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A&P 1: Lecture 5 Integumentary Systemskin

Terms in this set (45)

Skin
integument "covering" or integumentary system
2 distinct regions: epidermis & dermis
Epidermis
superficial region
top layer of skin "above"
consists of epithelial tissue & is avascular (no blood supply in epidermis)
Dermis
-underlies epidermis
-mostly fibrous, strong, flexible connective tissue & is vascular (has blood vessels)
-cells include: fibroblasts, macrophages, mast cells & white blood cells
-fibers in matrix bind body together
-contains nerves, blood vessels & lymphatic vessels
Hypodermis
subcutaneous layer deep to skin (below the skin)
superficial fascia (fibrous tissue that encloses an organ)
not part of skin but share some functions
mostly adipose tissue that absorbs shock & insulates
anchors skin to underlying structures: mostly muscles
Cells of the Epidermis
-keratinocytes, melanocytes, dendritic (langerhans) cells, tactile (merkel) cells
-mostly keratinized cells (stratified squamous epithelium)
Keratinocytes
-function: produce fibrous keratin (flaky dead cells at top of skin): protein that gives skin its protective properties
-tightly connected by desmosomes (hold cells together)
Melanocytes
-spider-shaped cells located in deepest epidermis
-produce pigment melanin, which is packaged into melanosomes (tanning)
-melanosomes are transferred to keratinocytes, where they protect nucleus from UV damage (tans are damaging)
Dendritic (Langerhans) cells
-Macrophages - key activators of immune system
patrol deep epidermis
(use phagocytosis)
Tactile (Merkel) cells
sensory receptors that sense touch
stratum basale
-deepest of all epidermal layers, the basal "bottom" layer, is firmly attached to dermis
-consists of a single row of stem cells that actively divide (mitotic), producing two daughter cells each time
-one daughter cell journeys from basal layer to surface, taking 25-45 days to reach surface
-other daughter cell remains in stratum basale as stem cell
stratum spinosum
-known as the prickly layer - keratinocytes appear spikey, so they are called prickle cells
-several layers thick
-cells contain weblike system of intermediate prekeratin filaments attached to desmosomes (starting to form)
-scattered among keratinocytes are abundant melanosomes & dendritic cells
(layer of epidermis)
layers of epidermis
stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum
(bottom to top)
(B,S,G,L,C)
stratum granulosum
-layer of the epidermis, 4 to 6 cells thick, but cells are flattened, so layer is thin
-cell appearance changes:
--cells flatten, nuclei & organelles disintegrate
--keratination begins - cells accumulate keratohyaline granules
--cells accumulate lamellar granules, a water-resistant glycolipid
--take on characteristics of top layers of skin (deteriorating)
-cells above this layer die (no blood here)
stratum lucidum
-found only in thick skin (like heal)
-consists of thin, translucent band of 2-3 rows of clear, flat, dead kerotinocytes
-layer of the epidermis
stratum corneum
-most superficial (last) layer of the epidermis
-20-30 rows of flat anucleated, keratinized dead cells
-accounts for 3/4 of epidermal thickness
-though dead, cells still function to:
--protect deeper cells from environment
--prevent water loss
--protect from abrasion & penetration
--act as a barrier against biological, chemical & physical assaults
-this skin is the first layer of defense
layers of dermis
1. papillary layer
2. reticular layer
papillary layer
-superficial layer
-composed of areolar connective tissue
-loose fibers allow phagocytes to patrol for microorganisms
-has dermal papillae "bump"
dermal papillae
-superficial region of dermis (in papillary layer) that sends fingerlike projections up into epidermis that contain capillary loops, free nerve endings & touch receptors
-in thick skin, it lies on top of dermal ridges, which give rise to epidermal ridges -> collectively ridges are called friction ridges (generates fingerprints)
-- enhance gripping ability
--contribute to sense of touch
--sweat pores in ridges leave unique fingerprint pattern
reticular layer
-makes up 80% of dermal thickness
-consists of coarse, dense fibrous connective tissue: many elastic fibers provide strength & resilience; bind water, keeping skin hydrated
-consists of flexure lines: dermal folds at or near joints, dermis is tightly secured to deeper structures, skin's inability to slide easily for joint movement causes deep creases
flexure lines
dermal folds at or near joints, where the dermis is tightly secured to deeper structures
skin appendages
-derivatives of the epidermis
-includes:
hair
hair follicles
nails
sweat glands
sebaceous oil glands
hair
functions:
-sense insects
-hair on head guards against physical trauma
-protect from heat loss
-shield skin from sunlight
structure:
-flexible strands of dead, keratinized cells
-contains hard keratin, not like soft keratin found in skin
-hair pigments are made by melanocytes in hair follicles
nails
-scale-like modifications of epidermis that contain hard keratin
-act as a protective cover for distal, dorsal surface of fingers & toes
-useful as "tools" to pick up small objects or scratch an itch
sweat glands
sudoriferous glands ("sudor" means sweat)
2 main types: eccrine (merocrine) & apocrine
eccrine sweat glands
-are merocrine glands
-most numerous type
-abundant on palms, soles & forehead
-ducts connect to pores
-function in thermoregulation = regulated by sympathetic nervous system
-their secretion is sweat: 99% water, salts, vitamin C, antibodies, dermcidin (microbe killing peptide) & metabolic wastes
apocrine sweat glands
-also merocrine glands
-secrete same components of sweat PLUS fatty substances & proteins
-bacteria break down sweat, leading to body odor
-begin functioning at puberty
-modified apocrine glands: ceruminous glands & mammary glands
ceruminous glands
modified apocrine sweat glands, located in external ear canal, secretes cerumen (earwax)
mammary glands
modified apocrine sweat glands that secrete milk
sebaceous glands
-oil glands
-widely distributed, except for thick skin of palms & soles
-most develop from hair follicles & secrete into hair follicles
-relatively inactive til puberty (stimulated by hormones, especially androgens (reproductive system)
-secrete sebum
-oily holocrine secretion (they rupture & release)
-bactericidal (bacteria-killing) properties
-soften hair & skin
functions of skin
-protection
-chemical, physical & biological barrier
chemical barriers of skin
-skin secretes many chemicals, such as antimicrobial proteins, sebum & defensins (kill bacteria)
-skin has a low pH
physical barriers of skin
Flat, dead, keratinized cells of stratum corneum surrounded by glycolipids, block most water & water- soluble substances
biological barriers of skin
dendritic cells of epidermis & macrophages of dermis protect from pathogens
Body temperature regulation
-function of skin
-under normal, resting body temperature, sweat glands produce about 500 ml/day of unnoticeable sweat
-if body temperature rises, dilation of dermal vessels can increase sweat gland activity
-cold external environment dermal blood vessels constrict
cutaneous sensation
-function of skin
-touch, cutaneous sensory receptors present in skin are part of the nervous system
metabolic functions of skin
-skin can synthesize vitamin D needed for calcium absorption in intestine
-chemicals from keratinocytes can disarm some carcinogens
Blood Reservoir (Skin)
skin holds 5% of the body's total blood volume
excretion of skin
skin can secrete limited amounts of nitrogenous wastes, such as ammonia, urea & uric acid (its the kidney's job to do most of this)
skin cancer
-Most skin tumors are benign & do not spread (metastasize)
-Risk factors: overexposure to UV radiation, frequent irritation of the skin
-3 types: Basal Cell Carcinoma, Squamous Cell Carcinoma, Melanoma
basal cell carcinoma
-least malignant & most common type of skin cancer
-stratum basal cells proliferate & slowly invade dermis & hypodermis
-cured by surgical excision in 99% of cases
squamous cell carcinoma
-2nd most common skin cancer
-can metastasize (& move to another tissue)
-involves keratinocytes of stratum spinousum
-usually a scaly reddened papule on scalp, ears, lower lip or hands
-good prognosis if treated by radiation therapy or removed surgically
melanoma
-cancer of melanocytes
-most dangerous -highly metazoic & resistant to chemo (can break away & grow somewhere else)
-treated by wide surgical excision accompanied by immunotherapy
-key to survival is early detection: ABCD rule
ABCD rule of melanoma
A = asymmetry; the 2 sides of the pigmented area do not match
B = border irregularity, exhibits indentations
C = color (contains several colors) may be blue, black, tan, brown
D = diameter; larger than 6mm (size of pencil eraser)
burns
-tissue damage caused by heat, electricity, radiation or certain chemicals
-damage caused by denaturation of proteins, which destroy cells
-immediate threat is dehydration & electrolyte imbalance
-burns can be classified by severity
Burn severity classification
-1st degree:
--epidermal damage only
--localized redness, edema (swelling) & pain
-2nd degree:
--epidermal & upper dermal damage
--blisters appear
3rd degree:
--entire thickness of skin involved
--no edema seen & area is not painful because nerve endings are destroyed
--skin grafting usually necessary
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