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HUBS192 > Lecture 3- Skin physiology (hard) > Flashcards

Lecture 3- Skin physiology (hard) Flashcards

1
Q

What are some touch receptors of the skin?

A
  • Free nerve endings
  • Tactile discs
  • Tactile corpuscles
  • Lamellar corpuscles
  • Bulbous corpuscles
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2
Q

Is there a perfect receptor-function relationship?

A

No, there is no one receptor-one function relationship. Receptors can often respond to several different stimuli but will be most sensitive to a particular type.

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3
Q

What is the most common receptor in the skin?

A

free nerve endings

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4
Q

What is the structure of free nerve endings like?

A
  • Mostly unmyelinated, small diameter fibers but also some myelinated small diameter fibers
  • Usually have small swellings at distal ends (sensory terminals)
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5
Q

What do the sensory terminals of nerve endings do?

A

Have receptors that function as cation channels that result in depolarization and action potentials that travel up to the somatosensory cortex

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6
Q

What do nerve endings respond to?

A
  • Detect lots of different things but mainly respond to:
  • temperature (hot/cold)
  • painful stimuli
  • some movement and pressure
  • some to itch (e.g. response to histamine)
  • some wrap around hair follicles (peritrichial endings) acting as light touch receptors which detect bending hairs (e.g mosquito lands on skin)
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7
Q

What are tactile (Merkel) dics/where are they found?

A
  • Free nerve endings located in the deepest layer of epidermis (stratum basale)
  • Associated with large disc shaped epidermal (merkel) cells
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8
Q

What is the communication that occurs for tactile epithelial (Merkel) cells?

A

Between the cells and nerve endings possibly via serotonin (5HT)

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9
Q

Where are tactile (merkel) discs abundant, what do they allow?

A

In fingertips, have small receptive feels so good for 2 point discrimination.

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10
Q

What are tactile (merkel) discs sensitive to?

A
  • an objects physical features (texture, shape and edges)

- fine touch and light pressure

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11
Q

Where are tactile (Messiner) corpuscles located?

A

-In papillary layer of dermis especially in hairless skin e.g fingerpads , lips, eyelids, external genitalia, soles of feet, nipples

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12
Q

What is the structure of tactile (Messiner) corpuscles receptors?

A

spiraling/branching unmyelinated sensory terminals, surrounded by modified Schwann cells (for support) and then by a thin oval fibrous connective tissue capsule (encapsulated)

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13
Q

For tactile (Messiner) corpuscles what happens when the capsule deforms?

A

Triggers entry of sodium ions into nerve terminal which depolarizes it causing an action potential

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14
Q

What do tactile (Messiner) corpuscles sense?

A
  • delicate ‘fine’ or discriminative touch: sensitive to shape and textural changes in exploratory touch like reading braille and movements of objects over the surface of the skin
  • light pressure
  • low frequency vibration (2 to 80 hertz)
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15
Q

Where are the Lamellar (Pacinian) corpuscles located and what does this mean in terms of there function?

A
  • scattered deep within dermis and hypodermis

- this means they are more responsive to deep pressure and vibration

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16
Q

What is the structure of Lamellar (Pacinian) corpuscle receptors?

A
  • single dendrite lying within concentric layers of collagen fibers and specialized fibroblasts
  • layers are separated by gelatinous interstitial fluid
  • dendrite is essentially isolated from other stimuli other than deep pressure
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17
Q

What happens when the capsule of Lamellar (Pacinian) corpuscles deforms?

A
  • opens pressure sensitive sodium channels in sensory axon

- inner layers covering axon terminal ‘relax’ quickly so action potentials are discontinued (they are rapidly adapting)

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18
Q

What are Lamellar (Pacinian) corpuscles receptors stimulated by?

A
  • deep pressure (when first applied)

- also vibration (as rapidly adapting)

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19
Q

What is the optimum frequency stimulation for Lamellar (Pacinian) corpuscles, what does this mean?

A

around 250Hz, this is similar to the frequency range generated upon fingertips by textures comprising features less than 1 micrometer.

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20
Q

Where are Bulbous corpuscles (Ruffin’s endings) located?

A

-In dermis and subcutaneous tissue (Hypodermis)

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21
Q

What is the structure of Bulbous corpuscles (Ruffin’s endings) ?

A
  • Network of nerve endings intertwined with a core of collagen fibers that are continuous with those of the surrounding dermis.
  • Capsule surrounds entire structure
22
Q

What are Bulbous corpuscles (Ruffin’s endings) sensitive to?

A

-sustained deep pressure and stretching + distortion of the skin

23
Q

What are Bulbous corpuscles (Ruffin’s endings) important for?

A
  • Important for signaling continuous states of deformation of the tissues such as heavy prolonged touch and pressure signals
  • Also found in joint capsules where help signal a degree of joint rotation (proprioception)
  • High density around fingernails so may have a role in monitoring slippage of objects across surface skin ( allowing modulation of grip)
24
Q

In terms of skin blood flow what are smooth muscles (in walls of arteries) and pre-capillary sphincters innervated by?

A

The sympathetic nervous system (autonomic)

25
Q

What are pre-capillary sphincters?

A

Branches of arteries that extend up and give rise to capillary loop

26
Q

What happens in skin blood flow?

A

-Noradrenaline acts on α1 adrenergic receptors on the
vascular smooth muscle in the skin
– GPCRs coupled to intracellular 2nd messengers result in increased intracellular calcium ions which allows more cross bridges to form and thus constriction
-This results in reduced skin blood flow
– Reducing SNS activity therefore causes relaxation (dilation) of arteries leading to skin and therefore increased skin blood flow

27
Q

What is skin blood flow important in?

A

Thermoregulation and blood pressure

control

28
Q

What is the optimum body temp and what are consequences of getting out of this set range?

A
  • Optimum/set point for body is at 37 degrees (36.5-37.5)
  • If too high proteins denature
  • If too low lose the ability to thermoregulate
29
Q

What are the primary mechanisms of heat transfer?

A
  • radiation
  • evaporation
  • convection
  • conduction
30
Q

How might we lose (or gain heat) via radiation?

A
  • We absorb and emit radiation from our surroundings
  • Generally we will lose more radiation than gain so lose heat however, in hot environments we can start to gain more than we lose so gain heat.
31
Q

How might we lose (or gain heat) via evaporation? Where is this particularly important?

A
  • Evaporate water from surface of skin to lose heat energy

- This is important in hot climates as it will be the only mechanism to lose heat (e.g. sweating)

32
Q

How might we lose (or gain heat) via convection?

A

Warm air rises and is replaced by cold air heat lose between body and surrounding air and body can then continue via conduction.

33
Q

How might we lose (or gain heat) via conduction?

A
  • Our bodies when in contact with something cold will lose heat to it e.g. warm up the surrounding air
  • In hot climates the temperature gradient can be the other way such that the environment is warmer than us so heats us up
34
Q

How do eccrine sweat glands work?

A
  • They are innervated by the sympathetic nervous system

- They are known as Sympathetic cholinergic as they release ACh onto mAChRs (a G class receptor)

35
Q

What can some eccrine sweat glands be stimulated by?

A

By Adrenaline in blood acting on β receptors – ‘nervous sweating’ (particularly forehead and palms of hands)

36
Q

What happens when body temperature increases?

A

If blood temp goes ABOVE ‘set point’ heat loss center is activated..
–lower SNS activation of α1 on skin blood vessels
results in vasodilation
– increase in SNS cholinergic activation of mAChRs
on sweat glands means more sweating and so heat loss via evaporative cooling
– Increase respiratory rate
– Behavioral changes (go to cooler place, take off clothes)

37
Q

What does the hypothalamus contain?

A

Preoptic area of hypothalamus contains
heat and cold sensitive neurons (central
thermoreceptors)

38
Q

When might Radiation, conduction and convection not be effective mechanisms for heat loss and why?

A

When environmental temp is greater than body temp temp gradient is the other way and lose too much water trying to compensate

39
Q

What happens when thermoregulators detect temperature BELOW ‘set point’?

A

Activates heat gain center…

  • heat generating mechanisms (shivering +non shivering +thyroxine)
  • conservation of body heat (vasoconstriction +countercurrent exchange)
40
Q

Explain vasoconstriction as a method to conserve body heat…

A

Vasomotor center increases blood flow to the dermis, thereby reducing loses by radiation and convection

41
Q

Explain countercurrent exchange as a way to conserve body heat…

A

Warm blood in arteries meets with cold blood in veins so heat transferred between and not lost to outside

42
Q

Explain how shivering leads to the generation of body heat…

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)

43
Q

Explain how non-shivering thermogenesis leads to the generation of body heat…

A

– Increase in 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)

44
Q

Explain how increases thyroxine would lead to generation of body heat…

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 this is therefore a much slower method

45
Q

What is the structure and function of the arrector pilus muscle?

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 hairy this traps a layer of warm air around the skin (insulating) and also makes you look bigger +more formidable in fight or flight situations
46
Q

What is the arrector pilus muscle an example of?

A
  • Temperature regulation is mostly done by negative feedback but this is an example of physiological feedforward
  • Receptors in skin inform brain and send a message to hypothalamus. The hypothalamus then takes action to prepare even though the core temperature hasn’t dropped yet.
47
Q

What is a 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 days
-Can get pain as nerve endings become exposed/sensitive due to inflammation

48
Q

What is the second degree burn? (more mild)

A

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

49
Q

What is the second degree burn? (more severe)

A

-deeper
– 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

50
Q

What is the third degree burn?

A

• Full Thickness i.e. extend into subcutaneous tissue
and may involve muscle and bone
• Varied color 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

51
Q

What are some direct implications of severe burns?

A
  • Hydration+ hypovolemic shock(not enough water in blood to be pumped-leads to fainting)
  • Infection/ Sepsis
  • Hypothermia

HUBS192 (38 decks)

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