Lecture 3 Flashcards
Skin Physiology
What are C-fibres?
Unmyelinated axons with small diameters
What are sensory terminals?
Free nerve endings which swell at the distal ends of axons
What is an A-delta?
Myelinated axons with small diameters
What are different types of sensory terminals?
Ion channels and chemically activated channels
What do free nerve endings primarily respond to?
Temperature, pain, itching, and the bending of hair in the root hair plexus
What are tactile disks?
Free nerve endings in the deepest layer of the epidermis that release serotonin. They have small receptive fields and are sensitive to touch, pressure, texture, shape, edges and low frequency vibration (5-15Hz)
What are tactile corpuscles?
Nerves within the papillary layer of the dermis, particularly in hairless skin. They are encapsulated and sensitive to delicate and discriminative touch, light pressure and low frequency vibration (10-50Hz)
What is the capsule of the tactile corpuscle made from?
Spiralling / branching unmyelinated sensory terminal are surrounded by modified Schwann cells and then by a thin oval fibrous connect tissue capsule
What does deformation cause in tactile corpuscles?
Entry of Na+ ions into the nerve terminal creating an action potential
What are lamellar corpuscles?
Nerves found in the dermis and hypodermis of which the single sensory axon terminal lies within concentric layers of collagen fibre and specialised fibroblasts separated by a gelatinous interstitial fluid. They are stimulated by deep pressure and high frequency vibration (250Hz)
What does deformation cause in lamellar corpuscles?
Capsule to open and Na+ to enter cell creating an action potential
What are bulbous corpuscles?
A network of nerve endings located in the dermis and subcutaneous tissue. They’re intertwined within a core of collagen fibres that are continuous with those of the surrounding dermis. Sensitive to sustained deep pressure and stretching of the skin (proprioception)
What is in the walls of arteries?
Smooth muscle tissue
What is smooth muscle tissue controlled by?
The sympathetic and parasympathetic nervous system
Constriction of arteries means to…?
Reduce blood flow
Dilation of arteries means to…?
Increase blood flow
What neurotransmitter do the SNS nerve fibres release?
Noradrenaline
At the arteries at the cutaneous plexus, what does the NE act on?
The alpha 1 adrenergic receptors
More SNS activity leads to more activation of the alpha 1 adrenergic receptors which further leads to…?
An increase of calcium inside the muscle cells -> more cross-bridges formed and therefore more muscle contraction
A decrese in SNS activity leads to less activation of the alpha 1 adrenergic receptors which further leads to…?
Relaxation (dilation) of arteries -> increased skin blood flow
What is core body temperature?
The temperature of the blood within and around the major organs of the body
What is the ideal body temperature for your average person?
~37 degrees celsius
What are the body’s primary mechanisms of heat transfer?
Radiation, evaporation, convection, conduction
How does radiation occur?
Anything not at absolute zero (0k) radiates heat energy through infrared rays. This allows the body to absorb heat from hotter surroundings or give away heat to colder surroundings.
How does evaporation occur?
The body produces the watery secretion from our eccrine sweat glands as a mechanism for heat loss. As this evaporates off our skin, it takes some heat energy with it.
How does convection occur?
Our bodies create a heat bubble surrounding us with air in thermal equilibrium, as hot air rises it is replaced with colder air and the process starts again. This makes us feel colder. (wind chill factor)
How does conduction occur?
Conduction is heat transfer through physical contact. Our bodies create a warm air bubble with the air surrounding us.
What are the eccrine sweat glands?
The sweat glands found all over the body that produce a watery secretion as a mechanism for heat loss
How do the eccrine sweat glands work?
SNS nerve fibres release ACh onto mAChRs which are coupled with the g-protein GPCRs to produce the secretion
What is nervous sweating?
When some eccrine sweat glands are stimulated by adrenaline acting on beta receptors. e.g. sweaty palms
Where are the central thermoreceptors located?
In the preoptic area of the hypothalamus
What happens when body temperature goes above the set point?
Decreased SNS activation of alpha 1 receptors on skin blood vessels leading to vasodilation. Increased cholinergic activation of mAChRs on sweat glands leading to sweating. Increased respiratory rate and behavioural changes.
When is the body’s heat loss mechanism through radiation, conduction and convection not effective?
When environmental temperature > body temperature
What happens when body temperature goes below the set point?
Shivering thermogenesis, Non-shivering thermogenesis and increased thyroxine
What is shivering thermogenesis?
Oscillatory contractions of agonist and antagonist muscles. ATP -> ADP + Pi + movement + heat
What is non-shivering thermogenesis?
Increased SNS nerve activity and increased circulation of adrenaline and noradrenaline from adrenal medulla.
Increased cellular metabolism (glycogenolysis)
‘uncoupling’ of oxidative phosphorylation (brown fat)
What does increases thyroxine do?
Increases basal metabolic rate in response to TSH and TRH. Only longterm
What are the arrector pili muscles?
Smooth muscle innervated by the SNS which attaches the hair follicle to upper dermis
What does contraction of an arrector pili muscle cause?
It pulls the skin up, forming a dimple (goosebump) and compresses sebaceous glands to prevent heat loss via evaporation
What are goosebumps an example of?
Physiological feed forward
What are potential complications of severe burns? Directly to skin function
Dehydration and hypovolemic shock, infection / sepsis, hypothermia
What are potential complications of severe burns? Related to other aspects of physiology
Electrolyte imbalances, hypermetabolism, gastrointestinal ulceration, renal failure, respiratory disfunction
