1
Q
What are the layers of the skin
A
- Epidermis
- Dermis
- Hypodermis
2
Q
Structure of Epidermis
A
- Superficial portion of skin
- Composed of epithelial tissue (keratinized stratified squamous epithelium)
-Avascular, meaning it has no blood cells
3
Q
Structure of Dermis
A
- Deeper layer of skin
- Composed primarily of connective tissue
- Contains blood and lymph vessels, nerves, and other structures.
- Made of two layers of connective tissue that compose an interconnected mesh of elastin and collagenous fibers produced by fibroblasts
4
Q
Structure of Hypodermis
A
- Also called the subcutaneous layer (sub Q)
- Lies deep and below the dermis
- Consists of areolar and adipose tissue which serves as an area for fat storage, blood vessel passage, and pressure nerve endings
- Serves to connect skin to the underlying fibrous tissue of the bones and muscles
5
Q
Name the layers of the epidermis
A
- Stratum basale
- Stratum spinosum
- Stratum granulosum
- Stratum lucidum
- Startum corneum
6
Q
Stratum basale
A
- Deepest layer of the epidermis and contains some stem cells capable of undergoing cell division to form new cells.
- Attaches the epidermis to the basal lamina (below the lamina is the dermis)
- Cells in this layer bond to the dermis via the basement membrane; which is intertwining collagen fibers
- Mostly a single layer of basal cells; which are cuboidal-shaped stem cells that help produce the keratinocytes of the epidermis.
- Keratinocytes are produced in this layer which then produce new cells
7
Q
Two other cells found among basal cells
A
- Merkel cells; functions as a receptor and is responsible for stimulating sensory nerves that the brain perceives as touch. (Abundant on the surfaces of hands and feet)
- Melanin: gives hair and skin its color and helps protect live cells of the epidermis from ultraviolet (UV) radiation
8
Q
Dermal papilla
A
- A finger-like projection or fold which is found superficially in the dermis.
- Increases the strength of the connection between the epidermis and dermis.
- The bigger the fold indications a stronger connection
9
Q
Stratum spinosum
A
- Provides strength and flexibility to the skin
- Spiny appearance due to the protruding cell processes that join the cells via the desmosome
- Desmosomes interlock with each other and strengthen the bond between the cells
- Composed of 8-10 layers of keratinocytes and Langerhans cells; which functions as a macrophage by engulfing bacteria, foreign particles and damaged cells that occur in the layer.
- Keratinocytes in this layer begin the synthesis of keratin and release a water-repelling glycolipid that helps prevent water loss from the body and makes the skin mostly water-proof
10
Q
Stratum granulosum
A
- Marks the transition between the deeper, metabolically active strata and the dead cells of the more superficial strata
- Also where a water-repellent sealant forms between the cells
- Has grainy appearance from he changes of the keratinocytes being pushed into this layer
- The cells in this layer become flatter, the cell membranes thicken, and they generate large amounts of the proteins keratin which is fibrous and keratohyalin.
- Keratohyalin accumulates as lamellar granules within the cells. When cells die they leave behind cell membrane, keratohyalin and keratin which help form structure of skin and nails.
11
Q
Stratum lucidum
A
- Present only in the fingers, palms and soles
- Smooth translucent layer
- Keratinocytes in this layer are dead and flattened
- Cells are densely packed with eleidin; which is a clear protein rich in lipids that are derived from keratohyalin which makes cells transparent and provides a barrier to water.
12
Q
Stratum corneum
A
- Most superficial layer; which consists of a lot of dead cells
- Has lamellar granules that make it water-repellent
- Constant exposure to friction causes this layer to increase in depth by forming a callus; which is an abnormal thickening of the epidermis
- Has increased keratinization; or cornification that gives the layer its name. Cornification is keratinization plus the lamellar granules that form lipids that hold the dead keratinocytes together.
- 15-30 dry dead layers that helps prevent the penetration of microbes and dehydration of underlying tissue.
- Provides a mechanical protection against abrasion for more delicate underlying tissue.
13
Q
Keratinization vs. Cornification
A
- Keratinization is the process of keratinocytes in the basal cell layer maturing and dying to produce the stratum corneum layer.
- Cornification is the increased keratinization plus the lamellar granules in the corneum that form lipids to hold the dead keratinocytes together.
14
Q
Four cell types of the epidermis
A
- Keratinocytes
- Melanocytes
- Langerhans cells
- Merkel cells
15
Q
Keratinocytes
A
- Produce the protein keratin; helps protect the skin and underlying tissue from heat, microbes, and chemicals
- Keratin produces lamellar granules, which produce water-repellent sealant
- Keratinization; replacement of cells contents with the protein keratin, occurs when cells move to the skin surface within 2-4 weeks.
16
Q
Melanocytes
A
- Produces the pigment melanin; which contributes to skin color and protects skin by absorbing damaging UV light.
17
Q
Langerhans cell
A
- Participates in immune response
- Act as an outermost guard of the cutaneous immune system and are likely to induce the first reactions against pathogens encountered via the skin
18
Q
merkel cell
A
- Touches a sensory structure called a tactile (merkel) disc and functions in the sensation of touch
19
Q
The two regions of the dermis
A
- The dermis is composed of connective tissue containing collagen and elastic fibres and has two regions
- The papillary layer
- The reticular layer
20
Q
Papillary layer
A
- Areolar connective tissue that contains fine elastic fibers, dermal papillae, corpuscles of touch (Meissner’s corpuscles), and free nerve endings for sensations of heal, cold, pain, tickle, and itch.
- Superficial layer projects into the stratum Basale of the epidermis to form finger-like dermal papillae.
- Sensory receptor in this layer is dermal papillae; indent the overlying dermis and house capillary loops and sensory receptors.
21
Q
Reticular layer
A
- Under the papillary layer is the much thicker reticular layer.
- Functions to strength skin and provide structure and elasticity.
- It is composed of dense, irregular connective tissue that contains bundles of collagen fibers and some elastic fibers.
- Sensory receptors in this layer is Pacinian corpuscles which detects pressure and vibration stimuli
22
Q
Epidermal ridges
A
- Feature of the papillary layer of the dermis.
- Caused by epidermis’s adaptation to the contours of the dermal papillae that are in the papillary layer of the underlying dermis.
- Increases friction for better grasping ability and provides the basis for fingerprints and footprints.
23
Q
Pigments responsible for skin and hair color
A
- Melanin (black, brown)
- Carotene (yellow, orange)
- Hemoglobin (in blood capillaries) -> lack of oxygen makes skin pale but with proper oxygen flow it returns back to normal pigment
24
Q
Melanin
A
- Two types of melanin; eumelanin (black and brown) and pheomelanin (red)
- Darker skin has more melanin produced by melanocytes than paler skin.
- Helps prevent the breakdown of folic acid which is required process in the human body.
- Too much melanin can interfere with vitamin D production which is needed to absorb calcium.
25
Accumulation of melanin
- The sun and UV rays stimulate keratinocytes to start manufacturing melanin by secreting chemicals that activate the melanocytes.
- Melanocytes are the cells that synthesize melanin. They are found in the organelle melanosome. And the melanosome is found inside the keratinocyte.
- A lot of melanin causes the skin to darken
26
Cell that synthesizes and stores pigments
- Melanocytes synthesize and store the pigment melanin
- Epidermal cells synthesize and store the pigment carotene
- Red blood cells synthesize and store the pigment hemoglobin in blood capillaries.
27
General structure of hair
- Hair consists of;
1. Hair shaft; which is above the surface of the skin
2. Root; that penetrates the dermis and subcutaneous layer
3. Hair follicle; consisting of two epidermal layers surrounding the root
- Non-living hair shaft and living hair root are continuous with each other and consist of an outer cuticle, inner medulla, and innermost cortex.
- Hair follicle consists of;
1. An enlarged base called the hair bulb
2. A hair papilla that has many blood vessels to nourish the growing hair
3. Hair matrix; that contains mitotically active cells to produce new hairs.
28
Hair function
- Provides protection
- Thermal insulation
- Sensing light touch
29
Glands associated with the skin
- Sebaceous (oil) glands
- Sudoriferous (sweat) glands
- Ceruminous glands
30
Sebaceous (oil) glands
- Usually connected to hair follicles; they are absent in the palms and soles.
- They produce sebum, which moistens hairs, waterproofs and softens the skin and inhibits bacterial growth.
31
Sudoriferous (sweat) glands
- Divided into apocrine and eccrine types;
1. Eccrine sweat glands; help to regulate body temperature through evaporation, and eliminate wastes such as urea.
2. Apocrine sweat glands are limited to the skin of the axilla, pubis, and areolae; their ducts open into hair follicles.
32
Ceruminous glands
- Modified sudoriferous glands that produce a waxy substance called cerumen.
- These glands are found in the external auditory meatus.
33
Functions of the skin
- Thermoregulation
- Protection through physical, chemical, and biological barriers
- Cutaneous sensations; touch, pressure, vibration, tickle, heat, cold and pain.
- Excretion and absorption
- Synthesis of vitamin D
34
Protection of skin through physical, chemical, and biological barriers
- Function of skin
- Acts as a protective barrier against water loss
- First line of defense against abrasive activity
35
Sensory function (cutaneous sensations)
- Function of skin
- Skin acts as sense organ because the layers of the skin contain specialized sensory nerve structures that detect touch, surface temperature and pain.
- Receptors are more accumulated on the tips of fingers, this includes the;
1. Meissner corpuscle (tactile corpuscle) that responds to light touch
2. Pacinian corpuscle (lamellated corpuscle) that responds to vibration.
36
Thermoregulation
- Function of skin
- Through association with the sympathetic nervous system it helps regulate temperature.
- Sweat glands release sweat to cool skin down.
37
Vitamin D synthesis
- Function of skin
- Epidermal layer of human skin synthesizes vitamin D when exposed to UV radiation.
- Vitamin D is essential for normal absorption of calcium and phosphorous which is required for healthy bones.
38
biology 1593
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