Integumentary System

Consists of:

- skin- hair- nails- sebaceous (oil) glands- sudoriferous (sweat) glands

Functions:

1. Thermoregulation - through sweating and adjusting blood flow in the dermis

2. Protection (from water loss, UV light)

3. Cutaneous sensations (tactile sensations like touch, pressure, vibration, tickling and thermal sensations like temperature and pain)

Functions (cont)

4. Excretion (sweat - contains water, salts, carbon dioxide, ammonia, urea)

5. Absorption (lipid soluble materials that penetrate the skin include Vitamin A, D, E, K, oxygen and carbon dioxide; toxic materials that can be absorbed include acetone, lead, mercury, arsenic, poison ivy & oak)

6.Vitamin D synthesis - requires activation in the skin by UV rays in sunlight

Skin● Largest organ of the body (~ 22 feet)● 16% of body weight● Thickness varies depending on location (.5mm -

eyelids - 4.0mm heels of feet)

dermatology - science dealing with the diagnosis and treatment of skin disorders

Dr. Pedicure’s Foot Exfoliating Mask

Layers of the skin1. Epidermis - superficial, thinner portion; epithelial tissue2. Dermis - deeper, thicker layer; connective tissue3. Subcutaneous layer - deeper to the dermis; not part of

skin- Contains aveolar and adipose tissue- Sometimes called hypodermis- Storage for fat and large blood vessels that

supply the skin- Contains lamellated Pacinian corpuscles - nerve

endings sensitive to pressure

Cells of the Epidermis- keratinized stratified squamous epithelium

- *WHAT THE HECK DOES THAT MEAN????*

- Keratin - a protein- Stratified - in layers- Squamous - thin (like a floor tile)- Epithelium - densely packed cells

Epidermal Cells-contains 4 types of cells

1. Keratinocytes - produce keratin, a tough fibrous protein that protects skin and underlying tissues from heat, microbes and chemicals -also produces lamellar granules - a “waterproof sealant”

Epidermal cells (cont)

2. Melanocytes - produce melanin - a brown/black pigment that gives skin its color and absorbs damaging UV light

3. Langerhans cells - arise from red bone marrow - participate in immune response from microbes that invade the skin

Epidermal cells (cont)

4. Merkel cells - located in deepest layer of epidermis

- Contain a tactile (Merkel) disc - the flattened process of a sensory neuron

- Functions in the sensation of touch

Epidermal Layers- most body regions have 4 layers- Where friction is greatest (fingertips, soles,

palms) there are 5 layers1. Stratum basale - deepest layer

- Sometimes called stratum germinativum (indicates its role in forming new cells)

- Single row of cuboidal or columnar keratinocytes (melanocytes, Langerhans cells and Merkel cells are scattered within)

Skin Graft- During a skin graft, they remove a small

amount of the epidermis and culture the keratinocytes to produce thin layers of skin!

- Here’s a video showing a really cool skin graft! **Disclaimer** if you are squeamish, you might want to not watch!!

https://vimeopro.com/orthotraumaassn/2015-surgical-technique-videos/video/147855151

Epidermal layers (cont)2. Stratum Spinosum - “thornlike”

- 8-10 layers of polyhedral keratinocytes fit together (langerhans cells and melanocytes as well)

Epidermal layers (cont)3. Stratum granulosum - 3-5 layers of flattened keratinocytes undergoing apoptosis (normal death of cells). Contains:

a. keratohyalin - a protein that organizes filaments into thicker bundles b. lamellar granules - release a lipid-rich secretion that acts as a water-repellent sealant to protect against fluid loss & guard against entry of foreign particles

Epidermal layers (cont.)4. Stratum lucidum - only present in skin of fingertips, palms and soles of feet

- 3-5 layers of clear, flat, dead keratinocytes

5. Stratum corneum - superficial layer; continuously shed and replaced

-25-30 layers of flattened dead keratinocytes with lipids from lamellar granules in between the cells

Keratinization

- the process whereby new cells formed in stratum basale accumulate more and more keratin as they move from one layer to the next, then undergo apoptosis, get sloughed off and replaced by underlying cells

- takes ~ 4 weeks

Dermis

- Made up of connective tissue containing collagen and elastic fibers

- Contains few cells - fibroblasts, macrophages & adipocytes

- Blood vessels, nerves, glands and hair follicles are embedded here

- Contains 2 regions: papillary region & reticular region

Papillary region- superficial; consists of connective tissue and elastic

fibers- dermal papillae - small fingerlike projections that

increase the surface area- indent the epidermis; contain loops of capillaries- some contain Meissner corpuscles - tactile

receptors (nerve endings sensitive to touch) and some contain free nerve endings (initiate signals pertaining to temperature, pain, tickling, itching)

Reticular region- deeper; consists of dense connective tissue with

bundles of collagen and coarse elastic fibers- spaces between fibers are adipose cells, hair follicles,

nerves, sebaceous gland & sudoriferous (sweat) glands- the combination of collagen and elastic fibers gives skin

strength, extensibility (stretch) and elasticity (return to shape after stretching)

- striae - “stretch marks”; small tears that occur in the dermis due to extreme stretching

Epidermal Ridges-seen on surface of palms, fingers, soles and toes

- develop during 3rd and 4th fetal month as the epidermis conforms to the contours of the underlying dermal papillae of the papillary region

- function to increase grip by increasing friction

- ducts of sweat glands open on top of ridges as sweat pores

- ridge pattern is unique for each individual and doesn’t change throughout life

Skin Color3 pigments contribute to skin color

1. Melanin - located in the epidermis;

- the number of melanocytes are the same in all races; what differs is the amount of pigment the melanocytes produce

2. Carotene - used to synthesize pigments for vision

3. Hemoglobin - the oxygen carrying pigment in red blood cells

Albinism-an inherited disorder where the body does not produce melanocytes.

- no melanocytes...no melanin...no melanin, no color

Malignant Melanoma-melano = dark; -oma = tumor

- cancer of the melanocytes

- due to repeated exposure to UV light, amount of darkness of the melanin increases...this is why tanning beds are dumb!!

Skin color as diagnostic clues-Cyanotic - bluish appearance of skin, nails and mucus membranes due to insufficient oxygen

-Jaundice - yellowish appearance due to buildup of bilirubin in blood (usually indicates liver disease)

-Erythema - redness of skin; caused by engorgement of capillaries in the dermis with blood (could be from injury, infection, allergy)

Transdermal Drug Administration

-drug contained on an adhesive skin patch passes across the epidermis and into the blood vessels of the dermis

- released at a controlled rate over one to several days

- Nicoderm (nicotine), Scopalamine (motion sickness)

Wound Healing-how a wound heals depends on the severity of the wound

- Epidermal Wound Healing - for wounds that only affect the epidermis, like abrasions and minor burns

- Deep Wound Healing - for injury to the dermis & subcutaneous layer

Epidermal Wound Healing-basal cells of the epidermis enlarge & migrate across the wound until they meet cells from the opposite side of the wound..when they meet, they stop migrating - contact inhibition

-epidermal growth factor - hormone that stimulates basal stem cells to divide & replace the ones that moved into the wound...continues until the wound is resurfaced

Deep Wound Healing4 phases

1. Inflammatory phase -blood clot forms in wound - involves inflammation - helps eliminate

microbes, foreign material & dying tissue2. Migratory phase - clot becomes a scab

- Epithelial cells migrate under the scab, fibroblasts synthesize scar tissue, damaged blood vessels begin to regrow

Deep Wound Healing (cont)3. Proliferative phase - extensive growth of epithelial cells,fibroblasts deposit collagen fibers randomly & blood vessels continue to grow

4. Maturation phase - scab sloughs off once the epidermis is restored to its normal thickness; collagen fibers are more organized, fibroblasts decrease, blood vessels are restored to normal

Fibrosis

-process of scar tissue formation

Hypertrophic scar - scar within the boundaries of the original wound

Keloid scar - scar that extends beyond the boundaries of the original wound

Aging of Skin

- Noticeable around 40 years of age- Fibroblasts decrease in number, which

causes a loss of collagen fibers and a decrease in elasticity, so you begin to see wrinkles

- With further aging, Langerhans cells decrease, macrophages are less efficient, sebaceous glands decrease so skin becomes dry

- Number of melanocytes decrease, so hair also begins to grey BUT...the size of the melanocytes increases so you see atypical skin pigmentation (liver spots)

- Subcutaneous fat is lost leading to “thinner” skin that takes longer to heal

Accessory Structure of the Integumentary System

- Hair, sebaceous glands, sudoriferous glands and nails all develop from embryonic epidermis

Hair

-also called pili

- present on most skin surfaces, except for the palms and soles of feet

- made up of columns of dead, keratinized cells held together by extracellular proteins

Functions of Hair

-guards scalp from injury and UV rays

- decreases heat loss from the scalp

- eyebrows, eyelashes, hair in nostrils and ear canals protect from foreign particles

-functions in sensing light touch

Parts of Hair

Shaft - superficial portion that projects from the skin

Root - deep to the shaft; penetrates the dermis (& sometimes the subcutaneous layer)

Hair Follicle - surrounds the root

Bulb - base of each hair follicle; houses the papilla of the hair which contains connective tissues and blood vessels and the matrix, which is responsible for growth

*both the shaft and root have 3 layers

1. Cuticle - outermost layer2. Cortex - middle layer3. Medulla - inner layer where pigment

granules are located

Parts of hair (cont)

Matrix cells - arise from the stratum basale

- Responsible for growth of existing hairs and produce new hairs when old ones are shed (this replacement process happens within the same follicle)

Parts of hair (cont)Arrector pili - smooth muscle associated with hairs

- Normally, hair is at an angle to the skin...under physiological or emotional stress, autonomic nerve endings stimulate contraction of arrector pili muscles which pull the hair shaft perpendicular to the skin resulting in “goose bumps”

Parts of Hair (cont)

Hair root plexus - dendrites of neurons that surround each hair follicle

- these are sensitive to touch

Hair GrowthHappens in two stages:

1. growth stage - cells of the matrix differentiate, keratinize and die- As new cells are added at the base of the root

hair, hair grows longer 2. resting stage - when growth stops

- Scalp hair grows for 2-3 years, rests for ~ 3 months

- Normal hair loss is ~ 70-100 hairs/day

Hair Color- due to the amount and type of melanin in its

keratinized cells- melanin is synthesized by melanocytes

scattered in the matrix of the bulb and it passes into the cells of the cortex and

- decreased melanin production and increased air in the hair shaft produces grey and white hair

Skin Glands

Three types:

1. Sebaceous (oil) glands

2. Sudoriferous ( sweat) glands

3. Ceruminous glands

Sebaceous (oil) glands

- connected to hair follicles

- secreting portion is in the dermis and opens into the neck of the hair follicle...in some places like the lips and eyelids, they open directly onto the surface of the skin (absent in the palms and soles)

- vary in size and shape

- secrete sebum

Sebum- an oily substance which is a mixture of fats,

cholesterol, proteins, inorganic salts and pheromones

- coats the surface of hairs keeping them from drying and becoming brittle

- prevents excessive evaporation of water from the skin, keeps skin soft and inhibits growth of bacteria

Clogged Sebaceous glandsBlackheads - accumulated sebum & enlargement of sebaceous glands in the face

Pimples - sebum acts as a nutrient to bacteria, which is why there’s that yucky pus

** Dr. Pimple Popper video**https://www.youtube.com/watch?v=SHNqEWXXIBE

Sudoriferous (sweat) glands-3-4 million

-release secretions onto skin surface through pores or into hair follicles

- function is to regulate temperature through evaporation

-2 types of sudoriferous glands:

1. Eccrine sweat glands2. Apocrine sweat glands

Eccrine Sweat Glands-”secreting outwardly”

- distributed throughout the skin

- most numerous on forehead, palms and soles

- secretory portion is in deep dermis and ends in a pore at the surface of the dermis

- 600 ml sweat produced/day (contains water, ions, urea, uric acid, ammonia, amino acids, glucose and lactic acid

Body Odorperspiration/sweat - comes from eccrine glands, which function to regulate temperature and excrete waste

**what’s the difference between antiperspirant and deodorant??**

Apocrine Sweat Glands-found mainly in axilla, groin, areola, beard of men

- secretory portion is located in subcutaneous layer and duct opens into hair follicles

- don’t begin to function until puberty

- stimulated during emotional stress

Ceruminous Glands

- Modified sweat glands in the external ear that produce a waxy secretion called cerumen, which helps provide a sticky barrier to dirt and debris

Nails

-plates of tightly packed, hard, keratinized epidermal cells

nail body - portion that is visible

free edge - part that extends past the distal end of the digit

nail root - portion buried in a fold of skin

lunula - white crescent shaped portion at proximal end of nail body

hyponychium - beneath the free edge

- secures nail to the fingertip

eponychium - cuticle

- narrow band of epidermis that extends from and adheres to the margin of the nail wall

nail matrix - epithelium deep to the nail root

- Contains cells that divide mitotically to produce growth

- Superficial cells of the matrix become nail cells...harder outer layer is pushed forward over the stratum basale

Nail Growth

-growth is determined by how fast the matrix cells divide

- it also varies according to season, time of day and temp

- on average, nails grow ~ 1mm/week