The average first aid training syllabus contains very little teaching of anatomy and physiology, mainly because knowledge of the subject above an extremely elementary level is not necessary for the successful rendering of first aid.

However, those who have already mastered the basics of first aid, and who wish to improve their skills and knowledge, will almost certainly find a need to increase their knowledge and understanding of anatomy and physiology.

This book is not aimed at medical professionals, for whom a deeper level of knowledge of anatomy and physiology is almost certainly required, but at volunteer first aiders, and those of similar training levels, particularly those involved in the more advanced levels of first aid practice and training.

As this book is aimed at the first aider, certain parts of the body (eg. the heart and circulation) are described in more detail than other parts (eg. the endocrine system) as they are more likely to be affected by medical conditions and injuries which a first aider may encounter, and are thus likely to be of more direct use and interest to the reader.

Although great care has been taken to aim the text at those who have not received formal medical training, it is impossible to describe and explain all topics without reference to scientific terms and concepts. It has therefore been assumed that the reader will have some knowledge of science, particularly of basic chemistry.

The list below has been compiled to assist the reader.
 

There are four main cavities within the body:

Cranial cavity. This is surrounded by the cranium, and contains the brain.

Thoracic cavity. This is the section of the torso above the diaphragm. It contains the lungs, heart, and major vessels.
The area between the lungs is known as the mediastinum.

Abdominal cavity. This is the section of the torso below the diaphragm, but above the superior edge of the pelvis. It contains the digestive system, and associated organs.

Pelvic cavity. This is the section of the torso which is surrounded by the pelvis. It is continuous with the abdominal cavity above. It contains the internal reproductive organs, the urinary bladder, and the rectum.
 

It is, however, well accepted that certain organs have less critical functions than others, and that survival is possible with these organs either malfunctioning, damaged, or removed.

There are twelve main systems within the body:
 

All cells have a similar structure, with the exception of red blood cells and platelets, which do not have nuclei.

Some cells, particularly certain types of white blood cells have the ability to surround and ingest foreign matter and dead cells, in a process termed phagocytosis.

Stem cells are unlike many other cell types in that they retain the ability to divide throughout their life and create cells of different and specialised types, taking the place of cells that die or are lost.

Stem cells are a fundamental part of the body’s ability to repair and renew its tissues.

Stem cells in bone marrow are particularly important as they provide the basis for blood cells.

Glands which secrete onto the surface of an organ - either directly or via a duct - are known as exocrine glands; glands which secrete into the blood are known as endocrine glands.

There are six main varieties of connective tissue:
 

Fibrocartilage, which is tough and slightly flexible, and found in intervertebral discs, other joints, and in ligaments.

Hyaline cartilage, which is smooth and solid, and found in the air passages, and at joints.

Elastic cartilage, which has elastic fibres, and is found in blood vessels.

Blood. This carries the body’s nutrients, and waste products; it is considered as a connective tissue.

Connective tissue is host to a series of specialist cell types:

Fibroblasts. These produce collagen and elastic fibres. They also assist in the repair of wounded tissue by binding severed surfaces together through the creation of fibres.

Macrophages. These form part of the body’s defence mechanisms by ingesting invading matter.

Mast cells. These produce the local hormones histamine and serotonin as part of the body’s immune response.

Plasma cells. These produce specific antibodies to combat invading organisms.

Nerve Tissue

Nerve tissue is formed from complex cells called neurones, which have the property of being able to transmit nerve impulses - electro-chemical messages - in response to stimulation.

Muscle Tissue

This has the ability to contract when given a nervous stimulus.

There are three varieties of muscle tissue:

Striated muscle. This forms muscles under voluntary control.

Smooth muscle. This forms muscles under autonomic control.

Cardiac muscle. This forms the muscle of the heart.

Bone Tissue

This provides the rigid structure of the skeleton.

There are two varieties of bone tissue:

Compact bone. This forms the hard outer shell of bones.

Cancellous bone. This forms the inner structure of bones.

There are three types of membrane:
 

Serous fluid is secreted between the two layers of membrane as a protective lubricant.

Synovial membrane. This lines the cavities of moveable joints. It is composed from connective and adipose tissues.

Synovial membranes secrete synovial fluid, a clear, viscous, oily fluid which acts as a lubricant for joints.

Synovial membranes have very smooth inner surfaces, which together with synovial fluid, provide a capability for movement which is almost frictionless.

In a benign tumour, cell structure is close to normal even though growth is abnormal.

The cells tend to remain inside a capsule of connective tissue and do not spread outside their original site.
 

A malignant tumour is characterised by rapid growth of abnormal cells.

These cells will eventually break out of their protective capsule causing structural changes in surrounding tissue.
 

Once the tumour has broken free from its original capsule, it will almost certainly spread to other parts of the body.

Malignant tumours may be classified according to the tissue type in which they originate:

Sarcoma. This may form in connective tissue or muscle, anywhere in the body.

Carcinoma. This forms in epithelial tissue, most commonly in the lungs, digestive tract, uterus, breasts, or on the skin.

Other forms of cancer include those which form in tissues of mixed cell type, in the cells of the nervous system, and leukaemias, which result in abnormal blood cells.

The cancer cells thus spread, or metastasize, throughout the body.

The bodies defence systems will attempt to destroy the cancer cells, and may succeed, but if not the cancer cells may then attach themselves to other tissues and organs, forming secondary tumours. Each secondary tumour then becomes a source of further cancerous cells.

There are several types of carcinogens, including X-rays and other electromagnetic radiation, substances such as benzenes, and some viruses.

The severity of a shock depends mainly on the magnitude of the current which flows. This is determined by the voltage applied divided by the impedance of the body, as defined by Ohm’s law.

The internal body impedance varies greatly, depending on the types of tissue involved. Muscles and blood vessels are good conductors, whereas bone and fat tissue are not.

The wrists and ankles consist of multiple bones with little other tissue and therefore have relatively high impedances.

The impedance of the skin also varies greatly and is inversely proportional to the contact area. Dry skin has a high DC resistance - over 10MW per square millimetre. However it has considerable capacitance and thus conducts AC with a decreasing impedance as the frequency increases.

The skin’s impedance falls dramatically if it is wetted, especially with a conductive solution. Breaking or abrading the skin further lowers its impedance.

Finally the skin’s impedance falls with increasing voltage, reaching almost zero at around 200V, when the skin’s structure begins to break down.

The consequences of the shock will be determined by the shock’s severity, its duration, and the path taken through the body by the current.

A shock which passes through the torso is likely to cause more harm than one which is restricted to a limb or a small area of the body’s surface.

Sensation

Electric current stimulates sensory nerves. The effects of AC increase as the current increases.

Only the making or breaking of a DC current causes actual pain. An increasing sensation of warmth is felt for any steady current above 2mA.

Muscular action

Electric current stimulates motor nerves and muscle tissue, including the muscles of respiration and the heart, as well as skeletal muscles. This gives the risk of respiratory and cardiac disturbances, or even arrest, at all but the lowest current levels.

The effects of AC increase as the current increases.

DC causes significant muscular contraction only when the current is made or broken.

The violent muscular action caused by an electric shock can damage the muscles themselves, tendons, ligaments, or even bones. Also, sudden muscular action may cause accidents and further trauma.

Currents above 10mA AC and 300mA DC tend to inhibit normal muscular action and prevent ‘let go’ of an electrical contact held in the hand.

Cardiac arrhythmias

An electric current flowing through the heart may disturb or overwhelm the heart’s normal electrical impulses.

With shock durations below 100ms, the probability of disruption is increased if the shock occurs during ventricular repolarisation (the T-wave of the ECG) - known as the vulnerable period of the cardiac cycle.

The effects of shocks from steady DC of less than 500mA are considerably less than those of an equivalent AC.

Currents of several Amps (AC or DC) for longer than 1 cardiac cycle tend to cause total contraction of the myocardium, and cardiac arrest. If significant tissue damage has not occurred, normal cardiac function may return following removal of the current. This phenomenon is known as defibrillation.

Cell damage

Tissue cell plasma membranes are electrical insulators (except to high frequency AC). Low levels of current - DC or low frequency AC - pass around the cells without harming them.

At currents above 100mA, the electric field developed around a cell draws water into the cell. This causes the cell’s pores to expand. Continued drawing in of water will rupture the plasma membrane, damaging or destroying the cell. This effect is known as electroporation.

Electroporation is reversible for currents up to 200mA applied for less than 5s; above these levels, it may cause permanent damage.

Burning

Heat is produced when electric current flows through tissue.

Heating tissue to over 45° C for any length of time is likely to cause damage.

200mA passing for 5s can heat body tissue to 45° C. 500mA passing for 5s can heat body tissue to 70° C, causing severe damage.

Electrical burns are mainly caused by heat, but electroporation contributes to the damage at higher current levels. The majority of damage tends to occur in deep tissues, thus the full extent of an electrical burn may not become apparent until some time after the injury.

High voltage, high energy sources are capable of passing currents of many Amps through the body. The high voltage forces the current through all types of tissue, generating intense heat, evaporating water from the tissues, and resulting in almost total destruction of tissue along the current path.

Contact burns

The points of contact with an electrical source are common sites for skin tissue damage.

Effects vary from reddening at current densities of 10 - 20 mA/mm², through discoloration and blistering at 20 - 50 mA/mm², to actual tissue destruction at current densities above 50mA/mm².

Flash burns

An electric arc occurs whenever electric current jumps through air. This produces heat; the heat from a large arc will be sufficient to cause instantaneous burning of any nearby body tissue.

The intense light levels produced by large arcs may cause damage to the corneas or retinas of the eyes. Such injuries are known as arc eye.

Specific conditions are discussed with those systems which they most affect.

Infectious diseases are spread by micro-organisms (usually bacteria or viruses), produced in the body of a sufferer, which when entering the body of another, multiply such that the disease develops.

Modes of infection include:

Droplet. The infecting organism is passed in droplets of fluid, such as saliva or mucus.

Blood borne. The infecting organism is passed by blood transfusion, by direct blood contact, or on contaminated objects.

Contagion. The infecting organism is passed through direct body to body contact.

Dust borne. The infecting organism is carried in dust, or other solid matter.

Sexually transmitted. The infecting organism is passed by sexual contact.

Carrier borne. Another person, food or water, or an animal or insect, carries the infecting organism without actually becoming infected.

Infectious agents

Viruses

A virus is a micro-organism, about 100nm in size, consisting of a strand of DNA inside a protein membrane.

Viruses can only live and reproduce inside other living cells.

Bacteria

The term bacteria is often used to describe moulds, yeasts, and Rickettsiae, which are disease causing micro-organisms sized between viruses and bacteria, as well as true bacteria.

A true bacterium is a minute organism, usually single celled, and generally no more than 1µm across.

Bacteria may be grouped according to their shapes:

cocci are round, streptococci are cocci arranged in chains, bacilli are long slender rods, spirilla are curved or wavy.

Bacteria reproduce by expanding and then splitting in two. Under favourable growth conditions, this splitting may take only about 30 minutes.

Some bacteria produce spores which subsequently produce bacteria on being brought or carried into suitable growth conditions.

It must be noted that many bacteria are benevolent, and are essential for continuing life.

The effects of poisoning depend very much on the amount poison absorbed, relative to the body weight. In small, controlled doses, some normally poisonous substances (atropine, for example) have potentially beneficial effects. Likewise, many substances (such as aspirin) which are classed as harmless or beneficial in normal use may have poisonous effects if taken in abnormally high quantities.

The action of many poisons on the body is complex, often affecting more than one organ or system, and may have consequences beyond the initial reactions. Damage may well result to organs such as the liver or kidneys through the toxic chemical action of the poison.

Poisons enter the body by four main routes:
by being swallowed,
by being inhaled,
by being absorbed through the skin,
by being injected.

Classifications of poisons

Poisons may be classified into four main groups:

Corrosives. These poisons react in a chemical manner with body tissue, such that they burn and destroy that with which they come into contact.

Examples include strong or concentrated acids, strong or concentrated alkalis, and other highly reactive substances.

Corrosive poisons tend to cause immediate pain and swelling at the points of contact, leading to burning and tissue destruction.

Irritants. These poisons aggravate the digestive system, particularly the stomach and bowels.

There are many examples, including many vegetable acids and salts, substances such as Arsenic, Lead, Copper Sulphate, Silver Nitrate, and parts or extracts from many plants.

Irritant poisoning usually results in vomiting, diarrhoea, with abdominal discomfort or pain, leading to hypovolaemic shock.

Narcotics. These poisons affect the central or peripheral nervous system, usually causing a reduction in sensation, bodily control, and the level of consciousness.

Examples include substances such as opiates, Potassium Cyanide, alcohols, and Carbon Monoxide (this also affects the ability of red blood cells to carry Oxygen).

Narcotic poisoning does not generally produce pain, but leads to dizziness, a loss of co-ordination, vision disturbances, and a falling level of consciousness.

Narcotico-irritants. These poisons initially have an irritant action upon the digestive system, and then act as narcotics.

Examples include phenol, strychnine, atropine, many plant parts or extracts and various fungi.

Narcotico-irritant poisoning initially causes vomiting, diarrhoea, and abdominal pain. It then leads on to delirium, maybe with convulsions, and eventual unconsciousness.