Victoria Booth
questions received:
Why does the skin of the fingers and toes become wrinkled after prolonged immersion in water?
What systems interact with the integumentary system?
Can you please give an outline of the physiology side of the integumentary system?
What exactly is the integumentary system?
How does skin function as a defence against disease?
What are a few fun facts about the Integumentary System?
What temperature from the sun will burn the skin?
I need to know how to link the skin in a life science and nursing perspective.
What is a recent information or discovery regarding the integumentary system?
responses:
Why does the skin of the fingers and toes become wrinkled after prolonged immersion in water?
The epidermis covering the palmar and plantar aspects of the hands and feet is thicker than on other parts of the body and more tightly bound to the underlying connective tissue and aponeurosis. This arrangement facilitates good grip for the fingers and toes and better resistance to the wear and tear that they experience. When the skin is immersed in water for long periods, particularly warm soapy water, the dead cells forming the outer layers of the epidermis become hydrated as the protective oils are leached away and the cells begin to swell, causing the skin to buckle and wrinkle. This becomes most noticeable over the tips of the fingers and toes.
(For further discussion of this and other questions about everyday puzzles, visit the New Scientist website https://www.last-word.com/)
What systems interact with the integumentary system?
23rd March 2025
Two major system come to mind immediately – the cardiovascular system and the nervous system. They both have important contributions to make to the skin: there is a rich network of blood vessels in the dermis (remember that the epidermis, like other epithelia, does not contain blood vessels, and depends on diffusion from deeper layers for supplies) and a rich nerve supply (sensory and motor) to skin structures. However, on reflection it will be seen that most – if not all – body systems have interactions with the skin. At first this may seem surprising, because it is not obvious how the digestive system, or the renal system, or the endocrine system might interact. Here are some examples to illustrate the connections:
vitamin D is synthesised in the skin by the action of ultra-violet light on precursor molecules. The vitamin D helps the digestive system by encouraging the uptake of calcium from our diet
the sweat glands in the skin secrete fluid onto the surface of the body to facilitate cooling, as for example during exercise. The kidneys are responsible for maintaining fluid balance in the body, so if we are sweating copiously the kidneys respond by producing correspondingly smaller volumes of more concentrated urine
the skin responds to circulating hormones in the blood. To continue the previous example, the sweat glands respond to antidiuretic hormone (ADH) in a similar way to the nephrons in the kidneys – as ADH levels rise, the volume of sweat produced will have a tendency to fall unless this effect is over-ruled by another control mechanism such as the autonomic nervous system
even the reproductive system has interactions with the skin, since sensory stimuli received by the skin can influence sexual behaviour and processes.
It is possible to work through a list of the major body systems and see that there are direct or indirect interactions between each of them and the integumentary system. This is generally the case in the body – there is considerable interdependence between body systems, and we should be aware that in subdividing the body for descriptive purposes we must be careful not to lose sight of the interconnections.
As well as interacting with the classical body systems as explained above, the integumentary system also contributes to numerous physiological processes, especially those involved in homeostasis. An example is provided by the way that the skin helps in temperature regulation by changes in the pattern of blood supply to the skin and by sweating, as mentioned above.
22nd March 2025
Integumentary system – the skin and its appendages
“The skin is much more than a simple boundary of the physical self, a simple frontier where the person ends and the outer environment begins. It is more than a mere enclosure that restrains our viscid interior from oozing out, thus guarding our integrity. It is also a custom-house for multifarious incident influences, a sensitive radar alert to the subtlest perturbations of the ambience, a clearing-house for impulses generated within the body or without, and a protective barrier, a living screen of unmatched efficiency, whose discernment fences in the good and fences out the untoward. Nor is this all: criss-crossed by a dense, intricate tuft of nerves and sensory receptors, the skin is the focal point of aesthesia, the conscious faculty that contributes to physical preservation, and, just as aptly say the ascetical foes of sensuality, to our spiritual perdition and moral ruin.”
Frank Gonzalez-Crussi, reviewing The body’s edge: our cultural obsession with skin‘, by M. Lappe, Holt 1996.
What follows is a bare outline of the integumentary system. We recommend that you refer to one or more of the excellent texts listed at the end for a more complete overview of the skin.
Components of the integumentary system
skin
hair
nails
glands
Structure of skin (diagram 1)
in terms of volume of tissue the skin is the largest organ of the body
two main layers: the outer epidermis and the inner dermis. Deep to the skin are the supporting tissues that include adipose tissue (fat) and connective tissue layers called fascia. There are differences in distribution of the subcutaneous fat in women and men.
epidermis
stratified squamous, keratinised epithelium
can be of different thicknesses and types: thick & hairless (eg: sole of foot); thin and hairy (eg: scalp)
new cells formed in basal layer
cells gradually migrate to surface
shedding (desquamation) of surface cells
pigmented cells: melanocytes
undulating interface with dermis to enhance attachment
invagination of surface to form hair follicles and glands.
dermis
connective tissue: fibroblasts, collagen
blood vessels
nerve supply: sensory and motor
Keratinization (diagram 2)
new cells formed in stratum basale
cells accumulate keratin & lipid-filled lamellar bodies (stratum spinosum)
keratohyalin & degenerating organelles – protein envelope forms (stratum granulosum)
cells die & become transparent (stratum lucidum)
dead cells containing soft keratin, surrounded by lipids, connected by desmosomes (stratum corneum)
takes 40-56 days
Hair
distribution of hair is related to age (lanugo, secondary sexual hair distribution, baldness)
has a protective role in relation to eyes, ears, and nasal cavities
protects head from ultra-violet light and cold
Nails
protective role
fingernails used in fine manipulation
Glands
sebaceous glands
sweat glands – merocrine, apocrine
mammary glands
ceruminous glands (ear)
Skin colour
melanin
carotene
blood supply
Functions
Physical barrier
the skin provides a physical barrier between the internal and external environment
Protection
the skin forms a major part of the body’s external defence mechanisms against infection and harsh chemicals
potentially harmful disease-producing micro-organisms (pathogens) are prevented from gaining entry into the body when the skin is intact
skin commensals such as Staphylococcus aureus cause no harm on the surface of the body but can cause serious problems if the skin surface is broken and the organisms enter deeper tissues. In severe burns infection is a major complication because underlying tissues will be immediately exposed to skin commensals and airborne organisms
the skin protects against fluid loss
the skin protects against ultra-violet radiation
the skin and nails protect against wear and tear
Sensation
the skin contains receptors for touch, pain, temperature, pressure, vibration and hair movement
Temperature regulation
the flow of blood through the dermis is regulated to help maintain a constant core temperature for the body. Temperature receptors inform the hypothalamus of temperature changes centrally and peripherally and the hypothalamus influences the vaso-motor centre in the brainstem. Sympathetic nerves under the control of the vasomotor centre bring about either vasoconstriction or vasodilation in peripheral blood vessels. Vasoconstriction reduces blood flow close to the surface and thus conserves heat, while vasodilation increases blood flow and allows dissipation of excess heat
heat is lost from the body by radiation, conduction, convection and evaporation of sweat:
radiation – the skin radiates heat in the form of infra-red rays and warms nearby objects
conduction – body heat is also transmitted by direct contact to objects in contact: e.g. clothing, the seat that one is sitting on or any objects being held
convection – air passing over the skin is warmed. This warm air rises and colder air is drawn in to take its place
evaporation – sweat on the skin surface evaporates and as a result the skin surface is cooled; providing the surrounding air is less than 100% humid. The skin therefore influences fluid homeostasis
adipose tissue has insulating properties in addition to being an energy store
Excretion
waste products are excreted through the sweat glands in the skin. Water and sodium are the most obvious examples but other substances can be excreted if their normal excretory pathway fails. For example, more urea is excreted by sweat glands when a person has renal failure, unless corrective measures have been instigated
Synthesis of vitamin D
the action of the ultra-violet component of sunlight on the skin converts a precursor molecule into vitamin D
vitamin D facilitates the uptake of calcium and phosphorus from the diet – a deficiency results in rickets
Body shape
The skin contributes to the shape of the body as does the skeleton, the muscular system and adipose tissue.
Recommended reading
Clancy, J., and McVicar, A.J. (1995) Physiology & anatomy: a homeostatic approach. London: Edward Arnold (The skin: regulation of body temperature, pp. 505-523).
Rutishauser, S. (1994) Physiology and anatomy: a basis for nursing and health care. Edinburgh: Churchill Livingstone (Chapter 15: Protection, defence and waste disposal, pp 275-279).
Seeley, R.R., Stephens, T.D., and Tate, P. (1995) Anatomy & physiology (3rd edition). St Louis: Mosby-Year Book, Inc (Chapter 5: Integumentary system, pp 142-162).
Can you please give an outline of the physiology side of the integumentary system?
14th April 2025
Here are some notes about the main functions of the integumentary system:
Protection
barrier function
the epidermis provides a barrier to fluid loss from the body (this protective function is impaired in patients with burns). However, the lipid matrix between epidermal cells that forms a barrier to water allows passive absorption of fat-soluble materials through skin and into body tissues
intact skin prevents the entry of micro-organisms into the body
antimicrobial peptides are produced by the epidermis – they act by piercing holes in the outer membranes of micro-organisms
human skin produces an inducible, transcriptionally-regulated antibiotic peptide (Harder et al, 2024)
this peptide (named hBD-2: human beta defensin -2) is more plentiful in people with psoriasis
hBD-2 is effective in killing Gram-negative bacteria such as E. coli and pseudomonas, and also Candida
disruption of this shield (as in cystic fibrosis) might be a reason for recurrent infections of skin and other epithelia
hBD-2 may become a useful therapeutic agent
resistance to wear and tear
there is a continuous replacement of the outer epidermal cells that wear off – new cells are produced in the deepest layer of the epidermis and gradually migrate towards the surface
Temperature regulation
the skin plays an important role in regulating body temperature. It can help to speed up the removal of heat from the body (by vasodilation and sweating) and help in heat retention (by vasoconstriction and the insulative properties of subcutaneous fat stores)
there are two main groups of glands in the skin: sebaceous glands and sweat glands. The oily secretions of sebaceous glands help to protect the skin and hair. Sweat glands excrete small amounts of waste products such as urea in addition to their temperature control function
Vitamin D production
Vitamin D can be synthesised in skin exposed to sunlight (vitamin D can also be obtained from the diet)
aging effects of sunlight
the skin provides a barrier to ultraviolet light. The melanocytes contain melanin, which absorbs UV radiation, and also distribute the pigment to neighbouring cells
skin exposed to sunlight becomes wrinkled and creased (Brash and Gilchrest, 1996)
changes seem to be due to disruption of collagen and elastin in dermis, and loss of fibroblasts which make them
in sun-shielded skin, losses are slower and abnormal proteins absent
enzymes are induced by sunlight and break down collagen and elastin
enzymes induced at exposures far below lethal dose: tenth to one hundredth
Hayflick limit: cells can divide for 50 generations or so before stopping dividing
arrest of division associated with changes in gene expression
telomeres shorten during aging of cells growing in culture – genetic “clock”
telomerase -an enzyme capable of rebuilding the telomeres – is active in germ cells and many tumours
exposure to sunlight slowly degrades the matrix proteins of the dermis, leading to wrinkles and elastosis
prevention of photoaging may be possible by inhibiting the enzyme production
treatments include retinoic acid and a glucocoticoid
retinoic acid has reversed aging in skin
aging of skin – like precancerous conditions and perhaps atherosclerosis – reflects the summation of small but recurrent assaults on the cells of the body
the tanning response is characterised by a brown colour in ultraviolet-exposed skin and histologically by an increase in epidermal melanin content (Eller, Yaar, and Gilchrest, 1994)
ultraviolet radiation directly stimulates melanogenesis in pigment cells
perhaps DNA repair is the initial signal for increased melanin synthesis
it may be possible to mimic the tanning signal without the need to expose the skin to ultraviolet light
sunlight and skin cancer
three types of skin cancer corresponding to three major types of skin cells: basal cells, squamous cells, and melanocytes (Leffell and Brash, 1996)
cancer of melanocytes – malignant melanoma – is the most lethal variety, but also the least common
if caught early, most cases of non-melanoma skin cancer are easily treated under local anaesthetic
whites in Australia have the highest rates of skin cancer of all types in the world
the damaging effects of sunlight can occur many years before tumours appear
ultraviolet light causes mutations at points on a DNA strand containing specific nucleotide bases, mainly C- to T- mutations
p53 gene is mutated in more than half of all cancers
p53 protein stops DNA-damaged cells from dividing until repairs have been carried out
elevated levels of p53 lead to apoptosis
sunburned cells undergo apoptosis
Sensation
the integumentary system is well-supplied with receptors for touch, pain, temperature, vibration and pressure
sensory information is relayed to the central nervous system via sensory nerves
Communication
social interactions are influenced by facial expressions, blushing, touching, etc.
References
Brash, D.E., and Gilchrest, B.A. (1996) Wrinkles waiting for GODOT. Nature, 379, 301- 302.
Eller, M.S., Yaar, M., and Gilchrest, B.A. (1994) DNA damage and melanogenesis. Nature, 372, 413-414.
Harder, J., Bartels, J., Christophers, E., and Schroeder, J-M (2024) A peptide antibiotic from human skin. Nature, 387, 861.
Leffell, D.J., and Brash, D.E. (1996) Sunlight and skin cancer. Scientific American, July, 38-43.
What exactly is the integumentary system?
23rd April 2025
When we describe the body we subdivide it into a number of systems for convenience. The label integumentary system’ is given to the skin and structures derived from the skin such as hair, nails, and some types of glands. The name is derived from the Latin word integumentum, which means the outer covering of something. If you would like to know more about this system, have a look at some of the other questions and answers about the integumentary system on Kings Road Medical.
How does skin function as a defence against disease?
20th April 2025
The skin provides an effective physical barrier between the external and internal environments. Whenever the skin surface is broken or compromised, pathogenic organisms can gain entry, multiply and spread. The skin consist of two main layers, an outer layer called the epidermis and an inner layer called the dermis. Deep to the dermis is the subcutaneous layer which is composed of adipose tissue. Glands and hair follicles dervived from the epidermis dip into the dermis. The epidermis is composed of stratified squamous epithelium and the dead outermost cells are constantly being shed. They contain a protein called keratin which provides waterproofing and protection against bacteria, chemical agents and minor degrees of trauma. Specialised cells called melanocytes are also situated in the epidermis. The melanocytes produce melanin and production is stimulated by both the action of the sun rays on the skin and melanocyte stimulating hormone produced by the anterior pituitary gland. Melanin protects the basal layer (stratum basale) of the epidermis – the source of new epidermal cells – from the harmful effects of ultraviolet radiation. Other cells contained within the epidermis form an integral part of the immune system. Body hair also provides protection. Each hair follicle is attached to smooth muscle cells (arrector pili). Stimulation of the arrector pili muscle makes the hair stand on end. When the surface of the body is exposed to cold this has the effect of trapping air close to the skin’s surface, thus reducing heat loss in animals provided with a thick coat, although this effect is less noticeable in humans. Scalp hair also reduces body heat loss. Sebaceous glands situated in the dermis produce secretions which are bactericidal in nature. These secretions together with sweat provide an environment which is un-conducive to survival for some pathothogenic organisms. The pH of these secretions is acidic at 5.5. Organisms favouring this degree of acidity however flourish.
In summary the skin, along with the mucous membranes, forms part of the body’s external defence mechanisms. Any form of damage to the skin permits entry into the body of substances within the surrounding environment, e.g. pathogenic organisms and chemical agents. Damage to the skin may be immediate, e.g trauma, or latent, e.g. as a result of over exposure to ultraviolet radiation. Health education is therefore directed towards helping people to understand the common causes of skin disease and the promotion of an attitude aimed at prevention.
What are a few fun facts about the Integumentary System?
26th April 2025
Did you know that the skin is waterproof? It doesn’t let water in, but more importantly it doesn’t let water out.
The outer surface of the skin is made of dead cells – these rub off in time but new cells are being continuously added from the deeper layers.
House dust is mainly skin flakes!
If you laid out all your skin on a flat surface, it would have an area of about 2 square metres.
Skin weighs about 2.5 kilograms – the largest organ in the body.
What hurts if you pull it, but doesn’t hurt if you cut it? Your hair, of course!
Skin is elastic – it springs back into shape when stretched.
Some medicines (eg: oestrogen, nicotine) can pass through the skin, but others cannot (eg: insulin). Why is that? Because only fat-soluble substances can enter the skin, not water-soluble ones.
Your hair stands on end and you develop ‘goose bumps’ because there are tiny muscles attached to the hair follicles and they contract when you are frightened or cold.
What temperature from the sun will burn the skin?
20th April 2025
Sun burn is due to exposure of the skin to ultraviolet light, not to heat. The ultraviolet component of sunlight has been subdivided into three bands:
band
wavelength (nm)
effect on skin
UVC (short)
200 – 290
does not reach earth – blocked by atmosphere
UVB (middle)
290 – 320
Causes sunburn and cumulative effect of sun damage
UVA (long)
320 – 380
Can produce elastic tissue damage and actinic skin damage, contributes to formation of skin cancer
It is therefore the action of UVB and UVA that causes sunburn – sunscreens which block these rays are particularly effective. Individuals differ in their susceptibility to sun burn and this is because the skin of some people contains more melanin than others – darker-skinned people have more melanin than lighter-skinned people. In terms of sensitivity there are six categories of skin type with a range between: Type 1 – very sensitive to Type 6 – insensitive. Melanin protects both the dermis and the basal layer from the harmful effects of the sun’s rays. It is contained within cells called melanocytes and when released is taken up by cells of epidermis. Melanin is synthesised in melanocytes from tyrosine, and its production is regulated by several factors which include melanocyte stimulating hormone (MSH) from the intermediate lobe of the pituitary gland, and the amount of exposure of the skin to ultraviolet light.
References
Lewis, S.M. and Cox Collier, I. (1992) Medical surgical nursing assessment and management of clinical problems (3rd edition). St Louis: Mosby-Year Book, Inc.
I need to know how to link the skin in a life science and nursing perspective.
16th November 2025
The skin could be linked in a life science and nursing perspective by first examining the structure and function of the skin and then going on to find out how the skin, as an organ, changes during the life span. The skin is also a useful indicator of a person’s physical and psychological health, and an observant nurse can learn a lot about someone’s health status by examining their skin. From here the prevention of skin diseases could be considered by looking at health promotion measures, together with the measures that are adopted to protect employees who work for example with substances that are known to be hazardous. This would include nurses who administer cytotoxic drugs and people working with harsh chemical substances.
Nurses help to educate people about how to care for their skin, for example giving advice to a mother about the care of her newborn infant’s skin, or helping people to understand the importance of protecting their skin from the potentially harmful effects of the sun’s rays. An important part of nursing care is protection of the integrity and health of the skin, particularly when a person is unable to move voluntarily or to maintain their own body hygiene or nutritional state.
Nurses also perform procedures which are designed to reduce the risk of pathogenic organisms gaining entry into the body when the skin surface has been damaged, for example following burns or scalds or when a surgical incision has been made. Wound care is an example of a procedure which is regularly practiced by nurses working in the acute areas of care. Evaluating the effects of procedures performed on the skin, whether these are preventive or as part of a treatment regime, is undertaken by nurses. Such an evaluation might incorporate observing for signs of adverse reactions to drugs. The antibiotic penicillin can produce skin rashes in some people and long term treatment with corticosteroids produces skin atrophy, acne and transparency of the skin. Evaluation may also form part of a nursing research exercise into the effects of nursing procedures performed on the skin.
It is not uncommon for people to mention to nurses skin problems that they have tolerated for several years. Nurses are often help people meet their personal hygiene needs and it is during such times that people are inclined to reveal problems which they have been tolerating. The nurse therefore is ideally placed to observe the overall condition of a person’s skin.
What is a recent information or discovery regarding the integumentary system?
4th June 2004
The integumentary system includes the skin and all the structures associated with the skin such as hair, nails, sweat glands and oil glands (known as sebaceous glands). The functions of the integumentary system include providing a protective barrier for the body to prevent the entry of potentially harmful things, a role in temperature regulation, the provision of sensory information to the brain, metabolic functions such as the synthesis of vitamin D, and excretion of waste materials through the sweat.
Research into the integumentary system therefore covers a wide range of topics. However, here is one area of recent research that you may find interesting. It is to do with the potentially damaging effect of the sun on the skin, particularly of children.
It feels very satisfying to have the sun shining on our skin. Somehow our skin feels and looks healthier when it has a bit of a tan. It is known that in moderation the sun’s radiation can improve some skin disorders such as psoriasis, atopic eczema, acne and pruritus. However, the ultra violet component of the sun’s radiation can also be harmful. We have known for a long time that prolonged exposure to the sun can speed up the aging of the skin and increase the risk of developing skin cancer. This is because the ultra violet radiation damages cells and the DNA they contain.
There are several types of skin cancer, some of which develop slowly and can be removed successfully, and one called malignant melanoma which spreads much more rapidly and is much more dangerous. Recent research has shown that if children experience severe sunburn they are particularly likely to develop skin cancer later, and the more frequent the burning episodes the greater the risk of the most dangerous form of cancer (Pfahlberg et al, 2024; Mancini, 2004). Of course, skin type is also a factor here, because a darker skin provides more natural protection against the harmful effects of ultra violet light than a lighter skin.
Knowing that excessive exposure to the sun is a problem for children, what can be done to reduce the risk? The best approach is prevention – for example, avoid exposing the skin suddenly to intense sunlight, particularly during the middle of the day when the sun is overhead and at its most powerful. Wear protective clothing such as a hat and sunglasses, try to build up a tan very gradually to produce natural protection against the sun’s damaging effects, and apply a sunscreen to exposed skin. It is important to remember that the protective effect of sunscreens becomes less over time, and we must avoid assuming that if we put on sunscreen early in the day that it will protect for the rest of the day (van Praag et al, 2024).
During recent years there has been intensive research into the development of treatments that reduce the harmful effects of ultra violet radiation. The retinoids are particularly interesting as they enhance skin repair after ultra violet damage and probably have an anti-cancer effect (Oikarinen, Peltonen, and Kallioinen, 1991).
References
Mancini, A.J. (2004) Skin. Pediatrics, 113(4 Suppl), 1114-1119 (Apr).
Oikarinen, A., Peltonen, J., and Kallioinen, M. (1991) Ultraviolet radiation in skin ageing and carcinogenesis: the role of retinoids for treatment and prevention. Ann Med, 23(5), 497-505.
Pfahlberg, A., Schneider, D., Kolmel, K.F., and Gefeller, O. (2024) Ultraviolet exposure in childhood and in adulthood: which life period modifies the risk of melanoma more substantially? [Article in German] Soz Praventivmed, 45(3), 119-124.
Truhan, A.P. (1991) Sun protection in childhood. Clin Pediatr (Phila), 30(12), 676-681 (Dec).
van Praag, M.C., Pavel, S., Menke, H.E., and Oranje, A.P. (2024) Protection from sunlight, particularly for children. [Article in Dutch] Ned Tijdschr Geneeskd, 144(18), 830-834 (Apr 29).
24th January 2005
As this is an assignment, probably the best thing I can do is give you a few ideas to start from and think about as you prepare your answer. I shall assume that you have a reasonable understanding of homeostasis – the processes by which the qualities of the internal environment of the body are keep within the limits that best suit all the cells of the body. By qualities, I mean things like body temperature, blood pressure, fluid balance, pH balance and so on.
The skin contributes in several ways to homeostasis, for example by providing a hard-wearing, infection-resistant and flexible outer boundary to the body, by generating sensory information that is relayed to the central nervous system, by helping in vitamin D production, by limiting fluid loss, by providing protection against ultraviolet radiation, and by helping to regulate body temperature, to name just a few. However, the assignment question specifies the skin’s renewal system, so that will allow you to concentrate on how the epidermis is constantly being created by cell division in the basal layer, and how the outer layers of dead epidermal cells are continuously being sloughed off. When the outer layers go, they take with them some of the micro-organisms that live on our skin, so that provides a natural cleansing process for the skin and helps to ensure that a healthy balance of microflora is maintained. I think that would be relevant to the assignment question.
Now clearly it benefits the body to have an intact boundary provided largely by the skin, otherwise the risk of infection would be much higher and so too would be the fluid loss. So the skin’s ability to resist wear and tear and also repair itself after injury might also be relevant in your assignment. If the skin is damaged, part of the wound-healing process is the growth of epidermal cells across the gap to restore the integrity of the skin. You will be the best judge of whether to include this in your assignment – have you started to look at wound-healing and inflammation in your course yet?
I hope this helps – good luck with your assignment.
hi can u help me to answer this experiment? Materials: Rubbing alcohol (70% isopropyl alcohol or ethyl alcohol, flammable), Cotton swab, Thermometer. Rub a small amount of alcohol on the back of the hand of a student volunteer. Ask the student to describe what is felt. The comment will be how cold the liquid feels. Ask students why they think the liquid feels cold. Place a thermometer into the bottle of rubbing alcohol to show that it is at room temperature. Ask student to account for the cold feeling, considering the liquid is at the same temperature as the room. Take the thermometer out of the alcohol and watch the temperature rapidly fall. Discuss why the temperature falls. Discuss the concept of evaporative cooling and the role of perspiration in cooling the human body. The alcohol applied to the surface of the skin illustrates the cooling effects liquids have as they evaporate from our skin. Alcohol’s cooling effect is much greater than human perspiration due to its higher vapor pressure (i.e., it evaporates easier).
26th June 2005
This experiment is a good way to demonstrate the cooling effect of an evaporating liquid. When a liquid changes to a vapour, heat is absorbed from the surroundings. The advantage of using alcohol is that it evaporates more readily than water, and the cooling effect is much more obvious. However, when sweat evaporates, it too absorbs heat from the skin and cools it. Vapour pressure is a measure of the pressure exerted by a vapour that is in equilibrium with its liquid. A liquid standing in a sealed beaker is actually a dynamic system: some molecules of the liquid are evaporating to form vapour and some molecules of vapour are condensing to form liquid. At equilibrium the rates of the two processes are equal. The vapour, like any gas, exerts a pressure, and this pressure at equilibrium is called the vapour pressure. Vapour pressure depends on various factors, the most important of which is the nature of the liquid. If the molecules of liquid bind to each other very strongly, there will be less tendency for the molecules to escape as a vapour and a consequent lower vapour pressure. If there is only weak interaction between the liquid molecules, there will be a greater tendency for the molecules to evaporate and a higher vapour pressure. Alcohols have a higher vapour pressure than water or sweat, and therefore the cooling effect is more noticeable when alcohol is applied to the skin. Remember also that the skin is usually at a higher temperature than the surrounding air, and this temperature difference will speed up evaporation. Of course, as the air becomes saturated with the vapour, evaporation slows and stops, so on a humid day sweat does not evaporate so easily and trickles instead.
