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First Aid Anatomy and Physiology
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FIRST AID ANATOMY AND PHYSIOLOGY
To be an effective first aider, it’s important to have a good understanding of anatomy and
physiology and how this can be affected by certain injuries and illnesses. This eBook revises a
lot of what you may have already learnt or be about to learn in your Fitness or Massage program.
The body is made up of the following 11 organ systems (remember the acronym SLINC
MURDER):
S - skeletal
L - lymphatic
I - integumentary
N - nervous
C - cardiovascular
M - muscular
U - urinary
R - respiratory
D - digestive
E - endocrine
R - reproductive
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THE CENTRAL NERVOUS SYSTEM (CNS)
The CNS consists of 2 main axes – the central (brain and spinal cord) and the peripheral (the 12
cranial nerves and 31 pairs of spinal nerves). In simple terms, the CNS is the command centre
that controls everything that happens in the body, and is also the main storage compartment for
everything we know or have experienced. The peripheral nervous system (PNS) uses all of your
senses (touch, taste, smell, hearing, sight, proprioception, nociception etc.) to feed information to
the CNS about what you are feeling and experiencing. The CNS is the boss, and the (PNS) is
the worker.
The CNS has two main autonomic states; the sympathetic (fight and flight) and the
parasympathetic (rest and digest). These are hangovers from evolution – they are what ensured
our survival.
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Sympathetic Nervous System (SNS)
The SNS is our fight and flight system. This can also be described as our
stress response. Imagine, you have just woken up and you need to go to the
loo. With bleary eyes you get out of bed and waddle to the bathroom. As you
enter the hallway you see a lion standing there with a hungry look in his eye.
He roars at you!! What happens? This is what people generally call an
“adrenaline rush”; you feel your heart start pounding in your chest, your
respiratory rate speeds up, your muscles tense ready to run and your pupils
dilate to let lots of light in. You could hear a pin drop and you can smell the
lion’s coarse mane. All of your senses become finely tuned to the situation
and your brain starts processing really quickly to get you out of there.
This is a much exaggerated example of SNS activation. When your brain recognises that you
need a boost, the CNS sends impulses to glands and smooth muscles and tells the adrenal
medulla to release hormones such as adrenaline and noradrenaline. This causes effects such as
an increase peripheral vascular resistance (so more blood gets back to the heart for increased
cardiac output), and increase in RR to increase oxygen supply to heart and lungs and an
increase in HR to pump the blood back out to the working muscles.
In a regular setting (let’s say a footy game) this SNS activation is a great thing. But in a first aid
emergency (let’s say, someone has had their leg chopped off!!) it can be really bad as it can
make the condition worsen (leg chopped off, means a lot of bleeding, SNS activation makes HR
go up, so without direct pressure the casualty may bleed even more).
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Parasympathetic Nervous System (PaNS)
The PaNS is the opposite of the SNS, it is responsible for resting,
relaxation and digestion. Imagine you have had a long day in the
gym; you are wired and over excited from all the great lifts you have
been helping your clients do and buzzing about their great results.
You need to go to bed because you have an early start tomorrow.
You go through your usual night time ritual, brush your teeth, put
your favourite PJs on, get a glass of water and climb under the
covers. You read a book for a few minutes, but gradually feel your
eyes blinking more, your breathing has slowed down, your body
feels heavy and you drift off to sleep. This is the PaNS at work. As
you rest, your PaNS works (through the release of hormones such
as dopamine) to slow down your body processes, HR , RR, BP lowers and your level of
awareness falls.
The PaNS also comes into play when you have eaten a meal. Chewing stimulates the vagus
nerve (the main PaNS cranial nerve), which kick-starts all of the digestive processes – peristalsis
in the stomach, bile release into the duodenum, motility through the small intestine. You can also
stimulate the vagus nerve manually; performing the valsalva manoeuvre (holding your breath and
bearing down, like bodybuilders do when performing a really heavy bench press) will kick the
PaNS into gear.
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Nervous System in the Primary and Secondary Survey
As a first aider, understanding the PaNS and SNS is vital to providing a good level of care. We
want to keep our casualty as relaxed and calm as possible, but we need them to stay awake and
alert so they can communicate with us. Reassuring a casualty that help is on the way, they are
safe, and good people are helping them goes a long way to managing an emergency. The most
important thing a first aider can do, in the absence of all other options is to reassure the casualty,
make them as comfortable and safe as possible. This avoids any unfavourable SNS/PaNS
activation that may make a condition worsen.
1
Nervous system primary survey
R - response: we are looking at a casualty’s level of consciousness. Use AVPU or COWS to help
you:
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Nervous system secondary survey
Pupils – are they equal and reactive to light?
Dizzy/lightheaded
Headache
Limb strength (unilateral or bilateral weakness)
Numbness or tingling anywhere
Speech disturbances – slurred
Facial or limb paralysis
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THE CARDIOVASCULAR SYSTEM (CVS)
The CVS consists of the heart, blood vessels and the blood.
Its primary role is the delivery of oxygen to and removal of
carbon dioxide from the tissues in the body. The blood
begins its journey in the left ventricle of the heart, where it is
expelled into the aorta. From the aorta it travels through the
lesser arteries, arterioles into the capillaries where
perfusion occurs into and out of the tissues. This is all an
active process – the force of the heart’s contraction drives
the flow of blood through this system. As the blood leaves
the capillary beds it returns to the heart via the venous
network. By now the force of the heart’s contraction has
gone and the veins rely on their system of valves and
movement of the body to work the blood back up toward the
right atria of the heart. Blood moves into the right ventricle and leaves the heart on its journey
through the lungs, where carbon dioxide is exchanged for oxygen. Re-oxygenated blood then
heads back to the left side of the heart to enter the left atria and flow into the left ventricle to start
the loop all over again!
So, what’s in the blood? Firstly we have red blood cells –
they are what give blood its colour. The red blood cells (RBC)
carry around 250 million haemoglobin molecules, who each
bind to 4 oxygen molecules. This means that each RBC is
capable of carrying 1 billion oxygen molecules to the tissues!
The RBC’s also have an affinity for carbon dioxide, and will
carry these molecules to the lungs for expiration. There are
also white blood cells (WBC) who are involved with immune
responses. Then there are platelets – these are like mini
band-aids that can clot together to create patches where an
injury has been sustained. All of these cells float in plasma,
which is a fluid with a low viscosity made mostly of water.
The heart is a remarkable organ. It sits in the middle of the chest (mediastinum), with 1/3 on the
right of the sternum, and the remaining 2/3 on the left of the sternum. The heart cells (myocytes)
have the ability to create their own electric signals which follow a set pathway, causing
contraction of the healthy heart (heart beats!). In an unhealthy heart this flow of electricity
becomes disrupted or disorganised. Often this is a result of a heart attack (myocardial infarction).
The heart has its own network of coronary arteries to feed the heart tissue, this can be altered in a
person who has a poor diet, sedentary lifestyle, diabetes, high blood pressure or a family history
of heart disease. Fatty deposits sit in the coronary arteries reducing the diameter of the vessel
and decreasing the amount of blood that can get through. This can lead to the myocytes being
starved of oxygen and eventually dying.
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Cardiovascular System in the Primary and Secondary Survey
1
CVS primary survey
C - compressions – good quality compressions in the middle of the chest pump the blood from
the left ventricle out to the body when the heart is no longer able to contract in a coordinated
fashion.
2
CVS secondary survey
HR – how many beats per minute?
BP – what is the pressure in the casualty’s vessels when the heart is contracted (diastole)
and at rest (systole)
Capillary refill – an indication of the casualty’s perfusion (<2 seconds is good)
Skin – Colour, temperature, clammy or dry?
Do they have any chest pain?
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RESPIRATORY SYSTEM (RS)
The RS is how we get the oxygen in and the carbon dioxide
out. Air we breathe in through our nose and mouth travels
through the pharynx into the trachea before diverting into the
left and right bronchi, into the bronchioles and terminating in
the air sacs (alveoli). It is in the alveoli where carbon dioxide
diffuses out of the capillaries and oxygen diffuses into them.
The respiratory system looks like an upside down tree. An
asymptomatic person at rest will breath regularly at around
12-16 times a minute.
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RS in the Primary and Secondary Survey
1
RS primary survey
A - airway; you need to check the casualty’s airway to ensure nothing is blocking the passage of
air causing their altered state of consciousness.
B - breathing; is the casualty breathing normally? Is there any gurgling, snoring, gasping,
wheezing or abnormal breath sounds? Also, you may need to give the casualty rescue breaths
while performing CPR to ensure the blood you are mechanically pumping around has enough
oxygen to perfuse the tissues (remember? well done!)
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RS secondary survey
Respiratory rate – how many times a minute they inhale/exhale
Quality of breaths – deep or short and shallow
Any shortness of breath?
Pain on inhalation of exhalation
Wheeze
Stridor – may be a sign of choking!
Are breath sounds absent?? If so, stay calm and do CPR!
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MUSCULOSKELETAL SYSTEM (MSS)
As the skeletal and muscular systems work together they are often referred to as one, under the
term musculoskeletal system. Collectively, this system involves the bones, ligaments, tendons
and muscles that support the body, protect the internal organs, and enable movement.
Most muscles used for movement work by contracting and relaxing in conjunction with a bone.
The action of raising your leg involves contraction of several muscles, creating an opposing force
in the leg, causing it to move upwards.
Some muscles do not need bones to work with, but function attached to large masses of tissue,
such as the diaphragm that makes the lungs expand and contract.
Injuries to the MSS are often referred to as soft tissue injuries. This includes sprains, strains and
dislocations. More serious (and more painful) injuries to bones are called fractures – this is when
the periosteum of the bone has been disrupted. Types of fractures include simple, compound,
comminuted, avulsion and spiral (we will discuss this more in eBook 6).
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MSS secondary survey
Pain – on rest, movement or palpation
Strength and range of movement
Deformity
Swelling
Bruising
Bleeding
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DIGESTIVE SYSTEM
This system includes the oesophagus, stomach and
intestines, as well as the accessory organs that assist with
the mechanical and chemical digestion of food, and the
metabolism of nutrients.
Fluids and solids are passed through the oesophagus into
the stomach where they are processed for further digestion.
They are then absorbed into the body through the
membranes of the intestines.
Some organs, such as the liver and pancreas, are
considered accessories to the digestive system as they help
process food into various chemical substances used by the
body.
If a casualty suffers from vomiting or diarrhoea this involves the digestive system. Also if a
casualty ingests a poison, this is an assault to the digestive system.
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Digestive system secondary survey
Pain – location
Nausea
Vomiting
Diarrhoea/constipation
Bloody stools
Firm abdomen on palpation
Guarding
Distension
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INTEGUMENTARY SYSTEM
This is the system that includes skin, hair, fingernails and
toenails. The skin is the body’s largest organ playing an
important role in protection from infections. The skin’s other
functions include acting as a shield against injury and
keeping body fluids in. The skin is made from tough, elastic
fibres that have the ability to stretch without tearing easily.
2
Integumentary system secondary survey
Lacerations
Haematomas
Abrasion
Bruising
Swelling
Redness/heat
Burns
Bleeding
Infection
Rash
Urticaria – itchiness
Bites/stings
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LYMPHATIC SYSTEM
The lymphatic system is a slow, one way moving system
where toxins such as venom tend to accumulate after a bite
or sting has occurred.
This system provides lymphatic fluid that drains from the
body’s tissues, which is important as a ‘flushing’
mechanism. Most toxins and infections that are absorbed or
injected into the tissues are collected by the lymphatic
system and ‘strained’ through lymph nodes in the armpits,
neck and groin. The lymphatic fluid eventually drains into the
blood stream. This is why we get swollen glands when we
are sick, it is our lymph system trying to fight the infection!!
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