Transcript Chapter 6

Chapter 6
Skin and the Integumentary
system
Skin contains
many
different
types of
tissue
General Structure
• Two distinct regions or layers compose the skin:
• Epidermis = outermost layer
– keratinized stratified squamous ET
• Dermis = inner layer
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keratinized epithelium (hair follicles)
glandular epithelium (sweat, sebaceous glands)
dense irregular CT (collagen)
smooth muscle tissue (arrector pili muscles)
nervous tissue (Meissner's & Pacinian Corpuscles)
blood vessels
• Subcutaneous layer (hypodermis)= adipose tissue
– distinct layer beneath skin
SKIN AND ITS TISSUES
(Cutaneous Membrane)
Skin Functions
Protection:
• Physical barrier
– from water loss
– from injury
– from chemicals and microorganisms
• Chemical barrier
– pH or 5-6
– prevents microorganism growth
• Biological barrier
– Langerhan’s cells (epidermis)
– Macrophages and mast cells (dermis)
• Excretion (minimal, most through kidneys!):
– urea
– uric acid
Functions cont.
• Regulation of body temperature
• Cutaneous Sensation:
– Light touch detection = Meissner's Corpuscle's
– egg-shaped
– located in dermal papillae
– populate areas in the fingertips, palms, soles,
eyelids, tip of tongue, nipples, clitoris, tip of penis
– Pressure detection = Pacinian Corpuscle's
– onion-shaped
– located in deep dermis and subcutaneous regions
Functions cont.
• Vitamin D Synthesis:
– UV rays in sunlight activate its synthesis
– Vitamin D is required for bone homeostasis
• Blood Reservoir:
– The dermis houses about 10% of the body's blood
vessels
– Skin only requires 1-2% of the body’s blood
• Immunity:
– Langerhan’s cells (macrophages)
– interact with T-helper cells in immune responses
Epidermis
• Four distinct layers determined by the
extent of keratinization in the epithelial cells
– thickest on palms and soles (0.8-1.4mm)
1. Stratum corneum = outermost layer
– composed of dead epithelial cells filled with the
protein keratin
• Stratum lucidum = translucent layer cells
separating s. corneum from s. granulosum
– extra layer only in thick skin of soles & palms
2. Stratum granulosum is composed of 3-5
layers of flattened granular cells (filled with
keratin granules)
Epidermis cont.
3. Stratum spinosum is composed of many
layers of spiky cells with large nuclei
4. Stratum basale (germinativum)= innermost
layer
– directly above basement membrane
– composed of a single row mitosing cuboidal
epithelial cells and
– composed of melanocytes
– specialized cells that produce the pigment
melanin
Epidermis Function
• Main Function = Protection (keratin):
– prevents moisture loss (waterproof)
– prevents injury by penetration
– prevents microorganisms/chemicals entry
• Pigment = Melanin:
– determines skin color
– is produced by melanocytes in stratum basale
(germinativum)
Dermis
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inner layer of skin
binds epidermis to underlying tissues
on average 1.0-2.0mm thick
Contains several tissue types and structures
Dermis
• Structure: two distinct layers
• papillary layer (20%) is below epidermis
– composed of loose areolar CT
– surface forms dermal papillae (finger-like
projections into the epidermis) that form
fingerprints in thick skin
– Meissner's Corpuscles (sensory receptor for
light touch)
Dermis cont.
• reticular layer (80%) = dense irregular CT
– which give skin its strength and resiliency bundles
of collagen fibers
– elastic fibers
– reticular fibers
– Pacinian corpuscles –sensory receptors for deep
pressure
• The dermis houses epidermal derivatives or
accessory organs (see below)
• Main Function = nourishment of epidermis
Subcutaneous Layer
• Subcutaneous Layer (hypodermis) =
beneath skin
• Structure = adipose tissue, blood vessels,
loose connective tissue
• Function = insulation
ACCESSORY ORGANS OF
THE SKIN
(Epidermal Derivatives)
Hair Follicles
• Structure:
– root or base in deep dermis
– follicle throughout dermis
– hair shaft in epidermis
• Keratinization
– made of epithelial cells
– cells in root = active mitosis
– cells in follicle = maturing & accumulating keratin
– cells in epidermis = dead epithelial cells
• full of keratin = exposed hair or hair shaft
Hair Follicles cont.
• Pigment = Melanin
• Arrector Pili Muscle = a bundle of smooth
muscle associated with every hair follicle
– causes hair to stand on end ("goose bumps")
when frightened or cold
Nails
• Epithelium undergoing keratinization (active
mitosis in lunula)
• Functions:
– manipulation
– protection of digit ends
Sebaceous Glands
• holocrine gland (simple cuboidal epithelium)
• Usually associated with hair follicles
• Secretion (holocrine) = sebum (i.e. oil)
– fat
– cellular material
• Sebum is secreted into hair follicle
• Function: Sebum keeps skin & hair soft, pliable and
virtually waterproof
• Disorders:
– acne (hypersecretion of sebum; ducts clog & inflame)
– seborrhea (hyperproduction of sebum; oily scales)
ACCESSORY ORGANS OF
THE SKIN
(Epidermal Derivatives)
Skin Glands
• Skin Glands (Sweat Glands or
Sudoriferous Glands)
• Two types (based on glandular secretion):
Merocrine (Eccrine) Glands
• Structure:
– coil in deep dermis
– duct in dermis
– pore at surface
Skin Glands cont.
• Characteristics:
– respond to elevated temperature / exercise
– no odor in secretion
– function throughout life
– not associated with hair follicles
• Location: forehead, neck, back
• Secretion (merocrine) = water plus
– salts
– wastes (urea and uric acid)
Skin Glands cont.
Apocrine glands
• Structure: ducts terminate into hair follicles
• Characteristics:
– respond to stress / emotions
– odor in secretion
– begin to function at puberty & continue through
life
– associated with hair follicles
• Location: armpits, groin
Skin Glands cont.
• Secretion (apocrine) = sweat similar to Merocrine
plus:
– oil and
– cellular debris
• Modified Apocrine Glands
– Ceruminous glands = external ear
• secretion = earwax
– Mammary glands = breasts
• Secretion=milk
• the above structures are epithelial in nature and are
actually specialized parts of the epidermis, even
though their location is within the dermis
REGULATION OF BODY
TEMPERATURE
Heat production and loss
• Heat production is mostly a by-product of
cellular metabolism
• Heat loss is controlled by regulating dermal
blood flow
• Vasodilation – increases dermal blood flow,
which also increases heat loss
• Vasoconstriction – decreases dermal blood
flow which decreases heat loss
Heat Loss
• Heat loss is by four methods
1. Radiation
– most heat loss by this mode
– infrared heat rays move from area of high heat
(i.e. the blood) to areas of low heat (i.e. the
environment)
2. Conduction
– less heat loss
– heat moves by physical contact
– the reason the seat you sit in is warm when you
stand up
Heat Loss cont.
3. Convection
– heat loss to surrounding air
– increases as air movement increases, that is why
turning on a fan cools your body
4. Evaporation
– heat loss varies
– if heat increases our sweating increases, so we
lose more heat by evaporating the sweat on the
surface of our skin
Heat Production
• Low body temperatures require heat loss to be
minimized
• The Hypothalamus signals for sweating to
decrease (decreasing heat loss by evaporation) and
dermal vasoconstriction (decreasing heat loss by
radiation)
– Usually this brings the body temperature back to normal
• If the body temperature remains low after the
above action
• Heat must be produced
• Shivering occurs and the tiny muscle contractions
involved produce heat
Figure 06.11
Problems in Temperature Regulation
• Hyperthermia – elevated body temperature
– Two common causes
– humid air decreases evaporation
– air temperature exceeds body temperature, thus
heat is gained not lost
• Hypothermia – low body temperature
– very dangerous if core body temperature drops
below 94 F
– limbs can withstand about 65 F because they
contain no vital organs
– cause is intentional during some surgical
procedures
Skin Color
• Genetic Factors
– People of different races have essentially the
same number of melanocytes
– the amount of melanin produced varies
(determined by DNA)
• Environmental Factors affect melanin
production: by affecting gene expression
– UV rays
– chemicals
– drugs (antihistamines & antibiotics)
Skin Color
• Physiologic Factors may affect skin color
(but not melanin production):
– Carotene may accumulate in s. corneum = orange
– Hemoglobin (Hb) in dermal blood vessels = pink
– Lack of Hb in dermal blood vessels = blue
(cyanosis.)
– Inability to breakdown Hb (liver problems) =
yellow (jaundice)
HEALING OF WOUNDS AND
BURNS
Cuts
• Epidermal cuts are closed by increased cell
division in the stratum basale
• Deep cuts involve blood vessel damage
resulting in bleeding.
– This activates blood clotting mechanisms
Burns
• Superficial partial-thickness burns (1st degree)
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Epidermis only
Reddening due to increased blood flow
Mild pain
Common in sunburn
Heals in a few days-2 weeks
• Deep partial-thickness burns (2nd degree)
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Epidermis and some dermal damage
Reddening and blistering caused by blood vessel damage
Moderate pain
Common to physical contact with hot objects
Heals in 2-6 weeks without scars unless infected
Burns cont.
• Full-thickness burns (3rd degree)
– Epidermis, entire dermis, and potentially
subcutaneal damage
– Dry, leathery tissue with red or black color
– Severe pain
– Caused by prolonged heat or chemical contact
– Healing rarely occurs due to lack of surviving skin
cells, skin replacements (grafts) are usually
needed, usually extensive scarring
• Autograft – transplant from undamaged area of yourself
• Homograft – temporary transplant from cadaver
Burns cont.
• Body Surface affected
• Estimated by “rule of nines”
– All of the percentages in the next figures are
multiples/fractions of 9
– Add up to 100%
• Important for determining treatment and
prognosis
Life Span Changes
•
Aging skin exhibits:
– wrinkling
– sagging
– age spots or liver spots
•
Efficient regulation of body temperature
declines with age
– The number of sweat glands changes
– Capillary beds in the skin shrink
•
Synthesis of vitamin D declines as skin
ages, which affects skeletal health