Transcript The Layers of the Epidermis

Integumentary system:
Did you know?
• A fingernail takes about 6 months to grow from base to
tip.
• A human being loses an average of 40 to 100 strands of
hair a day.
• Each square inch of human skin consists of 20 feet of
blood vessels.
• Every square inch of the human body has an average of
32 million bacteria on it.
• Humans shed about 600,000 particles of skin every hour
- about 1.5 pounds a year. By 70 years of age, an
average person will have lost 105 pounds of skin.
What is the
integumentary
system?
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Largest organ in the body
Integumentary = “covering”
Why is skin called an organ?
Components:
– Skin (cutaneous membrane)
and epidermal derivatives
(glands, hairs, hair follicles,
nails)
What are the regions of the
skin?
• Epidermis and dermis
– Epidermis: keratinized
squamous epithelium
– Dermis: areolar and
dense irregular CT
• Hypodermis
(subcutaneous layer):
loose CT (areolar and
adipose)
– Not technically skin
What does the skin do?
• Communication: sensory receptors
• Site of waste secretion: sweat
• Protection: serves as physical barrier against
– Abrasion, water loss, microorganisms, UV
damage
– Anti-microbial soaps (acid mantle, CDC study)
What does the skin do?
• Body temperature
regulation
– Hot: vasodilation,
sweat
– Cold:
vasoconstriction,
goose bumps
• Metabolic function:
– vitamin D synthesis
• Made from
cholesterol
• Important for
Ca2+ absorption
in small intestine
– Prevents folate
destruction
(reproductive
fitness protection)
What does the hypodermis do?
• Allows skin to move freely, shock absorber,
insulates against heat loss
• Not present everywhere
– E.g. none on shin
Which of these events occur as a result of
a decrease in body temperature?
A. blood vessels in the epidermis dilate, at
first
B. blood vessels in the dermis constrict if skin
temperature falls below 15 degrees C
C. contraction of arrector pili muscles
D. sweat is produced
E. all of these
The Layers of the Epidermis
How many types of skin are there?
• Two types
– Thin skin
• Most parts of the
body
• All but stratum
lucidum (total = four
layers)
• 75-150 µm thick
How many types of skin are there?
– Thick skin
• Palms & soles
• Includes stratum
lucidum (total = five
layers)
• 400-600 75-150
µm thick
Compare them against each other
Thin Skin
Thick Skin
Let’s look at the layers of the
epidermis…
• Stratum basale
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Closest to blood supply
Regenerative layer
keratinocytes
Contains melanocytes
Cancers include _____
and ______
• Stratum
spinosum
– Still some
division
– Cancer is
called ____
• Stratum
granulosum
– Organelles
disintegrate
 granules
• Stratum lucidum
– Only present in
thick skin
• Stratum corneum
– Packed keratin
Let’s look at them all together
So, what are all the cells found in
the epidermis?
• Keratinocytes
= most
common
• Melanocytes
• Langerhans
(dendritic)
cells
• Merkel
(tactile) discs
What types of cells are in the
epidermis?
• Keratinocytes: make keratin
– Structural protein, type of intermediate filament (tough)
• Hydrophobic!
– Desmosomes hold keratinocytes together, attach them to
basement membrane
• Connections required for skin integrity
• What happens without them?
Pemphigus bulgaris
Pemphigus bulgaris
Healthy skin
What types of cells are in the
epidermis?
• Melanocytes
– Spider-like pigment cells,
make/secrete melanin
– Keratinocytes endocytose pigment
and concentrate on sunny side
– Melanin absorbs UV, protects
basale layer from damage
• Sunlight increases melanin
production
– If cancerous: melanoma
In which layer of epidermis do the
nucleus and other organelles
disintegrate, and the cells die?
A. stratum basale
B. stratum corneum
C. stratum granulosum
D. stratum lucidum
E. stratum reticularis
Which of these qualities must a
medication possess if it is absorbed from
a skin patch?
A. lipid-soluble
B. water-soluble
C. must contain keratin
D. must be slightly acidic
E. must contain melanin
The Dermis
What about the dermis?
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Strong, flexible
Mostly dense irregular CT
With fibroblasts, wandering defense cells
Highly vascularized: control body heat,
nourish epidermis
• Large component of sensory receptors
What’s the purpose of the dermis?
• Blood supply
• Sensory perception
• Structural integrity
What two layers make up the
dermis?
• Papillary layer
– Areolar CT
– Fingerprints
– Open spaces for
________
• Reticular layer
– Dense irregular CT
– Collagen fibers in all
directions to
_____________
What else is found in the dermis?
• Hair follicle
– Note:
epidermis
dips down
here
• Sweat
glands
(more later)
• Blood
vessels
• Nerves
• Arrector pili
muscle
What are arrector pili?
• Small, smooth
muscles
• One per each
hair on your
body
• Goose bumps
Skin Derivatives
What are some examples of skin
derivatives?
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Hair, hair follicles
Sebaceous glands
Sweat glands
Nails
What do I need to know about hair?
• Three zones of
keratinized cells
– Bulb: where hair
originates in dermis
• Nerves surround
– Root
• Remainder of
hair in follicle
– Shaft
Shaft is portion outside epidermis
What do I need to know about hair?
• Three layers to hair
– Medulla
• Core of loosely
arranged cells and
air space
– Cortex
• Densely packed
keratinized cells
– Cuticle
• One layer of scaly
cells
What do I need to know about hair?
• Arrector pili: smooth muscle
What are nails?
• Modified epidermis
– Hard, keratinized
layers on a nail bed of
epidermal cells
– Three parts
• Root (embedded in
skin)
– Root contains nail
matrix (stratum
basale)
• Body
• Free edge
– Cyanotic: nail beds
bluish
What are sweat glands?
• Sweat (sudoriferous) glands
– 3-4 M/person
– Insensible sweat
What are sweat glands?
• Two types:
merocrine and
apocrine
• Merocrine (AKA
eccrine)
– Most common
• all but nipples,
axillary and
external
genitalia
– Secretes via
exocytosis on
apical side
– Sweat is blood
filtrate
– Sympathetic
nervous system
What are sweat glands?
• Apocrine: axillary
and groin areas
– Larger glands, type
of eccrine
– Ducts empty into
hair follicles
• Secrete sweat,
fatty acids and
proteins
• Bacterial break
down of fatty acids
causes odor
– Mammary: modified
sweat gland
– Ceruminous:
secrete wax
• Only in auditory
canal
What are sebaceous glands?
• Holocrine
glands:
excrete
broken
down cell
– Sebaceous
glands: oilproducing
glands of
scalp
What are some common skinrelated conditions?
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Erythema
Jaundice
Bronzing
Pallor
Albinism
Hematoma
Hemangiomas—if
you have them, you’ve
had them your entire
life!
The specific layer that shapes the ridges
for fingerprints and footprints is the
A. hypodermis.
B. papillary layer of the dermis.
C. reticular layer of the dermis.
D. underlying muscle layer.
E. superficial bony layer.
In which of these layers are
melanocytes found?
A. dermis
B. hypodermis
C. stratum corneum
D. stratum basale
E. stratum lucidum
Arrector pili muscles
A. consist of skeletal muscle fibers.
B. are attached directly to the hair shaft.
C. contract in response to frightening
situations.
D. cause sweat glands to contract.
E. assist in the production of sebum.
How does the skin repair itself?
• Two repair
processes (see Ch. 5)
– Fibrosis: production
of fibrous CT (scar)
– Regeneration:
replacement of
damaged tissue with
same tissue type
– Both repair
processes occur in
skin
– Scars = fibroblasts
Skin graft
Scar formation results from the
efforts of which cells?
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A. melanocytes
B. fibroblasts
C. keratinocytes
D. fibrocytes
E. Langerhans (dendritic) cells