Integumentary System

Skin, Hair, Nails & Glands

By the numbers…

• Accounts for 3% of total body tissue & 16% of total body mass

Overview

• 2 major components– Cutaneous membrane (epidermous & dermis)– Accessory structures (hair, nails & exocrine

glands)

• Does not function in isolation– Extensive network of blood vessels & sensory

receptors in dermis– Deep to the dermis, the subcutaneous

(hypodermis) layer is the interwoven CT that connects the skin to muscle & bone

Organ/ Component Primary Function

Cutaneous Membrane -Epidermis

-Dermis

Covers surface; Protects deeper tissues

Nourishes epidermis; Provides strength; Contains glands

Hair Follicles

Hairs

Sebaceous glands

Produce hair; Innervation provides sensation

Provides protection for head

Secretes lipid coating that lubricates hair shaft & epidermis

Sweat Glands Produces perspiration for evaporative cooling

Nails Protects & stiffens distal tips of digits

Sensory Receptors Provides sensation of touch, temperature, pressure & pain

Subcutaneous Layer Stores lipids; Attaches skin to deeper structures

Functions

• PROTECTION of underlying tissues & organs against impact, fluid loss & chemical/biological attack

• EXCRETION of salts, H2O & organic wastes• MAINTANENCE of body temp by insulation

or evaporation• SYNTHESIS of vitamin D, which is necessary

for calcium absorption• STORAGE of lipids for energy & insulation• DETECTION of touch, pressure, pain & temp

Epidermis

• Stratified squamous tissue• Avascular• Dominated by KERATINOCYTES

(contain protein keratin…hardener)• Thin skin (most of body surface) 4

layers & as thick as a plastic sandwich bag

• Thick skin (palms & soles) 5 layers & as thick as a standard paper towel

Layers of Epidermis

• 2 names– Stratum (pl. strata) means layers– 2nd name refers to the function or appearance

• In order, from superficial to deep:– Stratum corneum– Stratum lucidum– Stratum granulosum– Stratum spinosum– Stratum basale (germinitivum)

• “Come, Let’s Get Sun Burned”

Stratum Basale

• Location of mitosis (stem cells) where new cells are produced & pushed to the surface to replace dead ones

• Contain Merkel cells which are sensitive to touch• Contain Melanocytes which produce brown tones

& is responsible for skin tones• Epidermal ridges & dermal projections (papillae)

– The contours of the skin follow these ridge patterns (loops & whorls seen on palms & soles…fingerprints)

– Unique to every individual & do not ever change

Stratum Spinosum

• Cells are far enough away from dermal blood vessels that they begin to compact & die

• Consist of 8-10 layers of keratinized cells attached by desmosomes (cell glue)

• Appear “spiny” • Contains Langerhans cells, which assist in

immune response by stimulating a defense against– Microorganisms that manage to penetrate the

superficial layers– Superficial cancer cells

Stratum Granulosum

• Most have stopped dividing at this layer & begins to produce large amounts of keratin & the cells die

• Has a “grainy” appearance

Stratum Lucidum

• Only found in thick skin (palms & soles)

• Means “clear layer”• Thickened skin due to additional

wear & tear• Flattened, densely packed & filled

with keratin

Stratum Corneum

• Dead cells are filled with keratin & are so compact, they form sheets

• Cells are tough & offer protection• Cornification means keratinized• Replace cells worn away by wear &

tear• It takes 15-30 days for cells to move

from S. basale to S. corneum

S. Corneum (cont’d)

• Layer is water resistant, but not water proof– Insensible perspiration: unable to feel

water loss– Sensible perspiration: very aware

(sweating)

S. Corneum (cont’d)

• Freshwater exposure – Water is HYPOTONIC (less dissolved minerals

than body fluids) so H2O moves into the cells, causing them to swell (pruney fingers & toes when in the tub or pool for a long time)

• Saltwater exposure– Water is HYPERTONIC (more dissolved

minerals than body fluids) so H2O moves out of the cells, causing them to shrink (prolonged exposure to saltwater can lead to dehydration)

• Hypotonic (freshwater)

• Hypertonic (saltwater)

Concept Check

Dandruff is caused by excessive shedding of cells from the outer layer of skin on the scalp. Thus dandruff is composed of cells from which epidermal layer?

Stratum corneum

Concept Check

Why do paper cuts hurt so bad but do not bleed?

Because the epidermis is avascular (no blood vessels) but innervated (sensory

receptors)

Concept Check

A splinter that penetrates to the 3rd layer of the epidermis of the palm is lodged in which layer?

Stratum granulosum

Concept Check

Why does swimming in fresh water for an extended period cause epidermal swelling?

Freshwater is hypotonic so water moves into the cells, causing swelling

Concept Check

Some criminals sand or cut skin off the tips of their fingers so as not to leave recognizable fingerprints. Would this practice permanently remove fingerprints? Why or why not?

No, because cells are replaced every 15-30 days & the patterns that cause

fingerprints are genetic & never change

Epidermal Pigmentation(Skin Color)

• Epidermis contains 3 pigments: Carotene, Melanin & Hemoglobin

• Carotene is an orange-yellow pigment–Most apparent in light-skinned humans– Accumulates in fatty tissues in deep

dermis & hypodermis

Melanin

• Brown, yellow-brown, or black pigment produced in melanocytes– More dominant in dark-skinned humans– Highest concentration found in cheeks, forehead, nipples

& genitals– Freckles are small pigmented areas– Melanocytes are stimulated by UV light & increase

melanin production

• Melanin in kerotinocytes protects skin from harmful effects of the sun (UV radiation)

• Some sunlight is beneficial because it stimulates the production of a compound required for calcium absorption

Hemoglobin

• Red blood cells contain hemoglobin, which binds & transports O2 in the bloodstream– When bound to O2 = Bright red color

• In light-skinned people…– Flushed or red when blood supply is increased

(embarrassed, over heated, etc)– Pale or white when blood supply is reduced

(scared or nervous)– Cyanotic or blue when reduced blood supply is

prolonged (extreme cold, cardiovascular or respiratory disorders, etc)

Skin Conditions

Jaundice– Liver is unable to excrete bile so a

yellowish pigment accumulates in body fluids

– Skin & whites of the eyes become yellow

Vitiligo– Individuals lose their melanocytes– 1% of population, and often found in

people with thyroid disorders or when immune system malfunctions & attacks melanoctyes

– Cosmetic, especially for people with dark skin

Tumors of the Skin

• Benign, e.g. warts• Cancer – associated with UV exposure

(also skin aging)– Aktinic keratosis - premalignant– Basal cell - cells of stratum basale– Squamous cell - keratinocytes– Melanoma – melanocytes: most dangerous;

recognition:• A - Asymmetry• B - Border irregularity• C - Colors• D - Diameter larger than 6 mm

Melanoma

Concept Check

Why does exposure to sunlight or sunlamps darken skin?

Because UV rays stimulate melanocytes & increase production of melanin, resulting in a darker skin tone

Concept Check

Why does the skin of a fair skinned person appear red during exercise in hot weather?

Because oxygenated blood is increased to the surface to allow for heat loss

Concept Check

In some cultures, women must be covered completely except for their eyes, when they go outside. Explain why these women exhibit a high incidence of problems with their bones?

Without sun exposure on the skin, the individual cannot produce the compound necessary to absorb calcium, which is needed for strong bones

Next… the DERMIS

Dermis• Strong, flexible connective tissue: – Your “hide”

• Cells: – Fibroblasts, macrophages, mast cells, WBCs

• Fiber types: – Collagen, elastic, reticular

• Rich supply of nerves and vessels• Critical role in temperature regulation (the

vessels)• Two layers – Papillary – Areolar CT (loose), capillaries,

lymphatics, & sensory neurons– Reticular – “reticulum” (network) of collagen

& elastic fibers

*Dermis layers

*

*

*Dermal papillae

• Presence of Collagen & Elastic fibers permit stretching & recoil (skin turgor = elasticity)– Very strong – Resist stretching – Easily bent or twisted

• Water content helps maintain flexibility & resilience – Dehydration

• Extensive distortion (pregnancy or extreme weight gain) can result in stretch marks

• With age & environmental conditions, skin loses elasticity wrinkles result– Retin-A (derivative of Vitamin A) can be applied

as a cream or a gel to increase blood supply & stimulate dermis repair (reduces wrinkles)

Concept Check

Where are the capillaries & sensory neurons that supply the epidermis located?

Papillary layer of the dermis

Concept Check

What accounts for the ability of the dermis to undergo repeated stretching?

Presence of elastic fibers (skin turgor)

Hypodermis

• “Hypodermis” (Greek) = below the skin

• “Subcutaneous” (Latin) = below the skin– Also called “superficial fascia”“fascia” (Latin) =band; in anatomy: sheet of

connective tissue

• Fatty tissue which stores fat and anchors skin (areolar tissue & adipose cells)

• Different patterns of accumulation (male/female)

Clinical Note

• Accumulation of excessive amounts of adipose tissue increases the risk of diabetes, stroke & other serious conditions

• Liposuction is a “quick fix” but it can be dangerous. Risks include– Anesthesia– Bleeding (adipose is highly vascular)– Infection– Fluid loss

Skin appendages

• Derived from epidermis but extend into dermis

• Include–Hair and hair follicles– Sebaceous (oil) glands– Sweat (sudoriferous) glands–Nails

Hair

• Function– Warmth – less in man than other mammals– Sense light touch of the skin– Protection - scalp

• Root hair plexus– Sensory nerves surround the base of the hair– Feel every movement around every hair (early warning)

• Arrector pili muscles– Contracts & pulls on follicle, causing hair to stand erect

• Fear or rage• In our ancestors & other mammals, this makes animal appear

bigger to a potential enemy• Insulates us when cold (traps heat close to body)…Goosebumps

Hair Structure & Production

• Hair root– Portion that anchors the hair to the skin

• Hair shaft– Portion that extends from the body (exposed part)

• Hair bulb– Mass of epithelial cells that form a cap (where hair

growth begins)

• Hair papilla– Peg of connective tissue containing capillaries & nerves

surrounded by bulb

• Hair matrix– Layer of basal “daughter” cells are produced & pushed to

the surface

Hair and hair follicles: complexDerived from epidermis and dermis

Everywhere but palms, soles, nipples, parts of genitalia

*“arrector pili” is smooth muscle

*

Hair papilla is connective tissue______________

Hair bulb: epithelial cells surrounding papilla

• Core Medulla– Closest to center of matrix

• Intermediate layer Cortex– Farther from the center

• Edge Cuticle– Surface of hair

• As cell division continues, the hair gets longer & keratinized (cells are dead)

• Types of hair– Vellus: fine, short hairs (“peach fuzz”)

• Present at armpits, pubic area & limbs until puberty

– Terminal: longer, deeply pigmented, courser hair (eyebrows & eyelashes)

• Hair growth: averages 2 mm/week– Active: growing

– Resting phase then shed

• Hair loss– Thinning – age related

– Male pattern baldness

• Hair color– Amount of melanin for black or brown; distinct form of

melanin for red

– White: decreased melanin and air bubbles in the medulla

– Genetically determined though influenced by hormones and environment

Concept Check

What happens when the arrector pili muscles contract?

Goosebumps

Concept Check

Once a burn on the forearm that destroys the epidermis and extensive areas of the deep dermis heals, will new hair grow in the affected area?

Hair is a derivative of epidermis but the follicle is in the dermis. Once

destroyed, hair will not regrow

Sebaceous glands

• Oil glands (Holocrine glands) that discharge an oily secretion onto hair follicles– Secreted product is called

SEBUM

• Prohibits the growth of bacteria, lubricates & protects the keratin of the hair shaft & conditions the surrounding skin

Sudoriferous (Sweat) Glands

• Apocrine glands – Produce a sticky, cloudy & potentially smelly

(odorous) secretion on to hair follicles– Armpits– Enlarge & increase secretions during puberty

• Merocrine glands (or eccrine glands)– More widely distributed– Most on palms & soles– Function in cooling surface of skin to reduce

body temperature, excreting H2O & electrolytes, providing protection from environmental hazards

Sweat glands• Entire skin

surface except nipples and part of external genitalia

• Prevent overheating

• Humans most efficient (only mammals have)

• Produced in response to stress as well as heat

Other Glands

• Mammary glands– Breasts– Development controlled by sex hormones &

pituitary gland

• Ceruminous glands– Modified sweat glands– Secretions combine with those of sebaceous

glands, forming a mixture called cerumen– Together with tiny ear hairs along the ear

canal, trap foreign particles, preventing them from reaching the eardrum

Concept Check

What are the functions of sebaceous secretions?

Sebum lubricates & protects the hair shaft, lubricates & conditions the surrounding skin, & inhibits growth of bacteria

Concept Check

Deodorants are used to mask the effects of secretions from which type of skin gland?

Apocrine sweat glands

Concept Check

Which type of skin gland is most affected by the hormonal changes that occur during puberty?

Apocrine sweat glands enlarge & increase secretions

Nails

• Made of hard keratin• Corresponds to hooves and claws• Grows from nail matrix

Disorders of the integumentary system

• Burns– Threat to life• Catastrophic loss of body fluids• Dehydration and fatal circulatory shock• Infection

– Types• First degree – epidermis: redness (e.g.

sunburn)• Second degree – epidermis and upper dermis:

blister• Third degree - full thickness

BurnsFirst-degree(epidermis only; redness)

Second-degree(epidermis and dermis,with blistering)

Third-degree(full thickness, destroying epidermis, dermis, often part of hypodermis)

How a wound heals

See Textbook Pages 170-171