A&P 1 Integumentary system TCC SE Sam Yacoub

Integumentary system

Covers the body and consists of the skin and accessory tissues (nails; hair; sweat glands; sebaceous glands) that acts as a barrier to the outside world and a visual indicator of physiology and health

Integument

Another name for the skin also called the cutaneous membrane

Dermatology

The study of skin

Integument (organ)

The body's largest organ making up 7 to 8% of body weight and composed of all tissue types functioning in concert with thickness that depends on body location

Epidermis

The superficial layer of the integument made of keratinized stratified squamous epithelium

Dermis

The deeper layer of the integument composed primarily of dense irregular connective tissue

Subcutaneous layer (hypodermis)

The layer deep to the dermis made of areolar and adipose connective tissue that is not part of the integumentary system; also called superficial fascia

Stratum basale

The deepest epidermal layer (stratum germinativum or basal layer) made of a single layer of cuboidal to low columnar keratinocytes in contact with the basement membrane where cell division occurs; also contains melanocytes and tactile cells

Stratum spinosum

The spiny layer of the epidermis made of several layers of keratinocytes attached to neighbors by desmosomes and containing epidermal dendritic cells

Stratum granulosum

The granular layer of the epidermis made of 3 to 5 layers of keratinocytes with distinct granules in the cytoplasm where keratinization begins

Stratum lucidum

The clear layer of the epidermis made of 2 to 3 layers of anucleate dead keratinocytes filled with eleidin and seen only in thick skin such as the palms and soles

Stratum corneum

The hornlike most superficial epidermal layer made of 20 to 30 layers of dead flattened anucleate keratin-filled keratinocytes

Order of epidermal layers

From deep to superficial: stratum basale then stratum spinosum then stratum granulosum then stratum lucidum then stratum corneum

Living and dead epidermal layers

The first three layers (basale; spinosum; granulosum) are composed of living keratinocytes while the stratum lucidum and stratum corneum are composed of dead cells

Keratinocyte

The most abundant epidermal cell found in all layers that acts as a large stem cell and synthesizes keratin to strengthen the epidermis and make skin almost waterproof

Keratin

A protein that strengthens the epidermis (called cytokeratins in the epidermis) and makes skin almost waterproof

Melanocyte

An epidermal cell scattered among keratinocytes in the stratum basale that produces and stores melanin in response to ultraviolet light and transfers melanosomes into keratinocytes to shield nuclear DNA from UV radiation

Melanosome

A pigment granule transferred from melanocytes into keratinocytes

Tactile (Merkel) cell

A few scattered cells in the stratum basale that are sensitive to touch and release chemicals when compressed to stimulate sensory nerve endings

Epidermal dendritic (Langerhans) cell

The fourth epidermal cell type found in the stratum spinosum and stratum granulosum that initiates the immune response against pathogens and epidermal cancer cells

Desmosome

An intercellular junction that attaches nondividing keratinocytes to one another in the stratum spinosum

Keratinization

The process that begins in the stratum granulosum in which keratinocytes fill with keratin causing the nucleus and organelles to disintegrate leaving a dead but structurally sound cell

Eleidin

A translucent protein in the stratum lucidum that is an intermediate product in keratin maturation and helps protect from UV light

Keratinocyte migration

Keratinocytes originate from stem cells in the stratum basale and migrate to the stratum corneum over two weeks then remain in the stratum corneum another two weeks before being shed

Thick skin

Skin of the palms of hands and soles of feet with all five epidermal strata and sweat glands but no hair follicles or sebaceous glands that is 0.4 to 0.6 mm thick

Thin skin

Skin that covers most of the body and lacks a stratum lucidum but has sweat glands hair follicles and sebaceous glands and is 0.075 to 0.150 mm thick

Hemoglobin

An oxygen-binding protein in red blood cells that turns bright red upon binding oxygen and gives dermal blood vessels a reddish tint most easily seen in fair-skinned individuals

Melanin

A black brown tan or yellow-brown pigment produced and stored in melanocytes and transferred to keratinocytes; production is stimulated by UV light and varies with heredity and light exposure

Skin color and melanocytes

All people have the same number of melanocytes but darker-skinned individuals produce more and darker colored melanin

Carotene

A yellow-orange pigment acquired from yellow-orange vegetables that accumulates in subcutaneous fat and the stratum corneum and is converted to vitamin A which plays a role in vision and reducing free radicals and immune function

Albinism

An inherited recessive condition in which the enzyme for melanin is nonfunctional so melanocytes cannot produce melanin resulting in white hair; pale skin; and pink irises

Nevus

A mole that is a harmless localized overgrowth of melanocytes that rarely becomes malignant but should be monitored for changes suggesting malignancy

Freckles

Yellowish or brown spots representing localized areas of increased melanocyte activity with pigmentation based on sun exposure and heredity

Hemangioma

Skin discoloration due to a benign blood vessel tumor

Capillary hemangioma

A bright red to deep purple nodule (strawberry-colored birthmark) usually present at birth that disappears in childhood

Cavernous hemangioma

A hemangioma of larger dermal blood vessels that may last a lifetime such as port-wine stains

Friction ridges

Complex arches and whorls on the fingers palms soles and toes formed by large folds and valleys of dermis and epidermis that increase friction on contact and give each individual a unique pattern used for personal identification

UV radiation types

The sun generates UVA UVB and UVC rays; UVC rays are absorbed and do not reach earth while sunscreens block UVA and UVB rays if the SPF (sun protection factor) is high enough

Sunless tanners

Products that create tanned skin without UV light exposure but provide no protection against UV rays

Dermis (structure)

The layer deep to the epidermis that is 0.5 mm to 3.0 mm thick and composed of connective tissue proper (collagen with elastic and reticular fibers) with motile dendritic cells and blood vessels; sweat glands; sebaceous glands; hair follicles; nail roots; sensory nerve endings; and arrector pili

Papillary layer

The superficial layer of the dermis composed of areolar connective tissue that forms projections called dermal papillae

Dermal papillae

Projections of the papillary layer of the dermis that interdigitate with epidermal ridges to interlock and increase the area of contact between the layers

Reticular layer

The deeper and major portion of the dermis composed of dense irregular connective tissue with large interwoven bundles of collagen fibers surrounding hair follicles; glands; nerves; and blood vessels

Lines of cleavage (tension lines)

Lines indicating the orientation of parallel collagen and elastic fiber bundles that resist stress; surgical incisions parallel to them heal quickly while incisions perpendicular to them are more likely to open due to cut elastic fibers

Collagen fibers (skin)

Dermal fibers that impart tensile strength to the skin

Elastic fibers (skin)

Dermal fibers that allow the skin to stretch and recoil

Stretch marks (striae)

Marks that form when skin is stretched beyond its capabilities and some collagen fibers are torn

Subcutaneous layer functions

Pads and protects the body; acts as an energy reservoir; provides thermal insulation; and is a drug injection site because its extensive vascular network promotes rapid absorption

Subcutaneous fat distribution

Thicker in women and accumulating primarily in the breasts buttocks hips and thighs while thinner in men and accumulating primarily in the neck upper arms abdomen lower back and buttocks

Protection function of the integument

Acts as a physical barrier that protects the body from injury and trauma; harmful chemicals; toxins; microbes; and temperature extremes and protects deeper tissue from solar radiation

Prevention of water loss and gain

The epidermis is water resistant but not waterproof so water is lost by sweat and transpiration; dehydration is a danger with severe burns while water resistance also prevents water absorption

Vitamin D3 (cholecalciferol)

Synthesized by keratinocytes from a steroid precursor upon UV exposure then released into blood and transported to the liver where it is converted to calcidiol

Calcitriol

The active form of vitamin D formed in the kidney from calcidiol that is considered a hormone and increases absorption of calcium and phosphate and helps regulate their blood levels

Daily sunlight for vitamin D

10 to 15 minutes of sunlight daily is adequate for vitamin D synthesis

Secretion function of the skin

Waste products (urea; salts; water) are secreted onto the skin surface during sweating with adjustable amounts that play a role in electrolyte homeostasis; sebum lubricates skin and hair and helps make the integument water resistant

Absorption function of the skin

The skin is selectively permeable and absorbs certain chemicals and drugs while blocking others

Transdermal administration

Delivery of some oil-soluble drugs by adhesive patch that slowly penetrate the epidermis and are absorbed into blood vessels

Immune function of the integument

Epidermal dendritic cells in the stratum spinosum initiate an immune response against pathogens and attack cancer cells

Temperature regulation

Influenced by capillaries and sweat glands in the dermis with dermal blood vessels playing an important role in body temperature and blood pressure

Vasoconstriction

Narrowing of dermal blood vessels so less blood travels through them and blood is shunted away from the periphery toward deeper structures to conserve heat which makes us look pale when cold

Vasodilation

An increase in the diameter of dermal blood vessels so more blood travels close to the surface resulting in reddish or pink skin and a flushed face during exercise

Sensory reception (skin)

The skin has extensive innervation with touch receptors that monitor stimuli in the dermis and epidermis and send input to the brain

Epidermal derivatives

Nails; hair; and exocrine glands formed during embryonic development when portions of the epidermis invaginate into the dermis; hair and nails are composed of dead cells while exocrine glands are composed of living cells

Nails

Scalelike modifications of the stratum corneum on the dorsal edges of fingers and toes that protect the distal tips of digits and assist in grasping objects

Nail plate

The structure made up of the free edge and nail body and nail root

Free edge (nail)

The distal whitish part of the nail with no underlying capillaries

Nail body

The pinkish part of the nail with underlying capillaries

Nail root

The part of the nail embedded in the skin

Nail bed

A layer of living epidermis covered by the nail body

Nail matrix

The actively growing part of the nail at the proximal end of the nail body

Lunula

The whitish semilunar area on the proximal end of the nail body

Nail folds

Folds of skin overlapping the nail

Eponychium (cuticle)

A narrow band of epidermis extending from the margin of the nail wall onto the nail body

Hyponychium

The thickened stratum corneum over which the free nail edge projects

Hair distribution

Hair is found almost everywhere on the body except the palms and palmar surface of fingers; the sides and soles of feet and toes; the lips; and portions of the external genitalia

Pilus

A single hair shaped like a slender filament made of keratinized cells that grows from a hair follicle

Lanugo

Fine unpigmented downy hair that appears in the last trimester

Vellus hair

Fine hair that is the primary human hair found on the upper and lower limbs

Terminal hair

Coarser pigmented longer hair found on the scalp; eyebrows; eyelashes; and men's beards that replaces vellus hair in the axillary and pubic regions during puberty

Hair bulb

The swelling at the base of a hair where it originates in the dermis that surrounds the hair papilla and is the only region containing living epithelial cells

Hair papilla

A connective tissue structure surrounded by the hair bulb

Hair root

The zone of hair from the bulb to the skin surface

Hair shaft

The portion of hair beyond the skin surface

Hair matrix

The structure at the base of the hair bulb where epithelial cells divide to produce new cells that are gradually pushed toward the surface

Medulla (hair)

The innermost part of a hair that is a remnant of the matrix and made of flexible soft keratin

Cortex (hair)

Flattened cells closer to the outer hair surface that are relatively hard

Cuticle (hair)

A single cell layer around the cortex of a hair

Hair follicle

An oblique tube surrounding the hair root that extends into the dermis and sometimes the subcutaneous layer with an outer connective tissue root sheath from the dermis and an inner epithelial root sheath from the epidermis

Arrector pili

Thin ribbons of smooth muscle extending from the hair follicle to the dermal papillae that elevate the hair with contraction producing goosebumps

Functions of hair

Protection (scalp from sunburn and injury; nostril and ear hairs trap particles and foreign matter; eyelashes protect eyes; eyebrows keep sweat out of eyes); facial expression; heat retention; sensory reception of light touch; visual identification; and chemical signal dispersal

Pheromones

Chemical signals involved in attracting sexual partners that are dispersed by hair and secreted by specific sweat glands onto hairs in the axillary and pubic regions

Exocrine glands of the skin

Skin houses many exocrine glands with the two most common types being sweat glands and sebaceous glands

Sweat gland structure

A gland with a coiled tubular secretory portion in the reticular dermis and a duct that transports secretions to the surface and opens at the epidermal surface as a sweat pore

Sweat pore

The opening of a sweat gland duct on the epidermal surface

Myoepithelial cells

Cells that contract to squeeze a sweat gland and discharge secretions in response to sympathetic stimulation

Merocrine sweat glands

The most numerous and widely distributed simple coiled tubular sweat glands that discharge secretions by exocytosis onto the skin surface

Sweat

A secretion composed of 99% water and 1% other chemicals including electrolytes; metabolites; and waste products

Functions of merocrine sweat

Thermoregulation by fluid evaporation; loss of water and electrolytes; may help eliminate ingested drugs; dilute harmful chemicals; and antibacterial and antifungal activity

Apocrine sweat glands

Coiled tubular glands that discharge viscous cloudy secretions containing proteins and lipids by exocytosis into hair follicles in the axillae; around the nipples; and in the pubic and anal region; begin producing secretions during puberty and produce odor when acted on by bacteria

Sebaceous glands

Glands that discharge into a hair follicle and produce an oily bactericidal secretion called sebum that lubricates skin and hair; stimulated by hormones (especially androgens) and activated during puberty