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HUBS192 > LECTURE 3: skin physiology > Flashcards

LECTURE 3: skin physiology Flashcards

1
Q

types of skin receptors

A
  1. free nerve endings
  2. tactile discs
  3. tactile corpuscles
  4. lamellar corpuscles
  5. bulbous corpuscles
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2
Q

what do free nerve endings respond to

A
  1. temp
  2. painful stimuli
  3. some movement and pressure
  4. some to itch
  5. some wrap around hair follicles
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3
Q

what are free nerve endings

A

most common receptor in skin

Mostly unmyelinated small diameter fibres but also some small diameter myelinated fibres

Usually have small swellings at distal ends = sensory terminals

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4
Q

how free nerve endings work

A

Sensory Terminals have receptors that function as cation channels&raquo_space; depolarization&raquo_space; APs

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5
Q

what are tactile discs

A

Free nerve endings located in deepest layer of epidermis

- associated with large disc shaped epidermal (merkel) cells

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6
Q

what do tactile discs respond to

A

Sensitive to an objects physical features: texture, shape and edges + Fine touch and light pressure

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7
Q

how to tactile discs work

A

Communication between the tactile epithelial cell and nerve ending possibly via serotonin (5HT)

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8
Q

where can you find tactile discs

A

Abundant in fingertips and very small receptive fields. • So good for two point discrimination

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9
Q

where are tactile corpuscles located

A

located in papillary layer of dermis, especially in hairless skin e.g. finger pads, lips, eyelids, external genitalia, soles of feet, nipples

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10
Q

where are lamellar corpuscles located

A

Scattered deep in dermis and hypodermis

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11
Q

what are lamellar corpuscles

A

Single dendrite lying within concentric layers of collagen fibres and specialised fibroblasts

Layers separated by gelatinous interstitial fluid – Dendrite essentially isolated from stimuli other than deep pressure

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12
Q

how lamellar corpuscles work

A

Deformation of capsule opens pressure sensitive Na+ channels in sensory axon: Inner layers covering axon terminal ‘relax’ quickly so APs discontinued (rapidly adapting)

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13
Q

what stimulates lamellar corpuscles?

A

Pressure (when first applied)

Also vibration because rapidly adapting: Optimal stimulation frequency is around 250Hz which is similar to frequency range of generated upon fingertips by textures comprising features < 1 μM

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14
Q

where are bulbous corpuscles located

A

in dermis and subcutaneous tissue

Also found in joint capsules where help signal degree of joint rotation (proprioception): High density around fingernails so may have role monitoring slipage of objects across surface skin – Allowing modulation of grip

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15
Q

what are bulbous corpuscles

A

Network of nerve endings intertwined with a core of collagen fibres that are continuous with those of the surrounding dermis.

Capsule surrounds entire structure

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16
Q

what are bulbous corpuscles sensitive to

A

sustained deep pressure and stretching or distortion of the skin

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17
Q

what are bulbous corpuscles important for

A

Important for signalling continuous states of deformation of the tissues such as heavy prolonged touch and pressure signals

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18
Q

what are encapsulated corpuscles

A

Spiralling / branching unmyelinated sensory terminals surrounded by modified Schwann cells and then by a thin oval fibrous connective tissue capsule

Deformation of capsule triggers entry of Na+ ions into nerve terminal&raquo_space; Action Potential

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19
Q

what does deformation of encapsulated corpuscles do

A

triggers entry of Na+ ions into nerve terminal&raquo_space; Action Potential

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20
Q

what do tactile corpuscles sense

A
  • Delicate ‘fine’ or discriminative touch:
    Sensitive to shape and textural changes in exploratory touch e.g. reading Braille text. Movement of objects over the surface of the skin
  • light pressure
  • low frequency vibrations (2-80 Hz)
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21
Q

how skin blood flow can be controlled

A

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

  • Noradrenaline acts on α1 adrenergic receptors on this vascular smooth muscle in the skin: GPCRs coupled to intracellular 2nd messengers&raquo_space; increased intracellular Ca++&raquo_space; constriction = Reduced skin blood flow
  • Reducing SNS activity therefore causes relaxation (dilation) arteries to skin è Increased skin blood flow
22
Q

structure and function of eccrine sweat glands and their role in thermoregulation

A

Innervated by the sympathetic nervous system:
Sympathetic cholinergic i.e. release ACh onto mAChRs (GPCRs)
Some eccrine sweat glands can also be stimulated by Adrenaline in blood acting on β receptors – ‘nervous sweating’ esp. on palms and soles (and axilla to some degree)

23
Q

4 basic mechanisms of heat transfer

A
  1. radiation
  2. evaporation
  3. convection
  4. conduction
24
Q

non-effective heat loss mechanisms when when environmental temp ≥ body temp.

A

Radiation, conduction and convection

25
Q

preoptic area in hypothalamus has

A

heat and cold sensitive neurons (central thermo receptors)

26
Q

what happens when blood temp goes ABOVE set point

A

heat loss centre activated

27
Q

vasodilation

A

decreased SNS activation of alpha1 on skin blood vessels

28
Q

sweating

A

increased SNS cholinergic activation of mAChRs on sweat glands

29
Q

what happens to respiratory rate when temp is increased

A

increases

30
Q

what factors are effected by increase in body temp

A

vasodilation
sweating
increased respiratory rate

31
Q

heat gain centre activated by

A

Central Thermoreceptors detect temperature BELOW ‘set point’ = activation

32
Q

how heat gain centre responds to low body temp

A

increased generation of body heat

conservation of body heat

33
Q

heat generating mechanisms

A
  1. shivering
  2. non shivering thermogenesis
  3. increased thyroxine
34
Q

how to conserve body heat

A

vasomotor centre decreases blood flow to the dermis, thereby reducing losses by radiation and convection

35
Q

shivering

A
  • Increased tone of skeletal muscles
  • When tone rises above critical level, shivering begins due to oscillatory contractions of agonist and antagonist muscles mediated by muscle spindles (stretch receptors
36
Q

non shivering thermogenesis

A
  • Increased Sympathetic Nerve Activity and increased circulating Adrenaline/noradrenaline from adrenal medulla
  • Increased cellular metabolism e.g. increased glycogenolysis in liver and muscle
  • ‘uncoupling’ of oxidative phosphorylation i.e. heat produced instead of ATP (occurs in ‘brown fat’ particularly in infants)
37
Q

increased thyroxine

A
  • 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
38
Q

arrector pilli muscles

A
  • Smooth muscle innervated by SNS (α1 receptors)
  • Attach hair follicle to upper dermis
  • Contraction pulls hairs upright and dimples skin > goosebumps
  • Also compresses sebaceous glans which lubricates skin
39
Q

first degree burn

A
  • Superficial i.e only involve the outer layers of the epidermis
  • Red/pink, dry, painful
  • Usually no blisters e.g. a mild sunburn
  • Skin remains a water and bacterial barrier
  • Usually heals 3-10 day
40
Q

second degree burn

A
  • Epidermis + varying amounts of dermis
  • Painful, moist, red and blistered.
  • Usually heal in approx 1-2 weeks
  • Need good dressings (absorptive initially)
41
Q

deeper second degree burns

A
  • May include whiteish, waxy looking areas
  • Hair follicles, sweat glands may remain intact
  • Some tactile receptors may be lost
  • Usually heal in 1 month but may have some loss of sensation and scarring
42
Q

third degree burn

A
  • Full Thickness i.e. extend into subcutaneous tissue and may involve muscle and bone
  • Varied colour from waxy white through to deep red or black
  • Hard dry and leathery
  • No pain in these areas as sensory nerve endings destroyed
  • If more than a few cms may require skin grafting
  • Weeks to regenerate + scarring
43
Q

head % of TBSA in adult and children

A

A= 9%

C=15%

44
Q

upper limb % of TBSA

A 
A = 9% each
C = 9% each
45
Q

trunk % of TBSA

A 
A = 36% (front and back)
C = 32% (front and back)
46
Q

genitalia % of TBSA

A 
A = 1%
C = 1%
47
Q

lower limb % of TBSA

A 
A = 18% each
C = 17% each
48
Q

complications of severe burns for normal skin function

A
  1. dehydration and hypovolemic shock
  2. infection / sepsis
  3. hypothermia
49
Q

what is normal body temp

A

around 37 degrees is set point

36.5-37.5

50
Q

what happens if temp too low

A 
lose ability to thermoregulate
disorientation
loss of muscle control
loss of consciousness 
cardiac arrest
death
51
Q

what happens if body temp too high

A 
lose ability to thermoregulate
death
cell damage
convulsions
proteins denature

HUBS192 (10 decks)

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