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Skin and Its Appendages

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


Lies beneath dermis (insulation, rich in fat and loose connective tissue

Two types of skin

Thick and thin skin


Consitute more than 90% of cells present; principal structure of the outer skin, sometimes called corneocystes after they are fully hardened (epithethal cells)


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



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


"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)


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


(in epidermis)basic determinant is quantity, type, and distribution of melanin (color/pigment of the skin)

Types of melanin

Eumelanin and Pheomelanin


group of dark brown, almost black, melanins


group of reddish and orange melanins


Packets of melanin released by melanocytes

Melanosomes are ingested by

surronding keratinocytes and form a cap over the nucleus (protect from UV rays)


congenital absence of melanin

Age spots

Cumulative effects of UV ray exposure

Skin color

how much melanin you produce (more sun=more melanin (tan))


(makes vitamin A) group of yellowish pigments from food can also contribute to skin color


color changes occur as a result of changes in blood flow

Redder skin

blood flow increase to the skin (dilate blood vessels)


Bluish color caused by darkening of hemoglobin when it loses oxygen and gains carbon dioxide


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


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


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)


transfer of heat from one object to another without actual contact; important method of heat loss in cool environment (no contact)


transfer of heat to any substance in contact with the body; accounts for relatively small amounts of heat loss (contact)


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


fine and soft hair present before birth

Terminal hair

coarse pubic and axillary hair that develops at puberty


cluster of capillaries under germinal matrix


part of hair embedded in follicle in dermis


visible part of hair (dead)


inner core of hair (meat)


outer portion

Color of hair

result of different amounts, distribution, types of melanin in cortex of hair


growth and rest periods alternate; hair on head averages 5 inches of growth per year


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


consist of epidermal cells converted to hard keratin

Nail body

visible part of each nail


part of nail in groove hidden by fold of skin, the cuticle


moon-shaped white area nearest root

Nail bed

layer of epithelium under nail body, contains abundant blood vessels


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


superficial, thinner layer (epithelial layer)


the deep, thicker layer (dense and vascular connective tissue)

Friction ridges

form fingerprints or footprints, underlying dermal papillae are raised in curving parallel ridges


principal structure element of the outer skin (skin cells that become filled with keratin)




tough, fibrous protein


after dead and fully keratinized, flattened keratinocytes


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


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


thicker hair that replaces lanugo

germinal matrix

cap-shaped cluster of cells at the bottom of a hair follicle


covering layer



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