redness over the area swelling heat pain loss of functionThe skin, in terms of surface area covered, is the
largest organ of the body.
It is the organ we see first (and indeed one of the few organs
we can actually see when looking at a naked human body) and is of great importance in the
defence of the body and thus in the delivery of nursing care. Further, since it reflects
physiological and pathological changes in other areas of the body, skin changes can be
used to aid both nursing and medical diagnosis.
On each square centimetre of skin there may be up to 3
million micro-organisms, most of which are commensals.
A harmless association
exists between humans and their commensals (literally,'table companions', from the
Latin), to the sole benefit of the latter.
The bacteria commonly present as commensals on
the skin include Corynebacterium, and Staphylococcus epidermis.
The skin does not provide a very hospitable environment for bacteria unless they have become adapted through evolution to live there.
Commensals have, in general, become adapted to live off human skin scales and the slightly
acid secretions produced by the skin.
The micro-organisms tend to live in the deeper
layers of the stratum corneum near to their food source. Hence, they are not normally shed
with desquamation (loss of bits of outer skin by peeling or shedding or coming off in scales).
The application of strong deodorants, and the use of strong soaps that
alter the skin pH from acid to alkaline upset the fine balance that exists between our
parasites and us.
These tend to kill or inhibit the normal flora, leaving the area open to
potential colonisation by pathogens (a pathogen is any disease-producing agent (especially a virus or bacterium
or other microorganism).
Normally we live in harmony with our commensal bacteria
so long as the skin barrier remains intact. However if these bacteria are given the
opportunity to invade the dermis or body cavities, such as the bladder, then serious
infections can occur.
Babies are born without this resident bacterial flora.
During a normal delivery the baby will start to pick up these commensals during it's
passage along the vagina.
Because a healthy resident population of commensals makes
it much harder for pathogenic bacteria to survive a neonate is at much greater risk of
skin infection unless the skin is properly cared for.
As already mentioned bacteria need to invade the body in some way for infection to occur. Thus for each portal of entry to the body there is some form of innate defence mechanism.
The mouth, or buccal cavity, is lined with a reasonably tough mucous membrane that is constantly irrigated by a back flow of saliva. This flow is directed towards the throat and has the dual purpose of preventing micro-organisms from infecting the salivary glands and also trapping the organisms so that they can be swallowed.
Saliva contains an enzyme called lysozyme, which is antibacterial. It also contains mucous which contains the immunoglobulin IgA.IgA also helps fight bacteria as it is an antibody.
Thus patients who have become dehydrated and hence have a reduced flow of saliva are at a higher risk of mouth infections.
The resident bacteria of the mouth are generally harmless. Indeed some such as alpha haemolytic Streptococcus are of a positive benefit as they produce hydrogen peroxide (a bleaching agent) which helps to keep the mouth clean.
Patients who are on a prolonged course of oral antibiotics run the risk of having their normal flora wiped out. This can result in the opportunistic infection of the mouth by other micro-organisms. A common organism that can become problematic is the unicellular fungus Candida albicans that causes thrush.
The tonsils also assist in the protection of the buccal cavity. They are formed of lymphatic tissue and will be studied in further detail later in the course. The outer covering of the tonsils is extremely thin and is easily traumatised and as such the tonsils themselves become prone to infection especially during childhood.
The hydrochloric acid present in the gastric juices produced by the stomach lining is of a sufficiently low pH value to kill most organisms entering the body with food, drink or by being swallowed with the sputum.
Some organisms however can resist this strong acid. Examples include the tubercule bacillus, enteroviruses, salmonella and the eggs of parasitic worms.
Both milk and proteins are effective buffers against the stomach acid and organisms which enter the stomach accompanied by these foodstuffs stand more chance of escaping the damaging effects of hydrochloric acid.
Thus contaminated meat and dairy products tend to be more dangerous in terms of acquiring an infection.
Vomiting can also be regarded as a defence mechanism by ridding the body of irritants and toxins such as alcohol, drugs and bacterial toxins in some instances although this protection is by no means fully effective.
The small and large intestines rely to a great extent upon the stomach's bactericidal action.
In addition the normal flora of the area such as Escherichia coli, non-haemolytic Streptococci, and anaerobic Bacteroides contribute to the normal functioning of the gut.
The importance of their role becomes more evident when the administration of broad-spectrum antibiotics or indiscriminate use of laxatives removes them.
This can lead the intestines open to colonisation by pathogenic bacteria such as Staphylococcus pyogenes that can be resistant to antibiotics.
Such infections may have a lethal effect upon the debilitated patient.
In addition the small and large intestines are liberally supplied with lymphatic tissue throughout their length. These are involved in the bodies non-specific and acquired immune defence systems that will be the subject of further study later in the course.
Diarrhoea, like vomiting, may also be regarded as a defence mechanism although in most instances it occurs far too late in the course of an infection to be of much benefit.
Insects and large particles are prevented from entering the tract by the presence of hairs, or vibrissae, in the nose. The ciliated nasal mucosa secretes a backward-flowing stream of mucus that traps smaller particles and has both bactericidal (kills bacteria or slows down bacterial growth) and virucidal (kills viruses or prevents spread of viruses) properties. Lysozyme is also present in nasal secretions.
The epithelium of the upper respiratory tract is thin and is unfortunately prone to infections by rhinoviruses and adenoviruses which are not affected by the nasal secretions. Sneezing is a protective reflex that expels irritants.
The trachea and bronchi are lined with a ciliated mucous membrane that serves to trap any organisms in debris that may have escaped through the upper tract. Here the cilia beat upwards, and hence shift a stream of mucus away from the lungs and towards the pharynx to be swallowed. Should any organisms reach the alveoli, alveolar macrophages phagocytose them. The hilum of the lung is well supplied with lymph nodes that act as a further filter.
Coughing is a defensive reflex that removes particulate matter (such as dust that may have been inhaled) or excess mucous in the lower tract.
The constant downward flow of urine through the ureter and bladder tends to militate against ascending infections. Micturition itself irrigates the urethra. This is an effective response in the long male urethra, but less so in the female. The adult female urethra is only 2 or 3 cm long and hence forms a relatively short and readily available portal of entry for organisms to invade the bladder.
Sexual activity in the female may predispose to the occurrence of cystitis (inflammation of the urethra). The most common offending organism being coliform bacillus from the perineal area. Faulty aseptic technique during catheterisation can therefore result in urinary tract infections, which is one of the most common hospital acquired infections.
The resident flora of the vagina (most notably Lactobacillus) helps to maintain an acid environment thus forming an inhospitable habitat for invading pathogens. Some vaginal deodorants disturb the pH balance of the vaginal area and can result in infection. Here again the opportunistic Candida albicans can cause thrush.
In post menopausal females the production of acid in the vagina decreases and this can result in a condition known as senile vaginitis. This can be effectively treated with hormone replacement therapy (HRT).
If the diet is lacking in Vitamin A the production of lysozyme in the tears decreases and can result in a predisposition to eye infection.
Blinking is a defence reflex that both eliminates irritants and ensures even distribution of the tears.
In some conditions such as facial paralysis or stroke this reflex is lost and it becomes necessary to prevent the eye from drying up by keeping it closed or covered and by regular irrigation.
This is seen as a local non-specific defensive response to tissue damage. Its function is to eliminate the cause of the damage, remove the consequent dead cells and restore the constancy of the internal environment and as such is closely associated with wound healing which again will be covered in further detail later in the course.
Inflammation occurs immediately after a physical, chemical or microbiological injury. As such it may be due to a splinter, acid burn, heat burn or local bacterial infection of a hair follicle or pore of the skin.
The last mentioned which results in a boil is often quoted as a classic example of inflammation exhibiting the five characteristics of the process namely:
redness over the area
swelling
heat
pain
loss of function
The blood clotting process begins immediately on damage to a blood vessel. If the damage is due to laceration of the skin an effective barrier against invasion of the wound known as a scab will occur within a relatively short period of time.
Again this will be the subject of further study later in the course.
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