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113 terms

Chapter 6

Skin and Its Appendages
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The body's largest organ
Skin (Integument)
Integumentary system describes what
Skin and its appendages: hair, nails, and skin glands
What is skin classified as?
Cutaneous (dry) membrane
Two primary layers of skin.
Epidermis and dermis
What joins the two layers of skin?
Dermoepidermal junction
Hypodermis
Lies beneath dermis (insulation, rich in fat and loose connective tissue
Two types of skin
Thick and thin skin
Keratinocytes
Consitute more than 90% of cells present; principal structure of the outer skin, sometimes called corneocystes after they are fully hardened (epithethal cells)
Melanocytes
Pigment producing cells (5% of total; contribute to skin color and filter ultraviolet light
Epidermal dendritic cells
Branched antigen-presenting cells, play a role in immune response; also called Langerhans cells (recognize foreign antigen)
Tactile epithelial cells (Merkel cells)
Attach to sensory nerve endings to form "light touch" receptors
Dermal papillae
Form ridges
Tactile
touch
Stratum basale (base layer)
Single layer of columar cells; only these cells undergo mitosis and then migrate through the other layers until they are shed
Stratum spinosum (spiny layer)
Cells arranged in 8 to 10 layers with desmosomes that pull cells into spiny shapes; cells rich in RNA (produce keratin)
Stratum germinativum
Another name for stratum basale or stratum spinosum and stratum basale together
Stratum granulosum (granular layer)
Cells arranged in two to four layers and filles with keratohyalin granules; contains high levels of lysosomal enzymes
Stratum lucidum (clear layer)
Cells filled with keratin precursor called eleidin; absent in thin skin
Stratum corneum (horny layer)
Most superficial layer, dead cells filled with keratin (barrier area)
35 days
Turnover or regeneration time referred to time required for epidermal cells to form in stratum basale and migrate to the skin surface
Epidermal growth factor
Regulates epidermal growth and repair
Callus formation
Shortened turnover time will increase the thickness of the stratum corneum
Amount of stratum basale cells to enter mitosis daily
10 to 12%
Epidermal proliferating unit
Each group of 8 to 10 basal cells in mitosis with their vertical columns of migrating keratinocytes
Dermoepidermal junction
A basement membrane with unique fibrous elements and a polysaccharide gel "glue" the epidermis to the dermis below. The junction is a partial barrier to the passage of some cells and large molecules
Dermis
"true skin" gives strength to skin, serves as a reservoir storage area for water and electrolytes, rich vascular supply plays a critical role in temperature regulation
Structures in dermis
Arrector pili muscles and hair follicles, sensory receptors, sweat and sebaceous (oil) glands, blood vessels
Papillary layer
composed of dermal papillae that project into the epidermis; contains fine collagenous and elastic fibers and the demoepidermal junction; forms unique pattern that gives individual fingerprints
Reticular layer
contains dense, interlacing white collagenous fibers and elastic fibers to make the skin tough yet stretchable; when processes from animal skin, produces leather
Layers of dermis
Papillary layer Reticular layer
The dermis does not
continually shed and regenerate itself as does the epidermis
During dermis wound healing
fibroblasts begin forming and unusually dense mass of new connective fibers; if not replaced by normal tissue, this mass remains a scar
Cleavage lines
patterns formed by the collagenous fibers of the reticular layer of dermis; aka Langer's lines (incision lines)
Hypodermis
aka subcautaneous layer or superficial fascia (connective tissue) located deep to the dermis; forms connection between skin and other structures; not part of the skin
Melanin
(in epidermis)basic determinant is quantity, type, and distribution of melanin (color/pigment of the skin)
Types of melanin
Eumelanin and Pheomelanin
Eumelanin
group of dark brown, almost black, melanins
Pheomelanin
group of reddish and orange melanins
Melanosomes
Packets of melanin released by melanocytes
Melanosomes are ingested by
surronding keratinocytes and form a cap over the nucleus (protect from UV rays)
Albinism
congenital absence of melanin
Age spots
Cumulative effects of UV ray exposure
Skin color
how much melanin you produce (more sun=more melanin (tan))
Beta-carotene
(makes vitamin A) group of yellowish pigments from food can also contribute to skin color
Hemoglobin
color changes occur as a result of changes in blood flow
Redder skin
blood flow increase to the skin (dilate blood vessels)
Cyanosis
Bluish color caused by darkening of hemoglobin when it loses oxygen and gains carbon dioxide
Bruising
can cause a rainbow of colors to the skin
Functions of the skin Protection
Physical barrier to microorganisms, barrier to chemical hazards, reduces potential for mechanical trauma, prevents dehydration, protects from excess UV ray exposure
Emulsified protective barrier
formed by mixing of residue and secretions of sweat and sebacaous glands with sloughed epithelial cells from skin surface
Desquamation
shedding of epithelial elements (removing layers)
Functions of surface film
Antibacterial, anti-fungal activity, lubrication, hydration of skin surface, buffer of caustic irritants, blockade of toxic agents
Chemical composition from epithelial elements
amino acids, sterols and complex phospholipids (cell membrane)
Chemical composition from sebum
Fatty acids, triglycerides, and waxes
Chemical composition from sweat
water, ammonia, urea, and lactic and uric acid (kill bacteria)
Sensation of the skin
Skin acts as a sophisticated sense organ. Somatic sensory receptors detect stimuli that detection of pressure, touch, temperature, pain, and other general senses
Flexibility of the skin
skin is supple and elastic, thus permitting change in body contours without injury
Immunity of skin
Phagocytic cells destroy bacteria. Epidermal dendritic cells trigger helpful immune reaction working with helper T cells
Homeostasis of body temperature
To maintain homeostasis of body temperature, heat production must equal heat loss; skin plays a critical role in this process
Heat production
by metabolism of foods in skeletal muscles and liver. (more physical energy used=more heat the body produces)
Skin excretion
Water, Urea/ammonia/uric acid
Vitamin D production
started in the skin(exposure to UV light), blood transports precursor to liver and kidneys
Heat loss
approximately 80% of heat loss occurs through the skin
Evaporation
to evaporate any fluid, heat energy must be expended, this method is important when temperatures are high and its the only method heat can be lost from skin (sweating)
Radiation
transfer of heat from one object to another without actual contact; important method of heat loss in cool environment (no contact)
Conduction
transfer of heat to any substance in contact with the body; accounts for relatively small amounts of heat loss (contact)
Convection
transfer of heat away from a surface by movement of air; usually accounts for a small amount of heat loss (air movement)
Heat loss by the skin is controlled by
Negative feedback loop
Monitor the body's internal temperature
Receptors in the hypothalamus
Development of hair
hair follicles and hair develop from epidermis; mitosis of cells of germinal matrix forms hairs
Lanugo
fine and soft hair present before birth
Terminal hair
coarse pubic and axillary hair that develops at puberty
Papilla
cluster of capillaries under germinal matrix
Root
part of hair embedded in follicle in dermis
Shaft
visible part of hair (dead)
Medulla
inner core of hair (meat)
cortex
outer portion
Color of hair
result of different amounts, distribution, types of melanin in cortex of hair
Growth
growth and rest periods alternate; hair on head averages 5 inches of growth per year
Sebum
Skin oil
Male pattern baldness (androgenic alopecia)
results from combination of genetic tendency and male sex hormones
Two types of sweat glands
eccrine and apocrine
Eccrine sweat glands
most numerous, quite small, simple, coiled, tubular,function throughout life, secrete perspiration or sweat, eliminates wastes and help maintain a constant core temperature
Apocrine sweat glands
deep, limited distribution (axilla, areola of breast, anus), large, simple, branched, tubular, function begins at puberty, secretion shows cyclic changes in female with menstrual cycle
Nails
consist of epidermal cells converted to hard keratin
Nail body
visible part of each nail
Root
part of nail in groove hidden by fold of skin, the cuticle
Lunula
moon-shaped white area nearest root
Nail bed
layer of epithelium under nail body, contains abundant blood vessels
Onycholysis
separation of a nail from the nail bed
Nail growth
nails grow by mitosis of cells in stratum basale beneath lunula
Sebaceous glands
secrete sebum, lipid components have anti-fungal activity, simple, branched, in dermis expect for soles and palms, secretion increases in adolescence (may lead to pimples)
Ceruminous glands
Modified apocrine sweat glands, simple, coiled, tubular, empty contents into external ear, protect area, excess can cause blockage of ear canal
Cerumen (wax)
mixed secretions of sebaceous and ceruminous glands
Epidermis
superficial, thinner layer (epithelial layer)
Dermis
the deep, thicker layer (dense and vascular connective tissue)
Friction ridges
form fingerprints or footprints, underlying dermal papillae are raised in curving parallel ridges
Keratinocytes
principal structure element of the outer skin (skin cells that become filled with keratin)
Strata
layer
Keratin
tough, fibrous protein
Corneocytes
after dead and fully keratinized, flattened keratinocytes
Melanocytes
contribute colored pigments to the skin and serve to decrease amount of UV light
Dendritic cells (DCs) (Langerhans cells)
branched cells that play a role in immunity
Somatic sensory receptors
A specialized network of nerves and nerve endings in the dermis
dermal papillae
Projections from dermis into epidermis. Increase surface area of the dermis and stratum germinativum. Form ridges in epidermis and form fingerprints and footprints
Arrector pili muscles
smooth muscles of the skin, attached to hair follicles; when contraction occurs, the hair stands up, resulting in "goose bumps"
Skin ligaments
Bands of fibers running through the hypodermis help hold the skin to underlying structures such as deep fascia and muscles
hypothalamus
brain structure that acts as a control center for recognition and analysis of hunger, thirst, fatigue, anger, and body temperature
Hair follicles
tubular structure in the dermis that produces the hair shaft
Vellus
thicker hair that replaces lanugo
germinal matrix
cap-shaped cluster of cells at the bottom of a hair follicle
Cuticle
covering layer
alopecia
baldness