• is the largest system

Skin

of the body –16% of body weight

–you have 21 square feet of it

–it weighs 9 pounds

–it contains more than 11 miles of blood vessels

–you shed 50,000 cells every MINUTE!!!

Functions

• Protects

• infection

• desiccation

• UV rays

–temperature regulation

–excretion

of Skin

you from

• Important for

(insulation and evaporation)

• it releases 3 gallons of sweat each day!

of salts, water, and organic wastes (glands)

• Synthesizes vitamin D3

Detects sensations

Functions of Skin

–which you need to extract calcium from your diet and incorporate it into your bones!

• –touch, pressure, pain, and temperature: as a

huge sensory receptor, the skin is your constant communication with the outside world

Skin is 1 huge sensory organ!

–Nerve sensory receptors for •pain

• touch

•vibration

• pressure

•temperature

Components • Outer Epidermis :

– epithelial tissue • stratified squamous keratinized • loose and dense

• Inner Dermis : – connective tissue

of Skin

of Epidermis Types • Thin skin :

–Covers most of the body

–Has only a few layers of dead surface cells

: • Thick skin – Covers the palms

– This skin is also hairy skin for the most part

of the hands and soles of the feet

–Has many layersof dead surface cells

Dermis

Source of blood and nutrients for the epidermis

•

• Composed of 2 layers: – “papillary”layer: • loose connective tissue

– “reticular”layer: • dense irregular connective tissue

• Directs the characteristics of the epidermis

The Hypodermis

• AKA subcutaneous tissue or superficial fascia: – NOT a part of the “skin”

– Deep to the dermis

– Composed of loose connective tissue (primarily fat)

– Location of hypodermic injections

of the Epidermis Major Cell Types

• Keratinocytes : – the most abundant cells

Melanocytes : – secrete the pigment melanin

Langerhans cells : – antigen-presenting cells

in the epidermis – synthesize and secrete keratin(a waxy hydrophobic protein that creates a water barrier)

– responsible for the “keratinized”epithelium

•

• protects the keratinocytefrom the sun

• for the immune

response (a type of macrophage) – decrease in # with a sun tan!

lucid

granular

spiny

basal

Layers of the Epidermis and the Life Cycle of the Keratinocyteas it moves towards the surface:

Layers:

cornified

Basal

• Contains the stem cells

– Cells are attached to thebasement

– This is where mitosis

Layer

for keratinocytes – 1 layer thick – also contains melanocytes

occurs (about every 15-30 days)

• (psoriasis = ↑mitotic activity (turnover every 7 days)

membrane (by adherens junctions)

• hence the name of this layer

The Basal Layer meets the underlying Dermis

• Epidermal ridges (e.g.,fingerprints)

• Dermal papillae (tiny mounds): –strengthen attachment between epidermis and dermis

Spiny

adhering junctions

spines

Layer

• Contains 2–10 layers of keratinocytes attached to each other by many

• As the cells move away from the basal layer, they – begin to shrink • further from source of nutrition

– are still connected to adjacent cells by adhering junctions

– these connections look like

• hence the name of this layer

Granular

amounts of keratin

Layer • Contains 2-5 layers of keratinocytes

• By this point in their life cycle, keratinocytes are producing significant

– which accumulates in and around the cells

– they now take on a granular appearance

• hence the name of this layer

• The cells are now far enough away from the source of nutrition that they are dehydrating and flatteningas well

Stratum granulosum

Lucid

dying keratinocytes

Layer • The clear (or “lucid”,

hence the name of this layer) layer

• Contains 1-5 layers of

• The cells are now very flat so it is difficult to see individual cells

• The cytoplasm appears homogeneous all the major organelles have died and degenerated

Stratum lucidum

Cornified

layers of dead cells

• Layers slough off

Layer

• Contains 10 -100’s of

– depending on whether thick or thin skin

• Basically composed of flat sheets (scales) of keratin

• (desquamate) here

Stratum corneum

Skin Color

– the pigments carotene :

melanin :

– and blood

• Skin color depends on:

• Orange-yellow pigment

• Found in orange vegetables

• Accumulates in epidermal cells and fatty tissuesof the dermis

• Can be converted to vitamin A

– and • Yellow-brown or black pigment • Produced by melanocytesin the basal layer

• Transferred to keratinocytes

• Protects DNA in nuclei of keratinocytes from sun (UV) damage

circulation (red blood cells) • Oxygenated red blood contributes to skin color:

– blood vessels dilate from heat, skin reddens

– blood flow decreases, skin pales

Melanocytes

Basal layer

More facts about skin color

• With a tan –pre-existing melanin darkens

–the rate of new melanin synthesis increases

Illness

• Jaundice :

• Cyanosis :

Vitiligo :

and Skin Color

– buildup of bileproduced by liver – yellow color

– Bluish skin tint – Caused by severe reduction in blood flow or

oxygenation

• – loss of melanocytes – loss of color

Accessory Structures

• Originate in the dermis

• Extend through the epidermis to skin surface: –hair

–nails

–exocrine glands

• sweat

• sebaceous

Hair – protects and

insulates

– associated with touch receptors

• Functions:

• Composed of dead cells that are heavily keratinized

• Hair color is produced by melanocytes at the hair papilla

• Associated with: – Arrector pili: • smooth muscle

• causes hairs to stand up producing “goose bumps”

– Sebaceous glands

Interesting hair facts

• Hairs grow discontinuously –There are periods of growth and periods of rest •Scalp: – growth periods may last many years

– rest periods average 3 months

• Hair in different regions of the body grows at different rates

Nails

•Nails protect fingers and toes :

and Nail Production

– composed of dead cells packed with keratin

– metabolic disorders can change nail structure

• Nail production occurs in a deep epidermal fold near the bone called the nail root

Interesting nail facts

• Transparency of the nail provides a useful window re amount of oxygen in the blood! –Indicator used during surgery • No nail polish!

Sweat glands : – most are merocrine

• found in both thick and thin skin

• secrete water and ions

– apocrine glands: • found in axillary, areolar

and anal regions only

• secrete apical portion of the cell with the water and ions

• associated with body odor

• active at puberty

Exocrine Glands •

glands:

Sebaceous oil glands:

whole cell is secreted

with hair follicles

puberty • lubricate

skin only

Exocrine Glands

•

– holocrine glands:

– associated with thin

– mainly associated

– begin to function at

and protect the epidermis

• inhibit bacteria

Skin Cancer Facts

• 1/3 of all tumors are of the skin

• Rarely lethal (deadly) if diagnosed early: –Basal cell carcinoma: easily curable• derived from cells in the basal layer

–Squamouscell carcinoma: • derived from cells in the spiny layer

• Most serious and invasive tumors: –(Malignant) melanoma: • derived from melanocytes Any condition resulting in hair loss is called alopecia

The 2 major components of skin are:

A. dermis and hypodermis

B. epidermis and dermis

C. dermis and subcutaneous layer

D. epidermis and hypodermis

The skin functions include:

A. temperature regulation

B. protection from infection

C. synthesis of vitamin D

D. sensory organ

E. all of the above

Thin skin is found in all of the following locations EXCEPT:

A. back

B. legs

C. arms

D. face

E. palms

The most abundant cell type of the epidermis is the:

A. melanocyte

B. Langerhanscell

C. fibroblast

D. keratinocyte

E. basal cell

The layer of skin in which keratinocytes divide is the:

A. cornified layer

B. basal layer

C. granular layer

D. spiny layer

E. lucid layer

The layer of skin in which keratinocytes slough off is the:

A. cornified layer

B. basal layer

C. granular layer

D. spiny layer

E. lucid layer

Most of your sweat glands:

A. release only water and ions

B. release a part of the cell with the water and ions

C. release the whole cell with the water and ions

D. release oil

E. are found in thick skin only

Skin color is determined by:

A. melanin

B. carotene

C. blood

D. none of the above

E. all of the above