integumentary system

The integumentary system is composed of the skin, hair, nails, oil and sweat glands. The skin is the largest organ of the body. It can be about 22 pounds and has a very large surface area. Dermatology is the medical specialty for diagnosis of problems. The epidermis is the superficial layer. The dermis is deep to the epidermis. The hypodermis, while not a part of this skin is still discussed with the integumentary system.


Functions of the integumentary system include:

Body temperature (sweat)
Protection (physical barrier)
Sensation (somatic receptors)
Excretion (salts)
Synthesis of Vitamin D (vision)
Immunity (secrete oils that inhibit bacterial growth) Ø
Blood reservoir (10% of total blood flow) Ø .


The epidermis consists of 5 layers: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum and stratum corneum.

1. 1. Stratum Corneum
1. 20-30 layers
2. Dead cells w/ keratin
2. 2. Stratum Lucidum
1. Clear, lots of keratin
2. ONLY ON fingertips, palms, soles
3. Stratum Granuolsum
1. Granules - Water repellant
2. Cells get flatter
4. Stratum Spinosum
1. Strength & Flexibility
5. Stratum Basale
1. Corrugated border
6. Stem cells become all other cells of Epidermis

The dermis is composed of two regions: papillary region which is composed of areolar tissue and the reticular region which is composed of dense irregular connective tissue.  The dermis is a layer of connective tissue composed of collagen and elastic fibers (give skin toughness and elasticity, respectively), hair follicles, glands and nerves.  It is highly vascular.

The superficial region of the dermis is the papillary region. It has finger-like projections called dermal papillae.  It also has pain and touch receptors.  These are called free nerve endings and Meissner corpuscles.

The deep region of the dermis, reticular layer, makes up 80% of the dermis. This layer has blood vessels, sweat glands (a watery secretion), sebacious glands (secrete sebrum/oil) and Pacinian corpuscles. 

Different skin colors happen for different reasons.
Jaundice makes the skin a yellowish color.  It occurs when there is a buildup of bilirubin in the bloor because of a liver disease.
Cyanosis occurs when there isn't enough oxygen in the blood.  It makes the skin turn a bluish color
Erythema is a redness of the skin due to enlargement of capillaries in the dermis.  This occurs during inflammation or infection.
Vitiligo  is the partial loss of melanocytes in patches (supposedly the reason Michael Jackson bleach his skin was to hide the vitiligo.)
Freckles and age spots are the accumulation of melanin in patches.
Moles are a benign raised collection of melanocytes.
Albinism is the lack of ability to produce melanin.
Tan is the stimulus of melanocytes from UV radiation to produce more melanin

Skin Cancer
UV radiation breaks DNA, inflammation makes free radicals that promote mutations and blocks cellular response to DNA damage.
Basal Cell carcinoma is most common in fair-skinned white people with light eyes.  It is most common on the head and neck regions and invades the stratum basale into the dermis and hypodermis.
Squamous cell carcinoma is most commonly found in outdoor workers.  It is found in the stratum spinosum and metastasizes to lymph nodes.  It is also found in the head and neck regions.

Malignant melanoma is caused by severe sun exposure with blistering.  It is cancer of the melanocyte.  It metastasizes to lymphnodes and blood vessels.  It may appear as a mole that is asymmetrical, that has irregular borders, color variegation, a diameter greater than 6 mm and it changes over time.

Oncogenes and Tumor-Suppressor Genes
Oncogenes are genes that normally direct protein synthesis and cell growth.  In cancer, this cell is turned on permanently.
Tumor-Suppressor genes normally encode the protein that stops cell proliferation.  It might also be called an anti-oncogene.  In cancer, these cells don't turn on.

A piece of telomere is lost each time a cell divides.  Eventually, when enough of the telomere has been lost, the cell will no longer divide.  Cancerous cells have an enzyme that repairs the telomeres and makes the cell immortal.

Bed sores occur from prolonged pressure on the body.  It kills both the dermis and the epidermis.

Homeostatic imbalances of the skin include athlete's foot (a fungus), boils (inflammation of hair follicles) and contact dermatitis (an allergic reactions).

There are three different types of burns.
1st degree burn only burns the epidermis.  This makes the skin red and swollen.
2nd degree burn burns the epidermis and part of the dermis.  When this occurs, fluid filled blisters occur and separate the two layers of skin.
3rd degree burns destroy the dermis, epidermis and the epidermal derivatives.  The damaged area may become numb due to the loss of nerves.
The head is approximately 9%.  The trunk is 36% (18% for each side).  Each side of each arm is 4.5%.  The legs are each 18%

Appendages of the skin include
-hair and follicles
Hairs may also be referred to as pili and are present on all skin surfaces except our palms, and digits and soles.
The function is to shield the eyes and filter for the respiratory tract.
The hair follicle is the site of hair production with the skin.  Hair is composed of hard keritinized epithelial cells.  Melanocytes, like in skin coloring, also give hair its color.
The arrector muscle is a smooth muscle (involuntary) that is attached to the hair follicle.  It is the reason we get goose bumps.  
Other components include the root (the part of hair within the follicle), the shaft (the part that sticks out of the skin) and the bulb (where hair grows).
Hair growth occurs in cycles.  It has a growth stage and a resting stage.  The growth stage lasts for 2-6 years and the matrix cells at the base of hair root produce the length.  The resting stage lasts for 3 months and the matrix cells are inactive and follicle atrophies.  Old hair falls out as growth stage begins.  Normal hair loss is 70-100 hairs a day.
-nail
Nails are scale like modifications of the epidermis.  They consist of tightly packed keretinized cells.  The nail body is the part that is visible.  The nail root is buried under the skin.  The lunula is the white area on the nail and is caused by a thickened stratum basale.  The eponychium (cuticle) is a stratum corneum layer.
-exocrine glands
--sweat glands
--sebaceous glands

Epidermal wound healing occurs when we get a minor cut or burn.  The basal cells will migrate across the wound.  Contact inhibition will stop the migration.  The epidermal growth factor simulates basal cells to divide and replace the ones that have moved into the wound.  The thickness is a result of mitosis.

Deep wound healing has three stages.  The first stage, inflammatory stage, is when the blood clot unites the wound edges.  Fibroblasts secrete collagen matrix as a frame work for the epithelial cells.  Vasodilation and increased permeability of blood vessels deliver phagocytes.  The second stage, migratory stage, is when the epithelial cells bridge across the wound under the scab.  Fibroblasts begin scar tissue and damaged blood cells begin to grow.  During this phase the wound is called granulation tissue.  Maturation, the third stage, occurs when the scab falls off.  The epidermis has returned to normal thickness and the collagen fibers return to a normal state.  The fibroblasts being to disappear and the blood vessels return to normal.

Age and skin
Age mostly affects the dermis.  Collagen fiber, fibroblast, Langerhans cell and melanocyte numbers will decrease, elastic fibers will become less elastic, and phagocytes will be less effective.  Wrinkling, slower growth of hair and nails are also a part of aging.  Sebaceous glands are atrophic.  Walls of the blood vessels thicken so there is less nutrients available.  This causes people to get thinner.
Anti-aging treatments:
microdermabrasion, chemical peel, laser resurfacing, dermal fillers, Botuliism toxin injection and non-surgical facelifts
-sun screens and sun blocks help minimize photo damage from UV exposure