SKIN (Integumentary System)

The skin has six major functions 1. Protection: of underlying tissues 2. Excretion: of salts, water, waste 3. Maintenance: of body temp. 4. Synthesis: of vitamin D 5. Storage: of nutrients (fat) 6. Detection: of touch, pain, pressure & temperature

Skin color is produced by two pigments 1. Carotene: a orange-yellow pigment inside epidermal cells. Carotene can be converted to vitamin A which is needed for epithelial maintenance 2. Melanin: a brown, yellow-brown or black pigment produced by melanocytes in the stratum germinativum.

Skin with lots of melanin (left) and little (right)

Different skin colors is due to the level of synthetic activity in the melanocytes NOT in the number of melanocytes. Even albino individuals have normally distributed melanocytes, they just don’t produce melanin.

Skin color is due primarily to the amount of melanin produced by cells called melanocytes

SKIN CANCER There are three main types of skin cancer, most often caused by too much sun exposure which damages the chromosomes in the germinative cells

Basal Cell Carcinoma - most common form of skin cancer - appears as a slow growing, raised nodule - does not spread through the body

2. Squamous Cell Carcinoma - red, pink or opaque nodule - grows into a large, ulcerating, mushroom like tumor - can spread and cause death

3. Malignant Melanoma - less common than the other two forms - causes 75% of skin cancer deaths - appears as brown to black blemish with borders of shades of red, blue or white - often arises in pre-existing moles

Malignant Melanoma can be detected using the ABCD method A : Asymmetry: the shape of one half does not match the other half

B : Border: the edges are uneven, ragged or notched

C : Color: different shades of brown, black or tan

D : Diameter: moles that get to be. the size of a pencil eraser or D : Diameter: moles that get to be the size of a pencil eraser or bigger

The Integumentary System has two major components 1. Cutaneous membrane made up of the epidermis and the dermis 2. Assessory structures such as hair, nails and exocrine glands

The Epidermis - is stratified squamous tissue - is four (thin skin) or five (thick skin) layers thick - each layer of skin is at least 3 cells thick and some (stratum corneum) can be up to 30 cell layers thick - the outer layers (lucidum & corneum) are dead cells

Epidermis layers “skin” has four layers if it is thin skin and five layers if it is thick skin. The epidermis is stratified squamous tissue. Five layers starting with the innermost: 1. stratum germinativum (stratum basale): 3-5 cells thick and the closest to the underlying loose connective tissue of the dermis.

the stratum germinativum has. epidermal ridges that form the stratum germinativum has epidermal ridges that form fingerprints, undergoes mitosis and contains melanocytes which produce skin color. 2. Stratum spinosum: 8-10 cells thick. These cells also undergo mitosis. The spinosum contains Langerhans cells that aid the immune system as a defense against pathogens that penetrate the upper layers of skin

3. Stratum granulosum: 3-5 cells thick. These cells no longer divide 3. Stratum granulosum: 3-5 cells thick. These cells no longer divide. The cell nucleus and organelles start to degenerate. 4. stratum lucidum: 3-5 cells thick and has cells packed with keratin, a tough, durable and water resistant protein. Found only in thick skin (soles & palms).

5. stratum corneum: 15-30 layers thick 5. stratum corneum: 15-30 layers thick. All cells are dead and will be shed or washed away every two weeks.

If dead skin cells fall off every two week, what happens to them?

Dermis - below the epidermis - has two layers, the papillary layer that contains capillaries and papillae that help to form fingerprints - reticular layer that contains collagen and connects the skin to the underlying connective tissue

How wounds heal

Embedded in the dermis are the assessory structures of the skin including: hair follicles, nail beds, oil and sweat glands and nerve receptors. There are four key skin receptors. 1. Nociceptors: feel pain. These free nerve endings have large receptive “fields” and are sensitive to temperature extremes, mechanical damage and dissolved chemicals.

2. Thermoreceptors: feel temperature. Cold receptors are three times 2. Thermoreceptors: feel temperature. Cold receptors are three times more numerous than warm. Temperature sensations are conducted along the same pathway as pain. Thermoreceptors are active when temperature is changing but adapt quickly to a stable environment.

3. Mechanoreceptors: feel touch. There are different receptors for 3. Mechanoreceptors: feel touch. There are different receptors for hair movement, fine touch (Merkel’s discs), pressure (Meissner’s corpuscles), pulsing stimuli (Pacinian) and deep pressure (Ruffini). 4. Chemoreceptors: respond to specific chemicals in the body such as oxygen levels.

Burns Burns can be 1st degree burns which “only” damages the epidermis. First degree burns show a redness due to the inflammation of the damaged skin

2nd degree burns damages the entire epidermis and some of the dermis 2nd degree burns damages the entire epidermis and some of the dermis. Blistering, and swelling are symptoms. Healing takes 1-2 weeks and may scar.

3rd degree burns kill cells all the way through the epidermis, dermis and into the subcutaneous tissue underneath. Because the damage is so deep, skin can not repair itself, thus skin grafts are needed and until that point the burn remains a potential site of infection.

Fourth degree burns: burn all the way through the skin and into underlying fat, muscle and bone. Appears black and often results in amputation or even death.

Rule of 9’s

Skin grafts