Introduction
The branches of science that will help you understand the
body parts and and functions are anatomy and physiology. Anatomy
deals with the study of the human body (the component parts,
structure and position) and physiology the study how the body
functions.
Systems
An understanding of the function and the benefits of exercise
on the various body systems will be beneficial in an athlete's
development. The following systems are reviewed here:
- Skeletal
- Muscular
- Neurological
- Endocrine
- Cardiovascular
- Respiratory
- Digestive
Skeletal System
The skeletal system provides four basic functions:
- Support for tissues and muscle
- Protection for vital organs
- Movement through bones and attached muscles
- Storage for minerals and immature blood cells
Support
Bones and cartilage which make up the skeleton are the only
rigid materials in the body. The 206 bones of the skeleton
provide a framework and points of attachment for many of the
soft tissues of the body. The five main classifications of
bones are : Long (e.g. femur), Short (e.g. tarsal
bones of the foot), Flat (e.g. frontal bone of the
skull), Irregular (e.g. vertebrae) and Sesamoid
(e.g. knee cap)
Protection
These structures protect some of the vital tissues and functional
organs of the body. Typical examples are:
- Skull - protects the brain
- Vertebrae - protects the spinal cord
- Thoracic cage - protects the heart and lungs
Movement
Bones act as levers during movement and provide solid structures
to which muscles are attached. The joints allow movement between
bones and these movements are directly related to the type
of joint and range of motion. Joints fall into one of three
categories: Fixed fibrous or Synarthroses (e.g. bones
of the skull), Slightly moveable or Amphiarthroses
(e.g. symphysis pubis) and Freely movable or Diarthroses.
Freely Movable joints comprises of four main groups: Ball
and Socket (e.g. hip), Hinge (e.g. elbow), Pivot
(e.g. radius and ulna) and Gliding (e.g. carpal joint
of the wrist)
Storage
In some bones there is red marrow which produces red blood
cells, some white cells and platelets. Minerals, especially
calcium and phosphorous are also stored in bones and can be
distributed to other parts of the body.
Effect of exercise on the skeletal system
The condition of bone may be improved by exercise as it responds
to mechanical stresses. These mechanical stresses usually
take the form of skeletal muscle pulling at their points of
attachment being their origins and insertions. Where these
mechanical stresses are applied most it has been shown that
more mineral salts are deposited and more collagenous fibres
are produced. Therefore both the density and size of bone
in these areas may be increased and these changes in bone
structure are stimulated by increased loads being placed on
the skeleton. This has been borne out by greater bone mass
being observed in weight lifters than in other lighter endurance
athletes such as joggers. Other examples include racquet players
who have been shown to have greater bone density in their
playing arms. It has even been shown that if a leg is immobilised
by being placed in plaster, due to a fracture, that even after
a few weeks the bone becomes decalcified from lack of mechanical
stress.
Whilst it may therefore be considered beneficial to utilise
exercise to maintain healthy bones, great care must be taken
with children whose bones and muscles are still developing.
They should not be subjected to forms of sport involving high
degrees of mechanical stress, partly because of the weaknesses
which still exist within the bones, and also because of adverse
effects on the development of these bones before maturity.
Muscular System
Muscle tissue has four main properties: Excitability
(ability to respond to stimuli), Contractibility (ability
to contract), Extensibility (ability of a muscle to
be stretched without tearing) and Elasticity (ability
to return to its normal shape).
Through contraction the muscular system performs three important
functions:
- Motion - walking, running etc.
- Heat production - maintain normal body temperature
- Maintenance of posture - standing, sitting etc.
Motion
To understand how the muscles combine with the skeleton in
providing motion we must look at the basic mechanics of movement.
The main framework of the body is covered by muscle, whose
function is to permit movement. We know that to move or lift
a load against another force, it is easier to use levers,
and it is this principle which the musculoskeletal system
adopts and which we must examine.
The component parts which are used in a lever are as follows:
- Lever - nearly always the bone
- Fulcrum - pivot point of the lever, which is usually
the joint
- Muscle Force - force that draws the opposite ends
of the muscles together
- Resistive Force - force generated by a factor external
to the body (e.g. gravity, friction etc.) that acts against
muscle force
- Torque - the degree to which a force tends to rotate
an object about a specified fulcrum
There are different types of levers dependent upon the position
of fulcrum, effort and resistive force.
First Class lever: Muscle force and resistive force
are on different sides of the fulcrum e.g. the head resting
on the vertebral column. As the head is raised, the facial
portion of the skull is the resistance, the fulcrum is between
the atlas and occipital bone, and the effort is the contraction
of the muscles of the back.
Second Class lever: Muscle force and resistive force
act on the same side of the fulcrum, with the muscle force
acting through the level longer than that through which the
resistive force acts - e.g. raising the body up onto the toes.
The body is the resistance, the ball of the foot is the fulcrum,
and the effort is the contraction of the calf muscle.
Third Class lever: Muscle force and resistive force
act on the same side of the fulcrum, with the muscle force
acting through the lever shorter than that through which the
resistive force acts - e.g. adduction of the thigh. The weight
of the thigh is the resistance, the hip joint is the fulcrum,
and the contraction of the adductor muscle is the effort.
Most of the limbs of the human body are articulated by third
class levers.
Each of the movements of the muscles for the various parts
of the body are described by the following terms:
- Abductor - Moves a limb away from the midline
- Adductor - Moves a limb toward the midline
- Extensor - Increases the angle at a joint (extends
a limb)
- Flexor - Decreases the angle at a joint (flexes
a limb)
- Pronator - Turns a limb to face downwards
- Supinator - Turns a limb to face upwards
- Rotator - Rotates a limb
- Sphincter - Closes an orifice or opening
Heat production
Muscle contractions produce heat and as much as 70% of body
heat is produced by energy produced in muscle tissue. Blood
is an essential element in temperature control during exercise,
taking heat from the body core and working muscles and redirecting
it to the skin when the body is overheating. When the internal
heat of the body reaches too low a level thermoreceptors in
the skin relay a message to the hypothalamus in the brain.
In response to this signal the skeletal muscles contract and
relax in an involuntary manner (shivering) increasing muscle
activity to generate heat. In turn, muscles are also responsive
to exterior heat - cold air increases muscle tone, and hot
conditions have a relaxing effect on muscles.
Maintenance of posture
As well as enabling movement, muscles also maintain posture
and body position. Sensory receptors in the muscles monitor
the tension and length of the muscles and provide the nervous
system with crucial information about the position of the
body parts, therefore enabling posture to be maintained. Muscles
are never completely at rest, nor do they actually have to
shorten in length when they contract. The tension or tone
produced as a result of these contractions between various
opposing groups of muscle helps us remain in a static position,
even when we are asleep.
Neurological System
All of our body systems work in conjunction with each other
and none are capable of working in isolation. The nervous
system controls and coordinates the functioning of all other
systems in response to our surroundings. Each stimulus or
change in our environment is detected by our senses and messages
are interpreted by the brain which in turn, sends directions
to the various organs to respond and adapt according to the
external conditions which affect our body.
The function of the Neurological System is to transmit and
receive a constant series of messages via electrical impulses
to and from the control centre situated in the brain. These
messages are either those receiving "information" from various
body tissues via the sensory nerves, or those initiating the
function of other tissues such as organs, muscles, etc.
The nervous system is divided into the central nervous system
(CNS) which includes the brain and spinal cord, and the peripheral
nervous system (PNS) comprising cranial nerves and spinal
nerves. The PNS includes nerves emerging from the brain (cranial
nerves) and nerves emerging from the spinal cord (spinal nerves).
These nerves are divided into sensory nerves which conduct
messages from various parts of the body to the CNS, whilst
motor nerves conduct impulses from the CNS to muscles and
glands. The PNS is further divided into the Somatic System
(SNS) and Autonomic System (ANS), depending on the area of
the body these messages are transmitted to and from.
The SNS consists of sensory neurons from the head, body wall,
and extremities, and motor neurons to skeletal muscle. The
motor responses are under conscious control and therefore
the SNS is voluntary. Certain peripheral nerves perform specialised
functions and form the autonomic nervous system; they control
various activities which occur automatically or involuntarily
such as the contraction of smooth muscle in the walls of the
digestive system. The autonomic system is further divided
into the sympathetic and parasympathetic systems. These two
systems provide nerve stimuli to the same organs throughout
the body, but bring about different effects.
The Sympathetic Nervous System helps prepare the body for
"fight or flight" and create conditions in the tissues for
physical activity. It is stimulated by strong emotions such
as anger and excitement and will therefore speed up heart
rate, increase the activity of sweat glands, adrenal glands,
and decrease those of the digestive system. It also produces
rapid redistribution of blood between the skin and skeletal
muscles.
Conversely the Parasympathetic Nervous System slows down
the body and helps prepare for a more relaxed state, ready
for digestion and sleep. It will therefore increase peristalsis
of the alimentary canal, slow down the heart rate, and constrict
the bronchioles in the lungs. The balance between these two
systems is controlled to create a state of homeostasis which
is where the internal stability of the bodily systems are
maintained in response to the external environment.
Effect of exercise on the neurological system
Good coordination and balance is vital to the sports person.
The quicker the reactions, the more chance the individual
has of having "the edge" over the opposition, or of improving
his or her personal best. As with most of the Systems, the
neurological system can be trained and improved with repetitive
exercises. New and extended movements may be progressively
attempted, practised and perfected involving action through
the use of the musculoskeletal systems and, as importantly,
the voluntary nervous system to initiate those actions.
It is also important to realise that to some extent nerves
serving muscles under our conscious control work in pairs
and therefore when rehabilitating an injured part it is often
beneficial to exercise and stimulate the symmetrically uninjured
part as well.
We have already noted how other systems may benefit from
exercise and these improvements take place with the help of
the neurological system. Like other systems, the neurological
system may also be adversely affected by smoking, lack of
sleep, poor diet and stress.
Conversely the nervous system is adversely affected by age.
As we grow older neurons are lost and not replaced. There
is also a decreased capacity for transmitting impulses to
and from the brain. In addition, both voluntary and reflex
actions become slower.
Endocrine System
The endocrine system affects bodily activities by releasing
chemical messages, called hormones, into the bloodstream from
exocrine and endocrine glands. The function of hormones are
to:
- Control the internal environment by regulating its chemical
composition and volume
- Respond to environmental changes to help the body cope
with emergencies - infection, stress etc.
- Help regulate organic metabolism and energy balance
- Contribute to the management of growth and development
Hormones are chemicals which cause certain changes in particular
parts of the body. Their effects are slower and more general
than nerve action. They can control long-term changes such
as rate of growth, rate of activity and sexual maturity.
The endocrine or ductless glands secrete their hormones directly
into the blood stream. The hormones are circulated all over
the body and reach their target organ via the blood stream.
When hormones pass through the liver, they are converted by
the kidneys. Tests on such hormonal end products in urine
can be used to detect pregnancy.
The endocrine system consists of a series of glands which
secrete hormones; they are found throughout the body and include
the pituitary, thyroid, parathyroids, thymus, supra-renal
or adrenal glands, part of the pancreas and parts of the ovaries
and testes. Although these glands are separate it is certain
that they are functionally closely related because the health
of the body is dependent upon the correctly balanced output
from the various glands that form this system.
The Pituitary Gland (Hypophysis)
This gland has been described as the leader of the endocrine
orchestra. It consists of two lobes, anterior and posterior.
The anterior lobe secretes many hormones, including the growth-promoting
somatotropic hormone which controls the bones and muscles
and in this way determines the overall size of the individual.
Over secretion of the hormone in children produces gigantism
and under secretion produces dwarfism. The anterior lobe also
produces gonadotropic hormones for both male and female gonad
activity. Thyrotropic hormones regulate the thyroid and adrenocorticotropic
hormones regulate the adrenal cortex. It also produces metabolic
hormones.
The posterior lobe produces two hormones - oxytocin and vasopressin.
Oxytocin causes the uterine muscles to contract; it also causes
the ducts of the mammary glands to contract and, in this way,
helps to express the milk which the gland has secreted into
the ducts. Vasopressin is an antidiuretic hormone which has
a direct effect on the tubules of the kidneys and increases
the amount of fluid they absorb so that less urine is excreted.
It also contracts blood vessels in the heart and lungs and
so raises the blood pressure. It is not certain whether these
two hormones are actually manufactured in the posterior lobe
or whether they are produced in the hypothalamus and passed
down the stalk of the pituitary gland to be stored in the
posterior lobe and liberated from there into the circulation.
The Thyroid
The right and left lobes of this gland lie on either side
of the trachea united by the isthmus. Average size of each
lobe is 4cm long and 2cm across but these sizes may vary considerably.
The secretion of this gland is thyroxine and tri-iodothyronine.
Thyroxine controls the general metabolism. Both hormones contain
iodine but thyronine is more active than thyroxin. Under-secretion
of this hormone in children produces cretinism; the children
show stunted growth (dwarfism) and fail to develop mentally.
Under secretion in adults results in a low metabolic rate.
Over secretion in adults gives rise to exophthalmic goitre
and the metabolic rate is higher than usual. Such persons
may eat well but bum up so much fuel that they remain thin.
This is usually accompanied by a rapid pulse rate. This gland,
therefore, has a profound influence on both mental and physical
activity.
The Parathyroid Glands
There are four of these glands, two on either side lying
behind the thyroid. Their secretion is parathormone - the
function of which is to raise the blood calcium as well as
maintain the balance of calcium and phosphorus in both the
blood and bone structures. Under secretion gives rise to a
condition known as tetany in which the muscles go into spasm,
and over secretion causes calcium to be lost to the blood
from the bones giving rise to softened bones, raised blood
calcium and a marked depression of the nervous system.
The Thymus Gland
This gland lies in the lower part of the neck and attains
a maximum length of about 6cm. After puberty the thymus begins
to atrophy so that in the adult only fibrous remnants are
found. Its secretion is thought to act as a brake on the development
of sex organs so that as the thymus atrophies, the sex organs
develop. Recent research into the activity of this gland reveals
that it plays an important part in the body's immune system
by producing T lymphocy - the T standing for thymus derived.
The Suprarenal or Adrenal Glands
These are two in number, triangular in shape and yellow in
colour. They lie one over each kidney. They are divided like
the kidney into two parts -the cortex and the medulla. The
cortex is the outer part of the gland and produces a number
of hormones called cortico-steroids. Their function is to
control sodium and potassium balance, stimulate the storage
of glucose and affect or supplement the production of sex
hormones. The medulla or inner layer produces adrenaline,
a powerful vasoconstrictor. Adrenaline raises vessels and
raised the blood sugar by increasing the output of sugar from
the liver. The amount of adrenaline secreted is increased
considerably by excitement, fear, or anger, which has caused
the adrenals sometimes to be referred to as the glands of
fright and fight.
The Gonads or Sex Glands
These glands are naturally different in men and women because
they serve different, though, in many respects, complementary
functions. In the female the gonads are the ovaries and in
the male the testes. Female sex hormones are oestrogen and
progesterone. The male sex hormone is testosterone, though
each sex produces a small quantity of the opposite hormone.
The female hormones are responsible for developing the rounded,
feminine figure, breast growth, pubic and axillary hair and
all the normal manifestations of femininity and reproduction.
Male hormone is responsible for voice changes, increased muscle
mass, development of hair on the body and face and the usual
development of manliness.
Pancreas
The endocrine part of the pancreas consists of clumps of
cells called islets of Langerhans which secrete insulin. Insulin
regulates the sugar level in the blood and the conversion
of sugar into heat and energy. Too little insulin results
in a disease known as diabetes mellitus. This disease is divided
into one form, juvenile onset, which occurs before the age
of 25, and another form which begins in maturity. It is a
very common disease. It is known that some half million people
in the United Kingdom suffer from it sufficiently badly to
need treatment but is has been estimated that there are many
more people in whom the disease exists at a sub-treatment
level.
Cardiovascular System
The cardiovascular system comprises of the heart, blood,
blood vessels and lymphatic system.
Heart
The function of the heart is to pump blood around the body.
The heart is a hollow, muscular organ divided by a vertical
wall called the septum. These two chambers are further divided
into the thin walled atrium above, and a thick walled ventricle
below, making a total of four chambers. Between each pair
of chambers are valves preventing any back flow of blood.
Blood vessels leaving the heart generally carry oxygenated
blood through vessels known as arteries. These are large,
hollow elastic tubes with thick muscular walls which are designed
to withstand the high pressure with the blood leaving the
heart. Their size gradually diminishes as they spread throughout
the body, ultimately reaching fine, hair-like vessels known
as capillaries. Blood vessels which return blood to the heart
are known as veins which generally carry de-oxygenated blood
to the heart. They are elastic tubes containing valves to
help prevent back flow of blood. Blood is forced through arteries
by the pressure from the heart whereas venous flow is aided
by muscular contraction.
The only two exceptions to the above are the pulmonary artery,
which carries de-oxygenated blood from the heart to the lungs,
and the pulmonary vein, which carries oxygenated blood from
the lungs to the heart. The circulation is divided into two
principle systems known as the general or systemic circulation
which is the circulation around the body, and the pulmonary
circulation to and from the lungs.
Blood
The fluid which surrounds tissue cells throughout the body
is called interstitial fluid and is serviced by blood transporting
oxygen and nutrients to it whilst lymph removes toxins and
waste products. The blood has three main functions, transport,
regulation, and protection.
Transports
- oxygen from the lungs to the cells
- carbon dioxide from the cells to the lungs
- nutrients from the intestines to the cells
- waste material from the cells
- hormones from the endocrine glands to the cells
- heat from various cells
Regulates
- pH (concentration of hydrogen ions)
- body temperature
- salts
- water content in the cells
Protection
- Blood prevents loss by clotting and combats toxins
Lymphatic
As blood is the main transport system to the body, so it
may also bring bacteria to the tissues. The lymphatic system
is the protective system which picks up materials, cleanses
them of waste products and toxins, and returns them to the
blood. Although it is described as a separate system it is
really part of the vascular system, being intertwined with
the blood circulation.
Effect of exercise on the cardiovascular system
The effects of regular exercise on the vascular system:
- The supply of blood vessels to the heart will increase
thereby lowering blood pressure and improving the functioning
of the heart
- Lowers the cholesterol levels in the blood helping to
reduce the risk of arteries "furring up" and possible heart
disease
- The period needed for the heart rate to return to normal
after exercise is reduced
- The network of capillaries in a muscle will increase thereby
increasing the supply of blood, oxygen and nutrients to
the working muscle
Respiratory System
The respiratory system comprises of the nose, mouth, throat,
larynx, trachea, bronchi and lungs. The function of the respiratory
system is to facilitate gaseous exchange to take place in
the lungs and tissue cells of the body.
Oxygen is required by cells in the body to allow various
metabolic reactions to take place and to produce energy and
is therefore essential to life. The respiratory system may
be defined as the organs and tissues through which air is
passed into and out of the body to allow the necessary gaseous
exchanges to take place.
External respiration is the means by which oxygen from the
air passes into the blood stream for transportation to the
tissue cells and carbon dioxide is collected and transferred
back to the lungs and expelled from the body (see Vascular
System).
Internal respiration involves the vital chemical activities
which take place in every living cell requiring oxygen and
glycogen to combine and release energy, water and carbon dioxide.
The normal rate of inspiration and expiration, the respiration
rate, is about 16 times a minute in an adult.
Effect of exercise on the respiratory system
In the Cardiovascular section the benefits of exercise were
discussed in relation to the improved functioning of the heart
and the lowering of blood pressure. Combined with increased
maximum oxygen consumption (VO2 max), or lung capacity, these
are all vital contributors to being fit and healthy.
An athlete who has not properly trained their cardiovascular
system is likely to incur other injuries more easily by the
rapid onset of fatigue and the consequent lowering of motivation
and mental awareness. For anyone competing at varying altitudes,
they must allow themselves a considerable period to acclimatise
before an event. Even climbing to a moderate altitude decreases
the maximum uptake by 7% to 8% due to the change in atmospheric
pressure. This decrease in oxygen being supplied to the muscles
may decrease performance by 4 to 8% depending on the duration
of competition, a considerable disadvantage at the finish
line.
Even the athlete who prepares and acclimatises well may still
not match natives of high altitude areas such as the Andes,
who have a larger chest capacity, more alveoli, larger capillary
beds and higher red blood cell count. Since people may suffer
from altitude sickness when moving from low to high altitudes,
sufficient time must also allowed for these symptoms to disappear
before starting intensive training.
used with permission, The Sports Coach
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