Integumentary system Flashcards
How is the skin involved in maintaining homeostasis?
protects the body from pathogens
regulates body temperature
allows us to experience the external environment through sensations
absorbs and excretes substances
involved in formation of vitamin D
What are the three layers of the skin?
epidermis (outer layer), dermis, hypodermis (inner layer)
What is the epidermis?
thin, outermost layer of the skin
constantly sheds millions of dead cells with new and maturing cells moving towards the surface
this process lasts around 30-35 days
What are the five sublayers of the epidermis?
stratum basale (inner layer), stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum (outer layer)
What is the structure of the stratum basale?
bottom germative basal membrane
includes stem cells of the epidermis which mature and differentiate as they move towards the surface
What is the structure of the stratum spinosum?
cells are ‘spiny’ which enables them to adhere together and provide structural support to the skin
as cells are pushed further up they produce more keratin which flattens the cells
What is the structure of the stratum granulosum?
site of keratinisation
keratinocytes in this layer and the stratum spinosum produce glycolipids that spread over the cell, keeping them waterproof
this glycolipid layer and distance from a nutrient supply causes cell death
What is the structure of the stratum lucidum?
cells have clear protoplasm and flattened/no nuclei with melanin to protect against UV light damage
not present in all areas (e.g. absent from the eyelids)
What is the structure of the stratum corneum?
outermost layer
heavily keratinised and waterproof
cells are shed from the epidermis
The life cycle of the skin cell is dependent on synchronisation of what processes?
desquamation (shedding of the stratum corneum)
effective keratinisation of cells approaching the surface
continual cell division in the stratum basale with newly formed cells being pushed to the surface
What are the four main cell types found in the epidermis?
keratinocytes, melanocytes, Merkel cells, Langerhans’ cells
What is the function of keratinocytes?
produce keratin, a protein that gives skin its strength and flexibility and makes it waterproof
What is the function of melanocytes?
produce melanin, a pigment that gives skin its colour and protects it from UV radiation damage
What is the function of Merkel cells?
thought to have a role in touch reception
What is the function of Langerhans’ cells?
first line of defence in the skin
support the immune system by processing antigens
What is the dermis?
provides epidermis with nutrients
comprised of connective tissue (rich in collagen and elastin) with blood and lymph vessels and nerves
includes the accessory structures of the skin
What are the two primary sublayers of the dermis?
papillary layer and reticular layer
What is the papillary layer of the dermis?
fine and loosely arranged collagen fibres
interweaves with the epidermis
What is the reticular layer of the dermis?
dense irregular connective tissue
densely packed collagen fibres make this layer strong
What are the four main cell types found in the dermis?
fibroblasts, macrophages, adipocytes, sensory receptors
What is the function of fibroblasts?
synthesise the extracellular matrix (a collection of substances outside of cells that provides structural and biochemical support to surrounding cells)
produce collagen for wound healing
What are macrophages?
phagocytes involved in both innate and adaptive immunity
What are adipocytes?
fat cells that make up adipose tissue
What are sensory receptors?
three main groups
mechanoreceptors respond to mechanical pressure
nociceptors are pain receptors
thermoceptors respond to temperature
What is the hypodermis?
connects the skin to the rest of the body
primarily adipose tissue (subcutaneous fat) and areolar tissue
highly vascular
provides an energy store and insulation for the body
The skin has numerous accessory structures, largely found within which layer of the skin?
dermis
Why does the dermis have a rich supply of blood and lymph vessels?
blood vessels provide nutrients to the skin and its accessory structures and remove waste products
blood carries heat so constriction/dilation of blood vessels are involved in thermoregulation
lymph vessels collect extra fluid and return it to the blood circulation, and support immunity
Why does the dermis have sensory nerve endings?
dermal receptors monitor sensations from the external environment (e.g. touch, pressure, pain, temperature)
this protects the body from harm and allows us to experience pleasant sensations which are relayed to the brain through the spinal cord
Why are partial thickness burns more likely to be painful than full thickness burns?
partial thickness burns cause exposure of pain receptors in the skin
pain sensation is exacerbated by localised oedema and inflammation
Why are full thickness burns still likely to be painful?
the edges of the burn wound are likely to be partial thickness
the surrounding tissue is likely to have a heightened response to pain
What are the two main types of sweat glands in the skin?
eccrine glands and apocrine glands
What are eccrine glands?
widely distributed and the most numerous
abundant on palms of the hand, soles of the feet, and dermis of the forehead
their ducts open onto the skin surface
produce a clear, watery sweat controlled by the sympathetic nervous system in response to emotion or to cool the body
What are apocrine glands?
primarily in the armpits and anogenital areas
their ducts open into hair follicles
become active at puberty and produce sweat containing fats and proteins which makes the sweat thicker and cloudy
bacteria on the skin digest this sweat which produces odour
they produce pheromones thought to have a role in sexual arousal
this sweat has a limited role in thermoregulation
specialised apocrine glands produce ear wax (ceruminous glands) and milk (mammary glands)
What are sebaceous glands?
widely distributed but not found on palms of the hand or soles of the feet secrete sebum (oily substance that softens and lubricates skin, prevents hair from becoming brittle, reduces water loss from skin and has antimicrobial properties) largely secrete sebum into hair follicles some secrete sebum directly onto the skin surface
What are the functions of hair?
to assist in thermoregulation
to provide mechanical protection against friction
linked with arousal stimuli for pleasure
How is hair formed?
skin contains hair follicles which consist of a cluster of cells called the bulb
cell division occurs inside the bulb, producing cells which are pushed up and away from the follicle
as the cells move away from the follicle, they lose their nutritional supply, become keratinised and die
these cells bond together forming hair (known as the foot below the skin surface and the shaft above)
What are arrector pili muscles?
smooth muscle fibres attached to hair follicles
when these muscles contract they cause hair to stand up which traps air and insulates the body from heat loss
this occurs in response to cold and fear and is regulated by the sympathetic nervous system
What are nails?
tightly packed, dead, hard keratinised epidermal cells
provide protection for the ends of fingers and toes and facilitate fine motor movements
the nail has a root embedded within the skin and a nail plate
the plate has the bed below it, where the cells of the nail germinate
the pale, half-moon shaped area on the nail is the lunula, the visible part of the nail root
What are the six main functions of the skin?
sensation, thermoregulation, protection, excretion, absorption, synthesis of vitamin D
How does vitamin D regulate the health of the skin?
inhibits cell proliferation
stimulates cell differentiation including that necessary for the epidermis
promotes innate immunity
regulates the hair follicle cycle
suppresses tumour formation
Systemically, vitamin D has which fundamental roles?
mineralisation of bones through calcium absorption
prevention of cardiovascular disease
prevention of diabetes mellitus
prevention of cancer
prevention of immune dysfunction
How does the skin regulate body temperature?
alters the diameter of blood vessels in the skin to alter heat loss through radiation
produces sweat to lose heat through evaporation
uses hair to increase/decrease air insulation on the skin surface
What are the two categories of skin ageing?
chronological ageing - occurs due to the passing of time
photoageing - occurs due to sun exposure and pigmentation
What are intrinsic (genetic) factors related to skin ageing?
chromosomes have DNA sequences at the ends called telomeres
these are reduced in length at each cell division and are thought to control the cell lifespan
telomeres are maintained by the enzyme telomerase
skin cells lack telomerase which causes more rapid shortening of telomeres and cell exposure to oxidative damage
growth hormone influences the rate of cell proliferation and collagen production
lower levels of growth hormone due to ageing decrease skin thickness
What are extrinsic (environmental) factors related to skin ageing?
UV light triggers an inflammatory response that increases production of the enzyme collagenase
collagenase breaks down collagen in skin
increased collagen damage occurs with post-menopausal oestrogen deficiency
repeated muscle movements generate wrinkles in skin
sweat and sebum production decreases which inhibits thermoregulation and excretion
reduction in the dermal-epidermal junction surface area increases skin fragility as delivery of nutrients to the epidermis is less efficient
What is regeneration?
the body’s ability to replace lost or damaged tissue with the same tissue
epithelial, bone, connective and smooth muscle tissues can regenerate
cardiac, nervous and skeletal muscle tissues are limited in this ability
What is fibrosis?
occurs when there is damaged or lost tissue that is replaced with fibrotic (scar) tissue
scar tissue consists of collagen fibres which hold the tissues together but do not perform the original function
What is primary healing/intention?
wound edges are joined together and there is no tissue deficit to remedy - e.g. suturing, clipping or gluing
usually no wound infection and scar tissue formation is minimal
the initial union of wound edges occurs over 7-10 days, though the maturation stage of healing can take up to two years
What is secondary healing/intention?
there is a tissue deficit between the wound edges
the body must fill in and contract the wound area to restore tissue integrity - e.g. vacuum-assisted closure (VAC)
this involves the production of granulation tissue (delicate, pink connective tissue and tiny blood vessels) before scar tissue is formed
these wounds will always have more granulation tissue in relation to size than a wound healing by primary intention
the healing time is longer due to the additional need for tissue growth
What is tertiary healing/intention?
wound is intentionally kept open to allow oedema or infection to resolve or to permit removal of exudate - e.g. packing/placing a drain in a wound to intentionally keep it open and remove fluid
this causes more scarring than wounds that heal by primary intention but less than those that heal by secondary intention
What are the four key stages of wound healing?
haemostasis
inflammation
proliferation (migration, granulation and proliferation)
maturation (remodelling)
What happens in haemostasis?
vasoconstriction in arterial/arteriole walls reduces blood flow
thrombocytes aggregate at the injury site to form a fibrin clot which reduces active bleeding (haemostasis)
this causes localised tissue hypoxia and acidosis which triggers release of vasoactive substances (e.g. nitric oxide, adenosine, histamine) that cause vasodilation
the increased permeability of the vascular membrane allows inflammatory cells access to the injury site
What happens in inflammation?
increased blood supply to the injury site triggers an inflammatory response to prevent infection
leucocytes are attracted to the site by interleukins and growth hormone
neutrophils destroy bacteria and cell debris by phagocytosis and release substances toxic to bacteria
neutrophils release oxygen free radicals as a by-product, which are antibacterial and help to sterilise the wound by combining with chlorine
macrophages contain growth factors that trigger angiogenesis and tissue repair
lymphocytes assist in generation of new collagen fibres to restructure the damaged tissue
What happens in proliferation?
angiogenesis occurs once there is a fibrin-platelet clot and lymphocytes arrive
new blood vessels are weak (wound appears inflamed) and strengthen over time
epithelial cells from wound edges move across the wound bed, cover it and attract to the matrix underneath (granulation and contraction is needed in a large wound)
granulation tissue is formed by fibroblasts laying down structural proteins that produce collagen and replaces the fibrin-platelet clot
fibroblasts attach to granulation tissue and contract to close the wound
some wounds form eschar (dead tissue which is cast off or surgically removed) before healing can complete
What happens in maturation?
adapted fibroblasts attach to collagen fibres and contract to pull the wound margins together
collagen fibres and proteins are remodelled and realigned along tension lines
apoptosis of unnecessary cells occurs and the scar tissue continues to strengthen and gradually shrinks
the final tissue is pale in contrast to the pink colour of a newly formed scar
in people with darker skin pigmentation the scar will always remain paler than the skin it replaces
Why is the absence of necrotic tissue, bioburden and foreign debris a condition for optimal wound healing?
defective cell matrix and debris prolong the inflammatory phase and delay proliferation
bioburden (flora) competes with fibroblasts, neutrophils and macrophages to function optimally
Why is being free of and protected from infection a condition for optimal wound healing?
high bacterial count prolong the inflammatory phase, delay proliferation and compete for nutrients needed by fibroblasts, neutrophils and macrophages to function optimally
Why is the absence of dead space a condition for optimal wound healing?
dead space creates an environment for pathogens to survive and thrive
this increases the likelihood of infection
it promotes seroma formation (a pocket of clear serous fluid) which can cause maceration to the wound bed
Why is being insulated from local hypothermia a condition for optimal wound healing?
temperature affects the tensile strength of wounds
cells and enzymes function optimally at normal body temperature
a temperature drop of just 2°C is enough to affect the biological healing process
Why is maintenance of gas exchange a condition for optimal wound healing?
low oxygen levels interfere with protein synthesis and fibroblast activity
this causes a delay in wound healing
Why is a balanced moist wound bed a condition for optimal wound healing?
prevents tissue dehydration and cell death
accelerates angiogenesis in the haemostasis phase
increases the breakdown of non-viable tissue and fibrin
facilitates the interaction of growth factors with target cells
What is the core body temperature?
36.8 °C
What is hypothermia?
body temperature below 35 °C
this can occur due to environmental exposure to cold, metabolic disturbances or can be iatrogenic
metabolism slows and neurological dysfunction occurs
What is hyperthermia/pyrexia?
low-grade pyrexia is from normal temperature to 38.0 °C
moderate to high-grade pyrexia is 38-40 °C
hyperpyrexia is above 40.0 °C which causes serious cell damage
metabolism is disrupted and neurological dysfunction occurs
What is a fever?
body temperature is raised as the hypothalamic regulating centre has a set-point which is above the normal range, frequently due to infection
the person shivers and feels cold
inhibits microorganism growth and increases antibody production
What is the hypothalamus?
control centre in the brain
receives information on body temperature
initiates actions to adjust the balance between heat production and heat loss
this maintains the correct body temperature
What are the four key mechanisms for heat loss from the body?
radiation, conduction, convection, evaporation
What is radiation?
the transfer of heat by radiation
requires no physical contact between surfaces
accounts for 60% of heat loss
What is conduction?
heat loss due to contact with a surface colder than the body
accounts for 15% of heat loss
What is convection?
air is heated as it passes over the body
heated air rises and carries heat away from the body, replaced by cool air (convection current)
accounts for 5% of heat loss
What is evaporation?
the conversion of a liquid to vapour by heat which causes a loss of heat energy
accounts for 20% of heat loss
How does the body adapt to reduce body temperature?
cutaneous vasodilation, sweat production, behavioural responses
How does cutaneous vasodilation reduce body temperature?
more heat is lost from the blood to the atmosphere via convection or radiation
How does increased sweat production reduce body temperature?
liquid on the skin surface evaporates
this requires heat energy, resulting in heat loss
What are some of the behavioural responses to reduce body temperature?
people reduce activity (reduces metabolism), remove clothing and drink cold fluids to enhance cooling by conduction
How does the body adapt to increase body temperature?
cutaneous vasoconstriction, piloerection, shivering thermogenesis, metabolic thermogenesis, behavioural responses
How does cutaneous vasoconstriction increase body temperature?
less heat is lost from the blood to the atmosphere via convection or radiation
What is piloerection?
arrector pili muscles contract
this raises hairs on the skin and provides insulation
What is shivering thermogenesis?
a spinal reflex stimulates muscle contraction in antagonistic pairs
this generates heat through metabolic activity
What is metabolic thermogenesis?
autonomic and endocrine stimulation increases metabolic rate
endocrine stimulation comes from release of T3 and T4 from the thyroid gland and noradrenaline from the adrenal medulla
this increases appetite to provide nutrients for this increase
What are some of the behavioural responses to increase body temperature?
people increase activity (increases metabolism), add clothing and drink warm fluids to transfer heat by conduction
Why are older people more vulnerable to thermoregulatory issues and have a reduced ability to generate heat?
lower lean body mass
impaired mobility
malnutrition due to physical or cognitive impairment
reduced shivering response
Why do older people also experience increased heat loss?
ineffective cutaneous vasoconstriction
reduced heat sensation
inability to respond to being cold due to physical or cognitive impairment
exposure to cold due to poor housing, insufficient clothing or inability to access or afford heating
