Chapter 5: the integumentary system

integumentary system

Consists of the skin, hair, nails, sweat glands and sebaceous glands

Purpose of integumentary system

-Helps the body maintain its temperature

-Converts inactive vitamin D to its active form

-Provides sensory information

-Helps maintain homeostasis

regions of the skin

epidermis, dermis, hypodermis

Epidermis

superficial region, consists of epithelial tissue and is avascular

Dermis

underlies epidermis, consists of fibrous connective tissue and is vascular

Hypodermis

subcutaneous layer deep to the dermis, not a part of skin but composed of areolar and adipose tissue

Cells of the Epidermis

keratinocytes, melanocytes, dendritic cells, merkel/tactile cells

Keratinocytes of epidermis

-Produce fibrous keratin (protein that gives skin its protective properties)

-Major cells of epidermis

-Tightly connected by desmosomes

-Millions slough off every day

Melanocytes of epidermis

-Spider-shaped cells located in deepest epidermis

-Produce pigment melanin, which is packaged into

melanosomes

-Melanosomes are transferred to keratinocytes, where they protect nucleus from UV damage

dendritic cells of epidermis

-Langerhans cells

-Star-shaped macrophages that patrol deep epidermis

-Are key activators of immune system

tactile cells of epidermis

-Merkel cells

-Sensory receptors that sense touch

Types of skin

thin skin and thick skin

thin skin (hairy)

covers all body regions except the palms, palmar surfaces of digits, and soles

thick skin (hairless)

covers the palms, palmar surfaces of digits, and soles

-High abrasion areas

-Cells change by going through apoptosis

-Dead cells slough off as dandruff and dander

layers of epidermis

stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum

stratum basale

-Deepest layer, firmly attached to dermis

-Single row of cuboidal or columnar actively dividing stem

cells

-One daughter cell migrates to the skin surface and dies

-Produces new keratinocytes; melanocytes and tactile epithelial cells

-Other daughter cell remains in stratum basale as a stem cell

stratum spinosum

-Prickly layer, several cells thick

-Cells contain weblike system of intermediate pre-keratin

filaments attached to desmosomes

-Allows them to resist tension and pulling

-Scattered among keratinocytes are abundant melanosomes and dendritic cells

stratum granulosum

-Granular layer

-Four to six layers of flattened cells in which organelles

are beginning to degenerate

-Cells above this layer die

-Too far from dermal capillaries to survive

stratum lucidum

-Clear layer

-Found only in thick skin

-Consists of thin, translucent band of two to three rows of clear, flat, dead keratinocytes

-Lies superficial to the stratum granulosum

stratum corneum

-Cornified layer

-20-30 rows of flat, anucleated, keratinized dead cells

-3⁄4 epidermal thickness

function:

-Protect deeper cells from the environment

-Prevent water loss

-Protect from abrasion and penetration

-Barrier against biological, chemical, and physical assaults

Dermis

-Strong, flexible connective tissue

-Made of collagen and elastin fibers

-Includes nerves, blood vessels, and lymphatic vessels, hair follicles, oil glands, and sweat glands

-Cells found in the dermis include fibroblasts, macrophages, and occasionally mast cells and white blood cells

layers of dermis

papillary layer and reticular layer

papillary layer

-Superficial layer of areolar connective tissue consisting of loose, interlacing collagen and elastic fibers and blood vessels

-Loose fibers allow phagocytes to patrol for microorganisms

-Dermal papillae: superficial region of dermis that sends fingerlike projections up into epidermis

-Contains capillary loops, free nerve endings, and touch receptors (tactile corpuscles, also called Meissner’s corpuscles)

friction ridges

-In thick skin, dermal papillae lie on top of dermal ridges, which give rise to epidermal ridges

-Collectively ridges are called friction ridges

-Enhance gripping ability

-Contribute to sense of

touch

-Sweat pores in ridges leave unique fingerprint pattern

reticular layer

-~80% of dermal thickness

-Coarse, dense fibrous connective tissue

-Contains elastic fibers (stretch) and collagen fibers (strength)

-Binds water and hydrates skin

-Cutaneous plexus: network of blood vessels between

reticular layer and hypodermis

-Extracellular matrix contains pockets of adipose cells, hair follicles, and glands

tension lines

-Caused by many collagen fibers running parallel to skin surface

-Externally invisible Important to surgeons because incisions parallel to cleavage lines heal more readily

flexure lines

-Dermal folds at or near joints

-Dermis is tightly secured to deeper structures

-Skin's inability to slide easily for joint movement causes deep creases

-Visible on hands, wrists, fingers, soles, toes

skin tears and abrasions

-Extreme stretching of skin can cause dermal tears, leaving silvery white scars called striae “Stretch marks”• -Acute, short-term traumas to skin can cause blisters

-Fluid-filled pockets that separate epidermal and dermal layers

Burns

-tissue damage caused by excessive heat, electricity, radioactivity, or corrosive chemicals that denature (break down) the proteins in the skin cells

-Graded according to their severity

first degree burn

-Epidermal damage only, localized redness, edema (swelling), and

pain

second degree burn

-Epidermal and upper dermal damage (partial thickness burn),

blisters

third degree burn

-Entire thickness of skin involved (full-thickness burns)

-Skin colour turns gray-white, red, or blackened

-No edema and area is not painful because nerve endings are destroyed

-Skin grafting usually necessary

critical burns

->25% of body has second-degree burns• ->10% of body has third-degree burns

-Face, hands, or feet bear third-degree burns

-Treatment includes:• Debridement (removal) of burned skin

-Antibiotics

-Temporary covering

-Skin grafts

pressure ulcer

-When shedding of epithelium caused by a deficiency of blood flow to tissues occurs, pressure ulcers can develop

skin colour pigments

melanin, carotene, hemoglobin

Melanin

-Only pigment made in skin; made by melanocytes

-Made from amino acid tyrosine by tyrosinase

-Packaged into melanosomes that are sent to shield DNA of keratinocytes from damaging UV sunlight

-Skin color differences are due to amount and form of melanin

-Pheomelanin (yellow to red)

-Eumelanin (brown to black)

-Freckles and pigmented moles are local accumulations of melanin

pheomelin

causes yellow to red pigmentation

Eumelanin

causes brown to black pigmentation

Sun damage

-Elastic fibers clump, causing skin to become leathery

-Can depress immune system and cause alterations in DNA that may lead to skin cancer

-UV light destroys folic acid

-Photosensitivity is increased reaction to sun

Carotene

-Yellow to orange pigment

-Most obvious in palms and soles• -Accumulates in stratum corneum and hypodermis

-Can be converted to vitamin A for vision and epidermal health

Hemoglobin

-Pinkish hue of fair skin is due to lower levels of melanin

-Red blood cells in capillaries

cyanosis

blue colour, indicates low oxygenation of

hemoglobin

pallor

pale colour, indicates anemia, low blood pressure, fear, anger

erythema

red colour, indicates fever, hypertension, inflammation, allergy

jaundice

yellow cast, indicates liver disorders

bruises

-Ecchymoses or hematomas, clotted blood beneath skin • --As clot is broken down, colour of bruise changes

-Brown or black “necklace” or bruises• -Hyperpigmented dark areas in axillae and around neck

-Sign of insulin resistance and elevated blood glucose levels

Albinism

-the inherited inability to produce melanin

-Complete or partial absence of pigment in the skin,

hair, and eyes

vitiligo

-a chronic disorder, partial or complete loss of melanocytes from patches of skin producing irregular white spots

-Immune system malfunction in which antibodies attack melanocytes.

hair

-Also called pili: flexible strands of dead, keratinized cells

-Produced by hair follicles

-None located on palms, soles, lips, nipples, and portions of external genitalia

functions of hair

-Warn of insects on skin

-Hair on head guards against physical trauma

-Protect from heat loss

-Shield skin from sunlight

components of hair

-The shaft (above the skin surface)

-The follicle (below the level of the skin)

-A root that penetrates into the dermis

Hair Shaft Structure

1.Medulla: central core of large cells and air spaces

2.Cortex: several layers of flattened cells surrounding

medulla

3.Cuticle: outer layer consisting of overlapping layers of single cells

structure of hair follicle

extends from epidermal surface to dermis

hair bulb

expanded area at deep end of follicle

hair follicle receptors

sensory nerve endings that wrap around bulb

hair matrix

actively dividing area of bulb that produces hair cells, pushes old cells upward

arrector pili

small band of smooth muscle attached to follicle, "goose bumps"

hair papilla

dermal tissue containing a knot of capillaries that supplies nutrients to growing hair

components of hair follicle wall

-Peripheral connective tissue sheath

-Derived from dermis• -Also called fibrous sheath

-Glassy membrane: thickened basal lamina -Epithelial root sheath

-Derived from epidermis

hair growth

growth stage, regression stage, resting stage

growth stage of hair growth

cells of matrix divide

regression stage of hair growth

hair moves away from blood supply in papillary and follicle atrophies

resting stage of hair growth

old hair root falls out; new growth begins

Types of hair

lanugo, vellus, terminal

Lanugo hair type

Mostly gone at birth, sign of AN (fine soft hair)

terminal hair type

long, coarse, heavily pigmented hairs

villus hair type

short, fine and pale hairs

hirsutism

-excessive hair growth

-caused by excess production of male hormones

alopecia

hair thinning, and spot baldness, more common after age 40

baldness

Genetically determined and sex-influenced condition (X-linked)

male pattern baldness

caused by follicular response to DHT (dihydrotestosterone)

Telogen effluvium

abrupt hair thinning caused by an abundance of hair follicles entering resting phase at same time

Nails

-Scale-like modifications of epidermis that contain hard keratin

-Act as a protective cover for distal, dorsal surface of fingers and toes

-Consist of free edge, nail plate, and root

nail bed

epidermis underneath keratinized nail plate

nail matrix

thickened portion of bed responsible for nail growth

nail structure

nail folds, eponychium, hyponychium

nail folds

skin folds that overlap border of nail

Eponychium

nail fold that projects onto surface of nail body. Also called cuticle

Hyponychium

area under free edge of plate that accumulates dirt

• Lunule: thickened nail matrix, appears white

yellow appearance of nails

respiratory or thyroid gland disorder

thickened yellow nails

fungal infection of the nail

Koilonychia

an outward concavity of nail indicates iron deficiency, "spoon nail"

Beau's lines

horizontal lines across nails, indicator of diabetes, heart attack, or cancer

Skin glands

sebaceous glands, sudoriferous glands, ceruminous glands

sebaceous glands

-In the dermis

-Widely distributed, except for thick skin of palms and soles

-Most develop from hair follicles and secrete into hair follicles

-Relatively inactive until puberty

-Stimulated by hormones, especially androgens

-Secrete sebum: oily holocrine secretion that has bactericidal (bacteria-killing) properties

acne

infectious inflammation of sebaceous glands, results pustules or cysts (pimple)

combination of dead skin cells, oil and sebum

whitehead

blocked sebaceous gland

blackhead

open, oxidized secretion in sebaceous glands

Seborrahea

overactive sebaceous glands in infants, called cradle cap

sweat glands

-Called sudoriferous glands

-Regulate body temperature, remove waste, stimulated during

emotional stress

-On all skin surfaces except nipples and parts of external genitalia

-Contain myoepithelial cells that contract to force sweat into ducts

Two types of sweat glands

eccrine and apocrine

eccrine sweat glands

-Most prevalent

-Abundant on palms, soles, and forehead

-Ducts connect to pores

-Secretes sweat or perspiration into surface of epidermis

-99% water, salts, vitamin C, antibodies, antimicrobials, metabolic wastes

-Controlled by sympathetic nervous system

-Function in thermoregulation

apocrine sweat glands

-Only found in hairy areas (axillary and anogenital)

-Secrete sweat with lipids and proteins into hair follicle

-Bacteria break down sweat, leading to body odor

-Larger than eccrine sweat glands with ducts emptying into hair follicles

-Begin functioning at puberty

modified apocrine glands

ceruminous glands and mammary glands

ceruminous glands

lining of external ear canal; secrete cerumen (earwax)

mammary glands

breast; produce and secrete milk

Functions of the skin

1. Protection

2. Body temperature regulation

3. Cutaneous sensations

4. Metabolic functions

5. Blood reservoir

6. Excretion of wastes

protection

Skin is exposed to microorganisms, abrasions, temperature extremes, and harmful chemicals

Acts as a barrier:

1. Chemical barrier 2. Physical barrier 3. Biological barrier

chemical barriers

-Skin secretes many chemicals, such as:• -Sweat, which contains antimicrobial proteins • -Sebum and defensins, which kill bacteria• -Cells also secrete antimicrobial defensin

-Acid mantle: low pH of skin retards bacterial multiplication

-Melanin provides a chemical barrier against UV radiation damage

acid mantle

low pH of skin retards bacterial multiplication