Chapter 5

The Integumentary System

The largest organ in the body

(~18 sq. feet)

Cool facts about the skin

• There are approximately 19,000,000 skin cells on every square inch of your body

• Millions of skin cells are rubbed off daily

• You have over 2 million sweat glands

• All sweat gland tubules in the body would stretch into 6 miles of tubes

• Amount of sweat can vary from 100 to 8,000 mL/day

• Fastest growing hair is the beard

Functions of the skin

• Protection

– barrier between the internal and external environment

• Water Proofing and prevents water loss

• Regulates body temperature

• Sensation

– nerve endings that react to heat, cold, touch, pressure, vibration, and tissue injury

More functions….

• Excretion

– Through perspiration

• Production of Vitamin D

• Insulation and Cushion

• Contributes to skin color - Melanin

Skin Layers

• Superficial to Deep

– Epidermis • Stratified squamous

• Contains no blood vessels

– Dermis • Dense Irregular CT

• Contains blood vessels

– Hypodermis • Adipose

• Contains blood vessels

Epidermis

Characteristics

• Outermost layer of the skin

• Several strata (layers)

• Thinnest on the eyelids (0.05 mm )

• thickest on the palms and soles (1.5 mm)

• Avascular (no blood supply)

Stratified squamous

Strata of Epidermis

(superficial to deep)

Come Let’s Get Sun Burned

Stratum Corneum

• 25 – 30 rows dead plate-like envelopes filled with keratin that have migrated up underlying layers

• Cells are worn/sloughed off daily (desquamation)

• Total new epidermis every 35-45 days

• Flattened and hardened cells

• Contain Keratin (Keratinocytes or K-Cytes) – Keeps skin elastic and protects underlying cells from drying out

• Barrier against microbe invasion

Stratum Lucidum

• 3 – 5 rows of dead K-cytes

• As K-cytes are pushed up they get bigger and flatter and adhere together, and then eventually become dehydrated and die

• Found in thick skin areas

– palms, soles and elbows

• Not found in thin skin areas

– eyelids

Stratum Granulosum

• 3 – 5 rows

• Aka: granular layer

• have lost their nuclei and are characterized by dark clumps (grains) of cytoplasmic material.

• Begins the process of keratinization

Stratum Spinosum

• 8 – 10 rows of actively dividing K-cytes

• Spiny or prickly appearance

• Cells interlock to support the skin

Stratum Basale

• Aka: basal cell layer

• Deepest layer

• One cell thick, rests on the basement membrane

• Dividing continuously • As new cells form older ones are pushed up towards the skin

• Nutrients received from dermis below

Four Types of cells found in Epidermis

Cell type Where found Function

Keratinocytes All 5 layers Produce keratin Strength Waterproofing

Melanocytes

S. Basale Produce melanin (same # in all people skin color determined by amount of melanin produced)

Merkel cells (tactile cells) S. Basale Involved with touch reception

Langerhans’ Cells S. Basale Immune cells that “eat” bacteria and foreign debris

Dermis

• Composed of 2 regions

– Papillary region

– Reticular layer

• Vascular

– Has many blood vessels

• Sensory nerves

Papillary region

• Dense Irregular CT

• Contains Dermal Papilla – projections into papillary region that extend into and anchor the epidermis

– Form fingerprints and footprints

• Contain capillaries that nourish the epidermis

• Contains Meissner’s Corpuscles (sensory touch receptors)

Reticular Layer

• Dense Irregular CT

• Collagen fibers – strength and flexibility

• Elastic fibers – stretchable (maintain skin tension)

• Contains Pacinian Corpuscles – sensory receptors for deep pressure

Hypodermis • AKA: subcutaneous tissue

• Loose CT – Adipose

– Areolar

• Storage of energy

• Vascular

• Contains lymph vessels

• Insulation

• Protective padding

• Excessive adipose = obesity

Accessory Structures of the Skin

• Hair, nails, and glands

• Originates in the Epidermis

• Extends into the dermis

Hair

• Everywhere except palms, soles, lips, nipples, portions of external reproductive organs

• Stronger hair in the scalp region

• Puberty: – Axillary and pelvic hair growth in both sexes

– Beard growth in males

– Hirsutism-excess male sex hormone in females

Hair Growth

• Hair grows from hair follicles

• Follicle cells divide continuously

– pushed up and away from nutrients

– Keratinized and die eventually

• Life-span

– Eyelash 3-4 months

– Scalp 3-4 years

Hair Follicle and Associated Parts

• Hair follicle: – Root-portion within the follicle

– Shaft-portion beyond the follicle

• Sebaceous glands (oil glands) – 1 or more per hair

• Arrector pili (smooth muscle) – Attached to follicle

– Contraction causes “goose-bumps”

Hair Follicle and Associated Parts (Fig 5.1 and 5.2)

Nails

• Nail root-special epithelial cells from which nails growth

• Nail body-visible part of the nail

• Cuticle-skin fold that hides the nail root

• Lunula- whitish half moon – Thicker layer of rapidly producing cells

• Nail bed-area of dermis on which nail grows

Nail Growth

• Nails grow over the nail bed

• Keratinization

• About 1mm growth per week

• Pink color because of vascular dermis below

Nail Anatomy (Fig 5.3)

Sweat Glands

• AKA: Sudoriferous glands

• Two types

– Apocrine

– Eccrine

Sweat Glands

• Apocrine • Eccrine

Sweat Glands

• Apocrine

– Larger

– Duct leads to hair follicle

– Deeper in dermis

– More abundant in the axillary region

– Thicker/viscous sweat

• Eccrine

– Duct lead directly to surface of skin

– watery sweat

– Found all over body

• Ceruminous glands – modified sweat gland found in ear (secrete earwax or cerumen)

Sebaceous Glands

• Associated with a hair follicle

• Secrete Sebum – Oily (lipid) substance

– Flows into the follicle then out to the skin surface

– Lubricates hair and skin

– Waterproofs

– Weakens and kills bacteria

Mammary Glands

• Modified apocrine glands

• secrete milk after childbirth

Skin Disorders

•Athlete’s Foot – Fungal infection that involves soles and toes of feet

•Impetigo – Infectious disease caused by a bacterial infection that results in pustules that crust over.

•Psoriasis – chronic condition causing skin to develop reddish patches covered by silvery scales. Due to over active cell division.

Disorders Continued

•Eczema – an inflammation of the skin caused by sensitivity to various chemicals

•Dandruff – caused by an over accelerated rate of keratinization in certain areas of the scalp.

•Urticaria (Hives) – is allergenic reaction characterized by the appearance of reddish, elevated patches and often itching.

Athletes Foot

Impetigo

Psoriasis

Eczema

Dandruff

Urticaria

Skin Cancer

Nonmelanoma

• Basal Cells and Squamous

Cells

• Less likely to metastasize

• Usually found at sun

exposure spots

Melanoma

• Begins in Melanocytes

• Example unusual moles

• More likely to metastasize

Wound Healing 1. Puncture wound fill with blood

2. Chemicals released by damaged tissue cause blood to clot.

3. Clotting prevents pathogens and toxins from spreading.

4. Scab develops

5. Fibroblasts – Help with tissue regeneration

Basal Layer begins to form new cells

WBC – Fight infection

• Scar – collagen fibers arranged to provide maximum strength, devoid of feeling

Burns •Two factors affect burn severity: Depth & Extent

•First Degree Burns

• Only Epidermis

• redness and pain, but no blisters

•Ex. Moderate Sunburn

•Second Degree Burns

•Entire Epidermis & Part of Dermis

•Blistering can occur

•Ex. Severe Sunburn

Burns Continued

• Third Degree Burns – Full thickness burns, destroys the entire thickness of the skin

•Fourth Degree Burns - Involves tissue down to the bone.

Effects of Aging on Skin Layers

• Epidermis: – Maintains its thickness

– Decrease in the rate of cell mitosis

– Is held less tightly to the dermis (looser skin)

• Dermis: – dermal papillae flatten

– Dermis becomes thinner

• Hypodermis: – Decrease in the adipose tissue of face and hands (older

people feel cold)

Effects of Aging on Fibers in the Dermis

Collagen Fibers

• Collagenous fibers become coarser, thicker, and farther apart

• Overall less collagen than before

Elastic Fibers

• Elastic fibers in the upper layer are lost

• Elastic fibers in the lower dermis become thicker, less elastic, and disorganized

Why is there wrinkling of skin with age?

• Epidermis is loose

• Fewer and more disorganized fibers in the dermis

• Less padding in the hypodermis

Aging and Homeostasis

• Limited adjustment to heat due to: – less vasculature (fewer blood vessels)

– Fewer sweat glands

• Decrease in the number of hair follicles – Thinning of hair on scalp and extremities

• Decreased number of melanocytes (gray hair and paler skin)

• Some pigment cells get larger-blotches

• Decrease in the number of sebaceous glands – Cracking of skin

Aging and Sun Damage (UV radiation)

• Roughened skin

• Uneven pigmentation

• Fine lines, wrinkles, and deep furrows

• Benign skin growth

• Skin cancer

Skin and Homeostasis

• Protection

• Regulation of water loss

• Waste elimination (assists Urinary System)

• Production of Vitamin D

• Gathering of Sensory Information

• Body Temperature regulation

Skin’s Protective Functions

• Protective covering around the body against physical trauma and pathogens

• Melanocytes protect against UV radiation

• Outer keratinized cells prevent bacterial invasion

• Oily (acidic) secretions from sebaceous glands prevents bacterial growth

• Langerhans cells phagocytize pathogens and alert immune system

Regulation of Water Loss

• Waterproofing by outer keratinized cells

• Prevention of excess water entry into the skin by keratinized cells

Skin and Waste Elimination

• Sweat glands allow perspiration

– Sensible perspiration-can be felt

– Insensible perspiration-without awareness

• Perspiration contains

– Water

– Small amounts of salt, ammonia, urea, and other wastes

Skin and Vitamin D Production

• Vitamin D production in skin cells with the help of UV

• Small amount of UV needed

Vitamin D (skin) goes to the

Liver and Kidneys secrete

Calcitrol (hormone)circulates and regulates calcium and phosphorus levels

• Vitamin D helps prevent rickets (soft/deformed bones)

Skin and Sensory Information

• Sensory receptors in the epidermis and dermis

• Sense touch, pressure, pain, hot, and cold

• Greatest number of touch receptors in the fingertips!

Skin and Regulation of Body Temperature (97ºF-100ºF)

• Increase in body temperature:

– Dilation of blood vessels in the skin

– Increase in the amount of blood brought to skin

– Sweat glands become more active

– Evaporation leads to skin cooling

• Decrease in body temperature: opposite effect

– Shivering-due to muscle contractions, heat production

– Arrector pili muscles contract-goose bumps

– Frostbite-severe restriction of blood flow, dead skin

Hyperthermia- Body Temp. Above Normal

– Heat Exhaustion: Low BP, excessive sweating (salt loss), high body temperature

– Heat stroke: high body temperature (110ºF), no sweating

– Fever: high body temperature due to immune response and bacterial infection

Hypothermia-Body Temperature below Normal

• 90º-95ºF: – Uncontrollable shivering

– Incoherent speech, Lack of coordination

– Low pulse rate

• below 80º-85ºF: – Hallucinations or unconsciousness

– Shivering diminishes, rigidity sets in

– 50% mortality