skin as an organizing model

Frolich, Human Anatomy, Skin

Skin as an organizing modelSkin as an organizing model

What is it? (Anatomy)What is it? (Anatomy)What does it do? (PhysiologyWhat does it do? (Physiology))What is it made of? (HistologyWhat is it made of? (Histology))Where does it come from? Where does it come from? (Embryology)(Embryology)

Original Simplified View


Skin as an organizing modelSkin as an organizing model

What is it? (Anatomy)What is it? (Anatomy)What does it do? (PhysiologyWhat does it do? (Physiology))What is it made of? (HistologyWhat is it made of? (Histology))Where does it come from? Where does it come from? (Embryology)(Embryology)

[brainstorm—what questions remain?]


Skin revisited: Filling in the BlanksSkin revisited: Filling in the Blanks

• Anatomy—dermatomes and spinal nervesAnatomy—dermatomes and spinal nerves• HistologyHistology

–epidermal cells and layersepidermal cells and layers–dermal layersdermal layers–other structuresother structures

• PhysiologyPhysiology–details of skin protection functiondetails of skin protection function

• Pathology of skinPathology of skin–skin cancersskin cancers–burnsburns


What is it (anatomy)?What is it (anatomy)?

• Outer covering of bodyOuter covering of body• KeratinizedKeratinized

– Hair—head, pubic regionsHair—head, pubic regions– Nails—fingers, toesNails—fingers, toes

• Divided into segments called dermatomes Divided into segments called dermatomes (“Zebra-man”)(“Zebra-man”)– CE (clinical example): ShinglesCE (clinical example): Shingles



Dermatomes and spinal nervesDermatomes—more details


Dermatomes and segmentation in basic body plan

Dermatomes—more details


Hair and nails—modified structures of epidermis• Nails

– Scale-like epidermal structure– Cells bind together and have “hard” keratin– Grows out from root of nail

• Hair– Each shaft has three layers of keratinzed cells filled with “hard”

keratin– Flat, ribbon-like shaft produces kinky hair; oval shaft makes wavy

hair; round shaft makes coarse hair– Hair color due to amount of melanins of different colors made my

melanocytes at base of hair follicle; red hair also has iron-containing pigment; gray/white hair due to decreased melanin production

– Hair follicle• Fold of epidermal surface into dermis• Hair grows from here• Has nerve plexus to give touch/tickle sensation• Connective tissue sheath derived from dermis• Hair length due to relationship between active and inactive phases of

follicle (e.g., eyebrow follicles active only three to four months; head follicles can be continuosly active for years)

Epidermis anatomy—more details


Epidermis anatomy—more details

Nails—scale-like epidermis


Hairs and hair folliclesEpidermis—more detailEpidermis anatomy—more details


What is it made of?What is it made of?(histology—study of tissues)(histology—study of tissues)

• Layers of skin are two Layers of skin are two fundamental types of fundamental types of tissue organizationtissue organization– Epidermis = epitheliumEpidermis = epithelium– Dermis = connective tissueDermis = connective tissue



Layers of epidermis• Stratum basale/germinativum (“basal or “forming” layer)

– One layer thick mitotic cells– 10-25% melanocytes with processes into next layer– Merkel cells with sensory neurons

• Stratum spinosum (“prickly” layer)– Cells appear spiny due to numerous desmosomes– Many Langerhans cells

• Stratum granulosum (“grainy” layer– Cells flatten– Organelles/nuclei begin to disintegrate– Keratin precursor granules begin to form– Lamellated granules with water-proof lipid form and will be spewed out

between cells• Stratum corneum (“horny” layer)

– Cells are dead—too far from underlying capillaries to live– 20-30 cells thick up to ¾ of dermal thickness– Keratin, thickened membranes and glycolipids between cells provide

“overcoat” for body to protect against water loss and other possible “assaults” on body

Epidermis histology—more details


Cells in epidermis

• Keratinocytes—epidermal cells that make keratin

• Merkel cells—associated with touch sensory neurons

• Langerhans cells—macrophages (from dermis) migrate in to form spider-like immune barrier

• Melanocytes (at border with dermis) make pigment to give skin color

Epidermis histology—more details


Epidermis—a stratified epitheliumEpidermis histology—more details


Dermis—simple viewOriginal Simplified View


Dermal layers• Papillary layer (layer with “nipples” or tiny

projections)– Thin superficial layer of areolar connective tissue– Papillae house capillary loops, nerve endings,

sweat glands– In hands and feet papillae on dermal ridges

forming fingerprint patterns• Reticular layer

– 80% of thickness– Dense irregular collagen fibers, mostly parallel to

skin surface– Predominant direction of fibers forms cleavage or

tension lines in skin (important for incisions)– Flexure lines in skin at joints where reticular layer

is bound to underlying connective tissues to provide “give” when joint flexes

Dermis histology—more details


Glands and keratinized appendages: Is it dermis…or epidermis?

• Sebaceous glands– Clumps of epithelial tissue distributed within dermis– Secrete “sebum”—oily, fat-based substance that is also anti-bacterial– Located all over body

• Sweat glands– Microscopic clumps of epithelial tissue distributed within dermis, duct

extends out through dermis to pore (not “pores” of face complexion which are hair follicles)

– More than 2.5 million glands per person– Eccrine sweat glands, concentrated on hands and soles of feet and

forehead, secrete sweat to cool body, also “cold sweat” of fear, emotion.– Apocrine glands, concentrated in armpits and groin, analogous with

sexual scent glands of other animals, odor comes from bacteria that concentrate here.

– Ceruminous glands: modified sweat glands in ear canal produce ear wax– Mammary glands: modified sweat glands in female breast produce

mother’s milk

Epidermis/Dermis histology—more details


Skin GlandsEpidermis/Dermis histology—more details


What does it do?What does it do?

• PROTECTIONPROTECTION– Air = desiccationAir = desiccation– Water = bloating/”pruning”Water = bloating/”pruning”– Sun/u-v = burnsSun/u-v = burns– Cold/heat = frostbite/heat Cold/heat = frostbite/heat

stroke/thermoregulationstroke/thermoregulation• STRUCTURALSTRUCTURAL

– Integrity of bodyIntegrity of body– Muscle attachmentMuscle attachment



What does it do?What does it do?• PROTECTIONPROTECTION

– Chemical barriers—”acid mantle” from low “pH of skin secretions Chemical barriers—”acid mantle” from low “pH of skin secretions retards bacterial growthretards bacterial growth

– Water-proofing from lipid secretions of epidermisWater-proofing from lipid secretions of epidermis– Melanin from melanocytes and DNA in all skin cells prevents Melanin from melanocytes and DNA in all skin cells prevents

burning from sunburning from sun– Immune cells in dermis and epidermis fight infection and present Immune cells in dermis and epidermis fight infection and present

antigens to other immune cellsantigens to other immune cells– Evaporation of sweat cools bodyEvaporation of sweat cools body– Closing of dermal capillaries prevents heat lossClosing of dermal capillaries prevents heat loss– Supplement liver in “disarming” cancer-causing chemicals that Supplement liver in “disarming” cancer-causing chemicals that

penetrate epidermispenetrate epidermis• SENSATION—nerve endingsSENSATION—nerve endings• METABOLIC FUNCTION—vitamin D synthesisMETABOLIC FUNCTION—vitamin D synthesis

Physiology—more details


Pathology of skin• Skin cancer (what are the cells involved?)

– Basal cell carcinoma (a)• Common and benign, 30% of white people get, slow-

growing and easily incised surgically– Squamous cell carcinoma (b)

• Less common, faster-growing but still easily removed surgically

– Melanoma (c)• Highly metastatic (spreads rapidly)• Related to U-V exposure• Early detection key—can start in retina (importance

of ophthalmologic exams)



Pathology of skin

Burns• Rule of nines• Degree of burns• Synthetic skin from silicon

epidermis and spongy dermis made of collagen fibers and ground cartilage



Interrelationship with other systems• Systems are not isolated, but just one way of analyzing

how body works• Skin is tightly linked to other systems of body

– Skeletal: Skin forms “exoskeleton”—stiff attachment point for muscles; also synthesizes Vitamin D necessary for calcium deposit process

– Muscular: Many muscles attach on the skin; muscles lose heat through skin

– Nervous: Sensory cells (Merkel cells) transmit touch sensation to neurons; blood vessel, sweat, arrector pili muscles controlled by nervous system

– Cardiovascular: Skin as blood reservoir, heat exchange organ– Immune: Very important role of skin as “first barrier” with

Langerhans cells and macrophages as cellular immune response; edema or swelling common in infected skin regions

– Reproduction: skin responds to erotic stimuli; mammary glands are highly modified sweat glands in skin; stretching of skin to accomondate fetus during pregnancy



Electronic SkinNew Topic of Interest


Distribution of skin Color• Skin color around world

New Topic of Interest

http://anthro.palomar.edu/adapt/adapt_4.htm


Genetics of skin color

From Genetics Chapter On-Line Biology Book

New Topic of Interest

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgeninteract.html

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgeninteract.html

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookTOC.html

skin as an organizing model

Documents

layermerkel cells

base of hair follicle

wavy hair round shaft

kinky hair oval shaft

pigment graywhite hair

skin revisited

layers of keratinzed

root of nailhaireach