Skin S2M3

Derived from ectoderm

• Dense irregular connective tissue
• Type 1 collagen fibers
• Elastic fibers

Mesoderm

• Hypodermis/Subcutaneous tissue
• Not considered part of the skin

Subcutaneous fascia

Variable amounts of adipose tissue

• Thinnest in the eyelids
• Thickest on the palms and feet

• Epidermal pegs
• Dermal papillae

• Stratum corneum
• Stratum lucidum (thick skin only)
• Stratum granulosum
• Stratum spinosum
• Stratum basale
• "Corny Luci Grants a date to the Spineless Base"

15-30 days depending on the location of the skin

• Single layer of cells on a basement membrane
• Contains stem cells
• Lots of mitotic activity
• Desmosome bound cells
• All cells have keratin intermediate filaments

The number of keratin filaments increase until they amount to about half the total protein of the stratum corneum

• There are a few layers of polyhedral keratinocytes (prickle cells)
• Desmosomes give them a spiny appearance
• Keratinocytes in the deeper layers of the stratum spinosum are mitotically active

In the Stratum spinosum and basales layers

The name of the Spinosum and Basales layers together (mitotically acitve layers)

Another name for keratin intermediate filaments

• The most superficial layer which nuclei are still present
• 3-5 layers of flattened keratinocytes
• Cells are filled with keratohyalin granules

• Keratohyalin granules (only in thick skin)
• These granules bind the keratin filaments together but are not membrane bound and are not secreted

Stratum granulosum and stratum spinosum

• Small rod like structures that discharge their contents into the intercellular spaces of the stratum granulosum forming sheets of lipids
• These function like intercellular cement and act as a barrier for waterproofing skin

• Clear layer just superficial to the stratum granulosum
• This layer is only found in thick skin
• The keratinocytes in this layer do not contain their nuclei or organelles but do have keratin filaments

• Most superficial layer of the epidermis
• May consist of 15-20 layers of dead cells
• Cells are filled with keratin

Hair follicles and sebaceous glands and a stratum lucidum layer

• Keratinocytes
• Melanocytes
• Langerhan's cells
• Merkel cells

• Dendritic cell that is scattered among the basal cells of the stratum basales
• They have long processes that extend to the stratum spinosum
• Synthesize melanin

Neural crest cells

Melanocytes

They are degraded by lysosomes

The top layers because they don't have DNA to protect

Tyrosine

Light, this is why you tan in the sun

Stratum basale and stratum spinosum layers together

To the tips of the melanocyte processes, and are then transferred to keratinocytes of the malpighian layer

• Melanosomes are more active in darker individuals, but not more prevelant
• Lighter skinned individuals degrade melanin faster

They are found in the keratinocytes primarily close to the basal layer in white folks and all the way to the corneum layer in dark folks

• Yellow-red 'phoemelanins'
• Brown-black 'eumelanins'

Absence of Tyrosine activity or the inabilty of cells to take up Tyrosine

Common pigmentation disorder where melanocytes in skin are destroyed in patchy areas throughout the whole body

Antigen presenting cells and phagocytosing cells found in the epidermis

Precursors in the bone marrow (monocytes)

Stratum spinosum but are also found in the dermis

The charecteristics of the connective tissue that surround them as they form (dermis = langerhans; bone = osteoclasts ect..)

• Stratum basale
• Receive touch signals

Desmosomes

• In the Dermis
• they are derived from the epidermis and invade the hypodermis during embryogenesis

• Papillary layer
• Reticular layer

• Extensive cross linking of collagen fibers
• Loss or degeneration of elastic fibers

Maintaining body temp

Damage to vessels under the skin causing blood to collect

This is when the epidermis of the skin separates from the dermis due to collection of body fluids like pus

Thickening of the stratum corneum for extra protection from more then normal use

• Free nerve endings
• Meissners corpuscles
• Pacinian corpuscles
• Merkel cells
• Ruffini corpuscles

• Fine touch
• Heat
• Cold
• Pain
• Itching

Stratum Granulosum

They are free of connective tissue and schwann cell coverings

• Found in the stratum basale and are most abundant in the fingertips
• They are acute mechanoreceptors

• They are found in the deeper dermis and hypodermis
• Respond to mechanical and vibratory pressure

Displacement of the capsule lamellae

Onions

• Found in the dermal papillae especially in the genitals, lips, and nipples
• They respond to slight deformations of the epidermis

• They are found in the deep layers of the skin
• They are responsive to stretch

Nuclei

• Melanocytes
• Melanin is transferred to hair follicles in the same manner they are transferred to keratinocytes

A thickened basement membrane that separates the dermis from the epithelium of the hair follicle

Growth of hair

Goose bumps (cutis anserina) on the skin as they cause the hair to go erect

• Eccrine - Produce sweat and found all over body
• Apocrine - Found in arm pit, areola, & anal region (odorless until bacteria metabolizes it)
• Sebaceous - Found throughout body but most abundant on the face and scalp (secrete sebum)

• Found in the dermis (reticular layer)
• Simple coiled tubular gland
• Merocrine secretion (simple exocytosis)

• Dark cells - line the lumen (mucin granules present)
• Clear cells - Under Dark cells, electrolyte rich secretions
• Myoepithelial cells - beneath clear cells, these contract

Postganglionic fibers of the sympathetic nervous system

• Stratified cuboidal in the duct
• Columnar in the epithelium of the gland

• Apocrine sweat glands
• Sebeceous glands in most cases
• Not Eccrine glands!

Merocrine secretion

They store their secretions unlike the Eccrine glands which do not store theirs

Area distinct from the olfactory mucosa that in most mammals where pheromones are sensed

This is an oily secretions that is secreted by the Sebaceous glands for prevention of water loss and lubrication (it may have anti-fungal and antibacterial properties as well)

• Holocrine secretion (as a result they have stem cells to replace the burst cells)
• Causes acne when glands are plugged

• Injury
• Blood clot
• Inflammation and Neutrophil infiltration
• Late inflammation with macrophages
• Fibroblasts repair and remodel by secreting collagen

Fibrous tissue composed of collagen formed by fibroblasts

• Benign fibrous growths following tissue repair
• Fibroblasts are out of control making collagen

• Hyperpigmented spot caused by increased melanin production in the basal end of the skin
• Not due to more melanocytes!

An increase in melanocytes in the skin

Birth mark caused by many new blood vessels grouping together in one place on the skin

Benign epidermal growths caused by and infection of keratinocytes by papillomaviruses

• First degree - Effects top epidermal layer only
• Second degree - Strateum basale of upper epidermis is destroyed, blisters often form
• Third degree - All layers are toast, only skin grafts will fix the burn