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Original Simplified View. Skin as an organizing model. What is it? (Anatomy) What does it do? (Physiology ) What is it made of? (Histology ) Where does it come from? (Embryology). Skin as an organizing model. What is it? (Anatomy) What does it do? (Physiology )

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skin as an organizing model

Original Simplified View

Skin as an organizing model

What is it? (Anatomy)

What does it do? (Physiology)

What is it made of? (Histology)

Where does it come from?

(Embryology)

Frolich, Human Anatomy, Skin

skin as an organizing model2

Skin as an organizing model

What is it? (Anatomy)

What does it do? (Physiology)

What is it made of? (Histology)

Where does it come from?

(Embryology)

[brainstorm—what questions remain?]

Frolich, Human Anatomy, Skin

skin revisited filling in the blanks

Skin revisited: Filling in the Blanks

Anatomy—dermatomes and spinal nerves

Histology

epidermal cells and layers

dermal layers

other structures

Physiology

details of skin protection function

Pathology of skin

skin cancers

burns

Frolich, Human Anatomy, Skin

what is it anatomy

Original Simplified View

What is it (anatomy)?
  • Outer covering of body
  • Keratinized
    • Hair—head, pubic regions
    • Nails—fingers, toes
  • Divided into segments called dermatomes (“Zebra-man”)
    • CE (clinical example): Shingles

Frolich, Human Anatomy, Skin

hair and nails modified structures of epidermis

Epidermis anatomy—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)

Frolich, Human Anatomy, Skin

hairs and hair follicles

Epidermis anatomy—more details

Epidermis—more detail

Hairs and hair follicles

Frolich, Human Anatomy, Skin

what is it made of histology study of tissues

Original Simplified View

What is it made of?(histology—study of tissues)
  • Layers of skin are two fundamental types of tissue organization
    • Epidermis = epithelium
    • Dermis = connective tissue

Frolich, Human Anatomy, Skin

layers of epidermis

Epidermis histology—more details

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

Frolich, Human Anatomy, Skin

cells in epidermis

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

Frolich, Human Anatomy, Skin

slide14

Original Simplified View

Dermis—simple view

Frolich, Human Anatomy, Skin

dermal layers

Dermis histology—more details

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

Frolich, Human Anatomy, Skin

glands and keratinized appendages is it dermis or epidermis

Epidermis/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

Frolich, Human Anatomy, Skin

slide18

Original Simplified View

What does it do?

  • PROTECTION
    • Air = desiccation
    • Water = bloating/”pruning”
    • Sun/u-v = burns
    • Cold/heat = frostbite/heat stroke/thermoregulation
  • STRUCTURAL
    • Integrity of body
    • Muscle attachment

Frolich, Human Anatomy, Skin

what does it do

Physiology—more details

What does it do?
  • PROTECTION
    • Chemical barriers—”acid mantle” from low “pH of skin secretions retards bacterial growth
    • Water-proofing from lipid secretions of epidermis
    • Melanin from melanocytes and DNA in all skin cells prevents burning from sun
    • Immune cells in dermis and epidermis fight infection and present antigens to other immune cells
    • Evaporation of sweat cools body
    • Closing of dermal capillaries prevents heat loss
    • Supplement liver in “disarming” cancer-causing chemicals that penetrate epidermis
  • SENSATION—nerve endings
  • METABOLIC FUNCTION—vitamin D synthesis

Frolich, Human Anatomy, Skin

pathology of skin

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)

Frolich, Human Anatomy, Skin

slide21

Physiology—more details

Frolich, Human Anatomy, Skin

slide22

Physiology—more details

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

Frolich, Human Anatomy, Skin

interrelationship with other systems

Physiology—more details

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

Frolich, Human Anatomy, Skin

electronic skin

New Topic of Interest

Electronic Skin

Frolich, Human Anatomy, Skin

distribution of skin color

New Topic of Interest

Distribution of skin Color
  • Skin color around world

Frolich, Human Anatomy, Skin

genetics of skin color

New Topic of Interest

Genetics of skin color

From Genetics Chapter

On-Line Biology Book

Frolich, Human Anatomy, Skin

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