Download Healthy Systems of the Human Body

1
Foundation Certificate of Nutrition
Healthy Systems of the Human Body
Copyright © The Food Coach Institute™ 2011
Healthy Systems Human Body Version 2.2
May 2015
2
Contents
Page
1
Information for learners
3
2
Learning outcomes
4
3
Healthy Systems of the Human Body
5
6
Skin
7
7
Musculo-skeletal System
11
8
Cardiovascular System
15
9
Respiratory System
20
10
Digestive System
23
11
Renal System
27
12
Nervous System
28
13
Endocrine System
38
14
Reproductive System
43
15
Additional Resources
51
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Information for learners
Tips for Learners
v Read through the unit guide carefully once or twice. Make sure you understand all
the material. If there is anything you don’t understand, just send us an –email to
[email protected] and one of our support staff will help you
v Seek out other sources of information as well – some of these are listed at the end
of the unit guide – try the internet, libraries and reference books
Graphics
Each Body System has accompanying graphics illustrating the anatomy of the region.
These high resolution graphics files can be found as a graphics pack on the website at
www.foodcoachinstitute.com/resources
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Learning Outcomes
When you have completed reading the information contained in this unit guide,
You should be able to:
v Understand the basic structure of the healthy human body
v Understand the basic ways to keep your body healthy
Assessment
The purpose of this unit is to help you understand how your body works.
Once you have completed this unit you will be ready to take the assessment.
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Healthy Systems of the Human Body
The human body begins as a single cell- the fertilized egg. As new cells form by cell
division, cells become specialized to carry out particular tasks. Specialized cells begin to
group together to form tissues. Tissues are groups of similar cells that work together to
perform a particular function.
There are four types of tissue in the human body:
1. Epithelial tissue
2. Muscle tissue
3. Nervous tissue
4. Connective tissue
Epithelial tissue
o Is made of tightly connected cells that are arranged in flat sheets
o Prevents damage to cells beneath it
o Covers the inner and outer surfaces of internal organs
o Forms glands
Muscle tissue
o
Moves parts of the body
o
Is made of cells that contract then relax
o
Responds to electrical stimulation
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Nervous tissue
o
Found in the brain, nerves, and sense organs
o
Contains cells called neurons that generate and transfer electrical impulses to
other cells
Connective Tissue
o
Come in three types:
- defensive which defend the body from invaders
Example: white blood cells
- structural which give the body its support
Example: cartilage, tendons, ligaments
- sequestering which act like storehouses
Example: bone marrow cells store hemoglobin
Organs and Systems
The four types of tissues are combined in various ways to form organs. An organ is a
structure composed of a number of tissues that work together to perform a specific job
in the body, for example the liver. Organs work together to form organ systems.
Example: the circulatory system
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Skin
The skin is the largest organ in the body and is made of all four types of tissue –
epithelial, muscle, nervous and connective tissue. The skin regulates body temperature,
prevents water loss, and prevents entry of bacteria and stores water and fat. It is also a
sensory organ containing plenty of nervous tissue which makes it sensitive to touch,
temperature and pain. It is tough, flexible, and elastic (see graphics pack, Figure 1).
The skin also contains:
o
o
o
o
o
Nerves
Hair follicles
Blood Vessels
Muscles
Sweat Glands
The structure of the skin varies depending on different parts of the body. So the scalp
contains more hair follicles while the palms of the hands have none, while the skin is
much tougher and thicker on the palm.
The skin has two layers:
Epidermis - the outer layer
Dermis - the inner layer
The Epidermis
On the outside, the epidermis consists of watertight sheets of epithelial tissue. The cells
at the base of the epidermis continually divide and produce new skin cells. These move
up towards the surface and are eventually shed as they reach the outer layer.
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o
cells are replaced every 2-4 weeks
o
dead cells help to waterproof the skin
o
hair and nails are made of dead cells
o
pigments in the skin give it colour
o
brown pigment called melanin provides most skin color
o
albinos have no melanin
o
people with black skin have large amounts of melanin.
o
melanin helps provide protection from the sun
The Dermis
This is the inner part of the skin and contains nerves, hair follicles, blood and lymph
vessels, sweat glands and collagen. Collagen holds the dermis together and gives the
skin flexibility and strength. As we get older the skin contains less collagen which
causes sagging and wrinkles.
Nerves in your skin sense:
o
pressure
o
temperature
o
pain
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Muscles in your skin:
o
make hairs stand up when you are cold or afraid
Blood vessels
o
provide nourishment to cells
o
remove waste products
o
help regulate body temperature
Sweat glands
o
help remove excess heat
o
100 glands per square centimeter of skin
Regulation of body temperature
The skin gets rid of heat by increasing blood supply to the blood vessels in the skin. This
causes the skin to swell, redden, and sometimes to become puffy. Sweat is also released
from the sweat glands which releases heat as it evaporates.
When we are cold the blood vessels contract to conserve warm blood for the vital
organs. The skin becomes pale and shrunken. The tiny muscles in hair follicles contract
making the hairs stand up to further conserve heat around the skin. Our muscles
contract and relax to generate heat and this makes us shiver.
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Absorption and Detoxification through the skin
As the skin has a huge surface area we can easily absorb medications, nutrients and
water through the skin. So any creams you use will eventually be absorbed into the
body. At the same time, we can release toxins through the skin, so mud baths and
mineral spas can help us detoxify.
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Musculo-Skeletal System
Bones
Bone is connective tissue made of living cells. In adults, specialized bone cells constantly
break down and rebuild bone tissue.
Bone growth begins with cartilage. The basic shape of a bone is first formed in cartilage
when a baby. As the child grows, bone cells begin to replace cartilage cells. By
adulthood, the cartilage is all converted into bone. In adults, the bone marrow of the
long bones is used for storage of fat while the marrow of flat bones produces blood cells.
Four minerals - calcium, phosphorous, magnesium, and manganese - are built into bone
cells to make them strong. Vitamin D from sunlight is also needed to build and retain
good bone. Minerals make bones hard and rigid and this helps bones support the body.
Stress placed on bones can cause them to break. A broken bone is called a fracture.
Blood vessels inside the bone and the bone itself are damaged when a bone breaks.
There can be considerable bleeding as well as damage to surrounding tissue. Bones in
older people heal more slowly than bones in younger people.
In young adults, bone tissue is broken down and replaced at a steady rate. The cells in
our bones are constantly being renewed so that we completely replace all of the bone
cells over 7-10 years.
Good intake of all 4 minerals, vitamin D from sunlight and regular weight bearing
exercise is needed to build up good bone density during youth and until young
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adulthood. Bone density remains relatively constant in adults until age 40 when bone
replacement becomes less efficient.
Osteoporosis is a condition in which adults lose more than 10 percent of bone mass in
a 10 year period. Osteoporosis causes bones to become brittle and break easily. Women
are at greater risk of osteoporosis than men. Smoking and low weight appear to
increase osteoporosis.
To maintain good bone we need adequate intake of all 4 minerals, vitamin D from
sunlight and regular weight-bearing exercise. Good protein intake as well as Omega – 3
fatty acids appear to support bone density.
The Skeleton (see Figure 2)
The skeleton includes all the bones in the body – they total 206 in an adult. The skeleton
has three main functions:
1. support body weight
2. enable the body to move
3. protect the vital internal organs e.g. the ribcage protecting the lungs and heart
Joints
A joint is where two or more bones connect. Bones are joined together by ligaments
which are strong bands of connective tissue. Ligaments are elastic, but if stretched too
far can result in a tear or sprain.
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Muscles (see Figure 3)
The body contains over 600 muscles. Muscles move parts of the body such as the limbs.
Movement occurs when electrical signals cause muscle cells to contract and change
length.
There are three types of muscles:
1. Skeletal muscle
o
attached to the bones of the skeleton
o
help with movement
o
are voluntary muscles, meaning the individual controls the actions of these
muscles
2. Smooth muscles
o
involuntary muscles which are not under conscious control
o
perform actions that the person is not aware are happening
o
found in blood vessels and in the walls of internal organs like the gut
3. Cardiac muscles
o
found in the heart
o
generate their own electrical signals that cause contraction
o
cause the heart to beat
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Skeletal Movement
To move a bone, at least two sets of muscles must cooperate. Muscles exist in pairs
which run parallel to each other on either side of the bone. When a bone moves,
muscles on one side contract, pulling the bone in one direction. The muscles on the
other side relax which also helps the keep the bone in the desired position. Nerve
messages prevent both sets of muscles from contracting at the same time. When one
set of muscles contracts, the other set relaxes. To keep the body in any position,
requires a delicate balance between relaxed and contracted muscles.
Muscles are connected to bones by tendons. Tendons are made of the same tough,
elastic tissue as ligaments. Ligaments attach bone to bone while tendons attach muscle
to bone.
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Cardiovascular System
The Cardiovascular System transports oxygen, carbon dioxide, nutrients, hormones, and
other materials to and from the cells of the body. The circulatory system also carries
cells that help protect the body from disease. All of these functions help the body to
maintain balance or homeostasis and are essential to survival.
Blood
Blood is responsible for transporting nearly everything within the body. Blood is the only
liquid body tissue. The liquid substance in blood is known as plasma.
Blood is
o
55 percent plasma
o
45 percent cells (red blood cells, white blood cells, platelets)
Red Blood Cells
o
carry oxygen (needed for energy production) from the lungs to all cells in the body
o
carry carbon dioxide (a waste product) from the cells back to the lungs to be
exhaled
o
are filled with hemoglobin, an iron containing molecule which gives blood its red
color and carries the oxygen
White Blood Cells
o
protect the body against bacteria, viruses, or other foreign cells
o
are manufactured and stored in bone marrow until needed by the body
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o
the body produces more white blood cells when needed to fight infection
Platelets
o
help repair damaged blood vessels
o
stop the bleeding and harden into a patch over a damaged area of a blood vessel
Blood Vessels
There are over 60,000 miles of blood vessels in the human body. The blood in the body
travels through these blood vessels 1,440 times each day. Blood vessels carry blood
from the heart to the body and back to the heart.
Arteries are the blood vessels which carry blood away from the heart to the body’s
organs. Veins carry blood back to the heart. Normal blood pressure is maintained by
relaxing and contracting the blood vessels as well as hormones from the kidneys. During
the day our blood pressure goes up and down quite dramatically depending on what we
are doing. For example if we stand up quickly, the blood pressure needs to go up quickly
to maintain blood going to the brain. When we run for a bus, the blood pressure goes up
to send oxygen quickly to our muscles. When we are lying down resting, our blood
pressure can be reduced to a minimum. So the blood vessels need to be very flexible so
they can contract or relax at will to maintain the necessary blood pressure.
The Heart (see Figure 4)
The heart is a muscular organ that pumps blood throughout the body. The heart is
divided into two halves. The right half pumps blood to the lungs where gas exchange
occurs – oxygen is absorbed and carbon dioxide is released. The left half pumps the
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oxygen-rich blood to the rest of the body. Each half of the heart has an upper chamber
called an atrium and a lower chamber called a ventricle. Flap-like valves separate the
two chambers and keep the blood flowing in the right direction.
The atrium receives blood coming into the heart. The ventricle pumps blood out of the
heart. The contracting of the atria and ventricles cause the valves between these
chambers to open and close – to let the blood flow through and stop back flow. The
sound made by these valves is known as the heartbeat.
Circulation of the blood
Blood coming into the heart from the extremities of the body is very low on oxygen and
very high in carbon dioxide. This blood enters the right side of the heart and is pumped
to the lungs. It gets rid of the carbon dioxide and picks up fresh oxygen. Then the blood
returns to the left side of the heart where it is pumped around the body to supply organs
and muscles.
Heart disease
When the pumping action of the heart is not working efficiently the patient goes into
heart failure. This is when fluid starts to back up in various places like the lower legs
and lungs.
The muscles in the heart require a good blood supply of their own to keep working
efficiently so there are cardiac arteries bringing blood to the heart muscle. When those
blood vessels get blocked with hardening of the arteries, people suffer a heart attack.
This is when a cardiac artery either goes into spasm or a clot blocks the artery and this
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stops blood getting to the heart muscle. Angina is a temporary blockage or spasm of a
cardiac artery and this results in pain when the patient walks or exercises. When a
blockage or spasm is more serious, it causes permanent damage to the heart muscle
which causes the typical chest pain of a heart attack.
When the heart muscle is short of blood and therefore fresh oxygen, it may stop beating
properly in which case the person has a cardiac arrest. This can be reversed with
electric shock therapy to restart the heart beating.
CPR or cardio-pulmonary
resuscitation can keep the blood circulating until help arrives and electric shock therapy
can be started. For up to date information on how anyone can simply do hands-only
CPR go to YouTube and type in ‘hands only CPR Vinnie Jones’ or this address
http://www.youtube.com/results?search_query=hands+only+cpr+vinnie+jones&sm=1
Atheroma
When a healthy diet and lifestyle is not followed, then hardening of the arteries or
Atheroma occurs. This happens when inflammation in the lining of the blood vessels
causes small areas of damage. Inflammatory cells and cholesterol in the blood, stick to
the damaged area to try to repair it. Eventually calcium forms in this plug and forms a
permanent lump on the side of the blood vessel. This narrows the blood vessels and
causes resistance to the flow of blood. At the same time the blood vessel loses its
elasticity and becomes stiff where these calcified areas occur. So it’s more difficult to
relax and contract the vessel to maintain good blood pressure throughout the day.
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As the vessels become stiffer they produce more resistance to the flow of blood, the
blood pressure instead of going up and down normally, stays high for most of the day.
We diagnose high blood pressure or hypertension when a client’s blood pressure is
consistently higher than 140/90.
The two values occur when we measure blood pressure using a machine. The systolic
blood pressure (the higher value) occurs when we can hear the heart beat and the
diastolic blood pressure (the lower value) is measured when the heart beat disappears.
High blood pressure over a long period of time increases the risk of angina or a heart
attack in the blood vessels of the heart, a stroke in the blood vessels of the brain and
lack of blood flow to other parts of the body such as the legs and kidneys.
The Lymphatic System (see Figure 5)
Between the blood vessels and the body cells is a clear, watery fluid that is formed from
the parts of the blood that diffuse out of the blood vessels. This fluid is made of water,
proteins, and other nutrients.
To return this excess fluid and proteins to the blood, the body has a system of vessels
called the lymphatic system. This runs parallel to the veins bringing blood back from the
body and then enters the heart.
Lymph nodes located in various places along these vessels return water and nutrients
to the blood. The lymph nodes also contain white blood cells that help to defend the
body against cancerous cells and disease-causing organisms. So they are often swollen
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when there is a local infection such as a sore throat or a cancer nearby such as breast
cancer causing enlarged lymph nodes in the armpit.
Respiratory System
The respiratory system is where gas exchange in humans occurs. Humans obtain oxygen
and get rid of carbon dioxide through the respiratory system. (see Figure 6)
Breathing
The diaphragm is a dome-shaped muscle located below the lungs. During inhalation,
the diaphragm moves down and the rib cage moves up. This causes the chest to expand
and air to rush into the lungs. During exhalation, the diaphragm relaxes and air is forced
out of the lungs.
Air enters the body through the nose or mouth. These passageways warm and moisten
the incoming air. To get to the lungs air must pass through the following:
o
Pharynx - a tube at the back of the nose and mouth
o
Larynx - the voice box
o
Trachea - the windpipe
o
A ring of immune tissue – tonsils and adenoids
The trachea divides into 2 branches which lead to the right and left lungs. These
branches divide many times into smaller branches or tubes called bronchioles. The
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bronchioles are lined with tiny hairs and a protective layer of mucus which waft any
foreign particles out of the lungs. These bronchioles keep getting smaller and
branching off until they reach clusters of tiny air sacs called alveoli. The alveoli are
where gas exchange actually occurs. Each alveolus is surrounded by a network of tiny
blood vessels called capillaries. Blood from the capillaries picks up oxygen from the
alveoli and releases carbon dioxide to be exhaled. Each lung has about 150 million
alveoli.
Chest infections such as pneumonia are serious and can be fatal. With the advent of
anti-biotics the survival rate is much better. Our own immune system has a natural
barrier against chest infections by preventing bacteria and viruses getting into the lungs
as follows:
1) The nasal hairs and mucous trap bacteria, viruses and irritating particles
2) The circle of immune tissue of tonsils and adenoids means that the throat picks up
infections before they get to the lungs.
3) the villi and mucous of the lungs brings microbes and foreign particles such as dust,
debris and pollution out of the lungs to be coughed up or swallowed in the mucous.
In Asthma, small muscles in the bronchioles contract in response to contact with an
allergen, a virus or bacterial infection, or stress. The contraction of the muscles means
the airways are narrowed so sufferers can’t get air out. Stress plays a big part in asthma
attacks as well as allergies and general ill-health. Drug treatment of asthma includes
relaxing those muscles in the bronchioles to open up the airways and also decreasing
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the immune response to allergens. Other treatment includes reducing environmental
pollution, reducing allergens in processed foods, increasing gut health with probiotics
and healthy nutrients, managing stress to reduce anxiety.
Smoking causes permanent damage to the lung function. Cigarettes contain nicotine
which is very addictive and stimulates rapid pulse and blood pressure. There are
approximately 600 ingredients in cigarettes. When burned, they create more than 4,000
chemicals. At least 50 of these chemicals are known to cause cancer, and many are
poisonous. Check out this website from the American Lung Association for more
information.
http://www.lung.org/stop-smoking/about-smoking/facts-figures/whats-in-acigarette.html
Apart from containing harmful chemicals, cigarettes paralyze the villi reducing their
ability to clear the lungs of harmful debris. Smoking causes chronic cough and copious
mucous, and the long term diseases emphysema and chronic bronchitis.
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Digestive System
There are six essential nutrients the body needs. Foods contain all of these nutrients.
Three of these nutrients provide fuel for the body and are called macronutrients:
1. Carbohydrates
2. Lipids
3. Proteins
Three of these nutrients regulate how the body uses nutrients. Vitamins and minerals
are called micronutrients:
1. Water
2. Minerals
3. Vitamins
These six nutrients provide the body with what it needs to grow and to maintain and
repair itself. Nutrition is the science that studies how food affects the functions of the
body. Proper nutrition is necessary for health and a poor or imbalanced diet can lead to
disease and /or death.
Food contains energy that is trapped by chemical bonds. Once these bonds are broken,
the energy is released. A calorie or kilojoule is the unit of measurement used to
describe the heat energy that is released from food or is used by the body during
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physical activity. The gut is the organ which controls digestion of food and absorption of
nutrients (see Figure 7).
Digestion
o
Digestion begins in the mouth. Chewing breaks food down so that digestive
enzymes can begin the transformation process.
o
Salivary glands produce saliva which moistens food to make it easy to swallow.
o
Enzymes in saliva start the process of breaking down starches in food.
o
When food is swallowed, it travels down the esophagus to the stomach. Muscular
contractions of the esophagus, stomach and intestines are known as peristalsis.
Peristalsis ensures that food moves from the mouth to the stomach and on
through the intestines.
o
Once food reaches the stomach, it is mixed with hydrochloric acid and pepsin, a
digestive enzyme that breaks down proteins.
o
The stomach also produces a small amount of lipase, an enzyme which breaks
down lipids or fats.
o
The food may spend several hours in the stomach where it is reduced to a liquid.
o
Food then moves into the small intestine. In the first 25 cm of the small intestine,
known as the duodenum, the remaining carbohydrates and proteins are broken
down.
o
Fat which is not water soluble, is broken down by bile from the liver which travels
from the gall bladder into the small intestine. This helps to make it more water
soluble and breaks fat droplets into smaller particles. This allows lipase from the
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pancreas to break down the fatty chains into fatty acids which can then be
absorbed.
o
In the rest of the small intestine, nutrients are absorbed and transferred to the
blood and then to the liver.
o
Food spends three to six hours in the small intestine. During this time, nutrients
are absorbed into the bloodstream. Food goes through the final breakdown while
in the small intestine to make absorption possible. Both the liver and pancreas
secrete digestive enzymes which help break down food.
The Pancreas
o
secretes enzymes which break carbohydrates into simple sugar (glucose)
o
Splits proteins into amino acids.
o
divides fats into chains of fatty acids
o
secretes bicarbonate to neutralize acid in the stomach
o
controls blood glucose with insulin and glucagon
The Liver
o
stores vitamins and minerals
o
takes digested nutrients and sends them into the bloodstream as needed
o
regulates glucose storage in the body under the control of insulin
o
makes bile to help with fat digestion
o
filters and detoxifies blood
o
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Control of Blood Glucose by the pancreas
As a meal is eaten and digested, blood glucose levels rise, and the pancreas secretes
insulin. Insulin acts on liver cells to store ingested glucose as glycogen. Excess glycogen
not used up is stored long term as fat.
When it is needed for energy, glycogen is broken down and converted again to glucose.
For the next 8–12 hours, glucose derived from liver glycogen will be the primary source
of blood glucose to be used by the rest of the body for fuel.
Insulin and glucagon act together to keep the blood glucose constant: insulin being
made when blood glucose rises and glucagon when blood glucose falls too low.
The Large Intestine
The indigestible portion of food moves from the small intestine to the large intestine.
When food residue arrives in the large intestine, it is fairly liquid. As it passes around the
large bowel, the water is reabsorbed back into the body leaving solid material ready to
be eliminated. If enough water is not consumed the large bowel absorbs more and more
water making the stool dry and hard and difficult to pass. Plenty of water and a good
intake of fibre from fruit and vegetables prevents constipation.
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The Renal System
The Kidneys (see Figure 8)
As the body breaks down protein, nitrogen compounds such as ammonia are produced.
The body must get rid of these metabolic wastes. The body makes ammonia less
poisonous by combining it with carbon dioxide in the liver to form urea. Urea enters the
blood stream and travels throughout the body. The body eliminates some urea through
the skin as perspiration, but most must be eliminated by the kidneys.
The kidneys play an important role in maintaining balance or homeostasis:
·
Removes urea and other wastes
·
Regulates the amount of water in the blood
·
Adjusts blood pressure using hormones
·
Sends wastes in the form of urine to the bladder
The bladder stores urine for passing when convenient. When you are dehydrated the
urine becomes concentrated and a dark colour. This causes some burning and pain when
passing urine. At the same time, little urine is produced and sits for a long time in the
bladder, causing irritation. Eventually bacteria can grow and cause a urine infection. This
can be prevented by drinking plenty of water throughout the day and passing urine
frequently.
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Nervous System
Nerve cells, called neurons, are specialized cells which conduct information. Bundles of
neurons form thin cables called nerves. Electrical impulses travel along these nerves to
all parts of the body.
In humans, neurons run from the brain and spinal cord directly to muscles. Nerves can
be very long. Nerve impulses must travel quickly to all parts of the body. To accomplish
this, specialized cells speed up nerve impulses. These specialized cells are wrapped
around the nerves forming an insulating layer called the myelin sheath. The myelin
sheath contains gaps called nodes which allow nerve impulses to jump from node to
node in order to travel quickly.
Once the nerve impulse reaches the end of the nerve cell, it must cross a gap to the
next nerve cell called a synapse if the message is to continue. If the nerve impulse
cannot "jump" the synapse, it is carried across the synapse by chemical messengers
called neurotransmitters. These are the brain hormones serotonin, dopamine and
acetylcholine.
We need good levels of nutrients like zinc, magnesium and B vitamins to make adequate
levels of brain hormones. When our brain hormones are low, for example serotonin, we
can feel depressed. Dopamine is involved in our reward system and can be high in
people who are addicted to risk-taking or gambling. It is low in Parkinson’s disease
which often affects elderly people.
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Organization of the Nervous System
The nervous system has two parts:
1. Central nervous system
o Brain
o
Spinal cord
2. Peripheral nervous system
o Motor and Sensory Nerves
o The Autonomic Nervous System
Central nervous system
The brain is the control center of the body (see Figure 9). Although the brain accounts
for only about 2% of our weight, it consumes about 20% of our energy, so it needs
plenty of good fuel to work properly.
The largest portion of the brain is the cerebrum which is divided into two hemispheresright and left. Each hemisphere is covered by an outer gray layer called the cerebral
cortex. The cerebrum handles sophisticated functions of the brain such as processing
visual images and thinking. Beneath the rear of the cerebrum is a structure called the
cerebellum. The cerebellum controls coordination of movement. Underneath the
cerebellum is the brain stem. The brain stem controls life processes such as digesting,
breathing, and blood pressure.
Above the brain stem is the hypothalamus which is the center for emotions and
instincts. The hypothalamus is the area responsible for keeping everything in balance –
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or homeostasis. Like the thermostat on an air conditioner that decides whether to switch
on or off depending on the room temperature.
For example, the hypothalamus controls:
o
Hunger
o
Thirst
o
Body temperature
o
Water balance
o
Pain
o
Sleep cycles
o
Sexual satisfaction
o
Emotions such as anger, fear, happiness
o
It also regulates the Autonomic nervous system which regulates pulse, blood
pressure, breathing etc
The hypothalamus releases many hormones which control all of these functions. Most of
these hormones travel to the pituitary which then sends hormone signals to various
parts of the body like the thyroid, adrenals and reproductive organs. More about this in
the Endocrine System.
The control of Emotion
There are a number of organs in the brain called the limbic system which together coordinate our emotions and emotional reactions to situations. The limbic system includes
our hypothalamus, amygdala and hippocampus. When we are upset, the limbic system
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processes our feelings, memorizes them and sends messages to the rest of the body
controlling our reaction to the situation. This is why when we encounter the same
emotional situation again; our body remembers the physical response and the same
reaction is produced.
For example, when we feel fear – say we are attacked by a dog as a child; we get a
physical response – sweating, shaking etc. The limbic system remembers this and
produces the same physical changes every time we feel fear in the same situationevery time we encounter a dog. This is how a pattern of fears and phobias arises.
On the plus side, when we remember a pleasant memory, say from a childhood trip to
the beach, we can instantly remember how it smelled – the smell of the ocean, how the
sand felt on our feet, and the taste of ice-cream etc.
Spinal Cord
Messages from the brain travel along the spinal cord to all parts of the body. The spinal
cord is a cable of axons that extends from the brain stem. The spinal cord consists of a
column of gray matter covered by a layer of white matter. The backbone, a tunnel of
bones formed by the vertebrae, surrounds and protects the spinal cord.
Peripheral Nervous System (see Figure 10)
The peripheral nervous system consists of the nerves which reach from the spinal cord
and brain to all parts of the body. There are basically two types of neurons in the
peripheral nervous system - sensory neurons and motor neurons.
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Sensory neurons relay nerve impulses to the central nervous system:
o
Signals from sense organs
o
Signals from internal changes such as blood pressure or pain
So sensory neurons help the brain receive messages.
Motor neurons send messages from the brain to muscles and glands so that we can
move around and do activities.
In the event of danger which requires quick action, information is sent to the spinal cord
along sensory neurons then immediately back along motor neurons which trigger an
involuntary reaction called a reflex, like removing your hand from a hot plate.
Some motor neurons are active all the time, even when the body is asleep. These
neurons, called the autonomic nervous system, keep the body going, controlling such
actions as blood pressure and digestion.
The Autonomic Nervous System
This system is composed of two parts
o Sympathetic nervous system
o Parasympathetic nervous system
The Sympathetic Nervous System prepares our body for the fight or flight reaction.
When we have acute stress like a fright, our hypothalamus starts the ‘fight or flight’
response. This has evolved to help us deal with a sudden emergency like being attacked
by a sabre-tooth tiger. We get ready to fight or run away. Our brain sends messages to
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our adrenals to make lots of adrenaline. We start breathing heavily, our pulse quickens,
and we divert blood away from the gut to muscles, so that we can move rapidly. After
the emergency is over we quickly calm down and hormone levels return to normal.
So the Sympathetic nervous system:
o Increases the heart rate to help us move blood quickly
o Dilates the pupils so we can see well
o Stimulates the sweat glands to get rid of heat
o Dilates the blood vessels to the large muscles so they can work hard
o Constricts blood vessels to the rest of the body to conserve blood for the muscles
o Opens up the bronchial tubes of the lungs so we can breathe hard
o Stops the secretion of digestive juices to conserve energy for action
The Parasympathetic Nervous System is the counterbalance to the Sympathetic
Nervous System. It brings us back from that state of emergency and calms us down.
So the Parasympathetic nervous system:
o Constricts the pupils
o Decreases the heart rate
o Constricts the bronchial tubes
o Activates the salivary glands
o Stimulates secretions in the gut to restart digestion
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When we want to calm down after a stressful event we want to activate the
Parasympathetic nervous system. For example, deep, slow breathing will help to slow
the heart rate.
In today’s stressful world, many people exist with their sympathetic nervous system
activated all the time. Instead of a good balance between sympathetic and
parasympathetic, the sympathetic system is always active, always making adrenaline.
Eventually they run out of steam and become exhausted and run down. Regularly
activating the parasympathetic system with meditating, relaxation and deep breathing
prevents this from happening.
Chronic versus acute stress
In the case of chronic stress that occurs over months or even years, like work stress or
relationship problems, our hormone response is different. Our hypothalamus again
sends signals to our adrenals but this time they make cortisol. Normally our cortisol is
high in the morning and then gradually reduces as the day goes on. In highly stressed
people, the cortisol stays high all day long. Eventually the adrenals get exhausted and
cannot make enough cortisol anymore. Then adrenal fatigue sets in - we feel very tired
all the time and have no energy to do anything. This may be the cause in some chronic
fatigue sufferers.
The Sense Organs
The brain receives signals from the environment via sensory receptors (eyes, ears, skin,
nose, and tongue). These receptors contain different types of neurons that detect
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changes inside and outside the body. Some sensory receptors respond to internal
stimuli such as temperature changes, pain, pressure, and muscle contractions. Other
sensory receptors respond to external stimuli such as motion, sound, smell, lights, and
taste.
Receptors in the Ear
The ear detects sound waves and establishes equilibrium. The fluid-filled semicircular
canals and chambers in the inner ear contain receptor cells which detect movement and
send signals to the brain which enable you to keep your position steady.
The inner ear also senses sound waves. The outer ear captures sound waves and directs
them down the ear canal. When the sound waves strike the eardrum, it begins to
vibrate. The vibrations pass through three small bones inside the ear. One of these small
bones presses against a spiral shaped structure known as the cochlea. The cochlea
consists of fluid-filled canals lined with hair cells. The vibrations carried into the cochlea
cause the hair cells to vibrate. From the cochlea, signals are sent to the brain where
they are interpreted as sound. Damage to the hair cells will result in loss of hearing.
Listening to too much loud music can damage hair cells.
Balance
The other important function of the ear is to help maintain balance. There are 3 semicircular canals at right angles to each other in the 3 axes. These are filled with fluid.
Whenever the head is turned or the body’s position is changed, the resulting movement
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of fluid within these canals, helps the brain to detect the extent of movement and
positioning of the head.
Receptors in the Eye
The eye contains specialized receptor cells called photoreceptors that contain light
sensitive pigments. The energy in light changes these pigments triggering a nerve
impulse that travels to the brain. The human eye has two types of photoreceptors - rods
and cones.
Rods
o
Detect only black and white images
o
Generate grainy images
o
Work best in dim light
Cones
o
Detect color
o
Generate detailed images
o
Activity is reduced in dim light so we rely more on the rods in the dark
Rods and cones are packed tightly together in the retina, a layer which covers the back
surface of the eye. Light waves enter the eye through the pupil. The pupil is an opening
surrounded by a ring of muscle fibers. These muscle fibers contract or relax to regulate
the amount of light which enters the eye.
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After the light waves enter the pupil, they pass through an almond-shaped disk called a
lens. The lens bends the light waves so that they strike the retina stimulating the rods
and cones. From the retina, nerve impulses are sent along the optic nerve to the brain.
Receptors for Taste and Smell
The receptors for taste and smell are stimulated by chemicals. The receptor cells for
taste are located in the taste buds on the tongue. There are five basic taste senses:
sweet, sour, salty, bitter and umami. Each type of receptor is located on different areas
of the tongue.
Receptor cells for smell are located in the upper walls of the nasal cavity. There are
more than 1,000 different receptors for smell.
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Endocrine System
Hormones
A hormone is a chemical signal that regulates the body's activity. Hormones are made
in one place and delivered to another. Hormones are usually carried in the blood. Organs
that produce most of the hormones in the body are called endocrine glands.
General functions of hormones
o
Endocrine glands secrete hormones into the bloodstream
o
The hormone travels to a specific tissue or organ called a target.
o
At the target, the hormone elicits a specific response
o
Hormones enable the body to
- digest food
- use food as fuel
- grow and mature
- maintain homeostasis or balance
The Hypothalamus
The endocrine system and the nervous system work very closely together. As part of the
nervous system, the hypothalamus regulates body temperature, breathing, hunger, and
thirst. The hypothalamus also controls much of the activity of the endocrine system like
the CEO of a company.
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The Pituitary Gland
The hypothalamus produces hormones which are sent to the pituitary gland. The
pituitary gland then produces other hormones to send around the body like a foreman
implementing instructions from the boss.
The hormones released by the pituitary gland include:
o TSH Thyroid Stimulation Hormone which controls the thyroid
o ACTH AdrenoCorticoTrophic Hormone which controls the adrenals
o FSH (Follicle Stimulating Hormone) and LH (Luteinising Hormone) which control
ovulation
o Growth hormone which regulates the growth of the body particularly the
skeleton
o Prolactin and Oxytocin which causes milk production and release from the
breasts
o ADH Antidiuretic hormone which causes the kidneys to form more concentrated
urine, helping to conserve water in the body
Adrenal Glands
The adrenal glands are two almond-shaped glands located on top of the kidneys. Each
adrenal gland is two endocrine glands in one - the adrenal medulla and the adrenal
cortex.
The adrenal medulla helps the body react during a sudden emergency as described
earlier. The adrenal medulla is unusual in that it is not activated by a hormone. The
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nerves which connect the adrenal medulla to the hypothalamus directly stimulate the
medulla to rapidly release hormones such as:
o
Epinephrine (Adrenaline)
o
Norepinephrine (Noradrenaline)
These hormones are produced in response to
o
Fear
o
Anger
o
Pain
o
Physical exertion
The adrenal cortex or outer layer helps the body deal with long-term stress which may
last for hours, days, or weeks. The adrenal cortex produces the steroid hormone
cortisol.
Over production of Cortisol:
o
Causes the body to burn lean muscle tissue for energy so weakening the muscles
o
Increases the level of blood glucose to create energy but may lead to diabetes
o
May result in organ malfunction or mental burnout if produced for long periods of
time
o
Weakens the immune system when produced for long periods of time
o
Weakens our bones
o
Thins the skin
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The Thyroid Gland
The thyroid gland is located in the neck, just below the Adam's apple. It releases
thyroxin (T4) and other hormones containing iodine (T3) which regulate the body's
metabolic rate. Thyroid hormones are needed to:
o
control the basal metabolic rate
o
regulate metabolism of protein, fat, carbohydrate and vitamins
o
growth and development during childhood
o
reproductive functions
If the thyroid gland produces too much thyroxin, the resulting condition is known as
hyperthyroidism. The production of too little thyroxin is called hypothyroidism.
The Pancreas
The pancreas produces hormones which regulate how much glucose is dissolved in the
blood. Glucose circulates to all cells in the body, providing quick energy needed to fuel
cellular activities. The pancreas produces two hormones which work opposite to one
another to balance the blood sugar.
When food is digested, blood sugar levels rise. The rise in blood sugar triggers the
release of insulin, which helps the glucose get into the cells to provide energy.
Excess sugar not used by the cells is stored in the liver temporarily as glycogen or long
term under the skin as fat. When blood sugar levels begin to fall, the pancreas produces
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glucagon to raise the level of sugar in the blood. Low blood sugar can cause irritability,
headaches and muscle weakness.
When too much sugar is ingested over a long period of time, the pancreas becomes
exhausted and cannot produce enough insulin to control the blood sugar. The blood
sugar fluctuates a lot producing the disease diabetes.
As you can see, the nervous system and endocrine system work closely
together, using many hormones to control the various systems of the body. It
is vitally important to get plenty of nutrients from our food so that we can
make good levels of all these hormones and maintain balance and equilibrium
in all the systems in our bodies.
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REPRODUCTIVE SYSTEM
The Male Reproductive System
The Sperm
Sperm cells are different from any other cell in the body as a sperm cell has:
o
Only one set of chromosomes.
o
A long tail.
o
Mitochondria which provide energy to whip the tail back and forth.
o
A cap of digestive enzymes at the tip of the sperm's head which enables the sperm
to penetrate the egg.
Sperm are produced in organs called testes. Testes are located in a loose sac at the
base of the penis called the scrotum. Mature sperm are stored temporarily in the
epididymis which is located next to the testes. The urethra is the tube that carries
urine from the bladder to the outside of the body. It also carries semen during
ejaculation, the process by which sperm leave the male body. The seminal vesicles,
two small glands near the bladder, provide fluid which nourishes the sperm. Semen is
expelled from the penis during ejaculation.
The Female Reproductive System
The Egg
Females have organs called ovaries which produce eggs. Eggs also have only 1 set of
chromosomes, so that the fertilized egg has chromosomes from each parent. The
ovaries are located in the pelvis on either side of the uterus. Once each month, one
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ovary will release an egg into the fallopian tubes which carries the egg to the uterus.
The uterus is a hollow, muscular organ about the size of a small pear. The cervix, a
tubular ring of strong muscles, is located at the lower part of the uterus. Below the
cervix is a hollow tube called the vagina which connects the uterus to the outside of the
body.
The vagina has two functions:
o
Receives the penis and any sperm ejaculated by the male during intercourse.
o
Serves as the birth canal through which the baby passes during birth.
The Female Reproductive Cycle
Females produce hormones which cause changes in a sequence of events known as the
menstrual cycle. Once a month, an ovary will release an egg. This process is called
ovulation. As the egg matures, the uterus prepares to receive and nourish a fertilized
egg. The uterus becomes spongy and rich in blood and nutrients. About four or five days
after ovulation occurs, the uterus is ready. If no fertilized egg arrives, the lining breaks
loose from the uterus. Blood from broken blood vessels mixes with the lining and passes
through the vagina and out of the body. This process is known as the period.
Ovulation and menstruation stop when a woman is between 45 and 55 years of age. The
cessation of the ovarian and uterine cycles is known as menopause.
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Fertilization and Development
Fertilization is the fusion of the sperm and egg cells. Sperm which have been deposited
in the vagina must make a difficult journey before fertilization can occur. Most sperm
never leave the vagina. To reach the egg, sperm must
find and pass through the small opening in the cervix and escape from the mucus
which covers the opening.
o travel across the uterus
o enter the fallopian tube in which the egg is located.
o
Many sperm can arrive at an egg at the same time but only one sperm can penetrate
the egg. The fertilized egg travels through the fallopian tube into the uterus. The cells
inside divide and multiply. The journey to the uterus takes 4-5 days after fertilization
occurs. When the embryo reaches the uterus, it contains a hundred or more cells. The
embryo embeds itself in the uterine lining and releases hormones which prevent the
lining from washing away by the menstrual cycle. After about nine weeks, the
developing embryo is called a fetus. Once the embryo implants itself in the uterus, it
grows rapidly for approximately 40 weeks. This period of time is divided into threemonth segments called trimesters.
The first trimester begins with conception. Implantation occurs and cell differentiation
begins. The heart and central nervous system are forming. By the 8th week, the sex of
the fetus has been determined. Eyes, ears, arms, and legs begin to form. Vital organs
are formed.
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In the second trimester, the circulatory system is operating and sex organs are distinct.
The mother begins to feel movement. Hair forms on the body and head. Eyelashes and
eyebrows appear. The skin is thin, wrinkled and translucent. Body movements become
vigorous.
In the final trimester, the eyes open and survival outside the womb is possible. At 38-40
weeks, birth occurs.
While the fetus is in the womb, oxygen and nutrients from the mother's blood pass
though the walls of the uterus into the placenta and to the fetus via the umbilical cord.
Carbon dioxide and urea from the fetus pass back into the mother's bloodstream and are
eliminated by the mother's body.
The health of the mother and the activities in which the mother participates affect fetus
development:
o
Diet
o
Use of alcohol
o
Smoking
o
Use of drugs - prescription, over-the-counter, street drugs
o
Radiation (x-rays)
o
Diseases (rubella and toxoplasmosis)
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For Example, alcohol can cause severe birth defects:
o
Slow physical development
o
Mental retardation
o
Learning problems
o
Malformed organs
o
Misshapen spine
o
Impaired brain development
Use of street drugs like heroin during pregnancy can cause the baby to have:
o
Mental retardation
o
Learning disabilities
o
Personality disorders
At the same time good intake of nutrients is vitally important to support growth of the
baby and health of the mother. If nutrients are deficient, the baby takes as much as it
can, leaving the mother deficient in those nutrients in short supply.
Any woman wanting to have a baby needs to prepare her body with good nutrients long
before she tries to get pregnant. Both sperm and egg are reliant on good nutrients so
they can perform their functions properly. We are seeing more and more infertility in
young adults that is due to poor intake of nutrients and an unhealthy lifestyle.
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Sexually Transmitted Diseases
Many serious diseases are transmitted sexually:
o
AIDS
o
Hepatitis B
o
Human Papilloma virus leading to cancer of the cervix
o
Genital herpes
o
Syphilis
o
Gonorrhea
o
Chlamydia
Using barrier methods of contraception like condoms will decrease the chance of
catching diseases from sexual partners.
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How to keep the body healthy
Now that you have read about all the systems in the body you will realize how your
lifestyle can affect your health. Unhealthy diets and lack of exercise affects many
diseases like high blood pressure, high cholesterol, diabetes, arthritis and cancer.
Healthy diet
It is essential to have a healthy diet and we will cover this in more detail in the next
units.
Physical Exercise
This is also very important to keep our muscles strong and flexible. Exercise is also a
great de-stressor as it activates our parasympathetic nervous system. This counteracts
all the effects of stress on our sympathetic nervous system.
Healthy behaviours
We can see that other ways we behave can also affect our health.
o Excess alcohol affects our brain function as well as our body.
o Party drugs can have long-lasting effects on our brain and mental function as well
as physical effects.
o Multiple sexual partners increase the risk of sexually transmitted disease which
affects our health and our future fertility.
o Smoking causes permanent damage to our lungs and leads to lung cancer
Living a healthy lifestyle will not only help us live longer but will also allow us to live a
more active and enjoyable life, free from chronic disease.
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Children can enjoy an active, outdoor life with plenty of exercise, adequate sunlight and
lots of healthy foods.
Adults should be at the peak of their physical and mental fitness.
Middle age should be a time to enjoy other pursuits as the demands of child-rearing
decrease.
Old age does not have to consist of aches and pains, multiple medications and
immobility. Elderly people who keep their bodies fit and strong can enjoy sports, travel
and socializing right up until advanced age.
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Additional Resources
o Medical Terminology Simplified, Barbara A Gylys and Regina M Masters, 2nd Edition
o Innerbody.com: Your Guide to Human Anatomy Onlinehttp://www.innerbody.com/htm/body.html
o Baggaley, A (Ed.), (2001). Human Body: An Illustrated Guide to Every Part of the
Human Body and How it Works, London: Dorling Kindersley Limited.
o Introduction to Basic Human Physiologyhttp://www.free-ed.net/free-ed/HealthCare/Physiology/default.asp
o Effects of Smoking: World Health Organisation http://www.who.int/topics/tobacco/en
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