Lecture 3: Skin Physiology Flashcards
What are the different types of Touch receptors of the skin?
5
- Free nerve endings
- Tactile discs
- Tactile corpuscles
- Lamellar corpuscles
- Bulbous corpuscles
How are receptors adapted to different stimuli?
2
- Can often respond to several different stimuli
- Will be most sensitive to a particular type of stimulus
What is the most common receptor in the skin?
Free nerve endings
What is the structure of free nerve endings?
2
- Mostly unmyelinated/small diameter fibres
- some myelinated/small diameter fibres
Where are Sensory Terminals found?
The distal ends of free nerve endings
What are Sensory Terminals?
Small swellings at the end of free nerve endings
What do sensory terminals possess?
Receptors that function as Cation channels leading to depolarisation and action potentials
What do Free Nerve endings mainly respond to?
4
- Temperature
- Painful stimuli
- Some movement/pressure
- Some itch
What are Peritrichial nerve endings?
Free nerve endings that wrap around hair follicles
What do Peritrichial endings do?
Act as light touch receptors, by detecting the bending of hairs
How do Free nerve ending sense itch?
Histamine receptors on sensory nerve endings detect histamine and alert your body
What are Tactile discs?
Free nerve endings located in the deepest layer of epidermis
What are Tactile discs associated with?
Large disc shaped epidermal (Merkel) cells
What does a Merkel cell do?
2
- Detects stimulus
- Convert stimulus into a chemical message that is transmitted to sensory nerve endings
What is the chemical messenger used by Merkel cells?
Serotonin
Where are Tactile disks/Merkel cells most abundant in the body?
Finger tips
Are the receptor fields of Tactile disks/Merkel cells small or big?
Small
What are Tactile disks/Merkel cells good for?
Two point discrimination
What are Tactile disks/Merkel cells sensitive to?
An objects physical features e.g. texture, shape and edges
Where are Tactile Corpuscles located?
Papillary layer of the dermis
Where are Tactile Corpuscles especially prevalent in the body?
Hairless skin e.g. - finger pads - lips - eyelids soles of feet
What can the structure of Tactile Corpuscles be described as?
Encapsulated
What are the structural features of an Encapsulated Tactile Corpuscle?
(3)
- Branching unmyelinated sensory terminals
- Terminals provided support by modified Schwann cells
- surrounded by a thin oval fibrous connective tissue capsule
What do Tactile Corpuscles sense?
3
- Delicate/discriminative touch
- Light pressure
- Low frequency vibration (2-80 Hz)
Where are Lamellar Corpuscles located?
Scattered deep in the dermis/hypodermis
What are the structural features of Lamellar Corpuscles?
3
- Single dendrite
- Inside layers of collagen fibres/specialised fibroblasts
- Each layer separated by gelatinous interstitial fluid
What does deformation to the capsule of lamellar Corpuscles do?
opens pressure sensitive Na+ channels in sensory axons
What makes Lamellar Corpuscles rapidly adapting?
When inner layers covering the axon terminal are compressed they ‘relax’ quickly so action potentials are discontinued
What stimulates Lamellar corpuscles?
2
- Deep pressure
- Vibration (around 250Hz)
Where are Bulbous Corpuscles located?
In the Demis/subcutaneous tissue
What are the structural features of Bulbous Corpuscles?
3
- Network of nerve endings
- Intertwined with a core of collagen fibres that are continuous with the dermis
- Capsule surrounding entire structure
What stimulates Bulbous Corpuscles?
2
- sustained deep pressure
- stretching/distortion of the skin
What are Bulbous Corpuscles important for?
signalling continuous states of:
- deformation to tissue
- heavy prolonged touch/pressure signals
What are Bulbous corpuscles involved in at joint capsules?
Proprioception - degree of joint rotation
Where on the body is there a high density of Bulbous Corpuscles?
Around fingernails
What do Bulbous Corpuscles allow your grip to do?
Be modulated
What do Arteries do in context of the skin?
Supply blood to the skin and subcutaneous layer
Where do the branches of arteries extend?
They extend into the superficial layers of the dermis
What is the role of capillary loops?
2
- supply blood to the upper dermis/underside of the epidermis
- Drain blood into the venous plexus
Where is smooth muscle located?
In the walls of blood vessels
What controls smooth muscle in blood vessels?
Sympathetic nervous system
Where are Precapillary sphincters located?
At the start of capillary beds
What does Contracting smooth muscle of the Precapillary sphincter/Arteries do?
Restricts blood flow to the upper layers of the skin
What does Noradrenaline from the SNS act on in vascular smooth muscle in the skin?
Alpha 1 adrenergic receptors
What are Alpha 1 adrenergic receptors an example of?
G-protein coupled receptor (GPCR)
How do G-protein coupled receptors work?
They activate a secondary messenger system in the cell
How do GPCR’s work on vascular smooth muscle tissue in the skin?
(3)
- Secondary messenger system leads to increased intracellular calcium
- Intracellular calcium leads to constriction
- Constriction leads to reduced skinflow
What is the result of less SNS activity in the skin?
2
- Relaxation/dilation of arteries to the skin
- Increased skin bloodflow flow
What is the optimal body temperature?
37ºC
Range of 36.5 - 37.5ºC
What happens to cells at 40 degrees?
2
- They become denatured
- Lose ability to thermoregulate
What happens to cells when your body becomes too cold?
Nervous tissue lose function
What are the Primary mechanisms of heat transfer?
4
- Radiation
- Evaporation
- Convection
- Conduction
How is heat Transferred through radiation?
It is lost/gained through infrared rays
What % of heat loss is through Radiation?
60%
How is heat Transferred through Conduction?
Heat is transferred from/to objects that are in contact with the body
What % of heat loss to the air is due to Conduction?
15%
How is heat transferred through convection?
3
- Firstly by conduction
- Then warm air moves away and is replaced by cold air
- constant temperature gradient is maintained
How is heat lost through Evaporation?
Heat energy is transferred from the body to convert water from liquid to gas
What is the difference between water and air as a heat acceptor?
Water can absorb far more heat than air
What are Eccrine sweat glands innervated by?
Sympathetic cholinergic nerves
What are Sympathetic cholinergic nerves?
Nerves that release Acetylcholine
What is a muscarinic acetylcholine receptor?
Acetylcholine receptors that forms G protein-coupled receptor complex
What are only some Eccrine sweat glands stimulated by?
Adrenaline acting on Beta receptors
What is a results of Adrenaline acting on Beta receptors?
Nervous sweating
What are the bodily responses to temperature increase?
4
- Behavioural changes
- Vasodilation and shunting of blood to skin surface
- Sweat production
- Respiratory heat loss
What is the Preoptic area of the hypothalamus?
Area containing heat/cold sensitive receptors (central thermoreceptors)
What happens if blood temperature goes above set point?
Heat loss centre is activated
What are induced responses by the heat-loss centre?
2
- Decreased activation of SNS alpha 1 receptors leads to vasodilation
- Increase SNS cholinergic activation of mAChRs leads to sweating
Are radiation, conduction and convection effective heat loss mechanisms?
No
What happens when central thermoreceptors detect temperature below set point?
Heat gain centre is activated
What are induced responses by the heat-gain centre?
2
- Increased generation of body temperature
- Conservation of body temperature
What are examples of Heat generating mechanism?
3
- Shivering
- Non-shivering thermogenesis
- increased thyroxine increase
What are the features of shivering?
3
- increased tone of skeletal muscles
- Above critical level shivering occurs due to oscillatory contractions between agonist and antagonist
- muscles are mediated by muscle spindles
What are the features of Non-Shivering Thermogenesis?
4
- Increased sympathetic nerve activity
- Increased circulating adrenaline/noradrenaline
- Increased cellular metabolism
- ‘uncoupling’ of oxidative phosphorylation
What are features of increased thyroxine in generating heat?
3
- Occurs in response to TRH/TSH
- Increased basal metabolic rate
- May take several weeks of cold exposure to ensue
What are Arrector Pili muscles innervated by?
Sensory nervous system Alpha 1 receptors
How do Arrector Pili muscles attach to hair follicles?
By linking the hair follicle to the upper Dermis
What happens when Arrector Pili muscle contracts?
4
- Pulls hair upright
- dimples the skin
- leads to goose bumps
- Compresses Sebaceous gland
What are examples of different types of burns?
4
- First-degree burn
- Second-degree burn
- Deeper Second-degree burn
- Third-degree burn
What layer(s) of skin do First-degree burns effect?
superficial, outer layer of the Epidermis
What are symptoms of First degree burns?
4
- Red/pink colouring
- Dry skin
- Pain
- Usually no blisters
What is the healing time of a First degree burn?
3-10 days
What layer(s) of skin do Second-degree burns effect?
Epidermis + varying amounts of dermis
What are symptoms of Second-degree burns?
4
- Red
- Blisters
- Moist
- Painful
What is required to aid healing a second-degree burn?
Good dressings, initially absorptive ones
What layer(s) of skin do Deeper second-degree burns effect?
Epidermis + dermis
What are symptoms of Deeper Second-degree burns?
5
- Red
- Blisters
- Moist
- Painful
- May include whiteish, waxy areas
What are effects of Deeper second-degree burns?
2
- Hair follicles/Sweat glands may remain intact
- Some tactile receptors may be lost
What is the healing time of a Second-degree burn?
1-2 weeks
What is the healing time of a Deeper second-degree burn?
2
- One month
- May have some loss of sensation/scarring
What layer(s) of skin do Third-degree burns effect?
Full thickness extending into the subcutaneous tissue
What are symptoms of Third-degree burns?
5
- Varied colour from waxy white to deep red or black
- Hard
- Dry
- Leathery
- No pain
Why is there no pain in the area of Third-degree burns?
Sensory nerve endings have been destroyed
What is the healing time of a Third-degree burn?
Weeks to regenerate skin and for scarring to occur
What may be an additional requirement to heal from a Third degree burn?
Skin grafting
What % of Total body surface area would the face be?
9%
What % of Total body surface area would each Upper limb be?
9%
What % of Total body surface area would the trunk (front and back) be?
36%
What % of Total body surface area would the Genitalia be?
1%
What % of Total body surface area would each Lower limb be?
18%
What are potential complications of Severe burns?
3
- Dehydration/Hypovolemic shock
- Infection/Sepsis
- Hypothermia