Anatomy Unit 3

Integumentary System

The organ system consisting of the skin and its accessory structures, including hair, nails, and glands.

Protection

Protects against abrasion and UV light, blocks microorganisms, and reduces water loss.

Sensation

Contains receptors that detect temperature, pressure, pain, and touch.

Production

Produces vitamin D, keratin, and melanin.

Temperature Regulation

Helps maintain body temperature through sweating and changes in blood flow.

Excretion

Removes small amounts of water, salts, and urea through sweat.

Epidermis

The superficial layer of the skin made of epithelial tissue; it lacks blood vessels and nerves.

Dermis

The deeper skin layer made mainly of connective tissue; contains blood vessels, nerves, glands, and hair follicles.

Hypodermis

The subcutaneous layer beneath the skin, made of loose connective tissue and adipose tissue; it is not technically part of the skin.

Epidermis vs. Dermis vs. Hypodermis

Epidermis: epithelial tissue. Dermis: connective tissue. Hypodermis: loose connective and adipose tissue.

Keratinocytes

The most common epidermal cells (about 90%); produce keratin.

Melanocytes

Epidermal cells (about 8%) that produce melanin and transfer it to keratinocytes.

Langerhans Cells

Epidermal immune cells that act as phagocytic macrophages and help defend against invading microbes.

Merkel Cells

Cells in the deepest epidermal layers that connect with sensory neurons and form touch receptors called Merkel discs.

Keratin

A tough protein produced by keratinocytes that accumulates in epidermal cells and helps form a hardened, waterproof protective layer.

Keratinization

The process in which newly formed epidermal cells move upward, accumulate keratin, die, and eventually become part of the outer protective layer.

Desquamation

The shedding of dead cells from the stratum corneum.

Apoptosis

Programmed cell death; epidermal cells lose their nuclei and organelles as they move toward the surface.

Epidermal Turnover Time

The process from stem cell formation to shedding takes approximately 40–55 days.

Melanin

A pigment that contributes to skin, hair, and eye color and absorbs UV radiation.

Function of Melanin

Helps protect the DNA in keratinocyte nuclei by absorbing UV radiation.

Lamellar Granules

Structures in keratinocytes that release a lipid-rich, waterproof sealant into the spaces between cells.

Collagen

A protein fiber in the dermis that provides strength and structural support.

Elastin

A protein fiber in the dermis that allows skin to stretch and recoil.

Fibroblasts

Cells in the dermis that produce collagen and elastic fibers.

Macrophages

Immune cells in the dermis that help remove foreign material and damaged cells.

Adipocytes

Fat-storing cells found in the dermis and hypodermis.

Stratum Basale

The deepest epidermal layer; a single row of columnar keratinocytes with stem cells that produce new keratinocytes.

Stratum Basale: Cell Types

Contains stem cells, melanocytes, Merkel cells, and Langerhans cells.

Stratum Spinosum

The layer above the basale; contains 8–10 layers of closely connected, many-sided keratinocytes.

Stratum Spinosum: Important Feature

The most common location of Langerhans cells.

Stratum Granulosum

Contains 3–5 layers of flattened keratinocytes that undergo apoptosis and accumulate keratin.

Stratum Granulosum: Waterproofing

Cells release lipid-rich secretions that enter the spaces between cells and waterproof the skin.

Stratum Lucidum

A layer found only in thick skin; contains 3–5 layers of flat, clear, dead keratinocytes with large amounts of keratin.

Stratum Corneum

The outermost epidermal layer; contains approximately 25–30 layers of dead, flattened keratinocytes.

Stratum Corneum: Function

Provides a protective barrier and is continually shed and replaced.

Epidermal Layers: Deepest to Superficial

Stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum.

Stratum Lucidum Location

Found only in thick skin.

Papillary Region

The superficial upper 20% of the dermis; contains dermal papillae and sensory nerves.

Dermal Papillae

Small upward projections of the dermis that extend into the epidermis.

Papillary Ridges

Ridges formed by dermal papillae that create fingerprints on fingers and toes.

Meissner Corpuscles

Touch receptors located in some dermal papillae that detect light touch.

Reticular Region

The deep lower 80% of the dermis; made of dense irregular connective tissue.

Reticular Region: Structures

Contains collagen and elastic fibers, adipose cells, hair follicles, nerves, capillaries, sebaceous glands, and sudoriferous glands.

Papillary vs. Reticular Dermis

Papillary: upper 20%, dermal papillae, sensory nerves. Reticular: lower 80%, dense irregular connective tissue, follicles, glands, nerves, and capillaries.

Striae

Stretch marks caused by small tears in the dermis due to extreme stress, such as obesity or pregnancy.

Hypodermis Composition

Loose connective tissue and adipose tissue.

Hypodermis Function

Attaches the dermis to underlying tissues and organs.

Hypodermis: Sensory Receptors

Contains lamellated (Pacinian) corpuscles that detect pressure.

Hair

Composed of fused columns of dead, keratinized cells.

Hair Shaft

The superficial portion of hair that projects through the epidermis above the skin surface.

Hair Root

The portion of hair below the skin surface that penetrates into the dermis.

Hair Follicle

A structure that surrounds the hair root and consists of epidermal cells covered by connective tissue.

Hair Root Plexus

Nerve endings surrounding hair follicles that detect touch and hair movement.

Hair Bulb

The enlarged base of the hair follicle.

Hair Papilla

An indentation in the hair bulb containing blood vessels that provide nutrients to growing hair.

Hair Matrix

A region of cells in the hair bulb that divides to produce new hair cells.

Arrector Pili

A bundle of smooth muscle attached to the hair follicle; contracts and makes hairs stand on end.

Hair Growth

New cells are added at the base by the hair matrix, become keratinized, and die as the hair grows.

Nail Plate

The visible portion of the nail, made of dead cells filled with keratin.

Nail Bed

The skin located underneath the nail plate.

Distal Edge

The part of the nail plate that extends beyond the end of the finger or toe.

Nail Root

The portion of the nail that is not visible.

Nail Matrix

The area containing nerves, lymph vessels, and blood vessels that produces cells that become the nail plate.

Nail Growth

New nail cells form in the matrix; nails grow approximately 1 mm per week.

Cuticle (Eponychium)

The stratum corneum tissue covering the base of the nail.

Lunula

The whitish, crescent-shaped area near the nail root.

Sebaceous Glands

Oil glands typically connected to hair follicles that secrete sebum.

Sebum

An oily substance that prevents hair from drying out, keeps skin soft, and reduces water loss.

Sudoriferous Glands

Sweat glands that help regulate body temperature and eliminate wastes.

Ceruminous Glands

Glands found in the outer ear canal that contribute to the production of earwax.

Cerumen

Earwax formed by the combined secretions of ceruminous and sebaceous glands.

Cerumen Function

Works with hairs in the outer ear canal to create a sticky barrier against foreign bodies.

Sebaceous vs. Sudoriferous vs. Ceruminous Glands

Sebaceous: sebum/oil. Sudoriferous: sweat. Ceruminous: contributes to earwax.

Apocrine Sweat Glands

Sweat glands found mainly in the armpit and pubic regions that open into hair follicles.

Apocrine Glands: Activity

Become active at puberty and can be stimulated by emotional stress or sexual activity.

Apocrine Glands: Secretion

Produce a sticky, viscous secretion.

Eccrine Sweat Glands

Sweat glands distributed throughout the skin that open onto the surface through sweat pores.

Eccrine Glands: Secretion

Produce a more watery secretion than apocrine glands.

Eccrine Glands: Activity

Function throughout life and help regulate body temperature.

Apocrine vs. Eccrine Glands

Apocrine: armpit/pubic regions, open into follicles, active at puberty, sticky secretion. Eccrine: widespread, open onto skin pores, watery secretion, function throughout life.

Meissner Corpuscles (Mechanoreceptors)

Detect pressure, light touch, and low-frequency vibration or flutter; found in the upper dermis and project into the epidermis.

Pacinian Corpuscles (Mechanoreceptors)

Detect deep pressure and painful squeezes; found deep in the dermis and hypodermis.

Ruffini Endings (Mechanoreceptors)

Detect skin stretch and heat; found deep in the dermis.

Merkel Discs (Mechanoreceptors)

Detect light touch and edges; have small, well-defined receptive fields and are found near the basal epidermis.

Thermoreceptors

Sensory receptors that detect heat and cold; found in the dermis.

Krause End Bulbs

Cold receptors found in the dermis.

Ruffini Endings and Temperature

Detect warmth.

Nociceptors

Free nerve endings that detect pain; found in the dermis.

Mechanoreceptors

Receptors that respond to mechanical stimuli such as touch, pressure, vibration, and stretch.

Signal Transduction

The process by which sensory receptors convert external stimuli into electrical nerve impulses.

Signal Transduction: Basic Process

A stimulus changes a receptor's nerve endings and membrane permeability, producing a receptor potential that can trigger nerve impulses to the central nervous system.

Meissner vs. Pacinian Corpuscles

Meissner: light touch and low-frequency vibration, upper dermis. Pacinian: deep pressure, deep dermis.

Merkel vs. Meissner Corpuscles

Merkel: light touch and edges, basal epidermis. Meissner: light touch and flutter, upper dermis.

Sources of Skin Color

Melanin, carotene, and hemoglobin.

Eumelanin

The most common form of melanin; produces black and brown coloration.

Pheomelanin

A form of melanin that produces red coloration.

Carotene

A yellowish pigment that accumulates in lipids in the stratum corneum and fat cells of the dermis and hypodermis.

Hemoglobin

A pigment in blood flowing through dermal vessels that gives skin a pinkish tint.

UV Radiation and Melanin

Exposure to UV radiation increases melanin production.