Integumentary System & Bone Tissue: Key Concepts for Biology

Integumentary system

Consists of skin, hair, nails, and associated glands.

Skin / integument

Body's largest and heaviest organ.

Dermatology

Scientific study and medical treatment of the integumentary system.

Epidermis

Stratified squamous epithelium.

Dermis

Connective tissue layer composed mainly of collagen; also contains elastic and reticular fibers.

Thick skin

Covers palms, soles, and corresponding surfaces of fingers and toes.

Thin skin

Covers rest of the body.

Keratin

Provides physical protection.

Dermcidin, defensins, and acid mantle

Protect against bacteria.

Vitamin D synthesis

Skin carries out the first step.

Sensation

Many nerve endings react to various stimuli.

Thermoregulation

Alter blood flow to release or retain heat.

Cutaneous vasoconstriction

Helps retain heat by reducing blood flow to the skin.

Cutaneous vasodilation

Helps release heat by increasing blood flow to the skin.

Epidermis tissue type

Keratinized stratified squamous epithelium.

Avascular

Lacks blood vessels.

Keratinocytes

Great majority of epidermal cells; synthesize keratin.

Stem cells

Undifferentiated cells that give rise to keratinocytes.

Melanocytes

Synthesize pigment melanin that shields DNA from ultraviolet radiation.

Melanin

Pigment that shields DNA from ultraviolet radiation.

Melanosomes

Structures that distribute melanin to keratinocytes.

Tactile cells

Touch receptor cells associated with dermal nerve fibers.

Tactile disc

Collective term for tactile cell and associated nerve fiber.

Dendritic cells

Phagocytic immune cells that guard against toxins and microbes.

Stratum basale

Single layer of stem cells and keratinocytes resting on the basement membrane.

Stratum spinosum

Several layers of living keratinocytes joined by desmosomes and tight junctions.

Stratum granulosum

Three to five layers of flat, living keratinocytes.

Keratohyalin granules

Dark-staining granules in the stratum granulosum.

Stratum lucidum

Thin, pale layer found only in thick skin.

Eleidin

Protein packed in keratinocytes of the stratum lucidum.

Stratum corneum

Up to 30 layers of dead, scaly, keratinized cells.

Life history of keratinocyte

Keratinocytes are produced, pushed upward, flatten, make keratin, die, and exfoliate.

Mitosis in epidermis

Occurs in stratum basale or deepest part of stratum spinosum.

Lamellar granules

Lipid-filled granules produced as keratinocytes move upward.

Exfoliation

When keratinocytes flake off from the skin surface.

Dander

Specks of exfoliated keratinocytes.

Dandruff

Dander that may combine with oil.

Calluses / corns

Thick accumulations of dead keratinocytes on hands or feet.

Filaggrin

Protein that binds keratin into tough bundles.

Epidermal water barrier

Helps prevent dehydration.

Hypodermis

Layer of connective tissue beneath the skin.

Subcutaneous fat

Subcutaneous tissue comprised predominantly of adipose tissue.

Eumelanin

Dark melanin responsible for tan, brown, and black skin.

Pheomelanin

Reddish-yellow melanin responsible for yellowish to reddish tones.

Cyanosis

Blueness due to oxygen deficiency.

Erythema

Redness due to increased blood flow to skin.

Pallor

Paleness due to decreased blood flow to skin.

Hematoma

Bruising; clotted blood under skin.

Albinism

White skin due to genetic lack of melanin.

Jaundice

Yellowing due to bilirubin in blood.

Friction ridges

Markings on the fingertips that leave oily fingerprints.

Freckles

Flat, melanized patch.

Mole

Elevated, melanized patch, often with hair.

Hemangiomas

Patches of discolored skin caused by benign tumors of dermal capillaries.

Accessory organs / appendages

Hair, nails, and cutaneous glands.

Hair and nails

Composed of mostly dead, keratinized cells.

Soft keratin

Makes up stratum corneum of skin.

Hard keratin

Makes up hair and nails.

Disulfide bridges

Make hair and nails tougher and more compact.

Hair / pilus

Slender filament of keratinized cells growing from a hair follicle.

Lanugo

Fine, downy, unpigmented hair that appears on the fetus in the last 3 months of development.

Vellus hair

Fine, pale hair that replaces lanugo by time of birth.

Terminal hair

Longer, coarser, more heavily pigmented hair.

Hair shaft

Portion of hair above the skin surface.

Hair root

Portion of hair below the skin surface.

Hair bulb

Dilated end of the hair root.

Dermal papilla

Bud of vascular connective tissue that provides nutrition to hair.

Hair matrix

Mitotically active cells immediately above the papilla; growth center for the hair.

Medulla

Core of loosely arranged cells and air spaces.

Cortex

Bulk of the hair; layers of elongated cells.

Cuticle

Outermost region of hair with thin, scaly cells that overlap like roof shingles.

Epithelial root sheath

Extension of the epidermis lying adjacent to hair root.

Bulge

Source of stem cells for follicle growth.

Connective tissue root sheath

Derived from dermis but a bit denser; surrounds epithelial root sheath.

Arrector muscle

Bundle of smooth muscle attaching follicle to dermis; contracts to make hair stand on end.

Piloerection

Hair standing on end.

Anagen

Growth stage of hair cycle; lasts 6 to 8 years.

Catagen

Degeneration stage of hair cycle; lasts 2 to 3 weeks.

Telogen

Resting stage of hair cycle; lasts 1 to 3 months.

Club hair

Hair with a hard knot at the base; easily pulled out by brushing.

Alopecia

Thinning of the hair, or baldness.

Pattern baldness / androgenic alopecia

Hair is lost unevenly rather than thinning uniformly.

Hirsutism

Excessive hairiness in areas not usually hairy.

Nails

Clear, hard derivatives of stratum corneum.

Nail plate

Hard part of nail.

Nail body

Visible attached part of the nail.

Nail root

Part of nail under overlying skin.

Nail fold

Surrounding skin that rises around the nail.

Nail groove

Space separating the nail fold from the margin of the nail plate.

Nail bed

Skin underlying the nail plate.

Hyponychium

Epidermis of nail bed.

Nail matrix

Growth zone at proximal end of nail.

Lunule

White area caused by thickness of nail matrix.

Cuticle / eponychium

Narrow zone of dead skin that overhangs proximal end of nail.

Apocrine sweat glands

Sweat glands in groin, anal region, axilla, areola, and beard area in men.

Sex pheromones

Chemicals that can influence behavior of others.

Bromhidrosis

Disagreeable body odor.

Eccrine sweat glands

Most numerous skin glands; produce watery perspiration that helps cool the body.

Myoepithelial cells

Contract and squeeze perspiration up the duct.

Acid mantle

Inhibits bacterial growth.