccrine sweat gland ducts
• --> a high salt content in sweat = marker of CF

• large coiled tubular glands that open into hair follicles rather than directly onto the skin surface
• found mainly in the axilla (armpit) & genitals
• less numerous than eccrine glands
• apocrine glands can store their secretion, & various hormonal/neural stimuli will cause them to secrete

• to produce pheromones
• they become active at puberty
• mode of secretion = eccrine and apocrine (the secretory product as well as a portion of the cells themselves is released)

• left: apocrine - larger lumen for sweat storage
• right: eccrine - smaller lumen, no storage

• glands found all over the body EXCEPT at palms & soles that secrete sebum, which serves a natural lubricant of the hair and surface of the skin (contains TAGs, FAs, & cholesterol)
• sebaceous glands discharge contents via a SINGLE duct into the lumen of hair follicles
• mode of secretion = holocrine (entire cell & its product is released)

• fordyce spots (penis bumps)
• lip vermillion border

• caused when sebum production (puberty) exceeds the capacity of the short ducts to drain the glands
• can become colonized by surface bacteria
• while bacterium is a normal component found in healthy skin, prolonged colonization of sebaceous glands results in the release of lytic enzymes and damages gland & ducts

dead epithelial fibers composed of cross-linked keratin that is harder than that found on the skin, owing in part to the use of trichohyalin rather than filaggrin to bind tonofilaments into tonofibrils

• 1. shaft: part projecting from the skin surface
• 2. root: the portion embedded in the skin
• 3. follicle: the tubular invagination of the epidermis

• smooth muscle (arrector pili)
• contraction causes the hairs to become erect (goose bumps)
• arrector pili are absent in axilla, groin, eyelashes & eyebrows

• 1. anagen (a growth phase that may last for years)
• 2. catagen (a follicular regression stage which lasts weeks)
• 3. telogen, (a resting period lasting a few months).

• free nerve endings abundant in the epidermis
• skin at every part of the body functions as a sensory receptor

• rapidly adapting sensitive organs found in dermal papillae that confer high discrimination
• they stop firing after continued stimulation --> why we soon become unaware of the clothes touching our skin
• used for tasks such as reading braille

rapidly adapting sensory organs that respond to deep touch pressures (massage) found in the deep dermis and hypodermis

• stratum spinosum
• rail roads between cells --> desmosome connections between cells

keratohyalin

Langerhan's cells contain Birbeck granules (function unknown)

• eccrine gland
• dark = ducts (stratified cuboidal)
• light = gland
• thin surrounding gland = myoepithelium

• clear bubble = sebaceous gland
• thin pink line = smooth muscle (arrector pili)

all next to hair bulb/follicle