Skin Physiology Flashcards

1
Q

5 diff types of receptors

A
  • Free nerve endings (superficial)
  • Tactile discs
  • Tactile corpuscles
  • Lamellar corpuscles
  • Bulbous corpuscles (deep)
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2
Q

What is a characteristic of the receptors?

A

They respond likely to all types of stimuli but are sensitive to a particular type

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3
Q

What are free nerve endings?

A
  • Most common receptor in the skin
  • Branches into the epidermis
  • Mostly unmyelinated small diameter fibres but also some small diameter myelinated fibres
    – Usually small swellings at distal ends = sensory terminals
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4
Q

What do the sensory terminals have?

A

Receptors eg thermo, chemo and noci that respond to the different types of stimuli

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5
Q

What kind of channels present at the sensory terminals? What do free nerve endings mostly respond to?

A

Mostly ion channels but can be chemically activated eg when bitten, mast cells degranulate –> histamine release. Responds to this

Peritrichal endings i.e where free nerve endings wrap around the hair follicle to help with sensation

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6
Q

What are tactile (merkel) discs?

A
  • Free nerve endings located in the deeper layers of the epidermis
  • Associated with an epidermal merkel disc that relays info to the free nerve ending via 5HT (serotonin neurotrans)
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7
Q

What is a merkel disc also called

A

Tactile epithelial cell

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8
Q

Where are merkel disc mostly found?

A

In the fingertips with small receptive fields eg good 2 pt discrimination

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9
Q

What does the merkel disc distinguish between?

A

Helps to distinguish:
* Fine touch and light pressure
* texture, shape and edges

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10
Q

Another name for tactile corpuscles

A

Meissner corpuscles

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11
Q

Where are the tactile corpuscles located?

A

In the papillary lary of the dermis, just below the epidermis

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12
Q

Where are the meissner corpuscles found?

A

Hairless skin eg In the soles of feet, eyelids, nipples, external genitalia, lips, finger pads

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13
Q

Structure of a meissner corpuscle

A

Encapsulated
* Spiralling / branching unmyelinated sensory terminals
surrounded by modified Schwann cells (that just support but don’t myelinate the axons) and then by a thin oval of fibrous connective tissue capsule

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14
Q

What does deformation of the capsule do?

A
  • Triggers entry of Na+ ions into nerve terminal i.e mechanical gating&raquo_space; Action Potential
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15
Q

What does the 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 vibration (2 to 80 Hertz)

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16
Q

Another name for tactile corpuscles

A

Pacinian corpuscles

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17
Q

Where are the Pacinian corpuscles found?

A

– Scattered deep in dermis and hypodermis

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18
Q

Structure of a Pacinian corpuscle

A

– Single dendrite lying within concentric layers of collagen
fibres and specialized fibroblasts that secretes it.
– Layers separated by gelatinous interstitial fluid
– Dendrite essentially isolated from stimuli other than deep
pressure

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19
Q

What does deformation of the capsule do? Pacinian

A

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

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20
Q

What does the tactile corpuscles sense?

A

– Stimulated by deep 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 eg sandpaper

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21
Q

Another name for Bulbous corpuscles

A

Ruffini’s

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22
Q

Where are the Bulbous corpuscles found?

A

Located in dermis and subcutaneous tissue

Also found in joint capsules where help signal degree of joint
rotation (proprioception)
* in fingers may have role monitoring slippage of objects
across surface skin and so modulate grip

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23
Q

What does deformation of the capsule do? Bulbous

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, when collagen distorted, the nerve endings are activated

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24
Q

What does the bulbous corpuscles sense?

A
  • Sensitive to sustained deep pressure and stretching or
    distortion of the skin
    – Important for signaling continuous states of deformation of
    the tissues such as heavy prolonged touch and pressure
    signals
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25
Q

What extends from the subpap plexus?

A

Precapillary sphincters

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26
Q

What is the precap sphincters made of

A

Smooth muscle

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27
Q

What happens when the smooth muscle contracts?

A

The diameter reduces and the blood flow also reduces

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28
Q

How is smooth muscle activated?

A

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

29
Q

What does the NA act on?

A

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 bloodflow

30
Q

Reduced SNS activation results in

A

Reducing SNS activation of ⍺1 receptors therefore causes
relaxation (dilation) of arteries to skin increased skin
bloodflow

31
Q

Why is dilation and constriction important?

A

For thermoregulation and blood pressure control

32
Q

What happens in an injection to the spinal cord?

A

Some sym nerves are affected affecting the blood vessels so NE is injected to bring BP back up

33
Q

What is the core body temp?

A

36.5 - 37.5

34
Q

What happens at v low temps?

A

Loss of conciousness and muscle control, Cardiac arrest and DEATH

35
Q

What happens at v high temps?

A

Cell damage, convulsions, protein denaturation and death

36
Q

1º mechanisms of heat transfer

A

Radiation, conduction, evaporation and convection

37
Q

How does radiation cause heat loss?

A

As infrared rays

38
Q

What are infrared rays?

A

Electromagnetic rays with wavelength 5 – 20 micrometers which is 10 to 30 times that of light rays

39
Q

When are infrared rays radiated?

A

When object is not at absolute 0 temp

40
Q

Loss of body heat at room temp with no clothes

A

60%

41
Q

When is heat radiation absorbed into the body?

A

When the surroundings have a higher temp than the body.

42
Q

What is conduction?

A

Transfer of heat with media that we are in direct contact in

43
Q

How much % of heat is conducted to air?

A

15%

44
Q

Does conduction stop?

A

Yes, when the temp of the body and medium are the same

45
Q

What is convection?

A

When the initially warmed air is replaced by cooler air which causes conduction to keep occuring due to the gradient

46
Q

Why does a small amount of convection always occur?

A

Due to the tendancy for
air adjacent to the skin to rise as it becomes heated

47
Q

What is evaporation?

A

When H20 evaps from body, the heat energy used to evap it is also lost i.e 0.58ºC for eacg gm of H20

48
Q

How else is H2O lost besides sweating?

A

Through the respiratory tract about 600-700ml every day

49
Q

Why is more heat lost in H2O than in air?

A

Water has a specific heat thousands of times that of air and so can absorb far greater quantities of heat

50
Q

Which sweat glands are important for thermoregulation?

A

Eccrine sweat glands

51
Q

How are eccrine sweat glands activated?

A

By the sympathetic nervous system that is colinergic

52
Q

What kind of receptors is the Ach released onto?

A

Muscarinic acH receptors i.e not ion channels but G protein coupled receptors (GPCR)

53
Q

Other ways that eccrine glands can be stimulated

A

Through Adrenaline in blood affecting beta receptors –> sweating on palms, soles and axilla

54
Q

What allows the hypothalamus to detect changes in body temperature?

A

Preoptic are of the hypo has heat and cold sensitive neurons i.e central thermoreceptors

55
Q

What happens when the heat loss centre is activated?

A
  • Decreased SNS activation of alpha1 receptors on blood vessels –> vasodilation allowing heat loss through the heat transfer ways
  • Increased colinergic activity of the MAcHR –> increased sweating
  • increased respiratory rate so more air passes through allowing evap on tongue
  • Concious behavioural changes
56
Q

Effective heat loss mechanism when the envir temp is more than the body temp

A

Evap

57
Q

What do the central thermoreceptors do when the core body temp goes below the set point?

A

The heat gain centre is activated

58
Q

What happens when the heat gain centre is activated?

A
  • Vasoconstriction
  • The blood going out warms the blood coming in as the arteries and veins run close to each other
  • Shivering
  • Non shivering thermogenesis
  • Increased Thyroxine after long term exposure
59
Q

What does shivering do?

A
  • Oscillatory contraction of agonist and antagonist muscles
  • ATP → ADP + Pi + movement + heat
60
Q

What is 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)

61
Q

When is Thyroxine increased and what does it do?

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

62
Q

What do errector mucles do?

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
  • If you are a hairy mammal, this
    traps layer of warm air around
    skin and makes you look bigger,
    scarier and more formidable
  • not that useful for humans but
    can be a good example of
    physiological feed forward
63
Q

How to replace fluids for 2º and 3º burns…

A

A lot of H2O is already lost + inflam mediators that make the capillaries even more leaky
- Rule of nines to determine how much fluid should be replaced

64
Q

Head

A

Adult - 9%
Child - 15%

65
Q

Upper limb

A

Adult - 9% each limb
Child - 9%

66
Q

Torso (front and back)

A

Adult - 36%
Child - 36%

67
Q

Lower limb

A

Adult - 18%
Child - 17%

68
Q

Genitalia

A

1% for both

69
Q

Complications of burns

A
  • Sepsis as skin is a barrier
  • Dehydration and hypothermia as the H2O is gone and skin traps heat is gone
  • Hyperkaelaemia –> electrolyte imbalances as the K+ ends up in the bloodstream
  • Hypermetabolism due to ^ cortisol due to stress response
  • Ulcers
  • Renal failure
  • Respiratory dysfunction