Transcript Lecture Slides - Integumentary

Integumentary System
• Cutaneous membrane (skin) – our largest
organ
• Accounts for 7% of body weight
• Divided into two distinct layers
• Epidermis
• Dermis
• Accessory structures
• Subcutaneous layer (hypodermis)
Functions Of The Integument
• Cushions and insulates deeper organs
• Protects body from abrasion, trauma,
chemicals, pathogens, temperature extremes
and UV rays
• Excretion and secretion
• Contains sensory receptors associated with
nerve endings
• Synthesis and storage of nutrients (vitamin
D3)
Integumentary Structures
• Components of the Integumentary System
Figure 5-1
Skin Structures
The Epidermis- Four Main Cell Types
• Melanocytes - found in basal
layer, manufacture and secrete
pigment
• Merkel cells - basal layer,
attached to sensory nerve
endings
• Keratinocytes – Arise from
deepest layer of epidermis to
stratum spinosum
• Produce keratin – a tough
fibrous protein
• Produce antibodies and
enzymes
• Keratinocytes are dead at
skin's surface
• Langerhans cells - stratum
spinosum, part of immune
system macrophage-like
The Epidermis
• Stratified squamous epithelium
• Several distinct cell layers
• Thick skin—five layers on palms and soles
• Thin skin—four layers on rest of body
Layers of The Epidermis
• Stratum corneum
• Most superficial layer
• Dead, flattened
(squamous) cells
• Abundant keratin Keratinized (cornified)
tough, water-resistant
protein
• Protects skin against
abrasion and
penetration
• Stratum lucidum (clear
layer)
• Occurs only in thick
skin – palms and soles
• Composed of a few
rows of flat, dead
keratinocytes
Layers of The Epidermis
•
Stratum granulosum (grainy
layer)
•
Consists of keratinocytes
• Tonofilaments
• Keratohyaline granules
– help form keratin
• Lamellated granules –
contain a waterproofing
glycolipid
•
Stratum spinosum (spiny
layer)
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“Spiny” appearance caused
by artifacts of histological
preparation
Contains thick bundles of
intermediate filaments
(tonofilaments)
• Resist tension
• Contain protein
prekeratin
•
Contains star-shaped
Langerhans cells
Layers of the Epidermis
• Stratum basale
• Deepest layer of
epidermis
• Attached to underlying
dermis
• Stem cells actively divide
• Merkel cells – associated
with sensory nerve ending
• Melanocytes – secrete
the pigment melanin
Epidermal Cells and Layers of the Epidermis
Figure 5.3
Sources of Skin Color
• Melanocytes
• Make melanin from tyrosine
• Melanin provides UV
protection
• Gives reddish-brown to
brown-black color
• Carotene
• Contributes orange-yellow
color
• Provided from diet (carrots
and tomatoes)
• Hemoglobin - blood
pigment
• Caucasian skin contains
little melanin
• Allows crimson color of
blood to show through
Dermis
• Second major layer of the skin
• Provides mechanical strength, flexibility, and
protection for underlying tissues
• Highly vascular and contains a variety of sensory
receptors that provide information about the external
environment
• Two layers
• Papillary layer – includes dermal papillae
• Reticular layer - deeper layer – 80% of thickness of dermis
• Flexure lines - creases on palms
Layers of the Dermis
• Papillary layer
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Underlies epidermis
Named for dermal papillae
Aerolar connective tissue
Supports, nourishes epidermis
Provides sensory nerves,
lymphatics, and capillaries
• Reticular layer
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Tough, dense, fibrous layer
Dense irregular connective tissue
Collagen fibers - limit stretch
Elastic fibers - provide flexibility
Blends into papillary layer (above)
Blends into subcutaneous layer
(below)
Dermal Components
• Epidermal accessory
organs
• Cells of connective
tissues proper
• Communication with
other organ systems
• Cardiovascular
• Lymphatic
• Nervous
• Sensation
• Control of blood flow
and secretion
Subcutaneous Layer - Hypodermis
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Composed of loose connective tissue - areolar and adipose
Stabilizes skin position
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Contains many fat cells
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Loosely attached to dermis
Loosely attached to muscle
Provides thermal insulation
Cushions underlying organs
Safely receives hypodermic needles
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
• Chief parts of a hair
• Root – imbedded in the
skin
• Shaft – projects above
skin's surface
Hair
• Hair Shaft organized into three concentric layers
• Medulla – central core
• Cortex – surrounds medulla
• Cuticle – outermost layer
• Pigmented by melanocytes at the base of the
hair
Cross Section of a Hair
Figure 5.7a, b
Hair Follicle
• Root sheath extending from
the epidermal surface into the
dermis
• Deep end is expanded forming
a hair bulb
• Papilla - nipple-shaped
indentation with blood vessels
and nerves
• Matrix - germinal layer of cells
(actively dividing cells) right
above the papilla
• 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
• Arrector pili muscle - bundle of
smooth muscle contracts to make
hair stand erect
Longitudinal Section of Follicle
Figure 5.7c, d
Hair Follicles
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
Sebaceous Glands (oil glands)
• Occur over entire body - Except palms and soles
• Simple alveolar glands
• Holocrine secretion – entire cell breaks up to form secretion
• Secretes an oily substance called sebum
• Most are associated with a hair follicle
• Functions of sebum
• Softens and lubricates hair and skin
• Skin waterproofing
• Collects dirt
Sweat (Sudoriferous) Glands
• Two types:
• Eccrine (Merocrine)
• Most abundant sweat gland
• “True sweat”
• 99% water with some salts
• Contains traces of
metabolic wastes ~ 2%
urea
• Role in thermoregulation
• Widely present in skin (up to
500/cm2)
• Apocrine
• Odorous secretion
• Absent before puberty
• Present in axillary, areolar,
anal and genital areas
Eccrine (Merocrine) Gland
Figure 5.10b
Nails
• Scalelike modification of epidermis made of hard keratin
• Parts of the nail
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Free edge
Body - dense mass of keratinized cells
Root
Nail folds
Eponychium – cuticle
Skin Injury and Repair
Four Stages in Skin Healing
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Inflammation
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Blood flow increases
Phagocytes attracted
Scab formation
Cell division and
migration
Scar formation
Skin Injury and Repair
Bleeding occurs at the site of injury
immediately after the injury, and mast
cells in the region trigger an
inflammatory response.
Epidermis
After several hours, a scab has formed
and cells of the stratum germinativum are
migrating along the edges of the wound.
Phagocytic cells are removing debris,
and more of these cells are arriving with
the enhanced circulation
in the area. Clotting around the edges
of the affected area partially isolates
the region.
Scab
Dermis
Sweat
gland
Migratory
Macrophages epithelial
cells
and
fibroblasts
Granulation
tissue
Skin Injury and Repair
One week after the injury, the scab has
been undermined by epidermal cells
migrating over the meshwork produced by
fibroblast activity. Phagocytic activity
around the site has almost ended, and the
fibrin clot is disintegrating.
After several weeks, the scab has been
shed, and the epidermis is complete. A
shallow depression marks the injury site,
but fibroblasts in the dermis continue to
create scar tissue that will gradually
elevate the overlying epidermis.
Scar
tissue
Fibroblasts
Skin Injury and Repair
Table 5-1
Aging of the Skin
• Major Age-Related Changes
• Injury and infection increase
• Immune cells decrease
• Sun protection diminishes
• Skin becomes dry, scaly
• Hair thins, grays
• Sagging, wrinkles occur
• Heat loss decreases
• Repair slows
Effects of UV Radiation
• Beneficial effect - activates synthesis of
vitamin D3
• Harmful effects
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Sun burn
Wrinkles, premature aging
Malignant melanoma
Basal cell carcinoma
Types and Growth of Hair
Vellus hairs
• Body hairs of women and children
Terminal hairs
• Hair of scalp
• Axillary and pubic area (at puberty)
Hair thinning and baldness
• Due to aging
• Male pattern baldness
Burns
Classified by severity
• First-degree burn – only upper epidermis
is damaged
• Second-degree burn – upper part of
dermis is also damaged
• Blisters appear
• Skin heals with little scarring
• Third-degree burn
• Consume thickness of skin
• Burned area appears white, red, or
blackened
Estimating Burns Using the Rule of
Nines
Figure 5.11a
Skin Cancer
Basal cell carcinoma
• Least malignant and most common
Squamous cell carcinoma
• Arises from keratinocytes of stratum
spinosum
Melanoma
• A cancer of melanocytes
• The most dangerous type of skin cancer
Skin Cancer
Squamous
Squamouscell
cellcarcinoma
carcinoma
Basal cell carcinoma
Melanoma
Figure 5.12
The Skin Throughout Life
Epidermis
• Develops from embryonic ectoderm
Dermis and hypodermis
• Develop from mesoderm
Melanocytes
• Develop from neural crest cells
The Skin Throughout Life
Fetal skin
• Well formed after the fourth month
• At 5-6 months
• The fetus is covered with lanugo (downy
hairs)
• Fetal sebaceous glands produce vernix
caseosa
The Skin Throughout Life
Middle to old age
• Skin thins and becomes less elastic
• Shows harmful effects of environmental
damage
• Skin inflammations become more common