Chapter 5

The Integumentary System

Skin, hair, nails & cutaneous glands

• significant in physical exam

• Important for self image

• Provides Clues to health & disorders

  • Liver cancer, anemia, lung disease

Skin

Membrane covering external surface of body

2 layers

1. Epidermis: superficial epithelium

2. Dermis: deeper connective tissue

Hypodermis

Loose connective tissue b/w skin & muscles

Functions of the skin

1. Resistance to trauma & infection

• cells packed with tough keratin & linked by strong desmosomes

• Few organisms penetrate

  • Dryness of skin & protective acid layer helps keep organisms on skin in check

2. Water retention

• prevents body from losing or absorbing too much water

3. Vitamin D Synthesis

• first step is carried out by epidermal cells

• Needed for bone development, maintenance

4. Sensation

• largest sense organ; has nerve endings for temp., tofu, pressure, vibration, & injury

5. Thermoregulation

• regulates heat exchange with environment

• Increases or reduces blood flow close to body surface

• Sweat in response to overheating

6. Nonverbal communication

• numerous small facial muscles produce subtle & varied expressions

Skin characteristics

Body’s largest organ

• 8% of body weight

• Most of the skin is 1-2 mm thick

  • Ranges 0.5mm - 6mm mostly due to variations in dermis

• Lacks blood supply; depends on the vascultaure of the underlying dermis

  • As epidermal cells move up away from this blood supply, they die

Cells of the Epidermis

Keratinized stratified squamous epithelium tissue

• Most are keratinocytes

  • Packed with keratin

  • Deepest cells are rounded; become squamous as move superficially

• Dendritic cells

  • Alert immune system of infection

• Melanocytes

  • Produce melanin, protects underlying tissues from ultraviolet rays from the sun

  • Deepest layer of the epidermis

• Tactile cells

  • Specialized for touch

• Stem cells

  • Continually divide & replace keratinocytes that die

    
    

    
    

    
    

    
    

    
    

Layers of the Epidermis

Deepest to most Superficial:

Stratum Basale

• single layer of cells

• Contains stem cells, keratinocytes, melanocytes, tactile cells

Stratum Spinosum

• many layers of keratinocytes & dendritic cells

• Cease dividing as pushed upward, & start synthesizing keratin & flattening

Stratum Granulosum

• 3-5 layers of flat keratinocytes

• Keratin filaments in thick bundles produce water barrier

• Cells die; the water barrier cuts them off from nutrients

Stratum Lucidum

• present only in thick epidermis of palms & soles

• Clear layer or dead cells

Stratum Corneum

• up to 30 layers of dead keratinocytes; packed with keratin

• Gives skin toughness

• Cells flake off, exfoliate/dander

  • Replaced by new cells

• 30-40 days from “birth” to exfoliation

Dermis

0.2mm - 6mm thick

• consists mainly of collagen but also has elastic reticular fibers, & cells of fibrous CT

• many blood vessels, drive endings, sweat & sebaceous glands

• Hair & nails are rooted here

• Skeletal muscles attach on face

Dermal Papillae

Boundary b/w epidermis & dermis is made of upward waves

• finger like extensions of dermis

• Interlock with epidermis; helps resist slippage if epidermis

  • Give skin more resistance to stress

• Form fingerprints

• Blisters form here

• Dermal capillaries supply bloodless epidermis

Zones of the Dermis

1. Papillary layer

• thin zone of areolar tissue in & near dermal papillae

• Loosely organized; allows leukocytes to move around easily

2. Reticular layer

• deepest layer;4/5 of dermis

• Thick bundles of collagen, elastic fibers, fibroblasts, & clusters of Adipocytes

• Embedded are sweat glands, nail roots, & hair follicles

Hypodermis (subcutaneous tissue)

• underlies dermis

• Looser CT & Adipose tissue

• Binds skin to muscles or other tissues

• Pads body

• Energy reservoir; 50% of body fat is found

• Provides thermal insulation

• Differs in thickness, distribution b/w sexes

Melanin

Most significant factor in skin color

• produced by melanocytes, transferred to keratinocytes

• #. Of melanocytes is about the same in people of different skin colors, but darker skinned people make more

• Blocks UV radiation, which can cause DNA damage & skin cancer

  • In response melanocytes increase their production; tan

• Freckles & moles are local concentrations of melanin

Skin color factors

Hemoglobin

• red pigment of blood; reddish hue to skin

Carotene

• yellow pigment from veggies

• Concentrated in stratum corneum & subcutaneous fat

Cyanosis

• blueness of skin from oxygen deficiency in blood

• EX: drowning, emphysema, & cold weather

Erythema

• abnormal redness of skin

• EX: sunburn, exercise, hot weather

Hematoma

• bruise, mass clotted blood

• EX: trauma, platelet deficiency & diseases

Pallor

• temporary pale color form little cutaneous blood flow

• EX: stress, circulatory shock, & cold temp.

Albinism

• hereditary lack of pigment

• Inability to synthesize melanin

Jaundice

• yellowing of skin & whites of eyes

• EX: liver diseases & some blood diseases

Skin cancer

1. Basal cell carcinoma

• arises from stratum basale

• Most common, least dangerous

2. Squamous cell carcinoma

• Arises in stratum spinosum

• Easily cured, can be lethal if no found early

3. Melanoma

• rare but most deadly

• Aries from melanocytes of a preexisting mole

• ABCD rule is used for recognition

  • Asymmetry- mole should be symmetrical

  • Border - should be defined & regular

  • Color - should be one color

  • Diameter - should be smaller than 6mm

Burns

1st Degree

• involve only epidermis

• Redness, swelling, pain

  • Sunburns

2nd Degree

• involve entire epidermis & part of the dermis

• Partial thickness burn

3rd Degree

• destroys the epidermis & all of dermis

• Often needs skin grafts

• Need to worry about fluid loss & infections

• Full thickness burn

Accessory Organs (appendages)

Hair, nails & cutaneous glands

• originate in epidermis of embryo

  • Then penetrate deeply into dermis or Hypodermis

Hair

Slender filament of Keratinized cells growing from a hair follicle:

• A tube of epithelium & CT

• Made of stronger, harder keratin than epidermis

• Occurs everywhere expect lips, nipples parts of Benito’s, palms & soles, lateral fingers & toes

• Density is fairly consistent

  • Differences in hairiness is due to differences in hair texture & pigmentation

Hair structure

Shaft

Portion of hair above the skin surface

Root

Portion of hair below the skin surface

Bulb

Swelling at lower end of root

Dermal Papilla

Vascular CT growing into bulb; provides hair with nutrition

Hair matrix

Above bulb

Site of cellular mitosis & hair growth

Cuticle

Surface layer of hair

Cortex

Layer beneath cuticle; makes up most of hair bulk

Medulla

Central core of hair; found only in thickest hair

Root sheath

Layer of epithelium & demis alongside hair

Hair receptors

Nerve fibers coiled around follicle

Respond to hair movements

Piloerector (pilomotor) muscle

Smooth muscle associated with each follicle

Contracts in response to stimuli; makes hair stand upright (cold,fear)

Hair color

1. Eumelanin: color in black & brown hair

2. Pheomelanin: shades of blond to red

3. Grey & white hair: from air in medulla & little pigment

Hair growth

Grows by mitosis of cells in hair matrix

Hair functions

Scalp

• retain heat

• Protects scalp from sunburn & skin cancer

Beard, public, axilLarry

• begin puberty; advertise sexual maturity

• Absorb aromatic secretions

Hair on trunk & limbs

• largely an evolutionary remnant, but plays a sensory role

Eyebrows

• accentuate facial expressions

• Keeps sweat & debris out of eyes

Guard hairs (vibrissae)

• block foreign particles from nostrils, auditory canals, & eyes

Eyelashes

• shield eyes from debris

Cutaneous Glands

5 types

1. Eccrine sweat glands

2. Apocrine sweat glands

3. Sebaceous glands

4. Ceruminous glands

5. mammary glands

Sweat glands aka sudoriferous glands

Eccrine Sweat glands

Most sweat glands; widespread in skin

• produce sweat, cools the body

• Ducts empty onto skin surface

• Sweat

  • Begins as filtrate of blood plasma

  • 99% water

  • Insensible perspiration - no noticeable wetness

  • Diaphoresis - noticeable wetness from sweating

• Skin also loses water from cutaneous transpiration

  • Water diffuses b/w keratinocytes & evaporates off skin surface

Apocrine Sweat Glands

Groin, anal region, axilla, areola & beard

• sparse or absent in some ppl

• Ducts lead to hair follicles

• Sweat has more fatty acids than merocrine sweat

• Respond to stress & sexual stimulation

• Produce pheromones

  • Chemicals that influence other members

  • Scent is retained by pubic & axillary hair

Sebaceous Glands

Produce oily secretion, sebum

• keeps skin & hair from being dry

• Flask shaped with short ducts that open into hair follicle

• Holocrine glands

Ceruminous Glands

Found only in auditory canal

• secrete Cerumen (earwax)

• Simple, coiled, tubular glands have ducts leading to skin surface

• Keeps eardrum pitiable, waterproofs auditory canal & has bactericidal effect