The Skin

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The Skin

• Also known as the Integumentary System covers
  all body surfaces

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Skin Video
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Contains these tissues

• 1. Epithelial Tissue
• a. Found in outer layer of skin (covers body)
• 2. Connective Tissue
• a. Consists of tough, flexible fibers that holds
  the body together.
• 3. Muscle Tissue
• a. Push hairs up in skin (goose bumps)
• 4. Nervous Tissue
• a. Helps detect pain, pressure, heat, cold

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Consists of three major regions

• Epidermis outermost superficial region
• Dermis middle region
• Hypodermis (superficial fascia) deepest region

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Functions

• Covers all body surface
• inside and out
• Ex. Lung linings
• capillaries
• anchored by basement membrane
• reproduce rapidly
• tightly packed
• attached by desmosomes

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The Two Layers of the Skin(Outer and Inner)

• 1. Epidermis
• a. Outermost layer of skin
• 1. Exterior
• Consists of 25 to 30 layers of dead cells
  (continually being shed)
• Contains keratininized stratified squamous
  epithelium - protective protein
• Contains keratinocytes, melanocytes, Merkel
  cells, and Langerhans cells

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• b. Characteristics
• 1. No blood vessels
• 2. Newer cells below push up to surface
• 3. Older cells layer up and die
• 4. Hardening keratinizing
• 5. calluses form
• 6. shields against moisture loss
• 7. Prevents invasions of organisms
• 8. Ability to tan

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Over view.

• 2. Outer portion of the skin is exposed to the
  external environment and functions in protection

3. Interior Contains living cells (continually
forming new cells) Melanin (pigment) found in
this layer
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• 3. Epidermal ridges
• a. Known as fingerprints

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Identifying Markers
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Types of Fingerprints

• 1. Arch

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• 2. Whorl

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• 3. Loops

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• 4. Double Loops

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• 5. Mixed Combinations

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Layers of Epidermis

• From outer to inner
• 1. Stratum Lucidum (Clear Layer)
• 2. Stratum Granulosum (Granular Layer)
• a. Granular in appearance 3. Stratum
  Spinosum (Prickly Layer)
• a. Thick part
• 4. Stratum Basale (Basal Layer)b
• a. Deepest layer
• 5. Stratum Corneum (Horny Layer)
• a. Layer of hard cells

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Layers of the Epidermis Stratum Corneum (Horny
Layer)

• Outermost layer of keratinized cells
• Accounts for three quarters of the epidermal
  thickness
• Functions include
• Waterproofing
• Protection from abrasion and penetration
• Rendering the body relatively insensitive to
  biological, chemical, and physical assaults

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Layers of the Epidermis Stratum Lucidum (Clear
Layer)

• Thin, transparent band superficial to the stratum
  granulosum
• Consists of a few rows of flat, dead
  keratinocytes
• Present only in thick skin

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Layers of the Epidermis Stratum Granulosum
(Granular Layer)

• Thin three to five cell layers in which drastic
  changes in keratinocyte appearance occurs
  

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Layers of the Epidermis Stratum Spinosum
(Prickly Layer)

• Cells contain a weblike system of intermediate
  filaments attached to desmosomes
• Melanin granules and Langerhans cells are
  abundant in this layer

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Langerhans Cells
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Langerhans Cells..

• On infection of an area of skin, the local
  Langerhans' cells will take up and process
  microbial antigens.
• They are similar in shape and function to
  macrophages.

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Merkel Cells

• Merkel cells are present in small numbers in the
  stratum basale, or the deepest layer, of the
  epidermis.
• They are located near areas of well-vascularised,
  richly innervated connective tissue. Each Merkel
  cell is intimately associated with a nerve
  terminal, forming a structure known as a Merkel
  cell-neuron complex, or a Merkel disc.
• Merkel cells possess desmosomes and keratin
  filaments, which suggests that they may have an
  epithelial origin.

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Layers of the Epidermis Stratum Basale (Basal
Layer)

• Deepest epidermal layer firmly attached to the
  dermis
• Consists of a single row of the youngest
  keratinocytes
• Cells undergo rapid division, hence its alternate
  name, stratum germinativum

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• The basal cell layer contains cells called
  melanocytes.
• Melanocytes produce the skin coloring or pigment
  known as melanin, which gives skin its tan or
  brown color and helps protect the deeper layers
  of the skin from the harmful effects of the sun.
• Sun exposure causes melanocytes to increase
  production of melanin in order to protect the
  skin from damaging ultraviolet rays, producing a
  suntan.
• Patches of melanin in the skin cause birthmarks,
  freckles and age spots.
• Melanoma develops when melanocytes undergo
  malignant transformation.

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Skin Color

• Three pigments contribute to skin color
• Melanin yellow to reddish-brown to black
  pigment, responsible for dark skin colors
• Freckles and pigmented moles result from local
  accumulations of melanin
• Carotene yellow to orange pigment, most obvious
  in the palms and soles of the feet
• Hemoglobin reddish pigment responsible for the
  pinkish hue of the skin

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Layers of the Epidermis Stratum Basale (Basal
Layer)
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• 3. Dermis
• a. Known as the inner, thicker portion of skin
• b. Contains
• Blood vessels
• Nerves
• Nerve endings
• Hair follicles
• Sweat glands
• Oil glands

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• c. Attached to an underlying layer of
  subcutaneous (fat) layer.
• This fat layer helps absorb impacts, retain heat,
  store food.

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Dermis

• Second major skin region containing strong,
  flexible connective tissue
• Cell types include fibroblasts, macrophages, and
  occasionally mast cells and white blood cells
• Composed of two layers papillary (fingerlike
  projections) and reticular

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Layers of the Dermis Papillary Layer

• Papillary layer
• Areolar connective tissue with collagen and
  elastic fibers
• Its superior surface contains peglike projections
  called dermal papillae
• Dermal papillae contain capillary loops,
  Meissners corpuscles, and free nerve endings

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Layers of the Dermis Reticular Layer

• Reticular layer
• Accounts for approximately 80 of the thickness
  of the skin
• Collagen fibers in this layer add strength and
  resiliency to the skin
• Elastin fibers provide stretch-recoil properties

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Dermis Characteristics

• Uneven surface
• Contains
• Fingerlike papillae
• Fibrous and connective tissue
• Muscle fibers
• Hair follicles
• Blood vessels
• Nerve fibers
• Pacinian Corpuscles heavy pressure
• Meissners Corpuscles light pressure
• -- Sevbaceous glands
• --Sweat glands

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Sweat Glands

• Different types prevent overheating of the body
  secrete cerumen and milk
• Eccrine sweat glands found in palms, soles of
  the feet, and forehead
• Apocrine sweat glands found in axillary and
  anogenital areas
• Ceruminous glands modified apocrine glands in
  external ear canal that secrete cerumen
• Mammary glands specialized sweat glands that
  secrete milk

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Sebaceous Glands

• Simple alveolar glands found all over the body
• Soften skin when stimulated by hormones
• Secrete an oily secretion called sebum

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Structure of a Nail

• Scalelike modification of the epidermis on the
  distal, dorsal surface of fingers and toes

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Hair

• Filamentous strands of dead keratinized cells
  produced by hair follicles
• Contains hard keratin which is tougher and more
  durable than soft keratin of the skin
• Made up of the shaft projecting from the skin,
  and the root embedded in the skin
• Consists of a core called the medulla, a cortex,
  and an outermost cuticle
• Pigmented by melanocytes at the base of the hair

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Hair Function and Distribution

• Functions of hair include
• Helping to maintain warmth
• Alerting the body to presence of insects on the
  skin
• Guarding the scalp against physical trauma, heat
  loss, and sunlight
• Hair is distributed over the entire skin surface
  except
• Palms, soles, and lips
• Nipples and portions of the external genitalia

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Hair Follicle

• Root sheath extending from the epidermal surface
  into the dermis
• Deep end is expanded forming a hair bulb
• A knot of sensory nerve endings (a root hair
  plexus) wraps around each hair bulb
• Bending a hair stimulates these endings, hence
  our hairs act as sensitive touch receptors

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Hair Follicle
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Hair Follicle
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Types of Hair

• Vellus pale, fine body hair found in children
  and the adult female
• Terminal coarse, long hair of eyebrows, scalp,
  axillary, and pubic regions

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Hair Thinning and Baldness

• Hair Thinning and Baldness
• Alopecia hair thinning in both sexes
• True, or frank, baldness
• Genetically determined and sex-influenced
  condition
• Male pattern baldness caused by follicular
  response to DHT

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Functions of the Integumentary System

• Protection chemical, physical, and mechanical
  barrier
• Body temperature regulation is accomplished by
• Dilation (cooling) and constriction (warming) of
  dermal vessels
• Increasing sweat gland secretions to cool the
  body
• Cutaneous sensation exoreceptors sense touch
  and pain

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Functions of the Integumentary System

• Metabolic functions synthesis of vitamin D in
  dermal blood vessels
• Blood reservoir skin blood vessels store up to
  5 of the bodys blood volume
• Excretion limited amounts of nitrogenous wastes
  are eliminated from the body in sweat

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Skin Cancer

• Most skin tumors are benign and do not
  metastasize
• A crucial risk factor for nonmelanoma skin
  cancers is the disabling of the p53 gene
• Newly developed skin lotions can fix damaged DNA

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Skin Cancer

• The three major types of skin cancer are
• Basal cell carcinoma
• Squamous cell carcinoma
• Melanoma

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Basal Cell Carcinoma

• Least malignant and most common skin cancer
• Stratum basale cells proliferate and invade the
  dermis and hypodermis
• Slow growing and do not often metastasize
• Can be cured by surgical excision in 99 of the
  cases
• Hard, dry scaly growths with reddish base
• Fair skinned people most at risk
• Over forty and out in sun at risk
• Sun causes DNA damage

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Squamous Cell Carcinoma

• Arises from keratinocytes of stratum spinosum
• Arise most often on scalp, ears, and lower lip
• Grows rapidly and metastasizes if not removed
• Prognosis is good if treated by radiation therapy
  or removed surgically

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Melanoma

• Cancer of melanocytes is the most dangerous type
  of skin cancer because it is
• Highly metastatic
• Resistant to chemotherapy
• Known as melanocarcinomas
• Caused by sunburn

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Melanoma

• Melanomas have the following characteristics
  (ABCD rule)
• A Asymmetry the two sides of the pigmented
  area do not match
• B Border is irregular and exhibits indentations
• C Color (pigmented area) is black, brown, tan,
  and sometimes red or blue
• D Diameter is larger than 6 mm (size of a
  pencil eraser)

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Melanoma

• Treated by wide surgical excision accompanied by
  immunotherapy
• Chance of survival is poor if the lesion is over
  4 mm thick

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Burns

• First-degree only the epidermis is damaged
• Symptoms include localized redness, swelling, and
  pain
• Heals in 2 weeks, no scars
• Second-degree epidermis and upper regions of
  dermis are damaged
• Symptoms mimic first degree burns, but blisters
  also appear
• Damage is to dermis
• Third-degree entire thickness of the skin is
  damaged
• Burned area appears gray-white, cherry red, or
  black there is no initial edema or pain (since
  nerve endings are destroyed)
• Dermis destroyed

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Rules of Nine

• Body is divided into 11 areas, each accounting
  for 9 of the total body surface area (water
  loss)

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Rule of Nines

• Estimates the severity of burns
• Burns considered critical if
• Over 25 of the body has second-degree burns
• Over 10 of the body has third-degree burns
• There are third-degree burns on face, hands, or
  feet

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Developmental Aspects of the Integument Fetal

• Epidermis develops from ectoderm
• Dermis and hypodermis develop from mesoderm
• Lanugo downy coat of delicate hairs covering
  the fetus
• Vernix caseosa substance produced by sebaceous
  glands that protects the skin of the fetus in the
  amnion

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Developmental Aspects of the Integument
Adolescent to Adult

• Skin and hair become oilier and acne may appear
• Skin shows the effects of cumulative
  environmental assaults around age 30
• Scaling and dermatitis become more common

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Developmental Aspects of the Integument Old Age

• Epidermal replacement of cells slows and skin
  becomes thinner
• Skin becomes dry and itchy
• Subcutaneous fat layer diminishes, leading to
  intolerance of cold
• Decreased elasticity and loss of subcutaneous
  tissue leads to wrinkles
• Decreased numbers of melanocytes and Langerhans
  cells increase the risk of skin cancer

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Hypodermis

• Subcutaneous layer deep to the skin
• Composed of adipose and areolar connective tissue

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• Maintains homeostasis
• a. Skin sweats to cool off body when too hot.
  Blood vessels also dilate to radiate heat away
  from body.
• b. Goose bumps form to trap a layer of air next
  to the skin to keep warmer.
• c. Information sent to brain from skin about
  sensory changes.
• d. Vitamin D is produced when sun activates
  changes in the skin.
• e. Skin acts as a barrier.

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Skin is a Barrier
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Steps to healing an injury

• 1. Cut
• 2. Epidermal cells divide
• 3. Blood clots at injury site
• 4. A scab forms
• 5. White blood cells gather (pus)
• 6. Gap fills pushing scab loose.

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Shallow Cut

• New epithelial cells will fill in.

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Deep Cut

• Broken blood vessels allow clots to form
• Fibrin blood cells platelets
• Fluids dry to form scab
• Fibroblasts are attracted by chemicals at wound
  site
• New collagenous fibers form
• Phagocysts eat dead cells
• Scab falls off
• Connective tissue forms scars
• Deep wounds look granulated

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Burns

• 1. First degree burns
• a. Involve damage to epidermal cells
• B. Usually heal in one week

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• 2. Second degree burn
• a. Damage to both epidermis and dermis
• B. Blistering and scarring

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• 3. Third degree burns
• a. Destroys both the epidermis and dermis
• b. Skin function lost
• c. Skin grafts needed

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