Chapter 5- Integumentary System Flashcards
What are the two layers of the skin
- Epidermis
2. Dermis
Epidermis
unvascularized outermost portion of the skin, gets nutrients from diffusion from blood vessels in the dermis
What type of tissue makes up the epidermis
Stratified squamous epithelial tissue
Dermis
Vascularized, has nervous supply, makes up most of integument by mass
What type of tissue makes up the dermis
dense connective tissue
Hypodermis
Composed mostly of adipose tissue. Located below the dermis but superficial to the tough connective tissue wrapping (fascia) of the skeletal muscles
Functions of the hypodermis (4)
- Storage- easy to access energy source for the body
- Protection/shock absorption- prevents physical trauma to internal organs
- Insulation- prevents excessive heat loss
- Anchor- holds skin to underlying skeletal muscle tissue- is still flexible
Keratinocytes
produce keratin, the fibrous protein that helps give the epidermis its protective properties
How are keratinocytes linked
Linked by desmosomes (with some tight junctions) to hinder movement of water between cells
How do keratinocytes reproduce
Reproduce mitotically in stratum basale in response to epidermal growth factor, and from the bottom up- keratinocytes are dead once they approach the skin surface
Persistent friction to the epidermis causes
callus formation, a thickening of the epidermis to prevent excessive skin cell loss. Millions of cells are lost each day- you get a new epidermis every 25-45 days
Keratinocyte function
give the epidermis its protective qualities (tough and dry)
Where are melanocytes located in the epidermis
stratum basale
Melanosomes
Melanin producing organelle in the melanocytes
What happens to melanin after it’s produced by the melanosomes
Melanin is transferred to the keratinocytes and migrates to the superficial side of the keratinocyte to form a pigment shield that protects the nucleus and the nuclear DNA from the damaging effects of UV light. Melanin does not remain in the melanocytes
Dendritic cells (Langerhans cells)
Move to epidermis from bone marrow
Active macrophages- this activates the immune system
Located in the epidermis
Tactile cells (Merkel cells)
Present in epidermal-dermal junction
Associated with sensory nerve endings, resulting in sensory receptor function for 2 types of touch
What types of touch are detected by the tactile cells (2)
- Light touch
2. Vibration
What types of cells are located in the epidermis (4)
- Keratinocytes
- Melanocytes
- Dendritic cells
- Tactile cells
Layers of the epidermis (5)
- Stratum basale
- Stratum spinosum
- Stratum granulosum
- Stratum lucidum
- Stratum corneum
Stratum basale
innermost/deepest epidermal layer
Single layer of stem cells attached to dermis- the many mitotic nuclei in this layer suggests rapid cell division
Cell composition of the stratum basale
Mostly keratinocytes, 10-25% of cells are melanocytes
What happens in the stratum basale when cells divide
Reproduces from the bottom up. When cells divide, When cells divide, one daughter cell is pushed into the cell layer above to begin to specialize into a mature keratinocyte. The other remains in the stratum basale to make sure the layer is replenished
Stratum spinosum
Second deepest (spiny layer) due to spiny extensions of its keratinocytes, several cell layers thick. Contains pre-keratin- thick bundles of filaments that resist tension are are anchored to the desmosomes
Cell composition of the stratum spinosum
Dendritic cells are most abundant here
Stratum granulosum
Third deepest granular layer. Keratinization begins at this layer, has an
accumulation of two granule types (keratohyline and Lammelar granules). Cells here are especially tough and water resistant due to proteins within the keratinocytes and lipids deposited outside them
Keratohyline
One of the granule types that accumulates in the stratum granulosum, helps with formation of keratin in the upper layers of the epidermis
Lammelar granules
One of the granule types that accumulates in the stratum granulosum, ontains water resistant glyco-lipid that’s secreted into the extracellular space, the glycolipid plays a major part in slowing water loss across the epidermis along with tight junctions
Stratum lucidum
Fourth deepest layer. Relatively transparent, not found in thin skin. The cells in this layer are dead.
Stratum corneum
Most superficial “horny layer”, makes up most of the epidermis. These cells are dead.
Glycolipids between cells waterproof layer
Keratin inside cells protects from friction/abrasion and prevents huge amount of skin from being lost at once
These cells are shed regularly as dandruff or flakes from dry skin
Dermis
The “hide” of the body, makes up the bulk of the integument
Strong and flexible connective tissue with a semifluid matrix that is embedded with fibers and binds the entire body together
Fibroblasts and macrophages dominate here
It has 2 layers
What are the 2 layers of the dermis?
- Papillary dermis
2. Reticular dermis
Papillary dermis
Thin areolar connective tissue, fibers are thin- defensive cells wander freely here. Has projections called dermal papillae
Dermal papillae
Projections on the papillary dermis- increases the surface area of the dermis so the epidermis can be better attached to the dermis. Also, the amount of nutrients and oxygen passed on to the epidermis will increase
Can have either pain receptors or tactile corpuscles
The dermal papillae attach to the dermis, pulling it in, so the indents overlying the epidermis forms friction ridges
Fingerprints
Formed by the dermal papillae. Genetically determined feature- identical twins also have different fingerprints due to a combination of factors. These increase your sense of touch and help with grip
Reticular dermis
Lies deep to papillary dermis, dense irregular connective tissue, makes up 80% of dermal mass
Collagen and elastic fibers give the skin strength, resiliency, and stretch and recoil properties. Forms cleavage lines in the skin and flexure lines at/near joints
Cleavage lines
Formed by the reticular dermis. Not visible externally, lines are formed by alternating dense and less dense regions of fibers.
Very important for surgeons. The direction of the cleavage line determines the type of incision. Cutting perpendicular to the cleavage line will cause the fibers to snap and create a gaping hole- infection risk and makes sutures more difficult
Flexure lines
Formed by the reticular dermis. Dermis is tightly anchored here- does not move as easily.
It is forced to fold, forming creases that are externally visible (the lines on fingers and the palm). This gives the skin flexibility. These lines are found at the bottoms of feet, back of knees, front of elbow, fingers, palms
What is a blister?
A fluid filled pocket separating the epidermis and the dermis, caused by short term but acute trauma (like a burn or repeated friction)
Striae
Stretch marks. Extreme stretching of the skin, like during pregnancy, can tear the dermis and leave white scars called striae
What 3 factors help determine skin color?
- Melanin
- Carotene
- Hemoglobin
Melanin
polymer that comes in 2 forms: reddish yellow and brownish black. Skin color is dependent on the amount of melanin produced- the cells in the other 2 layers of the skin are composed of dead cells and don’t need to be protected, so they don’t get melanin. More melanin production= darker skin
Which enzyme synthesizes melanin?
tyrosinase
How does skin get darker?
Exposure to sun- DNA is damaged in the sun, repair is the first “signal” to produce melanin.
Keratinocytes release chemical to “activate” melanocytes
This defensive response causes tanning in individuals without very dark skin
Carotene
yellow orange pigment
Accumulates in stratum corneum and adipose tissue
Can be used by body to produce vitamin A- used for vision, epidermal health, also found in certain plant products (carrots)
Hemoglobin
pink/red pigment
Also found in red blood cells- red when bound to oxygen
Usually only seen in fair skinned individuals- pale skin results when blood moves away from the skin
Oxygenated pigment- color comes from blood supply to dermis (light skin is transparent so the color comes through).
How does a melanin buildup protect the DNA of skin cells?
A melanin buildup helps protect the DNA of skin cells from UV radiation by absorbing the rays and dissipating energy as heat