Chapter Five: Integumentary System (Openstax - Anatomy and Physiology BIO168)

Integumentary system

Most accessible organ system; accounts for approximately 16% of total body weight; surface area 1.5-2.0 m²

Cutaneous membrane

Skin component consisting of epidermis and dermis

Epidermis

Consists of stratified squamous epithelium; dominated by keratinocytes forming several layers called strata

Dermis

Consists of papillary layer of areolar tissue and reticular layer of dense irregular connective tissue

Accessory structures

Nerve fibers, corpuscles, exocrine glands, hair follicles, arrector pili muscles, arteries, veins, and lymph vessels forming cutaneous network

Hypodermis

Also called subcutaneous layer or superficial fascia; separates integument from fascia around deeper organs; NOT part of integument; contains adipose and areolar tissue

Thin skin

Covers most of body surface; contains four strata; about 0.08 mm thick

Thick skin

Occurs on palms and soles; possesses five strata; about 0.50 mm thick

Stratum basale

Deepest epidermal layer; single row of basal (germinative) cells undergoing rapid mitotic division; contains melanocytes and Merkel cells

Hemidesmosomes

Attach cells of stratum basale to basal lamina

Melanocytes

Produce melanin; located in stratum basale; 10-25% of cells in this layer

Melanin

Brown, yellowish-brown, or black skin pigment

Merkel cells

Sensitive to touch; release chemicals stimulating sensory nerve endings when compressed

Stratum spinosum

"Spiny layer"; 8-10 layers of keratinocytes bound by desmosomes and microfilaments of pre-keratin

Dendritic cells

Participate in immune response; stimulate defense against microorganisms and superficial skin cancers

Stratum granulosum

"Grainy layer"; 3-5 cell layers where keratinocytes become flattened and produce keratin and keratohyalin

Keratin

Tough, fibrous, water-resistant protein providing framework of hair, nails, and skin

Keratohyalin

Stored in granules in stratum granulosum

Stratum lucidum

Clear layer only in thick skin; cells are dead, flattened, and filled with keratin and keratohyalin

Stratum corneum

"Horny layer"; outermost layer; 15-30 layers of keratinized cells; accounts for up to three quarters of epidermal thickness

Keratinization

Formation of protective superficial layers of cells filled with keratin

Epidermal ridges

Extend into dermis adjacent to dermal papillae; increase surface area for attachment

Dermal papillae

Project upward to epidermis; small nipple-like projections for nutrient and binding support

Papillary layer

Superficial layer of dermis; highly vascularized areolar tissue; contains capillaries, lymphatic vessels, and sensory neurons

Reticular layer

Deep layer of dermis; dense irregular connective tissue; provides strength and flexibility

Lines of cleavage

Collagen and elastin fibers arranged in parallel bundles; clinically significant for wound healing and scarring

Skin color

Influenced by epidermal pigmentation and dermal circulation

Carotene

Orange-yellow pigment accumulating in epidermal cells; found in orange and yellow vegetables

Hemoglobin

Red pigment in red blood cells; bright red when bound to oxygen, darker red when oxygen is released

Flushed

Red skin appearance when body temperature rises and superficial blood vessels dilate

Cyanosis

Blue discoloration of skin due to poor circulation or insufficient oxygenation of blood

Hair follicles

Complex structure of epithelial cells and connective tissues responsible for hair formation

Hair bulb

Mass of epithelial cells at base of hair follicle surrounding hair papilla

Hair papilla

Peg of connective tissue containing capillaries and nerves

Root hair plexus

Sensory nerves surrounding hair bulb giving hair ability to detect touch

Arrector pili muscle

Bundle of smooth muscle cells that contract causing hairs to stand up

Hair shaft

Portion of hair extending through follicle and protruding above skin line

Hair root

Portion of hair located underneath skin

Cortex

Intermediate layer of hair containing thick layers of keratin giving stiffness

Medulla

Core of hair consisting of cells filled with soft keratin

Hair matrix

Multiple hair colors reflecting differences in hair structure

Nail body

Consists of dead, tightly compressed keratinocytes packed with keratin

Nail bed

Epidermis under nail body containing rapidly dividing cells

Nail root

Epidermal fold not visible from surface; anchors nail body

Free edge

Distal portion of nail continuing past nail bed

Eponychium

Portion of stratum corneum of nail root extending over exposed nail; cuticle

Lunula

Pale crescent-shaped area near root where dermal blood vessels are obscured

Sebaceous glands

Oil glands; simple alveolar glands found all over body except palms and soles; holocrine glands

Sebum

Mixture of triglycerides, cholesterol, proteins, and electrolytes secreted by sebaceous glands

Sweat glands

Sudoriferous glands distributed all over body except nipple, parts of external genitalia, and lips

Eccrine glands

Very numerous in palms, soles, and forehead; secrete hypotonic filtrate of blood by exocytosis; function in thermoregulation

Apocrine glands

Largely confined to axillary and anogenital areas; larger than eccrine; release secretions into hair follicles; begin functioning at puberty

Ceruminous glands

Modified apocrine glands lining external ear canal; secrete cerumen (earwax)

Mammary glands

Specialized apocrine sweat gland that secretes milk

Free nerve endings

Numerous unencapsulated nerve endings for pain and temperature detection

Meissner corpuscles

Receptors in dermal papillae responsible for detection of light touch

Pacinian corpuscles

Receptors in reticular layer of dermis responsible for detection of deep pressure and vibration

Thermoregulation

Skin regulates body temperature via vasodilation and vasoconstriction

Cholecalciferol

Vitamin D3 produced when epidermal cells convert cholesterol-related steroid upon UV exposure

Calcitriol

Hormone synthesized by kidneys from cholecalciferol; required for calcium and phosphorus absorption

Osteomalacia

Impaired bone growth and maintenance from inadequate calcitriol

Basal cell carcinoma

Most common skin cancer; originates in keratinocytes of stratum basale due to UV overexposure

Melanoma

Least common but most dangerous skin cancer; cancerous melanocytes grow rapidly and metastasize through lymphatic system

Squamous cell carcinoma

Originates in stratum spinosum; rarely metastasizes

Eczema

Allergic reaction manifesting as dry, itchy patches of skin

Acne

Occurs from overproductive, blocked sebaceous gland

First degree burn

Affects only epidermis

Second degree burn

Affects both epidermis and dermis

Third degree burn

Extends through epidermis and dermis to damage underlying tissue and nerve endings

Fourth degree burn

Includes damage to epidermis, dermis, muscle, and bone

Skin graft surgery

Required for full thickness burns that cannot be repaired by body

Scars

Collagen-rich skin formed after wound healing differing from normal skin

Keloids

Raised scars

Pressure ulcers

Areas exposed to prolonged pressure resulting in loss of blood flow and tissue necrosis

Stretch marks

Striae; result from skin stretched beyond normal capacity

Calluses

Form from areas of constant abrasion

Corns

Form from areas of constant abrasion

Solar lentigines

Pigment changes with age

Strata

Characteristic layered or stratified horny layers of epidermis

Cleavage lines

Linear collagen fiber bundles within dermis marking direction of maximal skin tension

Striae

Stretch marks; silvery-white scars from tearing of dermis during rapid skin stretching

Cutaneous network

Network of blood vessels marking boundary between dermis and hypodermis supplying skin

Melanosomes

Pigment-containing granules produced by melanocytes storing and transporting melanin to keratinocytes

The papillary layer of the dermis is most closely associated with which layer of the epidermis?

stratum basale

Langerhans cells are commonly found in the ________.

stratum spinosum

The papillary and reticular layers of the dermis are composed mainly of ________.

connective tissue

Which of the following is not a function of the hypodermis?

source of blood cells in the epidermis

In response to stimuli from the sympathetic nervous system, the arrector pili ________.

are responsible for goosebumps

The hair matrix contains ________.

a layer of basal cells

Sebaceous glands ________.

are associated with hair follicles

Similar to the hair, nails grow continuously throughout our lives. Which of the following is furthest from the nail growth center?

hyponychium

An individual using a sharp knife notices a small amount of blood where he just cut himself. Which of the following layers of skin did he have to cut into in order to bleed?

papillary dermis

As you are walking down the beach, you see a dead, dry, shriveled-up fish. Which layer of your epidermis keeps you from drying out?

stratum corneum

If you cut yourself and bacteria enter the wound, which of the following cells would help get rid of the bacteria?

Langerhans cells

Bedsores _____.

are preventable by eliminating pressure points

An individual has spent too much time sun bathing. Not only is their skin painful to touch, but small blisters have appeared in the affected area. This indicates that they have damaged which layers of skin?

epidermis and dermis

Squamous cell carcinomas are the second most common of the skin cancers and are capable of metastasizing if not treated. This cancer affects which cells?

keratinocytes of the stratum spinosum