13. Skin Flashcards
What are the 3 layers of skin?
Epidermis
Dermis
Hypodermis
What does the thickness of the hypodermis vary upon?
Upon different regions of the body and different people
In men, where is the hypodermis thickest in?
abdomen and shoulders
In women, where is the hypodermis thickest in and why?
hips, thighs, and buttocks- evolutionary advantage to store fat to produce milk
In both men and women where is the hypodermis relatively thick in?
palms of the hands and soles of feet - acts as a shock absorber
Where is the hypodermis found?
Lowest layer of skin
What is the hypodermis also know as?
sub-cutaneous layer
Describe the structure of the hypodermis
- Mainly contains adipose tissue (some neurovascular bundles/lymphatics)
- Loose connective tissue – fibroblasts/ macrophages/fibres/mast cells
What are the 5 functions of hypodermis?
- Provides energy store – provides fuel to generate heat
- Insulator for underlying muscle heat generation
- Shock absorber – cushions impacts/protection for underlying structures e.g. think about fat on the buttocks when sitting
- Connects skin to underlying muscle and bones
- Makes hormones, e.g. leptin to control eating habits
Where is the dermis layer found?
Between epidermis and hypodermis
What is the dermis also know as and when combined with epidermis?
Corium AND with epidermis - cutis
Describe the structure of the dermis layer
Three layers
• Papillary - upper
• Reticular - lower - connective tissue
• Dermal papillae – interdigitating
What are the 3 functions of the dermis?
- Contains hairs and sweat glands - thermoregulation
- Contains sensory structures – special senses - touch
- Gives structure to skin and so body shape
What is the location of the epidermis?
Outermost layer made of epithelial cells (keratinocytes)
Describe the structure of the epidermis
- Four layers of cells in thin skin
- Five layers in thick skin
- Held together (laterally) by adherens junctions - layers held together by desmosomes
- Some terminal nerve endings
- NO blood vessels
What are the 5 functions of the epidermis?
- Prevents water loss - can absorb water as well
- Prevents entry to bacteria and parasites
- Special cells that present pathogens to immune cells
- Synthesis of keratin
- Prevents underlying tissue loss due to abrasion
What are the 4/5 layers of the epidermis?
- Stratum corneum
- Stratum lucidum
- Stratum granulosum (granular layer)
- Stratum spinosum
- Stratum basale
Describe the stratum corneum layer
- Outermost layer made of squames (dead keratinocytes)
- Thick on palms and soles of feet – prone to injury
- Continuously shed
Describe the Stratum lucidum
- Only on palms and soles of feet
* Very thin layer
Describe the Stratum granulosum (granular layer)
• Stratified squamous epithelium
• contain Lamellar granules (filament-associated proteins that assemble keratin fibrils and secrete it)
• contain Tonofibrils (bundles of keratin filaments and keratohyalin granules)
made by lamellar bodies
Describe Stratum spinosum layer
• Cuboidal epithelium arranged in 3 layers (held together by
desmosomes)
• Producers of lamellar bodies (keratin factories)
• First time Golgi apparatus appears
Describe the Stratum basale (basal cell layer)
- Tall columnar epithelial cells
- Constantly renew keratinocytes by cell division
- As daughter cells differentiate they move away from the epidermis-dermis junction -They lose their ability to divide
- These make keratin filaments (tonofilaments)
- Also home to the melanocytes – produce melanin
Describe the keratin synthesis pathway
Starting at the bottom:
• Basal cell (keratinocyte)has intermediate keratin filaments(tonofilaments)
• As it divides, it makes cuboidal epithelial cells called spinous cells - first see the appearance of lamellar bodies (keratin forming factories )and mitochondria
• As the spinous cells move further away from basal surface, they differentiate into granular cells which contain keratohyalin granules and the Golgi apparatus
• This is where keratin is layed out
• As the cells move away from the surface, they die out(apoptosis) but are held together by desmosomes
• As they move further away, proteins are produced which break down the desmosomes - the squames can seperate
• The keratin fibrils are now called tonofibrils
Which cells synthesise keratin?
Keratinocytes - lamellar bodies found in keratinocytes.
Keratinocytes are found in basal layer and different into granular cells as they move up towards the stratum corneum
What are keratin the main constituents of ?
Hair, nail, animal horns
What is the normal transit time o a keratinocyte from basal layer to stratum corneum?
28-40 days
In which disease is the transit time reduced to 2-3 days?
Psoriasis
What does psoriasis result in?
• Psoriasis is a skin condition that causes red, flaky, crusty patches of skin covered with silver-coloured scales.
Describe what causes psoriasis
In individuals with psoriasis, the transit time from basal layer to stratum corneum is reduced. As a result, cells that have not yet fully matured accumulate in the stratum corneum and the outer layer of keratin, which is relatively thin is lost causing the signs of crusty red patches covered with silvery scales. The cells at the surface are also lost very quickly too as they are ‘rubbed’ off.
What are the 3 cells present in the epidermis?
Melanocytes
Langerhan cells
Merkel cells
What do melanocytes produce?
produce melanin, the main pigment that gives the skin its
colour produce more melanin
Are there more melanocytes in black or tanned skin?
No, Number of melanocytes not increased, but amount of melanin released, increased
What are langerhan cells?
highly specialised capacity to present antigens to T lymphocytes mediate immune reactions e.g. in allergic contact dermatitis
What are merkel cells?
mechanoreceptor cells associated with sensory nerve
endings. They account for approximately 6% to 10% of
the cells in the epidermis
What are the two types of skin?
Hairy, thin skin
Non hairy, thick skin
What are the exceptions to the rule of the two types of skin?
the lips, back of the ear, some areas of the external genitalia
Where are non hairy, thick skin found?
- Palmar surface of hand
- Plantar surface of the foot
- Area between fingers and toes (webs)
What is the structure of non hairy thick skin?
- Same as rest of body except:
- NO hair, arrector pili muscles, no sebaceous glands
- Thicker strata corneum
- Thinner dermis
- Increased density of mechanoreceptors
What are the 3 functions of non hairy skin?
- Prevent tissue loss due to abrasion
- Increased friction between skin and surfaces
- Increased sensation
What are the differences between thick non hairy skin and thin hairy skin?
> Thick skin have No hair follicles
thin skin have hair follicle
> thick skin have no sebaceous glands
thin skin have sebaceous glands
> thick skin have no arrector pili muscles
thin skin have arrector pili muscles
> thick skin have pronounced ridges and furrows on surface
thin skin have smaller ridges and furrows
> thick skin have regulate shaped dermal papillae
thin skin have irregular dermal papillae
> in thick skin, stratum lucidum is often seen
in thin skin, stratum lucidum is absent
What are skin appendages?
Skin appendages are skin-
associated structures that
serve a particular function
Give 5 examples of skin appendage
Hairs Arrector pili Sebaceous glands Sweat glads Nails
What are the 3 different types of hair?
Lanugo
Vellus
Terminal
What is lanugo?
The hair that cover the devoloping fetus
What is vellus?
The hair that replaces lanugo
Describe the appearance of vellus
Short, thin, light coloured and soft (not
connected to sebaceous gland)
Where is terminal hair found?
head (scalp and eyebrows, nasal passage), axillae, external genital region
Describe the appearance of terminal hair
Long, wide, dark coloured and coarse
What results in the production of terminal hair?
actions of testosterone
What are the 4 functions of hair?
Thermoregulation
Sexual attraction
Sensation
Protection
How are hairs involved in thermoregulation?
• Hair lays flat when body temperature is within normal range or elevated
• Hair stands erect when body temperature is lower than normal range
-Arrector pili muscle contracts when stimulated by sympathetic fibres from the autonomic nervous system
• Also acts a partial barrier to UV rays (scalp)
How are hairs involved in sexual attraction?
• Hair style can be alluring!
• Apocrine sweat glands secrete oils (pheromones) that attract the opposite sex.
Hairs trap these oils and accentuate their pungency
How are hairs involved in sensation?
Hairs have sensory nerve endings within the bulb.
Air movement, physical interaction, vibrations transmitted to the bulb sensed and transmitted to CNS.
Provides sensory awareness
How are hairs involved in protection?
- Eyelashes and nasal hair prevent dust and pathogens from entering the body
- Eyebrows reduce the amount of light and sweat from entering the eyes
- Axilla hair acts as a conduit to conduct sweat away from the body
What are arrector pili muscles?
The arrector pili muscles are small muscles attached to hair follicles in mammals. They consist of smooth muscle fibres attached to
papillary region of the dermis (origin) and hair bulb (insertion).
What is the role of arrector pili muscle?
- Involved in moving hair follicle
- It is a skeletal muscle cell
- attached to bulb of bottom of hair follicle
- When it contracts, it moves bulb towards itself which raises the hair so it stands up erect
• Fight or flight response’ or ‘cold’ causes involuntary contraction - ‘goose bumps’
• May also induce sebum release from
sebaceous gland - advantage in flight or fight as more slippery
What are the 7 mechanoreceptors in skin?
- End bulbs – thermoreceptor – register temperature
- Free nerve endings have nociceptors – register pain
- Tactile discs
- Meissner corpuscle
- Pacinian corpuscle
- Ruffini’s corpuscle
- Root hair plexus
What do thermoreceptors detect?
Temperature
What doe nociceptors register?
Pain
What do tactile discs sense?
touch, pressure and texture
What are the two types of tactile discs found in hairy and non hairy skin?
Merkel in non-hairy skin
Meissner in hairy skin
What does the meissner corpuscle detect?
Tapping and flicker movements
What’d ones the pacinian corpuscle detect?
Vibration
What does the Ruffini’s corpuscle detect?
joint movements and tissue stretch
What does the root hair plexus detect?
vibrations in the hair shaft
Describe the location of nails
Distal surface of phalanges (fingers and toes)
Describe the structure of nails
Consists solely of alpha keratin and has:
nail plate, the nail matrix and the nail bed below it, and grooves
surrounding it
What are the 4 functions of nails?
• Protection of distal phalanx and surrounding soft tissues from
(e.g. pulling out a splinter in one’s finger), and certain cutting or scraping actions
• Enhances precise delicate movements of the distal digits through
counter-pressure exerted on the pulp of the finger
• Enhancing the sensitivity of the fingertip (even though the nail itself
has no nerve endings)
• As a tool, enabling the so-called “extended precision grip”
What is the growth of nails correlated with?
Length of phalanx
What are the 8 functions of the skin?
- Protection and repair
- Temperature regulation and excretion of waste products
- Lubrication
- Storage
- Vitamin d synthesis
- Absorption
- Aesthetics
- Sensation
How is skin involved in protection and repair?
epidermis by keratinocytes and UV protection by melanocytes invasion by Langerhans cells
papillary dermis by fibroblasts (wound healing)
reticular dermis/hypodermis by fibroblasts/mast cells and macrophages
How is the skin involved in Temperature regulation and excretion of waste products?
Sweat glands – urea, sodium chloride and water, some CO2
How is skin involved in lubrication
Sebaceous glands release oil onto the surface (also acts as water barrier)
How I is the skin involved in storage?
White adipose cells provide lipids for energy
How is skin included in vitamin d synthesis ?
Cholecaliciferol produced in the skin is converted into 25-hydroxyl cholecalciferol (25-OH) by the liver and then into
1, 25-hydroxyl cholecalciferol (1,25 OH) VitD (the active vitamin) by the kidney
How is the skin involved in absorption?
Absorbs small amounts of water and O2 (some drugs – steroids can be applied and absorbed through the skin)
How is the skin involved in aesthetics?
Skin as a mode of communication or attraction (tattoos, piercing, hair-styles, etc.)
How is the skin involved in sensation
Specialised structures call mechanoreceptors (pain, pressure, touch, arousal, etc.)
