Skin Flashcards
What is the primary function of the skin?
Protection
Name the 3 layers of the skin
Epidermis, dermis and hypodermis
What 2 layers of the skin forms the cutaneous?
demis and epidermis
Which layer of the skin is most vascular?
the dermis
What are papules?
The wavy surface of the epidermis that creates increased surface area to maximise nutrient supply
What tissue type primarily makes up the epidermis?
Epithelial tissue
What is the difference between simple and stratified epithelia?
Simple = 1 layer of cells Stratified = stacked layers of cells
Describe the shape of squamous cells
flat, long, squashed etc.
Describe the shape of cuboidal cells
cube shaped, similar l and w proportions
Describe the shape of columnar cells
long, tall, columns, pillars
Name 3 types of epithelia
Squamous, cuboidal, columnar
Name the 5 layers of the epidermis in thick skin (in order from outside in)
- Stratum corneum
- Stratum lucidum (this is the bonus layer, not found in thin skin)
- Stratum granulosum
- Stratum spinosum
- Stratum basale
Describe cells in the stratum corneum
dead, dried out, no nuclei
Describe cells in the stratum lucidum
Transparent, only found in thick skin
Where is thick skin found in the body?
palms of hands and soles of feet
Describe cells in the stratum granulosum
contain granules that promote dehydration of the cell/cross linking of collagen fibres, secrete waxy material into intercellular space
Describe cells in the stratum spinosum
Linked by desmosomes (within this layer), get flatter as they go up
Describe cells in the stratum basale
columnar/tall regenerative cells, can divide, daughter cells migrate upwards to replenish layers above
How is the dermis anchored?
By hemidesmosomes, from the stratum basale of epidermis to the dermis
Name the 2 layers of the dermis
papillary and reticular layers
Describe the papillary layer of the dermis
Highly vascularised tissues for nourishment for dermis and epidermis
Describe the reticular layer of the dermis
‘Mesh-like’ structure of collagen and elastin fibres (for strength)
Name the plexuses of the dermis
cutaneous and subpapillary
What is a plexus?
A network (of blood vessels or nerves)
Where is the cutaneous plexus found?
at junction of dermis/hypodermis, in the reticular layer of the dermis
Where does the cutaneous plexus supply?
Supplies blood to hypodermis, lower dermis incl. capillaries for hair follicles and sweat glands
= nourishment
Where is the Subpapillary Plexus found?
Branches from the cutaneous plexus, deep to the papillary layer
Where does the subpapillary plexus supply?
Network of blood vessels providing O2 and nutrients to the upper dermis and epidermis
What cells dominate the hypodermis? What do they produce?
adipocytes that produce subcutaneous fat
Describe a 1st degree burn
- Superficial, only outer layer of epidermis
- Red/pink, dry, painful
- No blisters
- Skin retains water and antibacterial properties
- Heals in 3-10 days
Describe a 2nd degree burn
- Epidermis + varying amounts of dermis
- Painful, moist, red and blistered.
- Usually heal in approx. 1-2 weeks (needs good dressings)
What happens if a 2nd degree burn is deeper/more serious
○ White waxy layer secreted by stratum granulosum may be exposed
○ Hair follicles, sweat glands still intact
○ Heals in 1 month
○ May have loss of some sensation, scars
Describe a 3rd degree burn
- aka full thickness burns (because extend into subcutaneous and may involve muscle/bone)
- Colour: waxy white to red/black
- Skin = hard, leathery
- No pain in these areas because nerve endings destroyed
- May require skin grafting
- Weeks-years to regenerate, scarring
What is hair made of and where is it produced?
hard, dead, keratinised cells produced inside a hair follicle
What is the function of the erector pili muscle?
contraction pulls hair shaft upright = goose bumps, forms sealed pocket of air that traps body heat, helps with insulation
What is the root hair plexus?
A network of sensory nerves at base of each hair follicle resulting in heightened sensation
What do sebaceous glads secrete? Name 3 of its roles in the skin
Sebum = oily secretion
- Nourishes hair shaft (stops from going dry)
- Moisturises skin (too much = oily skin)
- Water repellent
Name 2 types of sweat glands
Eccrine and apocrine
Where are eccrine sweat glands found?
In most areas of skin
Where are apocrine glands found?
Armpit, groin, around nipples
What is the function and role of eccrine sweat glands?
Pour sweat directly onto surface of skin
- Important for thermoregulation
- Antibacterial
What do apocrine sweat glands secrete, and how?
Sticky/oily/odorous secretions poured onto base of hair follicle, then to skin
What influences apocrine sweat glands? (give an example)
Influenced by hormones (e.g. breastmilk)
What function do nails serve?
○ Backboard to fingertips for receptors to be pressed against and activated
Name 5 things that happen in the skin during aging
- Epidermis becomes thin (stratum basale dividing less rapidly, less cells to replenished)
- Dermis becomes thinner (reduced collagen -> less strength -> wrinkling)
- Slower repair
- Drier epidermis (thin .: less blood, nutrients .: less sebum)
- Impaired cooling (less sweat)
- Less pigmentation (low melanin = pale skin, grey hair)
How does smoking accelerate aging? (3)
- Chemicals target dermis -> damages collagen and elastin
- Nicotine reduces blood circulation in dermis .: affects other layers of the skin
- Poor wound healing, acne, skin and oral cancers
Where is melanin produced?
In melanocytes in the stratum basale
How is melanin transported towards the surface of the skin?
In vesicles called melanosomes that move/float up between gaps in cells until shed by the stratum conium
What is a mole?
cluster of melanocytes, produced in bulk from sun exposure
What are freckles?
melanocytes overproducing melanosomes, over-production triggered by sun exposure
Why is vit D needed in the body?
Leads to production of calcitriol which is essential for normal calcium metabolism and .: bone hardness, also mood regulation
What happens if not enough vit D?
Rickets (bowleg)
Explain why highly pigmented people more susceptible to vit D deficiency at extreme latitudes.
Melanin blocks out the little UV there is .: don’t meet UV requirements for vit D synthesis
Where/who/when is rickets most common?
- In NZ, UK overrepresented in maori, pasifika, asian, black populations
- In winter/spring
- In south island compared to north
Describe basal cell carcinoma
- Common, relatively benign
- Originates in stratum basale
- Spread is rare
Describe malignant melanoma
- Rare, but deadly if not treated
- Originates in melanocytes
- Uncontrollable growth, release of defective melanin in vesicles that can travel around body
- Spreads anywhere, can have tumors on organs
- Fatality depends on thickness of melanoma/tumor
Where is the ink of a tattoo depositied?
Deposited into dermis (not epidermis, which is shed), and absorbed by immune cells
Why do tattoos hurt?
because nerve endings and receptors in dermis layer
Give an example a component of the skin corresponding to each tissue type
Muscular - erector pili muscle
Nervous - nerve fibres in dermis
Connective - blood
Epithelial - epidermis
Name the 5 selected receptors of the skin
- free nerve endings
- tactile discs
- tactile corpuscles
- lamellar corpuscles
- bulbous corpuscles
Describe the basic structure of free nerve endings
- Unmyelinated (not always), small diameter fibres
- Usually have small swellings at distal ends = sensory terminals
- Have different types of receptors
Are free nerve endings myelinated or unmyelinated?
Generally unmyelinated, but can be myelinated
What is a sensory terminal?
The small swelling at the distal end of a free nerve ending
What stimuli do free nerve endings give info about?
· Temp
· Pain
· Some movement and pressure (e.g. touch)
· Some wrap around hair follicles (peritrichial endings) - light receptors that detect bending of hair (e.g. mosquito)
How do free nerve endings conduct a signal to the CNS?
If correct stimuli, receptors act as cation channel (Na+ and Ca2+ into cell -> depolarise -> AP to central nervous system)
What are tactile discs, and where do you find them?
Free nerve endings in deepest layer of epidermis
What are tactile discs associated with?
Associated with tactile epithelial cells called Merkel discs (detect the stimuli, relay to sensory nerve ending, for AP)
Where in the body are tactile discs abundant? Why?
Abundant in fingertips and very small receptive fields, good for two point discrimination
What are tactile discs sensitive to?
· texture, shape and edges
· fine touch and light pressure
Where in the skin are tactile corpuscles found?
In the dermal papillary layer
Describe the structure of tactile corpuscles
Spiralling, branching nerve terminals associated with Schwann cells (not making myelin), then surrounded by capsule
How do tactile corpuscles generate an AP?
Pressure causes deformation of capsule, allows Na+ to enter -> AP
What is the difference between tactile discs and tactile corpuscles?
tactile discs differentiate between smooth and rough, whereas tactile corpuscles differentiate between smooth and smooth or rough and rough
What are tactile corpuscles sensitive to?
• Fine/discriminative touch
○ E.g. braille, objects moving over skin
• Light pressure
• Low frequency vibration
Where are lamellar corpuscles found?
Scattered deep in dermis and hypodermis
Describe the structure of lamellar corpuscles
Single dendrite lying within concentric layers of collagen fibres produced and surrounded by specialised fibroblasts.
What separates layers of collagen fibres in lamellar corpuscles?
gelatinous interstitial fluid
What is the purpose of interstitial fluid in lamellar corpuscles?
Transmit force/pressure
How do lamellar corpuscles generate an AP?
Deformation of capsule opens pressure sensitive Na+ channels in sensory axon -> depolarisation -> AP
Why are lamellar corpuscles ‘fast adapting’?
After deformation of capsule, inner layers covering axon terminal ‘relax’ quickly so APs discontinued
What are lamellar corpuscles sensitive to?
· Deep pressure (when first applied)
· Also vibration because rapidly adapting/reset quickly
○ Optimal stimulation frequency is around 250Hz (which is similar to frequency range of generated upon fingertips by textures comprising features < 1 μM)
Where are bulbous corpuscles located?
In dermis and subcutaneous tissue
Describe the structure of bulbous corpuscles
- Network of nerve endings intertwined with a core of collagen fibres that are continuous with those of the surrounding dermis. Capsule surrounds entire structure
What are bulbous corpuscles sensitive to?
sustained deep pressure and stretching or distortion of the skin
Bulbous corpuscles are important for signalling…
…continuous states of deformation of tissues, such as heavy prolonged touch and pressure signals, as well as proprioception when found in joint capsules
What is the function of precapillary sphincters?
Contract/relax to control blood flow into capillary beds
What tissue primarily makes up the walls of arteries?
Smooth muscle
What is the function of smooth muscle in the walls of blood vessels?
- constrict or dilate to change amount of blood flow to skin
- Important in thermoregulation
What controls smooth muscle?
The SNS
How does an increase in nerve signals result in blood vessel constriction?
Nerves release noradrenaline, binds to alpha1 adrenergic receptors on vascular smooth muscle in skin = increase [Ca2+] inside cell = more cross bridges = more contraction
What is the range for regular core body temp?
36.5 - 37.5˚C
When does core body temp increase?
exercising, fever
What happens if core body temp too high?
proteins denature, seizures, convulsions, cell damage, death
When is core body temp lower?
if cold, low metabolic rate
What happens if core body temp too low
loss of muscle control, disorientation, coma, death
Name the 4 heat transfer mechanisms
Radiation
Conduction
Convection
Evaporation
What is radiation?
Heat transmitted to surrounding environment from anything at >0˚
What is conduction?
transmission of heat to another media/object outside body along a gradient
What is convection?
moving the medium/air you’ve heated and replacing it with a cold medium
What is evaporation?
when liquid evaporates from body, taking heat with it
eccrine sweat glands are innervated by…
the sympathetic nervous system
Describe the receptors on eccrine sweat glands (as a cooling mechanism)
Sympathetic cholinergic release ACh (rather than noradrenaline) onto muscarinic acetylcholine receptors (mAChRs) which are G-protein coupled receptors (GPCRs)
What causes nervous sweat?
Activation of B adrenergic receptors, which are sensitive to adrenaline/noradrenalin
What detects a change in core body temp?
heat and cold sensitive neurons (central thermoreceptors) in the preoptic area of hypothalamus
Explain what happens when the heat loss centre is activated (4)
○ reduce SNS activation of a1 receptors on blood vessels in the skin (blood vessel dilation) = loose more heat from skin to environment [convection, conduction, radiation, evaporation if sweating]
○ Increase SNS cholinergic activation of mAChRs on sweat glands -> sweat [evaporation]
○ Increase resp rate -> more air across tongue, increases evaporation
○ Behavioural changes (e.g. shade, take off clothes, drink water etc.)
Explain what happens to activate the heat loss centre
Central thermoreceptors detect that body temp > set point -> activate heat loss centre
What happens when environmental temp ≥ body temp?
Radiation, conduction and convection are not effective heat loss mechanisms .: only option is to sweat (evaporation)
List what happens when the heat gain centre is activated (5)
Non-shivering thermogenesis Shivering Uncoupling of oxidative phosphorylation Countercurrent system Increased Thyroxine production
What is non-shivering thermogenesis? What is its function?
Release of hormones to increase BMR
Results in:
• Increased SNS activity and circulating adrenaline/noradrenaline from adrenal medulla
• Breaking down glycogen stores in liver/muscle = increased cellular metabolism
What is shivering? What is its function?
- Increased muscle tone
- Activates muscle spindles
- Agonist and antagonist muscles contract in oscillatory pattern
= heat from muscles
Describe the uncoupling of oxidative phosphorylation
some animals/infants not moving around much/shivering, so brown fat mobilized (fat has good blood supply, lots of mitochondria -> break down produces heat instead of ATP)
Describe the countercurrent system. What is its function?
Anatomical feature in limbs where arteries close to veins
- Warm blood from artery transmits heat to cold blood coming back in vein
- Not all heat is going to skin/being lost to environment
Describe increased Thyroxine production
- In response to TRH and TSH
- Increases basal metabolic rate
- In adults humans may take several weeks exposure to cold before thyroid reaches new level of thyroxine secretion
When and how are arrector pili muscles activated?
Activated in very cold environments by the SNS (a1 receptors)
What is the function of arrector pili muscles?
- Draws hair shaft vertical
- Traps layer of air = insulation
Goosebumps act as physiological feedforward by…
Skin receptors indicating cold environment, warning that core body temp will drop after a period of time, encouraging preemptive action (more clothes etc.)
What non-physiological factor is important in maintaining homeostasis?
Behavioural mechanisms
In 2nd and 3rd degree burns, the loss of the epidermis means that….
the body can’t retain water
Tissue damage in 2nd and 3rd degree burns leads to…
lots of inflammatory mediators = leaky capillaries = lose fluid
What are the concerns of severe burns that help remind us of normal skin function
- Fluid loss -> dehydration and decreased BP -> hypovolemic shock
- Loss of antimicrobial barrier -> infection/sepsis
- Fluid evaporation from skin -> hypothermia
