HUBS192 Lecture 3 - Skin physiology Flashcards by Annika Tissies

5 touch receptors of the skin

1) free nerve endings
2) tactile discs
3) tactile (meissner) corpuscles
4) lamellar (pacinian) corpuscles
5) bulbous (ruffini) corpuscles

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what are free nerve endings?

mostly unmyelinated small diameter fibres have sensory terminals located at the distal end

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what are sensory terminals?

small swellings at distal ends

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function of sensory terminals

have receptors that function as cation channels which depolarise to produce AP’s

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what do free nerve endings respond to?

1) temperature
2) painful stimuli
3) movement
4) pressure

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what are peritrichial endings?

free nerve endings wrapped around hair follicles

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light touch receptors

peritrichial ending receptors that detect the bending of hairs

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what are tactile (merkel) discs and where are the located?

free nerve endings associated with large disc shaped epidermal (merkel) cells located in the deepest layer of the epidermis

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where is the tactile (merkel) disc abundant>

abundant in fingertips and very small receptive fields (good for two point discrimination)

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what are tactile (merkel) discs sensitive to?

1) texture
2) fine touch
3) light pressure

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tactile (meissner) corpuscles

branching unmyelinated sensory terminals surrounded by modified schwann cells which are then surrounded by a thin oval fibrous connective tissue capsule located in the papillary layer of the dermis

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where is the tactile (meissner) corpuscles abundant?

abundant in hairless skin

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what happens when the tactile (meissner) corpuscles capsule is deformed?

deformation of capsule triggers entry of Na+ ions into the nerve terminal inducing an AP

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what do the tactile (meissner) corpuscles sense?

1) discriminative touch (movement of objects over the skins surface)
2) light pressure
3) low frequency vibration of 2 to 80 hertz

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what are lamellar (pacinian) corpuscles and where are they located?

single dendrite lying within circular layers of collagen fibres and specialised fibroblasts scattered deep in the dermis and hypodermis

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how are the layers of lamellar (pacinian) corpuscles seperated?

separated by gelatinous interstitial fluid

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what happens when the lamellar (pacinian) corpuscles capsule is deformed?

deformation of capsule opens pressure sensitive Na+ channels in sensory axons
-inner layers covering axon terminal ‘relax’ quickly so AP’s discontinue (rapidly adapting)

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what are the lamellar (pacinian) corpuscles stimulated by?

1) deep pressure when first applied

2) vibration

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what are bulbous corpuscles (Ruffini’s endings) and where are they located?

network of nerve endings intertwined with a core of continuous collagen fibres surrounded by a capsule located in the dermis and subcutaneous tissue

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what are the bulbous corpuscles (ruffini’s endings) sensitive to?

1) deep sustained pressure
2) skin stretching
3) skin distortion

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what are bulbous corpuscles (ruffini’s endings) important for?

important for signalling continuous states of deformation of the tissue (heavy prolonged touch and pressure signals)
-involved in proprioception

precapillary sphincters

bands of smooth muscle

what does GPCR’s stand for?

G protein coupled receptors

how is skin blood flow controlled?

controlled by smooth muscle in the walls of arteries and pre-capillary sphincters innervated by the SNS (sympathetic nervous system)

what happens to reduce skin blood flow

-noradrenaline acts on alpha 1 adrenergic receptors on vascular smooth muscles in the skin GPCR's coupled to intercellular 2nd messengers increase intracellular Ca2+ causing vasoconstriction

what happens to increase skin blood flow?

SNS activity is reduced to cause vasodilation (relaxation) to the arteries of the skin

normal range of body temperature

between 36.5 and 37.5 degrees

what is radiation?

causes heat loss in the form of infared rays

what is evaporation?

heat is lost from the phase change of water form a liquid to a gas

what is convection?

the movement of heated air away from the skin to be replaced with cooler which results in heat loss

what is conduction?

transfer of heat by direct contact to another object/surface

what are eccrine sweat glands innervated by

innervated by the sympathetic nervous system

what happens at sympathetic cholinergic eccrine sweat glands?

ACh is released onto the GPCR - mAChRs

what happens when eccrine glands are stimulated by adrenaline?

when stimulated by adrenaline in the blood it acts upon beta receptors to cause 'nervous sweating'

relationship between beta receptors secretion and body temperature

beta receptors can release adrenaline independent to body temperature

pre optic area of the hypothalamus contains

thermoreceptors for the 1) heat loss centre 2) heat gain centre

what happens when the heat loss centre is activated?

1) decreased SNS activation of alpha 1 on skin blood vessels causing vasodilation 2) increased SNS cholinergic activation of mAChR's on sweat glands causing sweating 3) increased respiratory rate

what happens when the heat gain centre is activated in terms of increased generation of body heat?

1) non shivering thermogenesis | 2) shivering thermogenesis

what happens when the heat gain centre is activated to conserve body heat?

vasoconstriction thereby reducing losses by radiation and convection

what happens to cause shivering?

when the tone of muscles exceeds critical level, shivering begins due to contractions of agonist and antagonist muscles mediated by the muscle spindle (stretch receptors)

what is non-shivering thermogenesis?

- increased sympathetic nerve activity - increased circulating adrenaline/noradrenaline from the adrenal medulla - increased cellular metabolism - 'uncoupling' of oxidative phosphorylation

what causes increased thyroxine (a heat generating mechanism)?

- in response to TRH and TSH | - increases basal metabolic rate

what is an arrector pili muscle?

smooth muscle innervated by the SNS (alpha 1 receptors) that attaches the hair follicle to the upper dermis

what happens when the arrector pili muscle contracts?

1) goosebumps | 2) compresses sebaceous glands which lubricates skin

what is a first-degree burn and what are the features of it?

superficial burn to the outer layers of the epidermis that is red/pink, dry and painful

3 features of a first-degree burn

1) no blisters 2) skin remains a water and bacterial barrier 3) heals in 3-10 days

what is a second-degree burn?

burn to the epidermis + varying amounts of the dermis that is painful, moist, red and blistered

2 features of a second-degree burn

1) heals in 1-2 weeks | 2) needs absorptive dressings

what is a deep second-degree burn?

- may include whiteish, waxy areas - hair follicles, sweat glands may remain intact - some tactile receptors lost - heal in 1 month with possible loss of sensation and scarring

third-degree burn

burn that extends into subcutaneous tissue (may involve muscle and bone) that has varied colour

4 features of a third-degree burn

1) hard, dry and leathery 2) no pain due to destroyed nerve endings 3) if more than a few cms, skin grafting is required 4) weeks to regenerate + scarring

3 potential complications of severe burns

1) dehydration and hypovolemic shock 2) infection/sepsis 3) hypothermia