HTHS Mod 8

• also called skin, cutaneous membrane, dermis and epidermis
• largest organ in body
• *recall desmosomes and hemidesmosomes junctions which hold cells together. These are very important for skin structure and function
• is a keratinized stratified squamous epithelium

the branch of medicine that treats diseases of the skin

• these gap junctions are used by our skin
• desmosomes hold adjacent cells together
• hemidesmosomes attach these cells to the underlying connective tissue

• a dermatological (autoimmune) disease which the patient mounts an immune defense against the proteins of his own desmosomes and hemidesmosomes
• chronic blistering disease
• Therefore, the skin of these pt's literally falls apart.
• *Recall desmosomes are a type of cell junction that holds 2 or more cells together (spot welds)

diseases in which the body doesn't recognized itself , thinks its foreign

• waterproof
• cushion and protect deeper tissues
• excrete wastes
• regulate temp
• provide sensory info

Water can be absorbed by the proteins in our skin, but does not travel through our skin and into rest of the body

• 3 layers of skin, from superficial to deep: epidermis, dermis, subcutaneous
• *subcutaneous sometimes isn't included at skin layer
• The epidermal and dermal layers are the same thickness, the subcutaneous layer is very different

• mostly comprised of dead cells which have expelled their nucleus and all organelles and became simply bags of keratin
• stratified squamous keratinized epithelium
• Is avascular (no blood vessels), innervated (had nerves) and layers of squamous epithelium

• the protein which gives skin it's strength
• All layers of the epidermis contain keratinocytes.

• In general, living keratinocytes are found in deeper layers (starting w stratum basale)
• constantly made in stratum basale
• as cells are pushed more superficially, they lose their nucleus and organelles and become dead bags of keratin
• The stratum corneum consists entirely of two dozen rows of dead keratinocytes w no other cell types present.

• a living layer of tissue underneath the epidermis
• contains the blood vessels, nerves, glands, and living cells
• made of areolar (loose) and dense irregular conn. tissue
• hair roots are also found in the dermis along with a small bit of muscle called arrector pili

• muscle which controls the angle of each hair
• found in the dermis

• found beneath the dermis
• attaches dermis to the underlying muscle layer
• not technically part of the skin, but is a layer of areolar and/or adipose connective tissue
• Blood passes through this layer on it's way to the dermis.
• Lamellated corpuscles are found in lower dermis and upper part of subcutaneous layer
• common place for injections - subQ

• From superficial to deep:
• stratum corneum
• stratum lucidum
• stratum granulosum
• stratum spinosum
• stratum basale
• "Cher Likes Getting Skin Botoxed"
• Stratum - layer, get other name by their appearance (under microscope)

• top layer of skin
• "horn-like"
• NO NUCLEUS, dead cells

• if going superficial to deep, the 2nd layer of the epidermis
• "clear"
• found only in thick (hairless) skin
• makes calluses

• "grainy" ~ lipids are accumulated to give skin it's waterproof ability, which gives it the grainy appearance
• 3rd layer of epidermis

• 4th layer of epidermis
• "spiny" - in appearance, it looks like there are "spines" or junctions btwn the cells
• has other cell types besides keratinocytes

• 5th and deepest layer of epidermis
• layer from which all others regenerate
• single layer of cuboidal cells which continually (rapidly) divide (by mitosis) 
• *stem cells are produced, then divide. one cell remains in the stratum basale, the other progresses and becomes a keratinocyte (skin cell)
• As skin cells move up, the acquire keratin and lipids in other skin layers

found only in the deeper layers: basale and spinosum

• another name for the keratinocytes which are pushed superficially and become dead bags of keratin
• are constantly shed from surface of stratum corneum

• the shed flakes of skin
• humans shed about 600000 per hour
• an estimated 1/3 of "house dust" is shed skin flakes

• Thick and thin
• each w a different distribution of five skin layers

• (hairy skin) - lacks stratum lucidum
• covers everything except the palms, fingertips, and soles of feet
• the spinosum and corneum  layers are very thin
• have hair,  but less sweat glands than thick skin

• has prominent stratum lucidum
• also called glabrous skin
• found on palms and fingertips and soles of feet
• is from 6 to 45 times as thick as thin skin
• most of increased thickness is because of spinosum, lucidum and corneum layers
• do not have hair, more sweat glands than thin skin
• also has ridges cause of dermal papillae which underlie the epidermis

• Because sebaceous glands are associated with hair follicles
• Thick skin = no hair
• thin skin = hair

• stem cells
• melanocytes
• langerhans cells
• merkel discs

• a cell membrane surrounding the protein keratin, which gives skin it's strength
• make up about 90% of the cells of the epidermis
• takes 4 - 6 weeks for new cells to reach top layer

it's dividing

• carry & produce melanin, which give skin color
• make up about 8% of cells in epidermis
• tries to protect from energy (UV, etc.). So more UV you're exposed to, the more melanin is produced (which appears as a tan)

pigment granules in melanocytes, which give skin color

• one of 4 cell types in epidermis
• provide immune defense
• skins version of a macrophage cell or phagocyte

• the rarest epidermal cell (of the 4 types)
• cells that are attached to sensory neurons that detects light touch

• found in stratum basale
• full of intermediate filament protein keratin
• they divide to regenerate skin keratinocytes
• cells terminally differentiate as they move more superficially
• eventually lose nuclei & just become surrounded by membrane
• also secrete lipids that give skin waterproof and flexible properties

• skin protects the body and defends against microbial invaders
• also serves to cool the blood, when necessary, and detect sensory modalities of touch: pressure, vibration, pain and temp.
• keratin & lipids of skin help w waterproof seal
• skin is also critical in the activation of precursors which form Vit D

• 1. melanin - which there are two kinds (pheomelanin and eumelanin)
• 2. Hemoglobin
• 3. Carotene

• pheomelanin = is yellow to red - causes freckles
• eumelanin = brown to black
• Also found in hair

• cells which make melanin; where pheomelanin and eumelanin pigments are found
• normally scattered more-or-less evenly throughout epidermis, mostly in the deeper layers (spinosum and basale)
• almost everyone has roughly same #, where people differ is the amount of pigment in each melanocyte

• an organelle which makes melanin from the amino acid tyrosine
• the pigment is transferred to keratinocytes, give hair and epidermis it's color

• a mole
• happens when melanocytes (which are normally evenly scattered throughout epidermis) accumulate in one region

• little melanin is made and stored in melanocytes
• the color of skin is predominantly due to hemoglobin

• a red pigment in blood that gives the skin a pinkish cast
• oxygen carrying molecule in blood
• more blood flow you have, more redish skin is

• a skin pigment which forms deposits in the skin
• a precursor to Vit A found in intensely colored fruits and veggies

• causes jaundice (the symptom of turing yellow)
• happens in some diseases, such a liver failure, when the pigment bilirubin accumulates in the skin, giving it a yellow color
• especially easy to see in the "whites" of the eyes

• 1/5 areolar connective tissue and 4/5 dense connective tissue
• is strong and resilient, can be stretched and snaps back to original form
• are few cells, mostly collagen and elastic fibers
• two regions of dermis: Papillary region and reticular region

• 1/5 thickness of dermis ~ consists of areolar connective tissue w thin collagen and fine elastic fibers
• important for it's tight attachment to epidermis
• is thrown up into ridges that penetrate up into the epidermis
• each ridge tends to contain blood vessels (capillary loops) and Meissner corpuscles and free nerve endings

On palms, fingertips, and soles the underlying structure of dermis (the ridges) cause fingerprints - gives grip ability and sensitivity

• the remaining 4/5 of dermis ~ consists of dense irregular connective tissue w bundles of thick collagen and some coarse elastic fibers
• Spaces btwn fibers contain some adipose cells, hair cells, nerves, and glands
• nerves and blood vessels run here
• hair roots (if present) and glands are found here

• collagen and elastic fibers = strength and stretching
• Muscle tissue - arrector pili muscles @ base of hair follicles
• blood vessels = oxygen and nutrients to epidermis (DERMIS IS VASCULAR!)

• stretch marks
• caused by stretching of skin that causes tears in dermis, such as from obesity or pregnancy
• Is permanent

• If you mark with a permanent marker, it stains the top layer of skin, but you have to wait for those skin cells to sluff off for the mark to go away
• Tattoos are coloration of the DERMIS
• Is permanent

• *Recall it's a loose connective tissue made up of collagen, reticular and elastic fibers with adipose cells suspended in fiber matrix. Blood vessels and nerves traverse the layer
• Ex: subcutaneous layer of the skin

• serves to:
• thermoregulate (conserves heat)
• cushion btwn dermis and muscle tissue

• 4 types in two locations: in papillary region and at border of dermis & subQ layer:
• Meissner (touch) corpuscle
• Merkel (tactile) discs
• Free Nerve Endings
• Pacinian (Lamellated) Corpuscle
• they take energy from the environment and convert it to a signal that the nervous system can use

• Meissner corpuscles 
• Merkel discs
• free nerve endings

Pacinian (lamellated) corpuscle

receptors that pick up pain, temperature, itch, movement of hair

• a kind of nerve ending mediating the feeling of vibration & deep pressure
• found @ border of dermis and subcutaneous layer
• (lamellated means layer) it's layered like an onion
• special shape means that nerve ending inside the corpuscle responds preferentially to vibration

sensory nerve found in skin which detects light touch

• sensation from nerve network around hair roots in thin skin
• picks up hair movements

• The Pacinian (lamellated) corpuscle detects vibration
• scientists believe actual function of "vibration" receptors is to detect slippage of thick skin against a surface, as when you lose your grip on a branch

• Sudoriforous glands 
• Sebaceous glands

• sweat glands ~ two types:
• eccrine and apocrine

• is a sweat gland
• used to cool skin (thermoregulation) and restore homeostasis
• lie mostly in deep dermis and open to skin surface through a duct
• they secrete a sweat that is thin
• are active throughout life

• is a dilute solution of salt water with traces of urea, uric acid, ammonia, amino acids, glucose and lactic acid. (Usually U Are Among Good Liers)
• water is needed for evaporative cooling of skin
• Other components are waste products being released

• throughout skin of most regions of body, especially in skin of forehead, palms, and soles
• Becomes active soon after birth

• is a sweat gland ~ lie in subcutaneous layer
• Do not open to skin, but in hair shaft
• DOESN'T use apocrine secretion
• secretions are similar to that of eccrine, but more viscous
• Stimulated to release product during emotional stress and sexual excitement 
• secretions contain fat-soluble substances like pheromones which participate is sexual response 

natural odor molecules

• Skin of axilla, groin, areolae, bearded regions of face, clitoris, and labia minora
• Isn't active till after puberty
• *misnamed, but too late to change. Once thought to secrete by apocrine mechanism, but not true

• oil glands, found most often opening into the neck of the hair follicle
• secrete sebum
• found on lips & other hair free surfaces except palms and soles
• become active at puberty in response to androgens

• the oily secretion from sebaceous glands
• coat and protects the hair surface against drying and breakage
• gives hair it's flexibility

• an inflammation of the sebaceous glands
• some types of bacteria like living in sebum, and acne occurs predominantly in sebaceous follicles that are colonized by bacteria

• Apocrine and sebateous glands are associated with hair
• eccrine glands are not

• mechanical protection of fingertips
• grasping objects

• at distal end of dorsal surface of fingers and toes
• clear,tough covering or plate made of tightly packed keratin that is given rise by a fold of dermis
• *Nails are extensions of epidermis

• at proximal end of nail body, pushes out nail
• where rapidly dividing & growing cells are that makes nail

• the cuticle
• fills the space where the epidermis ends

• "little moon"
• sometimes seen near the cuticle as a slightly lighter area
• The lunula appears white because it's a bit thicker than the rest of nail, cant see through it as well to see blood flow

• also a derivative of the epidermis
• like skin and nails, is a specialized form of keratin
• beneath the surface of skin, the hair follicle and dermal root sheath surround the medulla, cortex and cuticle.
• at the base, there are blood vessels and melanocytes (pigment cells)

• located at base of hair follicle, 
• like nails, also where the rapidly dividing and growing cells are
• bottom has melanocytes (pigment cells)

• the part we see, are dead keratinized epidermal cells
• has 3 layers:
• the medulla = in center
• cortex = in middle
• cuticle = the outermost external hair, the part we see

• color comes from pigment granules (brown or black eumelanin; blonde or red pheomelanin) trapped along w the keratin protein in hair shafts
• White or gray hair occurs when pigment production is reduced or halted and air bubbles replace pigment

• has three layers not present on outer surface
• Internal root sheath, external root sheath, and dermal root sheath, which surrounds the whole root of the hair and holds all together
• at base, a small plexus of blood vessels supplies nutrition to the growing hair and melanocytes

• 3 stages:
• growth (anagen) stage
• regression (catagen) stage
• resting (telogen) stage
• varies from hair to hair

• 1st stage of hair cycle; the growing stage
• hair matrix cells at base of follicle divide
• this pushes hair a littler further out root and makes external hair bit longer
• as these cells are pushed upward, they turn to bags of keratin and die (just as epidermis)
• lasts 2 - 6 years

• 2nd stage of hair cycle; the regression stage
• cells of hair matrix stop dividing
• lasts 2-3 weeks

• 3rd and final stage of hair cycle; the resting stage
• hair falls out at end of resting stage, replaced by new hair in it's growth stage
• lasts about 3 month

because they have the highest density of nerve endings

• the outermost of the three embryonic layers
• the layer from which skin develops
• *The epidermis arises from ectoderm; dermis arises from mesoderm

by 11 weeks

at the beginning of 2nd trimester, 14 weeks

• a location near the spinal cord (in a developing fetus) from which melanocytes migrate into the skin
• they are among the last skin cells to arrive

• the toxins in cigarette smoke interfere with Vit C, which is necessary of collagen synthesis
• Therefore, smoking damages the underlying dermis

• common disease of aging skin
• characterized by dilated blood vessels and pimples, especially around nose and cheeks
• cause is unknown

• defined as those that do not penetrate the epithelium
• dividing cells of the stratum basale migrate into the "pit" of the wound, if necessary, then the normal process of cell division produced nucleated keratinocytes and finally these get pushed upward by the newly-divided keratinocytes are they mature into corneocytes

• penetrate blood vessels
• blood fills wound & clots into semi-solid mass
• Monocytes in clot mature into macrophages; neutrophils in clot work w macrophages to destroy invaders
• Cell of stratum basale migrate inward to replace epidermis
• Fibroblasts migrate into dermal portion of clot and lay down new fiber matrix to restore funtion and appearance of dermis
• If restoration of dermis is not complete, a scar may be left behind
• some scars remodel over a period of severl months or even yeard

• also called decubitus ulcers
• area's where bone is close to surface especially prone, cause less cushioning from adipose & muscle tissue
• Skin becomes trapped btwn fixed point (bed, cast, etc.) and blood supply is lost
• A few hours may produce discoloration, but damage is not permanent.
• If pressure continues for long time, small cracks develop in skin and skin flora begin dividing. W/o immune cells carried by blood, infection spreads and necrosis results

tissue death

• such as sunburn, only epidermis is involved
• skin reddens, but no permanent damage
• delayed blistering
• skin returns to normal in under a week

• heat energy penetrates deeply and both epidermis and dermis are damages
• Blood vessels leak fluid (though not cells) and blisters immediately form as skin fills with the filtrate of blood
• Hair follicles and glands are typically not damages

• also called full thickness burn
• destroys all layers of skin
• cells die and skin function is lost in affected area
• dead skin may be black, cherry-red or ash white

• classification of the extent of burns
• 11 regions of 9% each
• the remaining 1% is the perineum

• 1. head - 9%
• 2. right arm - 9%
• 3. left arm - 9%
• 4&5. anterior trunk - 18% (top 9, bottom 9)
• 6&7. posterior trunk - 18%
• 8. anterior right lower extremity - 9%
• 9. anterior left lower extremity - 9%
• 10. posterior right extremity - 9%
• 11. posterior left extremity - 9%

• the genital area
• takes 1% on rule of nines

• Receptors are located in the core, they sense temp. of blood
• the control center is the hypothalamus
• There are several effectors, skin being a major one in the homeostatic loop controlling body temp.

circulation and sweating

• They dilate to shed heat, constrict to conserve heat
• Arrector pili also helps constrict blood vessels by "goose bumps" (in animals w hair, it traps air and provides insulation)

• Adipose tissue in subQ layers insulates the blood vessels, helping to keep heat in
• Sweat glands shed heat by evaportation

• sweat glands release fluid to surface to cool skin by evaperation
• blood vessels dilate and shed more heat
• this makes skin appear pink or red ("flushed")
• same reaction can happen in response to emotional events (blushing)

• heat is conserved
• sweat glands stop production, blood vessels constrict
• blood stays internal to dermis, behind insulation layer of fat
• skin may appear pale or blue as blood is trapped deep in dermis and subQ region

with skin tissue, not cancer yet, but dysfunctional growth

• carcinoma is skin cancer
• in situ means it hasn't left it's compartment in the epidermis, hasn't broke through basement membrane into dermis

• one of most invasive and deadly forms of cancer
• symptom can be a mole with uneven color or irregular edges or both
• because response of skin to UV light is to produce more melanin, UV can damage DNA resulting in cancer

• most common type of skin cancer
• commonly seen on face
• caused by sun exposure
• cancerous but rarely metastatic (doesn't travel to distant sites)

• spreading to distant sites
• (referring to cancer cells)

• second most common type of skin cancer
• commonly seen on face
• caused by UV exposure
• begins above basal layer
• Cancerous and will metastasize (usually through lymphatic system)

• rarest form of skin cancer, also most worrisome and deadly
• arise from melanocytes
• spread avidly and can cause death with the metastasize
• if travels to lymph nodes, then 5 yr survival less than 1 in 3

• A = asymmetry
• B = border changes
• C = color variation
• D = diverse structure
• E = elevation

• mutation in gene that repairs DNA damage
• results when DNA editing mechanisms are broken
• not a cancer, but a predisposition to cancer
• Because UV light is constantly causing damage to DNA, and cannot be repaired in these pts, they have very high incidence of skin cancer, even multiple skin cancers

• staphylococcus spp. and enterococcus spp.
• resist dying and live for a long time

a bacteria which commonly cause pneumonia in hospitals