Unit 4:
Structure of Integument
and its Appendages
Regions of Integument (skin)
Epidermis – outermost
region
•Keratinized stratified
squamous epithelium
•Non-vascular
•4 cell types
•4 - 5 layers
4 Epidermal Cell Types
Keratinocytes – make keratin fibrous
protein
•Protective
•Hardens and waterproofs skin.
•Cells connected by desmosomes:
•prevent tearing and cell separation
from mechanical stress
•Arise from hightly mitotic stratum
basale
•Cells dead at free surface
4 Epidermal Cell Types
Keratinocytes – make keratin fibrous
protein
Langerhans’ Cells – star shaped,
epidermal dendritic phagocytic cells
•activate the immune system
•ingest foreign material
4 Epidermal Cell Types
Keratinocytes – make keratin fibrous
protein
Langerhans’ Cells – star shaped,
epidermal dendritic phagocytic cells
Merkel Cells – half-sun touch receptors
•associated w/ sensory nerve endings
4 Epidermal Cell Types
Keratinocytes – make keratin fibrous
protein
Langerhans’ Cells – star shaped,
epidermal dendritic phagocytic cells
Merkel Cells – half-sun touch receptors
•associated w/ sensory nerve endings
melanin
Melanocytes – makes brown pigment
melanin
•shields keratinocyte DNA from UV
damage
Layers of the Epidermis
Stratum corneum
Stratum lucidum
(absent in thin skin)
Stratum granulosum
Stratum
Spinosum
Stratum basale
Stratum Basale (Basal Layer)
•
•
•
•
•
AKA stratum germinativum
Deepest epidermal layer,
attached to the dermis
Single row of the youngest
keratinocytes
Rapidly mitotic, making new
cells daily
Melanocytes and Merkel cells
found here
Stratum basale
dermis
Stratum Spinosum (Prickly Layer)
Stratum
Spinosum
• Cells filled with
filaments connected to
desmosomes. (gives
prickly look)
• Melanin granules filling
cells in response to UV
or genetics
• Langerhans’ cells found
here
Stratum basale
dermis
Stratum Granulosum (Granular)
•
•
Stratum
granulosum
Stratum
Spinosum
•
•
Stratum basale•
dermis
3-5 cell layers
Keratinocytes change,
flatten, lose nuclei
Keratin granules
accumulate in the cells of
this layer
Lamellated granules release
extracellular glycolipids in
intercellular space that
waterproof skin
Too far from nutrient rich
dermal blood, cells begin to
die
Stratum Lucidum (Clear Layer)
Stratum lucidum would be
here, if present
Stratum
granulosum
•
Stratum
Spinosum
•
– Sole of feet, palms, calluses
•
Stratum basale
dermis
Transparent band of flat,
dead keratinocytes
Only in thick skin
Reduces friction between
the granulosum (inferior)
and the corneum
(superior)
Stratum Corneum (Horny Layer)
Stratum corneum
Stratum lucidum would be
here, if present
Stratum
• 20-30
granulosum
Stratum
Spinosum
•
Stratum basale
dermis
layers of DEAD
keratinized cells; ¾ of
epidermal thickness
Functions include:
– Waterproofing (due to
glycolipids)
– Protection from:
• Abrasion
• Penetration
• biological, chemical,
and physical assaults
Stratum Corneum (Horny Layer)
Stratum Corneum
Stratum Lucidum
Can
Little
Stratum Granulosum
Girls
Stratum Spinosum
Stratum Basale
dermis
Smell
Bad?
Let’s take a break from lecture to
draw the difference between thick
and thin skin.
• Use appropriate drawing and
coloring methods.
• Horizontal labeling with leader
lines
http://www.lab.anhb.uwa.edu.au/mb140/corepages/integumentary/integum.htm
#labepidermis
Regions of Integument (skin)
Epidermis – outermost
region
•Keratinized stratified
squamous epithelium
•Non-vascular
•4 cell types
•4 - 5 layers
Dermis – middle region
• Vascularized
• 80% dense irregular
connective tissue
• 20% areolar
connective tissue
Overview of the Dermis
• Cell types: fibroblasts,
phagocytes, mast cells and
white blood cells
• 2 layers
– papillary (upper) and
– reticular (lower)
• Rich with nerves, blood and
lymph vessels
• Most hair follicles, oil and
sweat glands derived here
Papillary Layer of Dermis
•Dermal papillae
•Areolar
connective
with:
tissue with collagen
•capillary loops
and
elastic
fibers
(thin blood
•Superior
surface
vessels)
with• Meissner’s
dermal
papillae:
peg-like
corpuscles
(touch), (reason for
projections
fingerprints)
•and free nerve
endings (pain)
Papillary Layer of Dermis
•Krause’s end bulb:
(cold)
•Ruffini end organs:
(heat and sustained
pressure)
In Reticular Layer:
Pacinian corpuscle:
(touch, deep vibrations,
transient pressure)
Reticular Layer of the Dermis
• 80% of the thickness of the dermis (dense
–irregular CT)
• Collagen fibers:
– add strength and resiliency
– Binds water, keeping skin hydrated
• Elastin fibers:
– stretch-recoil properties
• Rich in blood vessels:
– dilate or constrict in response to emotions or
temperature changes
Name the epidermal and dermal
layers (review)
5. Stratum Corneum (Epidermis)
4. Stratum Lucidum (Epidermis)
3. Stratum Granulosum
(Epidermis)
2. Stratum Spinosum (Epidermis)
1. Stratum Basale (Epidermis)
6. Papillary Layer (Dermis)
7. Reticular Layer (Dermis)
Regions of Integument (skin)
Epidermis – outermost
region
•Keratinized stratified
squamous epithelium
•Non-vascular
•4 cell types
•4 - 5 layers
Dermis – middle region
• Vascularized
• 80% dense irregular
connective tissue
• 20% areolar
connective tissue
Hypodermis (superficial
fascia)
•deepest region
•Mostly adipose (fat storage),
some areolar
•Vascularized
Hypodermis
(superficial or subcutaneous fascia)
• Composed mostly of adipose and some
areolar connective tissue
• Adipose cells swell and thicken with fatty
droplets during weight gain
• Connects skin to underlying muscle
• Absorbs shock
• Insulates
Skin Color
Three pigments contribute to skin color
1. Melanin: yellow to reddish-brown to black
– only pigment made in skin by melanocytes and passed
onto keratinocytes
– Freckles and pigmented moles – result from local
accumulations of melanin
2. Carotene: yellow to orange pigment
– Pigment incorporated into skin due to diet
– Accumulates in stratum corneum and in adipose
3. Hemoglobin: reddish pigment, gives pink hue to skin
– Due to oxygenation of red blood cells
Skin “Appendages”
Epidermal Derivatives include:
hair
Sebaceous Oil Glands
hair follicles
6
Sudoriferous Sweat Glands
Sudoriferous Sweat Glands
(2 types: Eccrine and Apocrine)
Eccrine glands
•
•
•
•
•
Covers entire body (3 million
p/person)
– Most abundant on palms, soles
of the feet, and forehead
Coiled in dermis
Duct opens on skin’s surface (pore)
“sweat” = hypotonic blood filtrate
released by exocytosis:
– 99% water, salts, antibodies,
anti-biotic proteins, and Nwastes, vitamin C
Evaporation of sweat cools the
body
Sudoriferous Sweat Glands
(2 types: Eccrine and Apocrine)
Apocrine glands
• Only 2000 p/person
• Found in axillary and
anogenital areas with
pheromone secretions
• Ducts empty into hair follicles
• Odorless initially.
–
–
Secretions contains lipids and
protein that bacteria feed on.
Decomposition of secretions by
bacteria produce “body odor”
Sweat glands modified
Ceruminous glands – modified apocrine glands
in external ear canal that secrete cerumen
(ear wax)
Mammary glands – specialized sweat glands
that secrete milk
Sebaceous “Oil” Glands
• Simple branched alveolar glands
• Holocrine: glandular cells rupture to release
secretions
• Sebum Secretions:
–
–
–
–
Oils + ruptured cell fragments
moisturize hair and skin
Slows water-loss
bactericidal
• Released onto hair within follicle
then flows onto skin surface.
• Acne due to blockage of hair
follicle w/ infected sebum
Video Summary
You tube: What is skin? The Layers of Human Skin
Hair (Pili)
• Strands of dead, hard-keratinized cells
made by follicles
– Softer keratin in epidermal cells
• Shaft projects from skin; Root embeded
within dermis and hypodermis
•3 concentric layers:
- Medulla: absent in fine hair
- Cortex: gives hair color
- Cuticle: overlapping keratin
•Split ends: cuticle worn
away, exposing cortex
Structure of Hair Follicle
Basement
membrane
medulla
Follicle created by
in-vagination of
epidermal surface
(epithelial root
sheath) into
dermis and
hypodermis to
create a “bag” or
“sac” that builds
hair
Structure of Hair Follicle
Deep end of follicle:
expanded forming a
hair bulb
Hair papilla supplies nutrients
to hair (via capillaries) and
signals growth
Melanocytes on superior
surface of papilla pigments
hair by creating melanin
Hair papilla created
from in-folding of
dermal tissue into
hair bulb
Structure of Hair Follicle
Arrector pili muscle – attached to hair follicle
and skin. When contracted, holds hair erect
•Root hair plexus
wraps around each
hair bulb
•Bending hair
stimulates these
endings, hence our
hairs act as
sensitive touch
receptors
Hair Shape
• Internal shape of shaft and follicle
determines hair shape
– Round shaft: straight hair
– Oval shaft: wavy hair
– Flat or ribbon like shaft: kinky, curly hair
** One head can have many shaft shapes resulting in interesting
hair textures.
Hair Types
• Vellus – pale, fine body hair
found in children and the adult
female (immature)
• Terminal – coarse, long hair of
eyebrows, scalp, axillary, and
pubic regions
• Hair growth influenced by:
– Nutrition
– Blood flow: reduced blood flow
 hair loss
Ex. Brick layer shoulders: increased blood flow
to area because of carrying heavy objects
results in hair growth
Hair Growth Cycles
• Hair has a life cycle:
– Period of Active
Growth (AG)
– Regressive Phase:
hair bulb shrivels and
matrix dies
– Resting Phase
– Cycle repeats: Older
hair falls out, replaced
by new hair
• Length of AG period determine length of hair
Ex:
Scalp: AG of 6-10 years
Brows AG: of 3 – 4 months
Balding or thinning hair: short AG
Hair Thinning and Baldness
• Alopecia – hair thinning in both sexes
– Rate of hair shed > Rate of hair growth
• Hirsutism: excessive hair growth in women.
Caused by excessive sex hormones usually
from an ovarian tumor.
• True, or frank, baldness
– Genetic
– Sex-influenced condition
• Male pattern baldness – caused by follicular response to
DHT (Dihydrotestosterone)
• Growth cycle is so short that hairs never emerge from
follicles before shedding
– Sex linked trait – carried on X chromosome, inherited
from mother
Hair Function
Functions of hair include:
– maintaining warmth
– Alerting the body to insects on skin
– Guarding the scalp against trauma, heat loss,
and sunlight
– Eyelashes and nose hairs act as barriers
against foreign substances
Hair Distribution
• Hair is distributed over the entire skin
surface except:
– Palms, soles, and lips
– Nipples and portions of external genitalia
Structure of a Nail
• Scale-like epidermal modification on the
distal, dorsal surface of fingers and toes
• w/ hard keratin
Figure 5.6
Back to Regions of Skin
20% Areolar Connective Tissue
Back to Regions of Skin
80% Dense Irregular Connective Tissue
Collagen fibers organized
in irregular patterns
•Strong and flexible
Back to Regions of Skin
Adipose Tissue of Hypodermis
Mostly fat
droplets
Dense irregular connective
tissue of reticular layer of
dermis
Adipose tissue of
hypodermis