Anatomy Lecture NotesChapter 5

I. functions

  • protection
  • prevents water loss
  • body temperature control
  • synthesizes vitamin D
  • sensory reception

II. basic structure

the skin is an epithelial membrane (cutaneous)

epithelial layer = epidermis (stratified squamous keratinized e.)

c.t. layer = dermis (areolar c.t. and dense irregular c.t.)

A. epidermis

1. cells

a. keratinocytes are found in all layers and produce keratin

b. melanocytes are found in the stratum basale

  • they make the pigment melanin and transfer it to keratinocytes
  • melanin protects keratinocytes from ultraviolet (UV) radiation
  • the lighter an individual's skin, the more of the melanin is degraded as cells move towards the surface
  • the amount of melanin in the skin increases with exposure to UV radiation

c. Merkel cells are found in the stratum basale

  • they are associated with dermal nerve endings
  • they may be used for the sense of touch

d. dendritic (Langerhans) cells are found in the stratum spinosum

  • they migrate to the skin from bone marrow and function as part of the immune system
  • they are sensitive to UV radiation

2. layers

a. stratum basale/stratum germinativum - single layer of cuboidal or columnar keratinocyte stem cells

  • attached to c.t. of dermis
  • cells undergo mitosis
  • one daughter cell migrates to the next layer and one stays in the stratum basale to be the new stem cell

b. stratum spinosum - 8 to 10 layers of keratinocytes

  • gradually change shape from cuboidal to squamous as they migrate towards the surface

c. stratum granulosum - 3 to 5 layers of keratinocytes with degrading nuclei

  • cells contain keratin precursor molecules (keratohyalin) and granules of glycolipids
  • the glycolipids are secreted into the extracellular space

d. stratum lucidum - 3 to 5 rows of flat, dead keratinocytes

  • contain eleidin, a precursor of keratin
  • found in thick skin only (palms of hands and soles of feet)

e. stratum corneum - 25 to 30 layers of dead keratinocytes on surface layer of skin

  • varies in thickness over body
  • cells contain no nuclei or organelles
  • keratin and glycolipids waterproof the skin
  • cells slough

B. dermis

1. layers

a. papillary layer - made of areolar c.t.

  • dermal papillae project into epidermis (increase surface area of contact for diffusion between layers and for adhesion)
  • papillae contain nerve endings and capillaries
  • on palms and soles, the papillae line up on top of dermal ridges
  • the dermal ridges push the epidermis up to form friction ridges
  • sweat glands open on the top of the friction ridges

b. reticular layer - deep to papillary layer, made of dense irregular c.t.

  • contains blood vessels. nerves and nerve endings, hair follicles, sudoriferous and sebaceous glands and arrector pili

2. nerve endings

a. free nerve endings

  • pain and temperature
  • touch (associated with Merkel cells)
  • root hair plexus wraps around hair follicle

b. encapsulated

Meissner's corpuscles / Pacinian corpuscles

C. hypodermis/superficial fascia/subcutaneous layer

  • areolar and adipose c.t.
  • anchors skin to underlying structures
  • is not part of cutaneous membrane/skin

D. skin color

1. melanin ranges from yellow to black and is present in the epidermis

2. carotene is yellow to orange and is found mostly in the stratum corneum and hypodermis

3. hemoglobin is the red pigment in blood and is present wherever there are blood vessels

III. derivatives of the epidermis

A. hair - located everywhere except palms, soles, nipples, parts of external genitalia

1. follicle = tube of epidermis and c.t. from which hair grows

c.t. root sheath – surrounds epidermal root sheath

epidermal root sheath

outer layer is an invagination of the epidermis

inner layer comes from matrix of hair

2. a hair is made of layers of dead cells containing hard keratin

a. shaft - projects above skin surface

b. root - inside follicle

c. bulb - expanded deep end of root; where growth occurs

matrix - layer of cells surrounding hair root papilla where mitosis occurs

hair root papilla - contains blood vessels

3. layers

a. medulla - central core absent from fine hair; consists of large cells separated by air spaces

b. cortex - middle layer made of several layers of flat cells

c. cuticle - surface layer made of a single layer of overlapping flat cells

B. sebaceous glands - located everywhere there is hair

  • gland is an outgrowth of the epidermal root sheath and opens into the side of the hair follicle
  • cells accumulate lipids (sebum) until they burst, then the whole cell is pushed into the follicle
  • sebum softens hair and skin, prevents skin cracking and has antibacterial properties

C. sudoriferous glands

1. eccrine - produce sweat for evaporative cooling

  • located everywhere except nipples and parts of external genitalia
  • sweat consists of water (more than 99%) and an insignificant amount of salt and waste
  • the gland is simple coiled tubular and is located in the dermis
  • the duct is simple cuboidal and extends from the gland to the surface of the skin (sweat pore)

2. apocrine - produce viscous fluid containing fats and proteins

  • located in axillary and pubic regions
  • ducts open into hair follicles
  • become active at puberty
  • bacteria break down the fats and proteins to produce body odor

D. other glands

1. ceruminous glands - modified apocrine glands in external ear canal the produce ear wax

2. mammary glands - sweat glands that are modified to secrete milk

E. nails are located on the digits and are made of hard keratin

dorsal viewlongitudinal section

free edge

nail body

lateral nail fold

lunula

epohychium

(stratum corneum)

proximal nail fold

nail root

nail matrix

Strong/Fall 2008page 1