-skin and its derivatives such as hair, nails, glands and specialized receptors

-occupies surface area of about 2 square meters

-Dermatology---medical specialty that diagnoses and treats skin disorders

Physiology

1. Regulate Body Temperature---sweat and changes of blood flow toward the surface of the skin

2. Protection---from abrasions, bacteria, dehydration and ultra-violet radiation

3. Reception of Stimuli---nerve endings specifically designed for pressure, temperature, touch and pain

4. Excretion---sweat helps to reduce levels of water, salts and other organic compounds

5. Synthesis of Vitamin D---helps in the manufacturing of Vitamin D which helps the body to absorb calcium and phosphorus from food

6. Immunity---certain cells help in your ability to produce antibodies

2 general structures plus epidermal derivitives 

-outer, thinner layer composed of keratinized stratifies squamous epithelium

-4 special cells found here

A) keratinocyte---produce keratin

B) melanocyte---

-found at the base of the epidermis

-produce melanin---responsible for skin color and the absorption of ultra-violet radiation

C) Langerhan's Cells---interact with helper T-cells of the immune system

D) Granstein Cells---

-resistant to ultra-violet radiation

-interact with other T-cells from the immune system

LAYERS OF THE EPIDERMIS

1. Stratum Basale---

-single layer of cells capable of continued cell division

-also called the stratum germinativum

-cells may migrate to the dermis to become glands and hair follicles

-areas with no hair contain nerve endings that are sensitive to touch (tactile disc)

 

2. Stratum Spinosum---

-8 to 10 rows of close fitting cells

-surface of the cells contain spine like projections that help to join cells together

 

3. Stratum Granulosum---

-3-to 5 rows of flattened cells that contain dark stained granules of keratohyalin which is involved in the first steps of keratin formation

-cells start to die in this layer

 

*4.* Stratum Granulosum---

-found ONLY in thick shin of palms, and the soles of your feet

-3 to 5 rows of clear, flat, dead cells

 

5. Stratum Corneum---

-25 to 30 rows of keratinized cells

-continuously replaced and shed

-consist of collagenous fibers and elastic fibers of connective tissue

-blood vessels, nerves, glands, and hair follicles are found here

-2 layers thick

1. Papillary Layer---

-upper 1/5 of the dermis

-dermal papillae---

-finger like projections that increase surface area

-projections that extend into the epidermis and may contain blood vessels or

meissner's corpuscles--- endings that are sensitive to touch

-cause ridges in the overlying epidermis (fingerprints)

2. Reticular Layer---

-formed by closely packed irregularly arranged connective tissue

-spaces between are filled by glands, hair, and nerves

-provides the skin with its strength and elasticity

-attached to underlying organs by the subcutaneous layer

Pacinian Corpuscles---

-located in the subcutaneous layer

-nerve endings that are sensitive to pressure

-develop from embryonic epidermis

-pili

-protects--guards scalp from the sun, eyes from foreign particles

-hair in the ear and nose protect these structures from foreign particles and insects that might be inhaled or crawl into the ear

Anatomy of the Hair

A) Shaft---

-superficial portion that most of which projects above the skin

-made up of 3 parts

 

1. Medulla---inner portion that contains air spaces

2. Cortex---

-middle portion that makes the majority of the hair shaft

-contain pigment granules of dark hair and mostly air in light hair

3. Cuticle---

-outer most layer

-cells heavily keratinized

-arranged like upside-down shingles

B) Root---

-portion that penetrates the dermis and even the subcutaneous

layer

-contains the 3 portion like the shaft

C) Hair follicle---

-surround the root

-continuation of the stratum basale and stratum spinosum layers of the epidermis

-base of each follicle enlarges and looks like an onion shaped bulb

D) Papillae of the hair---

-indentation of the bulb that is filled with loose connective tissue

and many blood vessels

Associates of the Hair Complex

1. Sabaceous (oil) glands---

-found in association with hair follicles except on the lips and eyelids

-secrete sebum---

-mixture of fats, cholesterol, proteins, and inorganic salts

Function

-prevents hair from becoming brittle

-forms a film that prevents excess evaporation of water from the skin

-keeps the skin soft and flexible

-inhibits the growth of certain bacteria

Clinical Application:

Blackheads

-sebaceous glands enlarge due to accumulated sebum

-color of blackhead is due to melanin and oxidized oil, not dirt

2. Suderiferous Glands---

-divided on basis of structure and location

-3 types

A) Apocrine---

-located in axilla and pubic region

-excretory duct open to hair follicles

-start to function at the onset of puberty

-omit an odor

B) Eccrine---

-more common

-ducts open to the surface of the skin

*both of these types of glands secrete

perspiration--- mixture of water, salts (NaCl), urea, uric acid, amino acids, ammonia, sugar, lactic

acid and ascorbic acid

 

Function:

-reduces body temperature by evaporation

-elimination of waste

 

C) Mammary glands---

-modified suderiferous glands

-reproductive unit

 

D. Ceruminous glands---

-found in external auditory meatus

-produce ear wax that protect your ears from foreign particles

-average growth is about 1 mm per week

-protect the end of the digits and aid in the manipulation of small objects

4 parts of a nail

1. Free Edge---sticks out past distal end of the digit

2. Body---

-majority of the visible nail

-lunula---semilunar whit par of the body

3. Nail Root---hidden part of the nail that lies above the nail matrix

4. Nail Matrix---function to bring about the growth of nails when superficial cells

become nail cells, they push the whole nail across the nail

bed

Common skin wounds

Abrasions---portion of the skin has been scraped away

Lacerations---irregular tear of the skin

Puncture---hole "popped" through the skin

Incisions---clean cut through the skin

Contusion---

-bruise

-tissue below skin damaged, but skin is not broken

Superficial Wound Healing

1. Basale cells in the area of the wound break contact with the basement membrane, that connects the epidermis to the dermis

2. Basale cells enlarge and migrate across the wound

3. Contact inhibition stops the migrating cells and turns cells in a new direction Continues until cells are surrounded by similar cells.

**malignant (cancer) cells don't follow the same rules they continue to spread and invade other areas

4. When the "Floor" of the wound is covered

-cells divide to form new strata (layers)

-this thickens the epidermis and fills in the wound from the bottom upward

5. If a scab was formed, it will fall off when the new epidermis is thick enough to protect itself.

Deep Wound Healing

-when the injury extends past the epidermis

-commonly due to accidental lacerations or surgical incisions

-scar formation will occur

-repair more complex (4 phases)

 

1. Inflammatory phase---

-inflammation is the vascular and cellular response to rid wound of bad stuff

-blood clot forms to keep the edges of the wound close together

-epidermal cells start to migrate

-vasodilation floods the area with phagocytic cells and fibroblast

 

2. Migratory phase---

-clot becomes scab and epithelial cells continue migrating and bridge the wound

-fibroblast synthesize scar tissue

-damaged blood vessels begin to regrow

 

3. Proliferative phase---

-epithelial cells grow under the scab

-collagenous scar tissue is deposited

-continued blood vessel growth

 

4. Maturation phase---

-scab falls off

-collagenous fibers become more organized

-blood vessels restored to normal

-scar tissue---

-dense collagenous fibers

-fewer blood vessels

-may not contain hair, glands, or sensory receptors

1. Melanin---

-pigment found primarily in the basale and spinosum layers of the epidermis

-varies skin color from yellow to black

-number of melanocytes about the same for all races

-skin color due to the amount of pigment the melanocytes produce

 

Disorders

Albinism---inability to produce melanin

Vitiligo---loss of melanocytes from an area of skin

Freckles---patches of melanin

Tanning---

-also associated with the melanin

-ultra-violet radiation increases melanocyte activity

 

2. Carotene---

-found in the stratum corneum

-people of Asian origin have carotene in fatty areas of the dermis

-gives a yellowish hoe to the skin

 

 

3. Capillaries---cause the skin to have a pink appearance

Disorders

Malignant Melanoma

-cancer of the melanocytes

-overexposure to ultra-violet light of the sun may causes

-most tumors involve basale cells, so they can be removed surgically

 

BEST TREATMENT IS PREVENTION

-examine your skin for moles that develop irregular borders,

uneven surfaces, or a mixture of colors or change in size or start to bleed

-any of these may be a sign of a developing melanoma

 

Wrinkles

Collagen fibers---stiffen, break apart and form a shapeless tangle

Elastic fibers-- some elasticity, thicken and fray

Subcutaneous fat---decreases

Sebaceous glands---atrophy leads to dry, cracked skin

 

other problems:

Melanocytes---

-decrease of functioning melanocytes lead to gray hair and atypical skin pigmentation

-increase of size of some melanocytes can cause liver spots

-older skin more susceptible to pathological conditions like cancer and senile pruritis (itching)

 

Cystic Acne---

-scarring as a result of severe acne

-surrounding epidermal cells might be replaced by connective tissue

-squeezing, pinching or scratching the lesion will increase the chance of developing cystic acne

 

Psoriasis---

-symptoms are distinct, reddish, small round skin elevations covered with scales

-caused by abnormally high rate of mitosis in the epidermal cells

-trauma, infection, stress, seasonal or hormonal changes can initiate

-treatments include steroid ointments and natural sunlight (ultra-violet light)

 

Sunburn---

-dead layers of cells peel off and leave unprotected layers of cells

-ultra-violet rays of sunlight damage the cell's DNA and RNA