Skin, Sense and Pain Flashcards
Why is the skin so important in Radiography?
Skin dose influenced by field size due to increased backscatter with increased size
Skin damage can be caused by cumulative dose from multiple diagnostic procedures
Can be mistaken for allergic reactions to defibrillator pads or electrode
Fluoroscopy time is a poor indicator of risk because it does not account for dose rate or acquisition mode
Patient related factors
Compromised skin integrity
Obesity including overlapping skin folds and location of skin irradiated
Light fair skin more at risk
Drugs can increase sensitivity particularly some chemotherapy drugs
The Integumentary System is made up of:
Made up of:
The skin
The accessory organs such as nails and hair
accessory glands; e.g. sweat / sebaceous
Supporting muscles / nerves
Overview of the skin
Largest body organ; average 2 square metres and 5kg (about 16%)
Made up of different tissues with varying functions
Ranges in thickness from 0.5mm (eyelids) to 4mm (calcaneum); average 1-2mm
Main parts:
Epidermis; superficial, thinner, epithelial
Dermis; deeper, thicker, connective tissue
Hypodermis/subcutaneous layer;
areolar and adipose tissue
connected to dermis and underlying tissue via connective fibres
Storage for fat and blood vessels to skin
Sensitive to pressure due to nerve endings (corpuscles of touch)
What is the Epidermis?
Stratified squamous epithelium
Contains keratin (also found in hair/nails),
insoluble tough, fibrous protein
Protects tissues from heat, microbes, and
Chemicals
Contains 4 layers usually, but
An extra layer stratum lucidum is found of the palms and soles.
Important to prevent water loss, injury, and stop chemicals and micro-organisms entering
new cells form and push old cells to the surface where they flake off
Lacks Blood vessels
Contains keratinocytesm melanocytes, Langerhans Cells and Merkel cells:
Keratinocytes: most abundant (@95%), essential for skin repair, provide a tight barrier preventing entry of foreign substances and minimize water loss, heat and salts.
Melanocytes: Cells that produce pigment melanin giving the skin it’s colour – production is varied; pigment to absorb UV light and shield cell DNA.
Merkel Cells: associated with sensory nerve endings – aid innervation of the epidermis
Langerhans Cells: bone-marrow derived immune cells
What is the dermis?
Dermal blood vessels carry nutrients to upper layers of skin and help to regulate temperature.
contains nerve fibres, sensory receptors, hair follicles, sebaceous glands, and sweat glands.
Deeper layer of skin; connective tissue of collagen and elastic fibres containing
Fibroblasts
Adipocytes
Macrophages
Nerves, hair follicles, smooth muscles, glands and lymphatic vessels extend into the dermis
Collagen and elastic fibres are responsible for the structural strength of the dermis – orientated in different directions to resit stretch
Divided into:
Papillary region
Reticular region
Dermis – papillary region
Superficial 1/5th of areolar connective tissue and elastic fibres (connect epidermis to dermis)
Dermal papillae (finger like projections) into epidermis increase surface area
Contain:
Loops of capillaries (nourish epidermis)
Corpuscles of touch (Meissner corpuscles
Free nerve endings; temperature, pain, tickling/itching
Corresponding interpapillary pegs of epidermis
(Fingerprints)
Epidermal ridges
Fingerprints (epidermal ridges) formed due to dermal papillae and interpapilliary pegs of epidermis
Sweat glands open on ridges; form fingerprints
Amplify vibrations triggered when fingertips brush across an uneven surface,
Better transmission of signals to sensory nerves involved in fine texture perception.
Assist in gripping rough surfaces and surface contact in wet conditions.
Dermis – reticular region
Net-like bundles of connective tissue; collagen / elastic fibres
Provide strength and elasticity to skin
Thicker = 4/5 of dermis
Spaces between fibres contain:
Adipose cells
Hair follicles
Sebaceous (oil) and sudoriferous (sweat) glands
Skin colour
Three pigments:
Melanin
Pale yellow to black
Mostly in epidermis from melanocytes particularly in mucous membranes
Changes in skin colour from pigment produced rather than number of cells
Accumulation causes freckles and liver (age) spots
UV light increases melanin production in melanocytes
Albinism; inability to produce melanin. Vitiligo; patches of lack of melanocytes
Carotene
Yellow-orange
Precursor of vitamin A; use in photopigments in retina
Found in stratum corneum, dermis, and subcutaneous layer
Haemoglobin
Red pigment in red blood cells in capillaries
Related to amount of blood and oxygen content; cyanosis / erythema / jaundice
Accessory structures
Nails
Hair
Glands
Sebaceous
Sudoriferous Ceruminous (see ear lecture)
Mammary (specialised sudoriferous)
Nerves
If the accessory organs remain intact the dermis is able to regenerate when injured.
Nails
Thin plate – consists of dead stratum corneum cells that contain hard keratin
Consist of:
Nail root – covered by the skin, extends from the nail matrix – can be seen through the nail body as the whitish crescent shaped lunula
Cuticle – extends into the nail body
Nail body - visible part attached to the underlying nail bed
Nails grow continuously from the nail matrix
Nail growth
Nail matrix; epithelium deep to nail root, surrounds new nail growth
Growth (~1mm per week)
Superficial cells in matrix transform into nail cells and push over stratum basale
Rate dependent on:
Age, health, nutrition
Season, time, and temperature
Finger/toenails
Length of digit
Hair
Found everywhere on the skin except palms, soles, lips, nipples, parts of the genitalia and distal segment of fingers and toes
Hair arises from a hair follicle (single flower in a vase)
The shaft of the hair protrudes above the skin surface, the root below
The hair bulb is an expanded base of the root where hair is produced
Hair has hard cortex surrounding a softer medulla
The cortex is covered by a cuticle that hold the hair in the follicle
Each hair follicle associate with smooth muscle cells – arrector
Hair produced in cycles – growth and resting stages
Colour determined by melanin – with age melanin decreases
Hair anatomy
Columns of keratinised cells bound together by proteins
Tougher than skin keratin
3 concentric layers:
Outer cuticle: single layer thin flat cells like scales
Middle cortex: thickest layer of elongated cells
Inner medulla: 2/3 layers polyhedral cells
2 inner layers contain pigment granules/air spaces
Shaft projects from skin surface:
Round cross-section: straight hair
Oval cross-section: curly
Root deep to shaft/surface, penetrates into dermis/subcutaneous layer
Root is surrounded by hair follicle
External root sheath;
Internal root sheath;
Surrounded by hair root plexus of nerves sensitive to
touch
Onion-shaped bulb at base
Indentation; papilla
Contains connective tissue and blood vessels,
Germinal layer of cells; matrix
Growth of existing / new hairs
Supported by smooth muscle called arrector pili
Extends from superficial papillary dermis to hair follicle
Contraction (e.g cold,fright) causes hair to lie flat
Subsequent skin elevation; “goose bumps”
Each hair associated with a sebaceous gland
What are glands?
Sebacceous glands:
simple branched acinar glands
Connected to superficial part of hair follicle
Produce sebum –oily , prevents drying and protects against some bacteria
Sweat glands – 2 types:
Eccrine – simple, coiled tubular glands
Release sweat by merocrine secretion, mostly water and salts
Numerous in palms and soles
Apocrine – simple, coiled, tubular glands
Produce thick secretion rich in organic substances – body odour
Release by merocrine and holocrine secretion
Armpits and genitalia
Active at puberty
Skin glands
Modified sweat glands, called ceruminous glands, secrete wax in the ear canal.
Mammary glands, another type of modified sweat gland, secretes milk
Functions of the brain
Protection
Vit D production
Temperature regulation
Excretion & absorption
Sensation
Protection of skin
Protection:
Physical barrier:
interlocked keratinised cells protect from abrasion and microbes.
Chemical barrier:
lipids in lamellar granules prevent water ingress and excess evaporation
Sebum prevents hair and skin drying out and contains bactericidal chemicals
Biological barrier:
Langerhhans cells form an immune response to microbes
Macrophages to phagocytise bacteria
Vitamin D production
Certain molecules in skins activated by UV light
Liver/kidneys modify molecule to form Vitamin D compounds
Calcitrol helps in absorption of calcium from GI tract
Thermoregulation
Releasing sweat for evaporation (increase/decrease)
Adjusting blood flow within capillary network in dermis
Acts as a blood reservoir (8-10% blood volume)
Amount increases during moderate exercise to release heat
Strenuous activity constricts vessels (to supply muscles/heart); temperature rises
Excretion and absorption
Minor roles in excretion and absorption
Excretion:
~400ml water evaporates daily in addition to >200ml sweat
Also excretes salts, CO2, ammonia and urea
Absorption:
Negligible water-soluble substances but some lipid-soluble:
Vitamins A,D,E and K
O2 and CO2
Can absorb some toxins, including
Acetone (nail varnish remover)
Heavy metal salts (e.g. lead, mercury, arsenic)
Some natural plant toxins
Skin as a sensory organ
Skin is the largest sensory organ in the body
Contains numerous sensory receptors – nerve endings within the dermis, close to the epidermis
Pain receptors (nociceptors) – sense tissue damage
Thermoreceptors – sense temperature changes
Mechanoreceptors – sense touch – pressure, stretch, tension, blood pressure
Thermal sensation
Thermoreceptors:
free nerve endings on skin surface (1mm fields of reception), receptors in dermis
Respond rapidly initially but then adapt to be less frequent with prolonged stimulus
Cold receptors:
between 10-40oC. Medium size myelinated fibres
Warm receptors:
32-48oC. Small diameter myelinated fibres (slower response)
Above/below these temperatures, pain receptors (nocireceptors) are stimulated
Mechanoreceptors – touch
Itch / tickle sensations (tactile)
detected by free nerve endings in skin surface to small unmyelinated fibres (slower response)
Itch caused by chemicals cause a local inflammatory response
Still unknown why you can’t tickle yourself!!
Four types of touch receptors two categories
Fast Adaption:
Corpuscles of Touch / Meissner corpuscles
Hair root plexuses – detect hair movement
Slow Adaption
Tactile (Merkel) discs –lips, genitalia, hands
Ruffini corpuscles: sensitive to stretch
Touch and pressure sensors
Pressure: Sensation sustained over larger area
Tactile (Meissner’s) corpuscles:
Detect fine touch and texture
Vibration
Lamellated (Pacinian) corpuscles:
Detect heavy pressure and vibrations
What is pain?
Needed for survival; signals presence of tissue damaging conditions
Nocireceptors (harm receptors); free nerve endings everywhere except the brain
Complex and not fully understood; very subjective
Two types
Fast/acute pain:
<0.1 second; medium size myelinated fibres
Only felt in superficial tissues, very localised
Slow/chronic pain:
>1 second, increases in intensity over seconds/minutes; smaller unmyelinated fibres
Occurs both in skin (may follow acute) and deeper tissues and organs, more diffuse
Superficial somatic pain; skin
Deep somatic pain; muscles, joints, tendons etc.
Visceral pain; of deeper tissues/organs. May not feel localised stimuli of somatic pain
Referred pain; visceral pain felt in/deep to skin overlying/remote from organ
Phantom limb sensation: patient continues to experience pain after amputation
Wound healing
Inflammation, in which blood vessels dilate and become more permeable, causing tissues to become red and swollen, is the body’s normal response to injury.
Superficial cuts :epidermal healing- filled by reproducing epithelial cells.
A deeper injury with broken blood vessels involves the formation of a blood clot
More complex as multiple layers involved; results in scar tissue
Deep wound healing
Inflammatory phase:
Blood clot forms to unite edges and protect deep tissues
Inflammation to remove microbes, foreign debris, and dead tissue
Migratory phase:
Clot becomes scab, epithelial cells migrate deep to scab to bridge wound
Fibroblasts start to develop early scar (granulation) tissue of collagen and glycoproteins
Proliferation phase:
Extensive growth of epithelial cells deep to scab
Fibroblasts continue to produce random matric of collagen
Blood vessels redevelop
Maturation Phase:
Scab comes off once epidermis of normal thickness
Collagen fibre matrix becomes more organised, fibroblasts reduced
Aging of the integumentary system
Changes start to become noticeable in late forties; mostly within dermis
Wrinkles:
Collagen reduces, becomes stiffer and more disorganised
Elastic fibres lose elasticity and thickened (accelerated in smokers)
Reduction in fibroblasts to produce new collagen/elastic fibres
Decreased immunity/protection:
Fewer Langerhans cells, less-efficient macrophages
Sebaceous glands smaller; dry/broken skin
Less sweat; heat stroke
Loss of melanocytes; skin cancer and liver spots/greying hair
Thinner skin:
Loss of subcutaneous tissue and slower migration of epidermal cells
Brittle and slower growing hair and nails
Skin cancer – basal cell
Commonest type of skin cancer
Typical patient – 70-80, fair skinned
Arises from the basal layer of the epidermis
Locally aggressive but low metastatic potential.
High rate of recurrance
Imaging
US
Small lesions have a well defined heterogenous appearance.
MRI
Lesion will look hyperintense and will enhance if gadolinium is given
Skin cancer – squamous cell
Common in the head and neck
Most common head and neck cancer
Arise from a mucosa or cutaneous origin
Can be external or within the
Nasopharynx
Sinuses
Mouth
Larynx
Treatment – depends on site, but generally surgery and radiotherapy / chemotherapy
Skin cancer – squamous cell
Disease of advancing age.
If it is within the mouth and throat – most common cause is smoking and HPV
Use of imaging
In diagnosis, staging and follow up
Contrast CT is usually the first line imaging method.
If the mass is in the neck, US and a US guided fine needle biopsy is used
MRI is increasing being used depending on availability
Imaging’s use in follow up is to assess for radio necrosis and recurrence
Follow up is generally performed with CT, PET if available.
Skin cancer – melanoma
Also called a malignant melanoma
Malignant neoplasm that arises from melanocytes in your epidermis. But can also grow in the eye
Has an aggressive tendency to metastasise most commonly to skin, lymph nodes, lung, liver, bone and brain.
Risk factors include – sunburn as a child or adult, fair skin, outdoor lifestyle, radiation exposure
Survival rates depends on thickness of tumour - <1mm up to 96% survival, >4mm, around 40%
Less than 5% of all skin cancers but is the leading cause of death in skin cancer stats
Skin cancer – metastatic melanoma
The most frequent site of involvement of metastatic disease is the lymphatic system – especially the lymph nodes in the area of the primary lesion
The detection of lymph spread is the most important predictor of survival.
Treatment depends on the extent of disease.
Excision of the primary tumour is the first treatment. Lymphadenectomy can also be performed.
Imaging is used to diagnose and assess progression and treatment outcomes
US – assess lymph nodes
CT – best imaging method for assessing lymph nodes. The nodes are assessed for size and density – should not he heterogenous
PET-CT – most sensitive for assessing the chest
MRI is the best imaging method for brain metasteses
Frostbite
This is tissue injury from direct tissue necrosis from freezing and indirect tissue injury from inflammatory changes
Most common sites are the hands, feet, face and ears
Imaging is mainly used to assess the bones and look for any secondary injuries
Radiographs
Can see tissue swelling and breakdown of the distal bones
Nuclear medicine
Can be useful to assess tissue viability – identify healthy and ischaemic tissue
Pressure sores
Occurs after long term pressure of soft tissue under bony prominences
They evolve over time and result from ischaemia and a local inflammatory reaction, bacteria colonizing the upper layers of skin eventually leading to skin erosion, and possibly muscles and bone
Most commonly seen on the sacrum, scapula, occiput, greater trochanter
Imaging
CT is the best imaging method to evaluate as it shows
The ulcer cavity, any loss of tissue, and abscesses or gas and any bone erosion
Chicken pox
Itchy rash across body
Complications
Encephalitis
Pneumonia
If mother is not immune, damage to an unborn fetus
Measles
Highly contagious.
Patients have a red, flat rash.
Complications can include
Pneumonia
Encephalitis (inflammation of the brain)
Revision notes – functions
Responsible for maintaining homeostasis
Temperature regulation
Protection of underlying tissues
Slows water loss
Houses sensory receptors
Synthesizes certain biochemicals
Excretes wastes
Part of the process to make vitamin D
