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The epidermis is derived from
Derived from ectoderm
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What is the dermis made up of
- Dense irregular connective tissue
- Type 1 collagen fibers
- Elastic fibers
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What is the dermis derived from
Mesoderm
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What lies below the dermis
- Hypodermis/Subcutaneous tissue
- Not considered part of the skin
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What is the hypodermis equivalent to in other portions of the body
Subcutaneous fascia
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What is contained in the hypodermis
Variable amounts of adipose tissue
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Where is the epidermis the thickest and thinnest in the body
- Thinnest in the eyelids
- Thickest on the palms and feet
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What are the different ridges on the dermis and epidermis where they meet
- Epidermal pegs
- Dermal papillae
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What are the layers of the epidermis
- Stratum corneum
- Stratum lucidum (thick skin only)
- Stratum granulosum
- Stratum spinosum
- Stratum basale
- "Corny Luci Grants a date to the Spineless Base"
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How often is the epidermis renewed
15-30 days depending on the location of the skin
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What are the features of the stratum basale
- Single layer of cells on a basement membrane
- Contains stem cells
- Lots of mitotic activity
- Desmosome bound cells
- All cells have keratin intermediate filaments
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What happens to cells as they travel from the basale layer to the corneum layer
The number of keratin filaments increase until they amount to about half the total protein of the stratum corneum
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What are the features of the Stratum spinosum
- 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
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Where are the only keratinocytes that divide
In the Stratum spinosum and basales layers
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Stratum germanitivum
The name of the Spinosum and Basales layers together (mitotically acitve layers)
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Tonofilments
Another name for keratin intermediate filaments
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What are the traits of the stratum granulosum layer of the skin
- The most superficial layer which nuclei are still present
- 3-5 layers of flattened keratinocytes
- Cells are filled with keratohyalin granules
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What is the identifying feature of the the stratum granulosum layer, and what is its role
- Keratohyalin granules (only in thick skin)
- These granules bind the keratin filaments together but are not membrane bound and are not secreted
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What layers contain lamellar granules
Stratum granulosum and stratum spinosum
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Lamellar bodies (granules)
- 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
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What are the features of the stratum lucidum
- 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
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What are the features of the stratum corneum layer of skin
- Most superficial layer of the epidermis
- May consist of 15-20 layers of dead cells
- Cells are filled with keratin
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Thick skin lacks what
Hair follicles and sebaceous glands and a stratum lucidum layer
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What are the cell types found in the epidermis
- Keratinocytes
- Melanocytes
- Langerhan's cells
- Merkel cells
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Melanocytes
- 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
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Melanocytes are derived from
Neural crest cells
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What cells in the epidermis do not have desmosomal attachments to the surrounding cells
Melanocytes
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What happens to melanin after it enters the keratinocytes
They are degraded by lysosomes
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What cells don't contain melanin in the epidermis
The top layers because they don't have DNA to protect
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What do melanocytes synthesize melanin from
Tyrosine
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Tyrosine is activated by
Light, this is why you tan in the sun
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Malpighian layer
Stratum basale and stratum spinosum layers together
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After melanin granules are formed they migrate where
To the tips of the melanocyte processes, and are then transferred to keratinocytes of the malpighian layer
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What determines skin color
- Melanosomes are more active in darker individuals, but not more prevelant
- Lighter skinned individuals degrade melanin faster
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How does the distribution of melanosomes differ in dark skinned and light skinned individuals
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
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What are the two types of melanin that can be synthesized
- Yellow-red 'phoemelanins'
- Brown-black 'eumelanins'
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Albinism is caused by
Absence of Tyrosine activity or the inabilty of cells to take up Tyrosine
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Vitiligo
Common pigmentation disorder where melanocytes in skin are destroyed in patchy areas throughout the whole body
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Langerhan's cells
Antigen presenting cells and phagocytosing cells found in the epidermis
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What are Langerhan cells derived from
Precursors in the bone marrow (monocytes)
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What layer are Langerhan cells found in primarily
Stratum spinosum but are also found in the dermis
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What determines the final differentiation of macrophages from the bone marrow
The charecteristics of the connective tissue that surround them as they form (dermis = langerhans; bone = osteoclasts ect..)
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Merkel cells are found where, with what function
- Stratum basale
- Receive touch signals
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How do Merkel cells connect to neighboring keratinocytes
Desmosomes
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Where are the sebaceous glands, hair follicles, and sweat glands found, and how did they get there
- In the Dermis
- they are derived from the epidermis and invade the hypodermis during embryogenesis
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What are the layers of the dermis
- Papillary layer
- Reticular layer
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What is the cause of wrinkling skin
- Extensive cross linking of collagen fibers
- Loss or degeneration of elastic fibers
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Changes in blood flow in the skin plays an essential role in
Maintaining body temp
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What is a bruise
Damage to vessels under the skin causing blood to collect
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What is a blister
This is when the epidermis of the skin separates from the dermis due to collection of body fluids like pus
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What is a callous
Thickening of the stratum corneum for extra protection from more then normal use
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What are the different types of nerve receptors found in the skin
- Free nerve endings
- Meissners corpuscles
- Pacinian corpuscles
- Merkel cells
- Ruffini corpuscles
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What do free nerve endings respond to
- Fine touch
- Heat
- Cold
- Pain
- Itching
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Where do free nerve ending terminate
Stratum Granulosum
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Why are they called free nerve endings
They are free of connective tissue and schwann cell coverings
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Where are Merkel cells found to be most abundant
- Found in the stratum basale and are most abundant in the fingertips
- They are acute mechanoreceptors
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Where are Pacinian corpuscles found, and what do they respond to
- They are found in the deeper dermis and hypodermis
- Respond to mechanical and vibratory pressure
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Movement of what in the pacinian corpuscles causes depolarization of the axon
Displacement of the capsule lamellae
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What do pacinian corpuscles look like
Onions
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Where are the Meissners corpuscles found and what do they respond to
- Found in the dermal papillae especially in the genitals, lips, and nipples
- They respond to slight deformations of the epidermis
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Where are Ruffini corpuscles found and what do they respond to
- They are found in the deep layers of the skin
- They are responsive to stretch
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Hair cells don't have
Nuclei
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What gives hair its color
- Melanocytes
- Melanin is transferred to hair follicles in the same manner they are transferred to keratinocytes
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Glassy membrane
A thickened basement membrane that separates the dermis from the epithelium of the hair follicle
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Proliferation of matrix cells accounts for what
Growth of hair
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Arrector pili muscle cause what
Goose bumps (cutis anserina) on the skin as they cause the hair to go erect
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What are the differences in the Eccrine, Apocrine, and Sebaceous glands
- 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)
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Eccrine glands are found in what layer of the skin, appear how, and have what mode of secretion
- Found in the dermis (reticular layer)
- Simple coiled tubular gland
- Merocrine secretion (simple exocytosis)
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What are the different cell types found in Eccrine glands
- Dark cells - line the lumen (mucin granules present)
- Clear cells - Under Dark cells, electrolyte rich secretions
- Myoepithelial cells - beneath clear cells, these contract
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What controls the Eccrine secretions
Postganglionic fibers of the sympathetic nervous system
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What type of cells make up the Eccrine glands
- Stratified cuboidal in the duct
- Columnar in the epithelium of the gland
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What glands open in to the hair follicles
- Apocrine sweat glands
- Sebeceous glands in most cases
- Not Eccrine glands!
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What type of secretion do the Apocrine cells perform
Merocrine secretion
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What is unique about the Apocrine glands
They store their secretions unlike the Eccrine glands which do not store theirs
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Vomernasal organ
Area distinct from the olfactory mucosa that in most mammals where pheromones are sensed
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What is the role of Sebum, and where does it come from
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)
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What is the method of secretion of the Sebaceous glands
- Holocrine secretion (as a result they have stem cells to replace the burst cells)
- Causes acne when glands are plugged
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What are the steps to wound healing
- Injury
- Blood clot
- Inflammation and Neutrophil infiltration
- Late inflammation with macrophages
- Fibroblasts repair and remodel by secreting collagen
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What is a scar
Fibrous tissue composed of collagen formed by fibroblasts
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Keloid
- Benign fibrous growths following tissue repair
- Fibroblasts are out of control making collagen
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What is a freckle
- Hyperpigmented spot caused by increased melanin production in the basal end of the skin
- Not due to more melanocytes!
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What is a mole
An increase in melanocytes in the skin
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Hemangioma
Birth mark caused by many new blood vessels grouping together in one place on the skin
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What is a wart
Benign epidermal growths caused by and infection of keratinocytes by papillomaviruses
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What is the difference between the different types of burns
- 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
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