Skin Flashcards
What is a function of the skin relating to protection?
It protects underlying tissues and organs from impact, abrasion, fluid loss and chemical attack
What are the 8 basic functions of the skin and the accessory structures?
- protection
- excretion
- maintaining body temperature
- producing melanin
- producing keratin
- making vitamin D3
- store lipids
- detection
What is the function of the skin relating to excretion?
the integumentary glands excrete salts, water and organic wastes
What is the function of the skin relating to maintaining body temperature?
It maintains normal body temperature through insulation or evaporative cooling
What is the function of the skin relating to the production of melanin?
Melanin protects the underlying tissue from UV radiation
What is the function of the skin relating to the production of keratin?
Keratin protects against abrasion and serves as a water repellent
What is the function of the skin relating to the synthesis of vitamin D3?
Vitamin D3 is a steroid that is converted to calcitriol
What is the function of the skin relating to the storage of lipids?
Lipids are stored in the adipocytes in the dermis and in the adipose tissue in the subcutaneous layer
What is the function of the skin relating to detection?
It detects touch, pressure, pain, and temperature stimuli, and relay that information to the nervous system
Skin is an ________ and is made up of how many of the four tissue types?
Organ
Four of them (ie. all)
What are the three layers of the skin called?
- epidermis
- dermis
- hypodermis
The cutaneous layer consists of which layer(s) of the skin?
epidermis and dermis
The subcutaneous layer consists of which layer(s) of the skin?
hypodermis
Briefly describe the epidermis
- stratified barrier
- mostly keratinocytes which contain lots of keratin
- no circulation (avascular) so you won’t bleed when grazed
Briefly describe the dermis
- does not shed (dead cells are broken down into the circulatory system)
- protein fibres (collagen and elastin) for strength
- vascular to nourish the epidermis
What are the layers of the dermis?
Papillary layer
Reticular layer
What is the purpose of the papillary layer of the dermis?
to increase the surface area for attachment, firmly binding the epidermis to the dermis
this allows a better transfer of nutrients to the epidermis
What is the purpose of the reticular layer of the dermis?
It is a mesh where collagen and elastin overlap to give strength
What are the 5 layers of the epidermis called?
- stratum corneum
- stratum lucidium (only found in thick skin)
- stratum granulosum
- stratum spinosum
- stratum basale
Describe the stratum corneum
dead, dried out cells without nuclei which provides an essential protective function
Describe the stratum granulosum
- contains granules that promote dehydration of the cell and cross-linking of keratin fibres to make hard barrier towards outside
- waxy material is secreted into intercellular spaces to act as a barrier
Describe the stratum spinosum
- cells are spiny when dried as desmosomes link the cells together to make barrier
Describe the stratum basale
- columnar (tall) regenerative cells
- like the stem cells of the skin making each cell as they grow and divide out
Which layer of the skin can be completely removed?
The stratum corneum
What tissue type dominates the epidermis?
epthelial
What are the two types of epithelial cells?
Simple
Stratified
What are the three types of epithelial cells that make up both simple and stratified epithelial cells?
Squamous
Cuboidal
Columnar
What epithelial cell does the epidermis mainly consist of?
Stratified squamous epithelium
Briefly describe the hypodermis
contains adipose tissue for insulation
Describe the difference between thick and thin skin
- thin sin covers most of the body whereas thick skin is found on the palms and the soles of the feet
- thin skin has hair whereas thick skin has no hair
- thick skin has an extra epidermal layer (stratum lucidum)
- the epidermis is much thicker in thick skin that in thin skin as there is also a lot of stratum corneum
What are 6 effects of ageing on the skin?
- thin epidermis
- thin dermis causing sagging and wrinkles as there is reduced collage
- slower skin repair
- drier epidermis as there is less sebum
- impaired cooling as there is less sweat
- less pigmentation causing pale skin and hair
Describe the keranocyte conveyor and its purpose
Cells are produced in the stratum basale and are moving their way out. If an infection affects the lower living cells, the infection is grown out and shed
Describe squamous epithelial cells
Flat cells, like scales
Describe columnar epithelial cells
long, tall cells
What are four accessory structures of the skin?
Hair
Sweat glands
Receptors
Nails
What four things does hair consist of?
hair shaft
hair follicle
arrector pili muscle
sebaceous gland
Where is the hair shaft located?
epidermis
Where is the hair follicle located?
dermis
Describe the role of the arrector pili muscle
It is attached to the hair follicle which makes the hair stand up and cause goosebumps when contracted
Describe the role of the sebaceous gland
produces sebum
Describe sebum including where it is located and what it does
Sebum is produced in the sebaceous gland in the dermis. It is waxy and oily and travels on the hair shaft to nourish the hair. It can also remain on the skin to act as a natural moisturiser and water repellent, especially on the head, shoulders, back and chest.
What causes acne?
sebum can block the hair follicles which can cause an infection
What are the two types of sweat glands?
Eccrine and apocrine
What is the difference between eccrine and apocrine sweat glands?
Eccrine sweat glands are everywhere and are responsible for thermoregulation whereas apocrine sweat glands are located in the nipples and armpits. They are specialised and situated deeper in the skin and release sweat into the base of hair follicles
What are the three types of receptors of the skin?
Tactile
Lamellar
Bulbous
What are the two roles of the nails?
Provide structural integrity to protect fingertips
Enhancing sensations
Where is melanin produced?
In the melenocytes
Melanin is transferred to outer layers of epidermal cells in vesicles called
melanosomes
What is a mole?
A cluster of melanocytes and over-proliferation can be caused by sun exposure
What is a freckle?
Melanocytes overproducing melanosomes but overproduction is triggered by sun exposure
Where are melanocytes located?
in the stratum basale
Where are melanosomes located?
throughout the epidermis and it’s shed with the keratinocytes
Does the density of melanocytes differ between races?
No
Describe a tattoo
artificial pigmentation deposited in the dermis and captured (but not broken down) by immune cells/scar tissue
What do receptors in the skin (especially the fingertips) work on the basis of?
They work on the basis of deformation (ie. how deformed the receptors come once we touch them).
How do the nails enhance sensation?
If we don’t have a backing on the fingers, we aren’t going to get enough deformation and not sense as much
What is the advantage of having melanosomes in the dead outer layers of the skin?
The melanin can absorb UV light before it reaches the living tissue
As we age, what happens to melanocytes/melanosomes?
There might be fewer melanocytes or less production of melanosomes so there is less pigmentation as we age.
Highly pigmented people tend to live around the _______ and why?
equator because there is higher levels of UV exposure
Why do we have less pigmentation at higher latitudes?
Because UV is essential for the production of vitamin D
What does vitamin D do?
normal calcium metabolism and strong bones and can affect mood
What are the five touch receptors of the skin called?
- free nerve endings
- tactile (Merkel) disks
- tactile (Meissner) corpuscles
- lamellar corpuscles
- bulbous corpuscles
Most receptors are responsive for more than ________ but each receptor will respond to best to a ________
one stimulus
particular stimulus
What is the most common touch receptor?
free nerve ending
Describe a free nerve ending:
- what is it?
- where is it?
- what does it look like?
- what features does it have and what do they act as?
- myelinated or unmyelinated?
- a sensory nerve terminal branching and extending to the epidermis
- there is swelling at the end (this is the sensory terminal)
- the sensory terminals have receptors which act as cation channels when the appropriate stimulus is applied
- mostly un-myelinated small fibres but also some small diameter myelinated fibres
What happens when cations come into the sensory terminals in free nerve endings?
Na+ and Ca2+ come into the terminal, there is a depolarisation and an action potential is propagated to the somatosensory cortex
What five things do free nerve endings respond to?
- temperature
- painfull stimuli
- some movement and pressure
- some to itch (eg. in response to histamine)
- some wrap around hair follicles acting as light touch receptors which detect the bending of hairs (eg. when a mosquito lands on your skin)
What is it called when free nerve endings wrap around hair follicles?
peritrichial endings
Describe tactile (Merkel) discs
- what are they?
- what are they associated with?
- where are they found?
- what are they sensitive to?
- free nerve endings in the deepest layer of the epidermis
- also associated with Merkel cells
- abundant in fingertips and very small receptive fields
- sensitive to an objects physical features (texture, shape and edges, fine touch and light pressure)
What are Merkel cells?
disc shaped epidermal cells
Explain how tactile discs interact with Merkel cells
Merkel cells detect stimuli and transduce that to the sensory nerve terminal.
There is a depolarisation of the sensory nerve terminal and an action potential is propagated to the somatosensory cortex.
Describe tactile (Meissner) corpuscles
- where are they located?
- what do they look like?
- what surrounds them?
- what happens when the _______ is deformed?
- located in the papillary of the dermis especially in hairless skin
- branching unmyelinated sensory nerve terminals surrounded by specialised Schwann cells (not for myelination but for support)
- then a thin layer connective tissue capsule around the outside
- when the capsule is deformed, Na+ channels will open and an action potential is propagated to the somatosensory cortex
What five things do tactile (Meissner) corpuscles sense?
- delicate/fine touch
- shape and textural changes in exploratory touch
- movements over the surface of the skin
- light pressure
- low frequency vibration
Describe lamellar (Pacinian) corpuscles
- where are they?
- what do they look like?
- what are the ______ separated by?
- what are deformed due to?
- what happens when they deform?
- are they rapidly adapting?
- deep in the dermis or hypodermis
- a single dendrite lying within concentric layers of collagen fibres and specialised fibroblasts
- layers separated by gelatinous interstitial liquid
- deformed due to deep pressure or vibration
- deformation opens pressure sensitive Na+ channels in sensory axon
- rapidly adapting
Why are lamellar (Pacinian) corpuscles rapidly adapting?
Because their collagen layers resume shape and respond to another stimulus. This is how they can detect vibration.
Describe bulbous corpuscles (Ruffini’s endings)
- where are they located?
- what do they look like?
- what happens when pressure is applied?
- where are they mostly found and why?
- located in the dermis and hypodermis
- network of nerve endings intertwined with a core of collagen fibres that are continuous with those of the surrounding dermis
- capsule surrounds the entire structure
- pressure in dermis distorts the bulbous corpuscles
- high density around fingernails so may have a role in monitoring of slippage of objects across the surface skin
Describe the role of blood flow in temperature regualtion
In the hypodermis, arteries are supplying blood to the venous plexus (veins). Some of the branches of artery are extending to the dermis and up to the epidermis, there are loops of capillaries.
In the blood vessels, there are muscles in the walls of the arteries and bands of smooth muscle (capillary sphincters) with can constrict or relax to control blood flow to the capillaries
Describe how the capillary sphincter is controlled and how it controls thermoregulation
The smooth muscles in walls of the arteries and the capillary sphincters are controlled by the sympathetic nervous system.
NE is released and this binds to α1 receptors on the vascular smooth muscle. This causes a second messenger molecule to be released and there is an increase in Ca2+ concentration to cause contraction and there is reduced blood flow to the skin. If the sympathetic nervous system activity is reduced, the muscles relax and there is increased blood flow to the skin.
What is the normal body temperature range for humans?
36.5 - 37.5 degrees celcius
What are the four primary mechanisms of heat transfer?
Radiation
Evaporation
Convection
Conduction
Briefly describe radiation
Heat loss due in the form of infrared rays
Briefly describe conduction
the transfer of heat to objects or media with which we are in contact
Briefly describe convection
it first involves the transfer of heat to air (or water) by conduction followed by the movement of the air (or water) away from the skin (ie. replaced the warm air around your body with cold stuff) to maintain the gradient of heat loss.
Briefly describe evaporation
water evaporates from (mainly) the surface of the skin and it takes the heat energy from our body
the eccrine sweat glands are innverated by the
sympathetic nervous system
Describe how the eccrine sweat glands release sweat (both temperature and nervous)
Unusually, the sympathetic nerves release ACh which binds to the mAChRs to release sweat
They can also be stimulated by adrenaline in the blood acting on β receptors
What happens when the body temperature increases?
- the heat sensitive neurons in the pre-optic area of hypothalamus are activated
- there is a decrease of SNS activation of α1 receptors which causes vasodilation
- there is an increase in SNS activation of mAChRs on sweat glands to cause sweating
- increase in respiratory rate
- behaviour changes
What is it called when the capillary sphincters open and blood can flow closer to the skin?
vasodilation
When are radiation, conduction and convection not effective heat loss mechanisms?
when the environmental temperature is higher than the body temperature
What 6 things happen when the body temperature decreases?
- the cold sensitive neurons in the preoptic area of the hypothalamus are activated
- shivering
- non-shivering thermogenesis
- increased thyroxine
- arrector pili muscle activation
- heat is transferred from the arteries to the veins so that the warm blood in the arteries doesn’t go to the skin but is transferred to the veins bringing cold blood to the core
Describe the process of shivering
- increased tone of skeletal muscles
- when tone rises above critical level, shivering begins due to oscillatory contractions of agonists and antagonist muscles mediated by muscle spindles
Describe non-shivering thermogenesis:
- increased ____ activity and increased circulating ____ and ______ from the _____ ______
- increased _______ _______ eg. increased ________ in the ____ and ______
- _____ of _____ _____ (ie. _____ produced instead of ATP)
- increased SNS activity and increased circulating adrenaline and NE from adrenal medulla
- increased cellular metabolism eg. increased glycogenolysis in liver and muscle
- uncoupling of oxidative phosphorylation (ie. heat produced instead of ATP)
Describe the process of increased thyroxine
- in response to TRH and TSH
- increased basal metabolic rate
Describe the activation of arrector pili muscles
- smooth muscles are innervated by SNS (α1) receptors
- contraction pulls the hair upright and dimples the skin, giving goose bumps
- compresses the sebaceous glands which lubricates the skin
- traps a layer of warm air around the skin
Describe a first degree burn
- what is effected?
- what does it look like and why?
- are there blisters?
- what does the skin retain?
- how long does it take to heal?
- only epidermis affected
- red, dry, painful because of the inflammation sensitising nerve endings
- no blisters
- skin retains a water and bacterial barrier
- heals within 7 - 10 days
Describe a second degree burn
- what is affected?
- what does it look like and why?
- how long does it take to heal?
- it can look ____
- what remains intact?
- what may be lost?
- epidermis and varying amounts of the dermis affected
- painful, moist, red and blistered because water proof keratin layer gone
- heal 1-2 weeks
- can look waxy
- hair follicles and sweat glands remain intact
- some tactile receptors may be lost
Describe a third degree burn
- where is it?
- what does it look like?
- is there pain? If not, why not?
- what may be required?
- extends into the subcutaneous tissue
- waxy white or deep red or black
- hard dry and leathery
- no pain because nerve endings are destroyed
- may require skin grafting
Why is fluid loss a major consideration for burn sufferers?
because the waterproofing epidermal layer has gone
How can we work out the fluid replacement?
using the rule of nines to find the amount of body burnt and weight of person
Describe the rule of nines
For adults:
- head 9%
- upper limb 9% each
- trunk 36%
- genitalia 1%
- lower limb each 18%
What are potential complications of severe burns directly related to skin function? (4 things)
- dehydration and hypovolemic shock (shock from loss of blood pressure)
- infection/sepsis
- hypothermia (due to large areas of evaporative heat loss)
What are potential complications of severe burns not directly related to skin function? (5 things)
- electrolyte imbalance
- hypo-metabolism
- gastrointestinal ulceration
- renal failure
- respiratory dysfunction
The presence of what two fibres enable the dermis to tolerate limited stretching?
Collagen fibres and elastic fibres
Collagen fibres are very
Strong and resist stretching, but are easily bent and twisted
elastic fibres permit
stretching and then recoil to their original length
Ageing, hormonal changes, and the destructive effects of ultraviolet radiation permanently reduces
the elasticity of the dermis and the results are wrinkles and sagging skin
What is the acronym to remember the order of layer so the epidermis?
CLGSB
