Download Chapter 7 The Integumentary System

The Integumentary System
– Consists of the skin and its accessory organs; hair, nails,
and cutaneous glands
• Inspection of the skin, hair, and nails is significant part of a
physical exam
• Skin is the most vulnerable organ
– Exposed to radiation, trauma, infection, and injurious
chemicals
• Receives more medical treatment than any other organ system
• Dermatology—scientific study and medical treatment of the
integumentary system
Functions of the Skin
• Resistance to trauma and infection, protection
• Other barrier functions
– Waterproofing, UV radiation
• Vitamin D synthesis
– Skin first step, liver and kidneys complete the process
• Sensation
• Thermoregulation
– Vasoconstriction/vasodilation
• Transdermal absorption
– Administration of certain drugs steadily through thin skin
via adhesive patches
The Skin and Subcutaneous Tissue
• The body’s largest and heaviest organ
– 15% of body weight
– Most skin is 1 to 2 mm thick
• Two layers
– Epidermis: stratified squamous epithelium
– Dermis: connective tissue layer
– Hypodermis—another connective tissue layer below the dermis
• Thick skin—on palms and sole, and corresponding surfaces on
fingers and toes
– Has sweat glands, but no hair follicles or sebaceous (oil) glands
– Epidermis 0.5 mm thick
• Thin skin covers rest of the body
– Epidermis about 0.1 mm thick
– Possesses hair follicles, sebaceous glands, and sweat glands
The Integumentary System (Skin)
The Epidermis
– Dead cells at the surface packed with tough protein called
keratin
– Lacks blood vessels, has some verve endings for touch and
pain.
– Depends on the diffusion of nutrients from underlying
connective tissue
• Composed of stratified squamous epithelium which can be 20 40 cell layers thick depending on location
– the major cell type is the keratinocyte
• The cells of the epidermis are arranged into 5 structurally and
functionally distinct layers called strata
– each strata is made of one or more types of cells each
providing a specific function for the epidermis
Cells of the Epidermis
1. Stem cells
• Undifferentiated cells that give rise to keratinocytes
• In deepest layer of epidermis (stratum basale)
2. Keratinocytes: synthesize keratin
3. Melanocytes
• Occur only in stratum basale
• Synthesize pigment melanin that shields DNA from
ultraviolet radiation
4. Tactile (Merkel) cells
• Touch receptor cells in basal layer associated with dermal
nerve fibers
5. Dendritic (Langerhans) cells
• Macrophages found in stratum spinosum and granulosum
• Guard against toxins, microbes, pathogens that penetrate skin
Cells of the Epidermis
Sweat pore
Stratum corneum
Stratum lucidum
Stratum granulosum
Exfoliating
keratinocytes
Dead keratinocytes
Sweat duct
Living keratinocytes
Stratum spinosum
Dendritic cell
Tactile cell
Melanocyte
Stem cell
Stratum basale
Dermal papilla
Tactile nerve fiber
Dermis
Dermal blood vessels
Layers of the Epidermis
• The most superficial layer of the epidermis are the cells that are
subjected to the physical forces that come from the outside of the
body
– friction, abrasion, puncture…
• As a result, these cells continuously fall off from the surface of the
skin
– exfoliation
• The exfoliated cells are constantly replaced by cells in the deepest
strata of the epidermis which are constantly dividing (mitosis)
maintaining a constant epidermal thickness
– the rate of mitosis equals the rate of exfoliation
Stratum Corneum
• Outermost strata made of keratinized cells
• Resistant to abrasion, penetration, and water loss
• Made of up to 30 layers of dead keratinocytes
– accounts for up to 75% of the epidermal thickness
• Most superficial layer of keratinocytes exfoliate from the surface of
the body
Stratum Lucidum
• Thin translucent zone seen only in thick skin found on the palms of
the hand and souls of the feet (calluses)
• Cells have no nucleus or organelles
Stratum Granulosum
• Three to five cell layers deep made of keratinocytes
• Keratinocytes accumulate vesicles (granules) filled with the protein
keratin and glycolipids which are exocytosed
– the exocytosed keratin wraps around the cell membrane of the
keratinocyte creating a thick coat which provides protection from
abrasion and puncture
– the exocytosed glycolipids fills the extracellular spaces between
the keratinocytes and provides a waterproofing property to skin
• forms a barrier between surface cells
and deeper layers of the epidermis
• cuts off nutrient supply to the cells of the lucidum and corneum
to die
Stratum Spinosum
Several cell layers deep made of:
• Keratinocytes
– become somewhat flattened and “spiny-shaped”
• Langerhans (dendritic) cells
– phagocytose foreign substances such as bacteria and viruses that
attempt to enter the body through the skin
– alert the immune system to the presence of foreign substances
Stratum Basale (germinativum)
Deepest of the epidermal strata made of a single layer of cells (consisting
of 3 cell types)
• Keratinocytes
– undergo mitosis rapidly to replace the cells that are exfoliated from
the surface
– as these keratinocytes “move” up through the more superficial
strata
• Melanocytes
– produce the brown pigment melanin to protect against UV
radiation (sunlight) damage to DNA of keratinocytes
• Merkel (tactile) cells
– touch receptors that provide sensory perception
Melanocytes
• Occur only in the stratum basale
• Melanin is shed from the melanocytes onto neighboring keratinocytes
of the strata spinosum and basale.
– 2 Forms of Melanin
• Eumelanin: brownish-black pigment.
• Pheomelanin: reddish-yellow, sulfur-containing pigment.
• Dark skin: produces greater quantities of melanin, and breaks it down
more slowly. Melanin will accumulate into several epidermal layers.
• Light skin: produces less melanin, and breaks it down quickly so that
it doesn’t spread beyond the stratum basale.
• UV exposure increases the productivity of melanocytes.
The Dermis
• Dermis—connective tissue layer beneath the epidermis
– Ranges from 0.2 mm (eyelids) to 4 mm (palms, soles)
– Composed mainly of collagen with elastic fibers, reticular
fibers, and fibroblasts
– Well supplied with blood vessels, sweat glands, sebaceous
glands, and nerve endings
• 2 Layers:
– Papillary layer
– Reticular layer
Dermis
Papillary layer
Reticular layer
The Dermis
• Papillary layer—superficial zone of dermis
– Thin zone of areolar tissue in and near the dermal papilla
– Allows for mobility of leukocytes and other defense cells
should epidermis become broken
– Rich in small blood vessels
– 20% of the thickness of the dermis
– Its superior surface contains fingerlike projections called
dermal papillae which keep it firmly attached to the
superficially located epidermis
– Dermal papillae contain sensory receptors such as tactile
corpuscles (touch receptors) and free nerve endings (sense
pain)
• Reticular layer
– 80% of the thickness of the dermis
– Elastic fibers provide stretch-recoil properties
– Location of:
• hair and associated follicles
• pacinian corpuscles (pressure receptors)
• blood vessels
• glands
The Hypodermis
• Hypodermis
– Subcutaneous tissue
– Mostly adipose
– Pads body
– Binds skin to underlying
tissues
• Drugs introduced by injection
– Highly vascular and absorbs
them quickly
• Subcutaneous fat
– Energy reservoir
– Thermal insulation
– 8% thicker in women
Skin Colors of diagnostic value
• Cyanosis—blueness of the skin from deficiency of oxygen in the
circulating blood (airway obstruction, lung disease, cardiac arrest,
cold weather)
• Erythema—abnormal redness of the skin due to dilated cutaneous
vessels (exercise, hot weather, sunburn, anger, or embarrassment)
• Pallor—pale or ashen color when there is so little blood flow
through the skin that the white color of dermal collagen is visible
(emotional stress, low blood pressure, circulatory shock, cold,
anemia)
• Albinism—genetic lack of melanin that results in white hair, pale
skin, and pink eyes
• Jaundice—yellowing of skin and sclera due to excess of bilirubin
in blood (cancer, hepatitis, cirrhosis)
• Hematoma (bruise)—mass of clotted blood showing through skin
Hair
• Filamentous strands of dead keratinized cells produced by hair
follicles
• Contains hard keratin which is tougher and more durable than the soft
keratin of the epidermis
• The long thin hair shaft is visible above epidermis
• The hair root is in the dermis within a follicle
• Pigmented by melanocytes at the base of the follicle
Hair Function and Distribution
• Hair is distributed over the entire skin surface except
– palms, soles, and lips, nipples and portions of the external genitalia
• Functions of hair include:
– Retain body heat
• The follicle of the hair is connected to piloerector muscles that
contract when cold
– raises hair on skin surface (goose bumps) increasing the
thickness of the insulation barrier at the surface of the skin
– Provide sensory perception
• Limbs and trunk have 55 to 70 hairs per cm2
– Face about 10 times as many
– 30,000 hairs in a man’s beard
– 100,000 hairs on an average person’s scalp
– Number of hairs does not differ much from person to person or
even between sexes
Structure of the Hair and Follicle
Hair shaft
Sebaceous
gland
Piloerector
muscle
Hair receptor
Bulge
Hair root
Hair matrix
Hair bulb
Apocrine
sweat gland
Blood
capillaries
in dermal
papilla
(a)
Dermal
papilla
• Hair is divisible into three zones
along its length
– Bulb: a swelling at the base
where hair originates in
dermis or hypodermis
• Only living hair cells are
in or near bulb
– Root: the remainder of the
hair in the follicle
– Shaft: the portion above the
skin surface
• Dermal papilla—bud of vascular connective
tissue encased by bulb
– Provides the hair with its sole source of
nutrition
• Hair matrix—region of mitotically active cells
immediately above papilla
– Hair’s growth center
• Three layers of the hair in cross section from
inside out
– Medulla
• Core of loosely arranged cells and air
spaces
– Cortex
• Constitutes bulk of the hair
– Cuticle
• Composed of multiple layers of very
thin, scaly cells that overlap each
other
Connective
tissue
root sheath
Epithelial root
sheath
Hair medulla
Hair cortex
Hair matrix
Hair bulb
Dermal
papilla
(b)
0.5 mm
Hair Texture and Color
• Texture—related to differences in cross-sectional shape
– Straight hair is round
– Wavy hair is oval
– Curly hair is relatively flat
• Color—due to pigment granules in the cells of the cortex
– Brown and black hair is rich in eumelanin
– Red hair has a slight amount of eumelanin but a high
concentration of pheomelanin
– Blond hair has an intermediate amount of pheomelanin and
very little eumelanin
– Gray and white hair results from scarcity or absence of melanin
in the cortex and the presence of air in the medulla
Hair Texture and Color
Three layers of hair
(c.s.)
• Medulla
– Core of cells
and air spaces
• Cortex
– Constitutes bulk
of the hair,
several layers of
keratinized cells
• Cuticle
– multiple layers
of very thin,
scaly cells that
overlap each
other
Eumelanin
Pheomelanin
Cuticle
Cortex
(c) Red, wavy
Air
space
Eumelanin
Pheomelanin
Medulla
(b) Black, straight
(a) Blond, straight
(d) Gray, wavy
Hair Growth
• The Hair Cycle:
– 3 Stages:
• Anagen: 90% of hair, hair cells multiply in the follicle
and push the hair deeper into the dermis. Also forms
the hair root sheath. Hair root sheath cells transform
into hair cells which produce keratin and then die as
they are pushed away from the papilla.
• Catagen: Mitosis in the sheath ceases. The base of the
hair hardens and is no longer anchored in the papilla.
• Telogen: Rest period.
*When anagen begins anew, the new hair will push out
the old.
Nails
•
•
hard derivatives of the stratum corneum.
composed of very thin, dead, densely packed cells, filled with
parallel fibers of hard keratin.
– Nail plate: the hard part of the nail.
– Free edge: end which overhangs the tip of the finger or toe.
– Nail body: the visible attached portion of the nail.
– Nail root: extends proximally under the overlying skin.
– Nail bed: the skin underlying the nail plate. It’s epidermis
is called the hyponychium.
 Nail matrix: A growth zone
at the proximal end of the
nail, composed of stratum
basale.
 Mitosis (1mm/week).
 Lunule: white crescent at the
proximal end of a nail.
 Cuticle (eponychium): a
narrow zone of dead skin.
Exocrine glands of the skin
• Sweat glands
– merocrine sweat glands
• secrete water to cool of the body
– apocrine sweat glands
• scent glands that secrete a milky substance rich in fatty acids in
response to stress or sexual stimulation
• Sebaceous glands
– secrete an oily substance (sebum) into a hair follicle
• softens the skin
• Ceruminous glands
– secrete a waxy substance (cerumen) in the ear canal
• keeps eardrum flexible
• kills bacteria
Skin Cancer
• Skin cancer—induced by the UV rays of the sun
–
–
–
–
–
Most often on the head and neck
Most common in fair-skinned people and the elderly
One of the most common cancer
One of the easiest to treat
Has one of the highest survival rates if detected and treated
early
• Three types of skin cancer named for the epidermal
cells in which they originate
– Basal cell carcinoma, squamous cell carcinoma, and malignant
melanoma
Skin Cancer
(a) Basal cell carcinoma
• Basal cell carcinoma
- Most common type
- Least dangerous because it seldom metastasizes
- Forms from cells in stratum basale
- Lesion is small, shiny bump with central depression and beaded edges
Skin Cancer
(b) Squamous cell carcinoma
• Squamous cell carcinoma
- Arise from keratinocytes from stratum spinosum
- Lesions usually appear on scalp, ears, lower lip, or back of the hand
- Have raised, reddened, scaly appearance later forming a concave ulcer
- Chance of recovery good with early detection and surgical removal
- Tends to metastasize to lymph nodes and may become lethal
Skin Cancer
(c) Malignant melanoma
• Malignant melanoma
- Skin cancer that arises from melanocytes; often in a preexisting
mole
- Less than 5% of skin cancers, but most deadly form
- Treated surgically if caught early
- Metastasizes rapidly; unresponsive to chemotherapy; usually fatal
Burns
• Classified according to the depth of tissue involvement
• First-degree burn: partial-thickness burn; involves only the
epidermis
• Marked by redness, slight edema, and pain
• Heals in a few days
– Most sunburns are first-degree burns
• Second-degree burn: partial-thickness burn; involves the
epidermis and part of the dermis
• Leaves part of the dermis intact
• Red, tan, or white
• Two weeks to several months to heal and may leave scars
• Blistered and very painful
• Third-degree burn: full-thickness burn; the epidermis and all of
the dermis, and often some deeper tissues (muscles or bones) are
destroyed
• Often requires skin grafts
• Needs fluid replacement and infection control
Degrees of Burn Injuries
Partial-thickness burns
(a) First degree
Full-thickness burns
(b) Second degree
(c) Third degree
Tissue Repair
• Damaged tissues can be repaired in two ways:
– Regeneration: replacement of dead or damaged cells by the
same type of cell as before
• Restores normal function
• Skin injuries and liver regenerate
– Fibrosis: replacement of damaged cells with scar tissue
• Holds organs together
• Does not restore normal function
– Severe cuts and burns, healing of muscle injuries, scarring of
lungs in tuberculosis
• Healing of a cut in the skin:
– Severed blood vessels bleed into cut
– Mast cells and damaged cells release
histamine
– Dilates blood vessels
– Increases blood flow to area
– Makes capillaries more permeable
1 Bleeding into the wound
• Blood plasma seeps into the wound
carrying:
– Antibodies
– Clotting proteins
– Blood cells
• Blood clot forms in the tissue
– Loosely knitting edges of cut
together
– Inhibits spread of pathogens from
injury site to healthy tissue
Scab
Blood clot
• Forms scab that temporarily
seals wound and blocks
infection
• Macrophages phagocytize and
digest tissue debris
Macrophages
Fibroblasts
Leukocytes
2 Scab formation and
macrophage activity
• New capillaries sprout from
nearby vessels and grow
into wound
• Deeper portions become
infiltrated by capillaries and
fibroblasts
Scab
– Macrophages remove the blood
clot
Blood
capillary
– Fibroblasts deposit new
Granulation
collagen
tissue
– Begins 3–4 days after injury and
lasts up to 2 weeks
Macrophages
Fibroblasts
3 Formation of granulation tissue
(fibroblastic phase of repair)
Tissue Repair
• Surface epithelial cells around
wound multiply and migrate into
wound area beneath scab
• Epithelium regenerates
• Connective tissue undergoes
fibrosis
• Scar tissue may or may not show
Epidermal
through epithelium
regrowth
tissue
• Remodeling (maturation) phase Scar
(fibrosis)
begins several weeks after injury
and may last up to 2 years
4 Epithelial regeneration and connective
tissue fibrosis (remodeling phase of repair)