Chapter 7 Body Systems

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Introduction- Chapter 6

• Skin (integument) is bodys largest organ
• Approximately 1.6 to 1.9 m2 in average-sized
  adult
• Integumentary system describes the skin and its
  appendages the hair, nails, and skin glands

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Structure of the Skin

• Skin classified as a cutaneous membrane
• Two primary layersepidermis and dermis joined
  by dermal-epidermal junction
• Hypodermis lies beneath dermis

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Structure of the Skin

• Thin and thick skin
• Thin skincovers most of body surface
• 1 to 3 mm thick
• Thick skinsoles and palms
• 4 to 5 mm thick
• Makes fingerprints
• No hair

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Structure of the Skin

• Epidermis
• Cell types
• Keratinocytes
• Melanocytes
• Langerhans cells

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Keratinocytes

• constitute over 90 of cells present
• principal structural element of the outer skin
• Arranged in strata, or layers

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Melanocytes

• pigment-producing cells (5 of the total)
• contribute to skin color
• filter ultraviolet light decrease the amount of
  UV light that can penetrate into the deeper
  layers of the
• skin

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Langerhans cells

• they play a role in immune response
• Originate in the bone marrow
• Function with specialized leukocytes called
  helper T cells, to trigger immune response

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Structure of the Skin

• Epidermis
• Cell layers- 5 Layers (deep ? superficial)
• Stratum germinativum (growth layer)describes the
  stratum spinosum and stratum basale together
• Stratum basale (base layer)
• Stratum spinosum (spiny layer)
• Stratum granulosum (granular layer)
• Stratum lucidum (clear layer)
• Stratum corneum (horny layer)

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Structure of the Skin

• Epidermis
• The cells form in the basale layer and degenerate
  and fill with keratin as they move up to the
  surface
• This is keratinization

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section reveals epidermis containing basal,
spinous, granular keratinocytes and stratum
corneum. Dermis contains numerous viable
fibroblasts. 400X)
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1. Stratum basale (base layer- deepest)

• single layer of columnar cells
• only these cells undergo mitosis
• ? migrate through the other layers until they
  are shed
• The renewal of the human
• epidermis takes
• about 3 to 4 weeks.

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2. Stratum spinosum (spiny layer)

• cells arranged in 8 to 10 layers with desmosomes
  (bridges) that pull cells into spiny shapes
• cells rich in RNA ? protein synthesis to produce
  keratin

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3. Stratum granulosum (granular layer)

• cells arranged in two to four layers
• filled with granules ? makes keratin
• contain high levels of lysosomal enzymes ?
  theyre starting to degenerate
• Nuclei absent
• May not be in regions of thin skin

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4. Stratum lucidum (clear layer)

• Closely packed and clear keratinocytes
• cells filled with eleidin (ay lee din) ? blocks
  water penetration or loss (eventually makes
  keratin)
• absent in thin skin (in thick skin- hands and
  feet)
• Nuclei absent

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5. Stratum corneum (horny layer)

• Dead, squamous cells
• most superficial layer
• dead cells filled with keratin ? water-repellent
  protein
• Cell membranes are thick and chemically resistant
• Also called barrier area because it functions to
  prevent water loss

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Structure of the Skin

• Thick Skin

• Thin Skin

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Wrinkled Fingers and Toes

• FYI
• dead cells in stratum corneum absorb water
• (deeper layers do NOT)
• When swollen water-filled cells expand over the
  normal sized cells below, the skin wrinkles

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Structure of the Skin

• Epidermis
• Epidermal growth and repair
• Turnover or regeneration time refers to time
  required for epidermal cells to form in the
  stratum basale and migrate to the skin surface
  about 35 days
• Shortened turnover time will increase the
  thickness of the stratum corneum and result in
  callus formation

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Structure of the Skin

• Epidermal growth and repair continued
• Normally 10 to 12 of all cells in stratum
  basale enter mitosis daily
• Each group of 8 to 10 basal cells in mitosis with
  their vertical columns of migrating keratinocytes
  is called an epidermal proliferating unit, or EPU

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Structure of the Skin

• Dermal-epidermal junction
• Definite basement membrane
• glues the epidermis to the dermis below
• Partial barrier to the passage of some cells and
  large molecules

Specific staining of the indicated protein is
displayed as a red band localized at the
dermal/epidermal junction.
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Blisters

• FYI
• Caused by injury to cells in epidermis OR
• From separation of dermal-epidermal junction

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Structure of the Skin

• Dermis (corium)
• Sometimes called true skinmuch thicker than
  the epidermis and lies beneath it
• Gives strength to the skin

Sunburn cell formation in EpiDerm-FT following
solar UV-irradiation. HE stained paraffin
sections were prepared from EpiDerm-FT 24 hr
after irradiation. Sunburn cells are indicated by
arrows.
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Structure of the Skin

• Dermis (cont.)
• Contains various structures
• Arrector pili muscles and hair follicles
• Sensory receptors
• Sweat and sebaceous glands
• Blood vessels
• Rich vascular supply plays a critical role in
  temperature regulation? homeostasis

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Structure of the Skin

• Dermis (cont.)
• 2 Layers of dermis
• Papillary layer
• Reticular layer

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Dermis-Papillary Layer

• composed of dermal papillae that project into the
  epidermis
• ? fingerprints- used for grasping and gripping
  tools
• contains loose connective and elastic fibers
• contains the dermal-epidermal junction
• Like egg crate foam mattress pad

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Dermis- Reticular Layer

• contains interlacing collagenous fibers and
  elastic fibers
• ? make the skin tough yet stretchable
• when processed from animal skin, produces leather
• Attachment point for muscle fibers (smooth and
  skeletal)
• Contains arrector pili muscles

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Arrector pili muscles

• Bundle of smooth muscles on each hair follicle
• Makes the hair stand on end
• Occurs due to fright or cold
• Causes erection of nipples and elevation of testes

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• Where are the arrector pili?
• Where is the adipose tissue?
• Is adipose deep or superficial to the stratum
  lucidum?

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Dermis

• Dermal growth and repair
• The dermis does NOT continually shed and
  regenerate
• During wound healing, begins forming a dense mass
  of new connective fibers ? scar
• If elastic fibers in dermis stretch too much,
  they TEAR and form ? stretch marks
• Eventually lose color- NOT due to cocoa butter

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FYI

• If an incision cuts across cleavage lines
  (Langers lines), stress tends to pull the cut
  edges apart and may retard healing.
• Surgical incisions parallel to cleavage lines are
  subjected to less stress and tend to heal more
  rapidly.

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Hypodermis

• Also called subcutaneous layer or superficial
  fascia
• Deep to the dermis
• forms connection between the skin and other
  structures
• NOT part of the skin

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Skin Color

• Melanin
• Basic determinant of skin color
• Melanin formed by melanocytes
• Albinism
• congenital
• absence of
• melanin

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Functions of the Skin (Table 6-1 Page 171)

• Protection
• Physical barrier
• Prevents dehydration
• Sensation
• Pain
• Heat and cold
• Pressure and touch

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Functions of the Skin contd (Table 6-1 Page 171)

• Movement growth
• Imagine moving without elastic skin
• Endocrine (hormones)
• vitamin D production
• Excretion (minor role)
• Water Urea/ammonia/uric acid

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Functions of the Skin contd (Table 6-1 Page 171)

• Immunity
• Phagocytic cells (phago- to eat) (-cyte-
  cell)
• Langerhans cells
• Temperature Regulation
• Heat loss or retention

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Temperature Regulation- Vasodilation

• Heat lossapproximately 80 of heat loss occurs
  through the skin
• Increased blood flow to epidermis
• Decreased blood flow to organs
• Redness after exercise

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Temperature Regulation- Vasoconstriction

• Heat retention
• Decreased blood flow to skin
• Increased blood flow to organs
• Turning white
• Vasoconstriction

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How do we sense touch?

• MANY receptors in our skin (mostly dermis) allow
  for different touch stimuli
• Meissners corpuscle- detects light touch-
  superficial dermis
• Pacinian corpuscle- detects pressure- deep dermis
• ?Receptors send signals to the brain (those
  signals were called?)

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Somatosensory Cortex in Brain

• Receptors send action potentials to specialized
  part of brain ? somatosensory cortex (soma-
  body) (cortex- outermost, superficial)
• Each part of the body
• corresponds with a
• particular area in the
• cortex
• Also a corresponding
• Motor cortex

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Homunculi (Page 394)

• Both sensory motor cortex have homunculi
  (little man)
• Hands and face- large part of cortical area
• Most important for survival

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Two point discrimination

• The density of receptors varies
• If the hands and the face have the most cortical
  area, where do you think the densest area of
  receptors will be?

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Skin Glands

• 3 Types
• Sweat (2 types)
• Sebaceous
• Ceruminous

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Skin Glands- Sweat Glands

• Eccrine glands
• Most numerous sweat glands very small
• Distributed over total body surface except a few
  places (ear
• canal, lips)
• Simple, coiled, tubular glands
• Secrete sweat ? constant
• core temperature

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Skin Glands- Sweat Glands

• 2. Apocrine glands
• Located deep in subcutaneous layer
• Limited distributionaxilla (armpit), areola of
  breast, and around anus
• Large (gt 5 mm in diameter)
• Connected to hair follicle
• Begin to function at puberty

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Skin Glands

• Sebaceous glands
• Secrete sebum (oil)
• Hair and skin
• prevents excessive water loss from the skin
• antifungal activity
• dermis except in palms and soles
• Secretion increases in adolescence
• Oxidated sebum accumulations ? blackheads

Stages of acne. (A) Normal follicle (B) open
comedo (blackhead) (C) closed comedo
(whitehead) (D) (E) pustule v
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Blackhead
Whitehead
Papules
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Skin Glands

• Ceruminous glands (se ROO mi nus)
• Modified apocrine sweat glands
• Mixed secretions of sebaceous and ceruminous
  glands called cerumen (wax)
• protects from dehydration

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Cycle of Life Skin

• Children
• Skin is smooth, unwrinkled, and characterized by
  elasticity and flexibility
• Few sweat glands
• Rapid healing

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Cycle of Life Skin

• Adults
• Development and activation of sebaceous and
  sweat glands
• Increased sweat production
• Body odor
• Increased sebum production
• Acne

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Cycle of Life Skin

• Old age
• Decreased sebaceous and sweat gland activity
• Wrinkling
• Decrease of bodys ability to cool itself

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The Big Picture Skin and the Whole Body

• Skin is a major component of the bodys
  structural framework
• Skin defines the internal environment of the
  body
• Primary functions are support and protection