Describing & explaining how the human circulatory system works
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Doc Brown's
school biology revision notes: GCSE biology, IGCSE biology, O level
biology, ~US grades 8, 9 and 10 school science courses or equivalent for ~14-16 year old
students of biology
heart, lungs and body connection; blood vessel system - structure of arteries,
capillaries & veins; blood system - function of red blood cells, white blood
cells, platelets & plasma; causes & treatment of cardiovascular disease
This page will help you answer questions
such as ... What is the mammalian double
circulatory system work? What is the function of veins, arteries
and capillaries in the blood circulation system? How is the structure of veins, arteries
and capillaries adapted for their functions? What are the causes and problems of
cardiovascular disease?
Sub-index for this page
1.
A double
circulatory system - heart and lung connections
2. The
human heart and its pumping action - diagrams and explanation
3.
The structure and function blood
vessels, arteries, capillaries, veins, flow rates
4.
What's in the blood? - red and white blood cells, platelets,
plasma
5.
Cardiovascular disease
(CVD)
& treatments, heart disease, stents, statins
6.
Scientific
developments in treating cardiovascular disease and emergencies e.g.
surgery, artificial blood, and artificial hearts
See also
Respiration - aerobic/anaerobic including in animals
and
Examples of surfaces for the exchange of substances in
animal organisms
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1. A double
circulatory system - advantages
Oxygen is needed to produce energy from
respiration chemistry to power the cells of any organism. Carbon dioxide is
the waste product from respiration. So, a gas exchange system is required -
this takes place in the alveoli of the lungs.
This is described on
Gas exchange in the
lungs by diffusion, so here we
concentrate on the double circulatory system and how the heart works.
The circulatory system transports substances
around the body
We humans, like other mammals, have a
double
circulatory system consisting of two closed circuits joined together with the
heart acting as the central pump.
From the right ventricle of the
heart, the first circuit pumps
deoxygenated blood to the lungs to absorb fresh oxygen before being
returned to the heart (right diagram).
Deoxygenated means the
haemoglobin molecules in red blood cells are not carrying oxygen
molecules, therefore the blood itself, is not carrying oxygen.
Oxygenated
means the haemoglobin molecules in red blood cells are carrying oxygen
molecules, therefore the blood itself, is carrying oxygen.
In the second circuit, the
left ventricle of the heart pumps oxygenated
blood from the lungs to all the organs and associated structures (the rest
of the body except for the lungs) and returns it to the heart (left
diagram).
After circulating round the body
discharging its oxygen to all the cells of the body, the heart pumps the blood back to the lungs to be
re-oxygenated.
Blood is pumped out of the heart under high pressure into the arteries.
The blood flows through the arteries to
the capillaries and then the veins, in doing so , the pressure decreases.
The whole double circulation system is pretty complicated (right
diagram).
The diagram is a simplified
diagram of the double circulatory system of the human body as an example of
the mammalian circulation structure.
Apart from the lungs, the blood vessel
system must pass near all the rest of the exchange surfaces too e.g.
the villi in the gut (small intestine) to
absorb food molecules and water,
the kidneys, where the blood is filtered
to remove urea,
and the liver filters the blood from the
digestion system e.g. one of its functions is the detoxification of various
chemicals.
The advantages of the mammalian double circulatory system
Adaptations
Because the blood is returned to the
heart after its absorbed oxygen, it can be pumped out around the body
at a higher pressure AND at a faster rate.
This increases the rate of blood flow
increasing the supply of oxygen to all the tissues and organs of
the body.
This is vital for mammals to
maintain their optimum body temperature - warm blooded animals.
Also, the oxygenated blood is
flows separately from the deoxygenated blood.
Note on fish:
Fish have a single circulatory
system in which deoxygenated blood from the fish's body is pumped to
the heart, which then pumps it through the gills to absorb oxygen from
the water and round through the rest of the body in one continuous loop
- just one circuit in operation (unlike the double circulatory system of
mammals).
For more on fish gills see
Examples of surfaces for the exchange of substances in
animal organisms
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2. The
human heart and its pumping action - diagrams and explanation
The heart is an organ and pumps blood around
the body
Need to refer to the diagram of the
structure of the heart above.
Much of the wall of the heart is made
from muscle tissue which continually contracts and relaxes.
This cardiac muscle
contains lots of mitochondria to provide the cells with
lots of ATP
for respiration - lots of energy is needed to work, so to
contract the heart muscles.
Heart muscles need their own
blood supply to continually access a source of nutrients and
oxygen so they can work non-stop - a continuously beating heart
to keep all of us mammals alive!
The cardiac muscles are
supplied with blood from two coronary arteries which branch from
the base of the aorta. They ensure a constant supply of glucose
and oxygen for respiration, that can diffuse through the thick
walls of the heart into the heart muscle cells .
The heart has valve systems
that ensure the blood only flows in the right direction - one way
only, no reverse flow allowed.
The heart has two pumps to
work the double circulation system that beat together, typically 60 -
100 times per minute.
Each pump has an upper chamber (atrium)
that receives blood and a lower chamber (ventricle) that
pumps blood out.
Both atria and ventricles fill
and pump blood at the same time.
The natural resting heart rate is
controlled by a group of cells in the right atrium which act as a
pacemaker.
Know that there are four main chambers of the heart
(left and right atria and ventricles) to pump the blood around and the associated control valves which only allow flow
in one direction.
See the diagram of the heart above/below where the important
parts of the organ are labelled and the white arrows show the direction of
flow of the two circuits for:
(i) the oxygenated blood from the
lungs to the rest of the
body (the organs etc.)
and (ii) the deoxygenated blood to the lungs.
Note: For visual simplification, note
that oxygenated blood is shown as bright red and deoxygenated blood as blue (even
though it is a dark red colour in reality!).
Repeated diagram for visual convenience
The mechanism by which the heart works
The blood flows from the heart to the organs,
including the lungs,
through arteries and returns through veins.
Blood is supplied to the heart by two
coronary arteries which branch from the base of the aorta - the largest
artery in the body.
The heart itself needs a good supply of
oxygen and glucose for lots of energy to keep the heart muscles continuously
working.
The four major blood vessels associated with the heart
are the pulmonary artery,
pulmonary vein, aorta, vena cava.
The aorta (main artery) -
transports oxygenated blood
from the left ventricle to the body.
The vena cava (main vein) -
transports the deoxygenated
blood flow from the body into the right atrium.
The pulmonary artery -
transports the
deoxygenated blood from the right ventricle to the lungs
The pulmonary vein - brings the
oxygenated blood to the heart from the lungs into the left atrium.
Flow and valve action:
The heart has valves to ensure the
blood only flows in the one correct direction.
When the ventricles
contract, the valves to the atria close and the valves to the blood
vessels open.
This prevents any reverse blood flow
Ventricles have thicker walls than
atria because they operate at a higher pressure to pump the blood further.
The left ventricle has a thicker wall than the right
ventricle because the muscle tissue must be stronger because it operates at
a higher blood pressure to pump blood around all of the body.
The right
ventricle muscle tissue is thinner because it only has to pump the blood to
the lungs.
The blood enters the two atria
(right atrium and left atrium, atria) of the heart from the vena carva and the
pulmonary vein.
The left atrium and ventricle pump oxygenated blood
from the lungs around the body (see diagram above).
The left atrium receives the oxygenated blood from the
lungs via the pulmonary vein and is pumped through the aorta to the rest of
the body. It passes into the left ventricle to be pumped around the body.
The right atrium and ventricle pump deoxygenated
blood
The right atrium of the heart receives the
deoxygenated blood from all of the body, entering the heart by the vena
cava.
The deoxygenated blood flows through the right ventricle which pumps
it to the lungs via the pulmonary artery to be oxygenated.
The basic sequence of heart function
is:
The heart relaxes and the blood
enters both atria.
The atria contract
at the same time forcing blood into the ventricles.
The ventricles
contract from the bottom upwards which forces blood out of the heart through the pulmonary artery and aorta.
The atria fill up again and the whole
cycle is repeated
The valves in
the heart ensure that blood flows in the correct
direction.
How is it, that normally the heart
can beat at a regular rate?
In the right atrium are a group of cells
that act as a pacemaker.
They control the heart beat by producing
tiny electrical impulses (signals) that spread into the surrounding muscle
cells causing them to contract.
If this group of cells are
malfunctioning leading to an irregular, and dangerous heartbeat, an
artificial pacemaker can be surgically implanted under the skin
and wired up to the heart.
This device produce tiny electrical
signals at the right frequency to generate a correct and regular
heartbeat.
The pumping rate of the heart
The cardiac output is the total
volume of blood pumped by a ventricle every minute.
It is calculated using the following
equation:
cardiac output (cm3/min)
= heart rate (beats/min) x stroke volume
(cm3)
Abbreviated rearrangements:
heart
rate = cardiac output / stroke volume and stroke volume =
cardiac output / heart rate
Your heart rate is the number of
beats per minute e.g. when you measure your pulse rate.
The stroke volume is the volume of
blood pumped by one ventricle every time it contracts.
Example questions
Q1 A person has a
heart rate of 60 beats/min and average stroke volume of 70 cm3.
Calculate the cardiac output.
cardiac output = heart
rate x stroke volume = 60 x 70 =
4200 cm3/min
Q2 An athlete
sprinter heart rate is 120 beats per minute and a cardiac output of
6000 cm3/min.
Calculate the athlete's
stroke volume.
stroke volume =
cardiac output / heart rate = 6000 / 120 =
50 cm3
Q3 The cardiac
output from a person is 3600 cm3/min.
If the person's stroke volume
is 60 cm3, what is the pulse rate?
heart rate beat = cardiac
output / stroke volume = 3600 / 60 =
60 beats/min
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3. The structure and function blood
vessels
The circulatory system operates by a network of
blood vessels that carry all the substances that the body wants, and
doesn't want, around the body to requisite locations.
The blood flows from the heart to arteries,
arterioles (smaller arteries), capillaries, venules (smaller veins),
veins and then returned to the heart - reminder diagram of the double
circulation system below.
There are three types of blood vessel and each is
designed ('adapted') for its particular function.
Arteries
Arteries transport (i) oxygenated blood
(except for the pulmonary artery)
from the heart to the tissues and organs of the body and (ii) deoxygenated blood away
from the heart to the lungs.
The arteries carry blood under high pressure
with a pulse,
so the artery walls need to be thick and strong with muscle
tissue-fibre but these blood vessels must be elastic too.
The thick walls are an adaptation for high
pressure flow.
The artery walls are relatively thick compared to the
size of the 'hole' the blood flows through.
The thick artery walls are not
permeable.
The 'hole' is called the lumen and
is small.
The artery walls are made of a combination of
thick layers of strong muscle cells AND elastic fibres
which allow flexibility i.e. allowing the artery walls to be
stretches and spring back when the pressure is relaxed - a
biological example of elasticity.
The arteries branch into the narrower
arterioles.
Capillaries
Capillaries exchange materials with tissues.
Arteries branch into arterioles which then branch
into numerous much thinner
capillaries.
The pressure falls in arteries and the pulse
disappears.
There are no valves in arteries.
In the organs, in fact in
all tissues, blood flows through very narrow, thin-walled blood vessels
called capillaries which branch out from the arteries-arterioles.
The network of capillaries in tissues art called
capillary beds.
The substances
needed by the cells in body tissues pass out of the
blood capillaries, and substances produced by the cells pass
into the blood, through the thin permeable walls of the capillaries - which are only
one cell
thick - thin wall adapted for efficient exchange of materials.
This ensures a short distance
and movement time for particles - fast
diffusion in and out - fast exchange between capillaries and
cells - sugars, minerals, amino acids, oxygen into
surrounding cells and carbon dioxide, urea and other waste products out of
cells.
The blood in capillaries
will slowly lose its dissolved oxygen.
The capillaries are the smallest
blood vessels, and although these fine blood tubes carrying blood are dispersed in
all the tissues of every organ, you can't see individual capillaries, but
they reach every cell.
The capillaries have
adapted to have large surface area to make exchange
of substances as fast and efficient as possible.
Capillaries are the main interface for
material exchange eg of sugars, amino acids and other nutrients, oxygen and
waste carbon dioxide.
Some capillaries are so fine
that blood cells cannot pass through them.
The blood flow through capillaries is the
slowest of any of the types of blood vessels. This is important
because it allows more time for the exchange of substances
through the capillary membranes - more efficient diffusion.
Capillaries eventually join up
to form wider blood vessels called venules which connect to veins (next section).
Veins
From the capillaries, the venules eventually join up to form
veins to carry deoxygenated blood back to the heart.
Blood flows at a lower pressure in the
veins compared to the blood pressure in the arteries and contain
valves to ensure the blood flows in the right direction (diagram
below).
The adaptation of a larger
diameter lumen offers the least flow resistance for the
returning blood in the veins (to the heart).
Veins return and transport (i) deoxygenated
blood from the tissues and organs to the heart AND (ii) convey oxygenated blood to the heart
from the lungs and exit the heart via the aorta arteries to the rest of the
body.
Veins have non-permeable thinner walls (operating at lower pressure) and
periodically have valves to prevent back-flow of blood.
The diagram above shows a cross-section of
a vein and the valve system to ensure one-way flow.
If the blood attempts to flow 'backwards',
the tissue flap valves close preventing 'back-flow' in the wrong
direction - another wonderful adaptation of biological
engineering!
Since the pressure in the veins is lower,
their walls don't have to be as thick and the lumen is bigger in
cross-sectional area.
The bigger lumen allows good blood flow
despite the lower pressure, but bits of tissue act as one-way valves
- best appreciated in the diagram above.
If the blood attempts to go in the 'wrong
direction' the 'flaps' of the valve close together and stop any
reverse flow happening.
The relative diameter, cross-section areas
and flow rates of blood vessels
The larger the cross-sectional area of a
blood vessel the average velocity of the blood decreases.
Therefore, blood flows more slowly through
capillaries than arteries or veins.
However, although capillaries are
relatively small in average diameter, their total
cross-sectional area is very large, so all the large blood flow
from the arteries is dispersed through them.
The slow flow through capillaries is
important because it allows more time for the exchange of
substances through the capillary membranes.
It also means that the mean blood pressure
is highest in the arteries because they are directly connected
to the heart (closest).
In fact the total cross-sectional area of
the capillaries is greater than that of the arteries which
actually causes a fall in blood pressure.
Summary note
on 'connections'
Strictly speaking, arteries and veins do not
connect directly with capillaries. Arteries branch into arterioles
which have a much smaller diameter. Arterioles then branch out into
the even smaller capillaries. The capillaries then connect to
venules which join together to form veins.
Initially the blood vessels get narrower
conveying fresh blood, nutrients and oxygen and then get larger
conveying deoxygenated blood and waste products away from the
tissues.
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4. What's in the blood?
Blood is a tissue
- it is a mixture of cells (e.g. red and white), solutes (dissolved
substances) and a liquid (mainly water).
The liquid is called plasma and is straw coloured
when separated from the red blood cells.
Know the structure and function of the following
parts of the blood.
Red blood cells
Red blood cells carry oxygen from the lungs to
every living cell of the body via the blood stream.
It's the red blood cells that give blood
its red colour and unlike white blood cells, they have no nucleus.
Red blood cells
are a squashed from both sides 'doughnut' shape (biconcave disc) to give them a
large surface area for the iron
containing haemoglobin molecules to capture the oxygen.
The large surface area gives efficient
absorption of oxygen to combine with the haemoglobin molecules
by the reversible reaction:
haemoglobin
+ oxygen
oxyhaemoglobin (bright red
pigment molecule)
The oxygen molecule is weakly bonded to
the haemoglobin molecule by a reversible reaction, so it
is easily released to be consumed in respiration.
A high oxygen concentration favours the
formation of oxyhaemoglobin (reaction moves to right), and low
oxygen concentration favours its dissociation to free oxygen
(reaction moves to left) - this follows from Le Chatelier's
Principle you learning in chemistry about reversible
reactions and chemical equilibrium. See GCSE chemistry notes:
Reversible Reactions
and
Reversible reactions and
chemical equilibrium
The red
blood cells do not have a nucleus, allowing more space for
haemoglobin molecules.
Note the four red blood cell adaptations:
(i) the haemoglobin molecule is adapted to
carry the oxygen molecule O2 for cellular respiration
in all the body's tissues,
(ii) the biconcave disc shape gives a large surface area
/ volume ratio for absorbing oxygen molecules - increases
efficiency of diffusion of oxygen in and out of cells and
reduces distance to centre of cell,
(iii) no nucleus - extra space
for oxygen carrying haemoglobin molecules - nucleus not required,
(iv) red blood
cells are very small and flexible and can easily pass through tiny
capillaries.
In the lungs the oxygen molecule attaches
itself to the iron atom at the centre of the large complex
haemoglobin molecule to form oxyhaemoglobin.
The process is reversed in
the body tissues to release oxygen for cell respiration (equation above).
If we don't have
enough iron in our diet we can suffer from anaemia, a potentially
serious condition where the blood can't carry enough oxygen needed for
all the respiration demands of the cells.
White blood cells
White blood cells have a nucleus and are part of the body's
immune system to fight diseases.
Some white cells can change shape to engulf
and destroy potentially harmful microorganisms.
These cells are called phagocytes
and their action is called phagocytosis.
Other types of white blood cells called lymphocytes
and have variety of functions.
Type B lymphocytes produce antibodies
(type of protein) to inhibit and fight the action of invasive
microorganisms e.g. harmful bacteria.
Some white blood cells produce antitoxins to counteract
the effect of
toxins produced by microorganisms.
When your body is subjected to an infection,
your white cells multiply to fight it - giving you a high white
blood cell count.
Measurement of your white blood cell count is
an important diagnostic indicator of the state of your body's
defences.
Having a low white blood cell
count increases your risk of infection, but having a very high white
blood cell count may mean you have an infection or even a more
serious condition like a blood cancer e.g. leukaemia.
Platelets
Platelets do not have a nucleus.
Blood platelets are ever present small
fragments of cells that help to clot blood and cover over an open
wound in tissues e.g. cut in the skin.
This reduces blood loss from bleeding AND
prevents potentially harmful bacteria (microorganisms) getting into your body via the
blood system.
If this didn't happen, blood would just keep
pouring out of your body!
If your platelet concentration is low you may suffer
from excessive bleeding (blood loss) and bruising.
Plasma
Blood plasma is the straw coloured (pale
yellow) liquid fluid that carries everything in the blood, so its
the major transportation fluid in the body.
Plasma looks straw coloured when separated
from the red blood cells.
The constituents of blood can be separated
in a centrifuge - high speed rotation of a container (of liquid
mixture), that separates substances out by sedimentation, with the
most dense material moving the most outwards in the radial
direction.
About 55% of blood is plasma, which itself
is 90% water.
Blood plasma carries everything needed for
every cell in the body:
(i)
red cells (oxygen), white cells (and the antibodies and antitoxins
they produce) and
platelets,
(ii) nutrients e.g. amino acid and sugar
products from the digestive
system - the soluble products of digestion from the gut,
(iii) waste products (carbon dioxide from
the organs to the lungs, urea from the
liver to the kidneys where it is removed in urine),
(iv) proteins for enzymes and tissue
growth
(v) control system hormones ('chemical
messengers') from the glands to
their target and activate the functions of organs.
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5. Cardiovascular disease
(CVD), heart attacks, strokes
and treatments
Cardiovascular disease is a medical term to
describe diseases of the heart or blood vessels.
CVD is usually associated with the narrowing
and blocking of the blood vessels (arteries) that convey oxygenated
blood away from the heart.
Arteries become narrowed due to the build up
of fatty deposits on the lining of damaged artery walls - often the
damage is caused by high blood pressure. The fatty deposits can also
cause blood clots.
One such example is coronary heart disease.
Heart disease is one of the major causes of
death in the UK and other developed countries.
Cholesterol is made in the liver and
transported in the blood. Cholesterol is important and we need a
small amount of blood cholesterol because the body uses it to: build
the structure of cell membranes, make hormones like oestrogen,
testosterone and adrenal hormones. Cholesterol also helps your
metabolism work efficiently is essential for your body to produce
vitamin D.
However, high levels of cholesterol are
associated with heart disease.
Smoking is also very bad for you, and not just for causing lung
cancer.
When breathed in, the chemicals in tobacco smoke harm your blood
cells.
They also can damage the function of your heart and the
structure and function of your blood vessels.
This damage increases your risk of atherosclerosis - a disease
in which a waxy substance called plaque builds up in the
arteries.
Coronary heart
disease
Coronary heart disease is when the coronary
arteries that supply blood to heart muscle become blocked with
layers of cholesterol, fats and other materials deposited on the
inside of artery walls.
This effectively narrows the arteries
restricting the blood flow.
This decreased blood flow means less oxygen
is carried to the heart muscles.
A lack of oxygen to work the heart muscles can
lead to a heart attack.
There is also an increased risk of blood clots
forming - these can block the flow of blood completely, greatly
increasing the chance of a heart attack.
Strokes
A stroke occurs when a narrowed artery that
supplies blood to the brain, becomes blocked by a blood clot.
This deprives the brain of oxygen leading to a
life-threatening situation..
Without rapid treatment, the results can be
disastrous - death, injury to the brain (e.g. memory) and central
nervous system (paralysis and physical coordination).
Recovery can be prolonged and often never
complete.
Treating cardiovascular diseases
If the heart or blood vessels are severely
damaged major surgery might be required.
Surgical techniques and other procedures
are described in a later section.
Use of Stents and bypass
surgery
Coronary heart disease can be treated with
stents - see diagram below.
Stents are very thin-walled wire mesh tubes inserted
into arteries to widen them and keep them open to ensure a good supply of
blood to the heart muscles.
A good blood flow keeps the heart beating
regularly and so keeps you alive, particularly for people suffering
from cardiovascular disease!
1. A normal artery,
no hardened fat deposits (plaque) on the inner surface of the artery
wall, so there is no
restriction of blood flow away from the heart.
2. Fatty deposits
(plaque) can build up on the
inside wall of the artery restricting blood flow.
The cross-section
of the lumen is reduced e.g. the equivalent of narrowing a 'pipe'
and reducing blood flow - reducing the rate of oxygen transfer to
heart muscles.
Cholesterol is a fatty substance the body
needs to build cell membranes.
However, too much of fatty substances,
including 'bad' LDL cholesterol, in your blood stream can lead
to an excessive and dangerous build up of fatty deposits on the
walls of the arteries.
The fatty deposits harden over time to
form lots of atheromas which restricts blood flow.
These bits of atheromas damage the blood
vessel and if one breaks off it can cause a blood clot.
This damage to the arteries causes high
blood pressure with increased risk of heart attacks, angina and
strokes.
Thick fat deposits can block a blood
vessel or cause blood clots to form which can block the flow of
blood completely.
If this involves an artery supply blood to the
heart muscle, the heart muscle is deprived of oxygen and
glucose and can
cause a heart attack.
There is less energy available for the
heart muscles to contract.
Such blockages can also deprive the brain
of oxygen causing a stroke.
3. With
the help of a catheter, whose position is monitored by X-rays, a very thin-walled tubular
bare metal stent is
inserted that pushes against the inside artery wall. The stent squashes the
fat deposits and so widening the artery to allow normal blood flow -
increases the cross-section area of the artery, so increasing flow
rate - hopefully bringing the oxygen supply to the heart back to normal!
By allowing normal blood flow rate, stents are a very effective way of
lowering the risk of a heart attack or a stroke for people suffering from
coronary heart disease.
After the operation, recovery time is
short and the stents have a long working life of many years.
Repeat surgery might be necessary if the
artery narrows again.
However, such procedures are not without
risk -
(i) there may be complications during
the operation (including, ironically, a heart attack),
(ii) there is always a risk of
infection with any surgical procedure, and,
(iii) a risk of a blood clot
developing in the patient near the stent - known as a thrombosis. This restricts blood flow and possibly
stopping the flow - not good!
NOTE An alternative stent
A
drug-eluting stent (DES) is a peripheral or coronary stent (a
scaffold) placed into narrowed, diseased peripheral or coronary
arteries that slowly releases a drug to block cell
proliferation.
This prevents the
artery from getting narrowed by the growth of tissue cells.
4. Bypass surgery
There
is little risk in having stents implanted, but the fatty deposits
can build up again.
However, if the coronary artery is too
badly damaged, bypass surgery must be used.
The blood vessels may be so badly blocked
that stents won't work.
In this situation, the blood flow to the
heart can be improved with coronary bypass surgery.
A healthy blood vessel (e.g. a vein in the
leg) is transplanted and surgically inserted and connected to
bypass the blocked damage artery.
Bypass surgery has the advantage of no
rejection, but still carries risks of any major surgery.
It is a more invasive procedure than
having stents fitted, requires a longer hospital stay and
requires a longer recovery time.
There is a lower chance that repeat bypass
surgery would be necessary, whereas with stents, this may be
needed if the artery narrows again.
Cholesterol and the use of statins
Cholesterol is an important lipid that is
essential for the functioning of your body.
BUT, there are two types of cholesterol:
(i) Too much of LDL cholesterol
('bad cholesterol') can cause health issues.
Too much LDL cholesterol in your
bloodstream contributes to fatty deposits on the inner
walls of the arteries, restricting blood flow, causing
coronary hear disease (see diagram in stents section).
(ii) 'Good cholesterol', known as
HDL cholesterol, helps remove other forms of cholesterol
from your bloodstream.
The ratio of LDL to HDL seems to
be an important factor to have healthy levels of the
different types of cholesterol.
Statins are drugs used to treat to high
a level of bad cholesterol
Statins slow down the rate at which
fatty deposits are formed on artery walls.
For some patients, they are now
considered as life-long medication.
Advantages of statins
(i) Statins have been
clinically proven to reduce the level of 'bad cholesterol'
(LDL cholesterol) in
the bloodstream. This in turns slows down the rate at which fat
is deposited on the walls of the arteries. This reduces the
risk of strokes, heart attacks and suffering from
angina and coronary heart disease and.
Angina is chest pain
caused by reduced blood flow to the heart muscles.
(ii) Statins can increase the
amount of 'good cholesterol' (HDL cholesterol) in
the bloodstream as well as reducing the level of 'bad
cholesterol' (LDL cholesterol) - all helping the
benefits described above.
(iii) There has been some evidence
that statins may prevent other diseases.
I can't find out anything about
(iii), but research references to
Alzheimer's disease and
motor neurone disease
Disadvantages of statins
(i) There are adverse side effects
from taking statins e.g. headaches,
diarrhoea and
aching muscle fatigue
and damage. In extreme cases you can suffer kidney
failure, liver damage and memory loss.
(ii) The artery can age and narrow
over time because stints can cause irritation and make
scar tissue grow, therefore a CVD patient may have to
take extra medication to stop blood clots forming on the
stent.
(iii) Statins are a drug that must
be taken regularly over a long period of time and the
patient should ensure they don't forget to take their
medication.
(iv) It takes some time for
statins to take effect in reducing your cholesterol
level, you need to be a patient-patient!
Other drugs used to treat
cardiovascular disease conditions
Anticoagulants - advantages
and disadvantages
Anticoagulant drugs like Warfarin are prescribed to reduce the risk of
blood clots forming with patients suffering from
cardiovascular disease.
Anticoagulants allow the blood to flow
more freely to vital organs and reduce the risks of
heart attacks and strokes.
BUT, a disadvantage, there is a risk of excessive
bleeding if you cut yourself in an accident.
If the wound is severe, there is
the danger of losing a significant amount of blood
leading to a life threatening situation. There is also a
danger, that the injury, combined with taking an
anticoagulant, that internal bleeding occurs.
Antihypertensives
- advantages and disadvantages
Antihypertensives are
medications prescribed to reduce blood pressure.
They help prevent damage to blood vessel due to
excess higher blood pressure and reduce the risk of excessive
fatty deposits forming on the arteries.
There are different types of
antihypertensives, that help reduce blood pressure in
different ways e.g.
ACE inhibitors relax the
blood vessels to ease blood flow.
Beta blockers cause the
heart to beat more slowly and less forcefully.
Diuretics help remove
excess water.
However, they can have side
effects - dizziness, fainting, headaches, feeling
sick - looking at the information on my own blood
pressure tablets, there is quite a long list of
possible side-effects !!
Other possible CVD treatments
Tissue replacement
A section of blocked blood vessel
can be replaced by taking a section of healthy blood
vessel and bypassing the affected section.
This is called coronary bypass
surgery.
Alternatives to statins and other
CVD medications - lifestyle
'action'
You can make lifestyle changes to
reduce your risk of developing cardiovascular disease
(CVD) AND such changes would be advised as part of your
treatment if you already suffer from CVD - to reduce the
risk of further heart attacks or strokes.
Lifestyle changes that can reduce
your cholesterol level and cardiovascular disease
risk include:
Eating a healthy balanced diet -
low in saturated fat, plenty of wholemeal grains
(cereal or bread). fruit and vegetables etc.
Saturated fat can increase
blood cholesterol levels,
Exercising
regularly - doesn't have to be excessive - at 74 in 2020,
I do, weather permitting), a brisk walk every day for a minimum of
an hour! (now the regular Covid-19 pandemic routine!)
Maintaining a healthy weight -
lose excess weight with diet and exercise.
Limiting the amount of alcohol you
drink, stop smoking - not good for lungs, therefore not
good for your vital oxygen circulation!
Just like type 2 diabetes, you
can do a lot for yourself!
AND there are NO NEGATIVE
SIDE-EFFECTS !!!!!
TOP OF PAGE
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6.
More on
scientific developments to help treat cardiovascular disease and emergency
situations!
Appreciate that modern developments in
biomedical and technological research enable us to help when the circulatory
system is not working well.
Surgical techniques
Transplanted donated heart or an artificial heart
In the case of a total patient heart
failure and severe cardiovascular disease, surgeons may perform a heart transplant or even a combined
heart and lung transplant if the lungs are diseased to.
The donor organs must come
from other people who have recently died.
However, donor organs might
not be immediately available, or they are not for some other
medical reason not the best option, doctors may fit an
artificial heart.
Even after the heart
transplant operation, the new heart does not always start
pumping the blood immediately - stimulation might be required.
Also, the patient has to take suppressive drugs
(immunosuppressant drugs) to stop the body
rejecting the 'foreign' tissue of the new heart (rejection) - these drugs
can have side effects and the patient more vulnerable to
infection.
Any major surgery like a hear
transplant operation carries its own risk of bleeding, blood
clots and infection from microorganisms including some
potentially fatal bacterial infections like MRSA.
A transplant can greatly
improve the quality of life (a factor that applies to all
these surgical techniques), BUT the disadvantages are:
it requires major risky
intrusive surgery - unforeseen complications or infection,
patients must take
immunosuppressive drugs for the rest of their life,
the application of
anti-rejection drugs - may cause a greater infection risk
because the body's natural immune defence system is
suppressed,
and, sadly, a shortage of
donors - does require the death of somebody and permission
to use their heart.
BUT, we are balancing
risks versus survival.
Artificial hearts are machines
inserted by surgery into a patients chest to pump the blood around the
circulatory system, ideally temporarily, until a donor heart can be found.
These mechanical devices are
able to pump blood around a person who's heart has failed.
They are usually a temporary
fix to keep the patient alive until a donor heart can be found.
They can also be used to help
a patient recover while the heart is rested and healing.
Artificial hearts can be
permanent solution, with the advantage of reducing the need for
a donor heart.
Artificial hearts have an advantage of
being much less likely to be
rejected by the body, as donor hearts can be, because the immune system
doesn't recognise the plastic or metal parts as an invasive ('foreign') microorganism to
be attacked - like it might with living tissue.
However, any major surgery
in fitting an artificial heart or transplant carries risks eg from bleeding, infection.
Also, artificial heart machines are
subject to wear and tear themselves and are not as efficient as a real heart
and there are still risks from heart attacks and strokes.
Parts of the heart machine
can wear out or the electric motor fail.
The blood flow is not as
smooth causing blood clots leading to strokes.
Heart patients have to
take drugs to thin their blood to make sure this doesn't
happen.
Unfortunately, such drugs
cause problems if the patient has an accident and excessive
bleeding occurs.
I'm afraid it just
another case of medical treatment where you are balancing
risks ('bad' outcomes') versus 'good' outcomes!
Surgical techniques - heart valve
replacement
Heart valves can be damaged or
weakened by heart attacks, infection or just old age - you can't
stop aging processes!
The damage may cause the valve
tissue to stiffen and prevent the valve from opening and closing
properly.
If the valve leaks, blood can
flow in the wrong direction instead of always going forward in
the right direction.
This results in poor
circulation of blood, which causes its own problems.
Tiredness and lack of energy and breathlessness are symptoms
of leaky valves.
Poor circulation can
cause pain in the legs, feet, arms, and hands.
Cold hands
and feet may ache or throb.
When the blood does
not circulate correctly, oxygen and nutrients cannot reach
tissues effectively, which can result in stiffness and
cramping.
Badly damaged valves can be
replaced with artificial valves or other animal biological
valves.
Replacement valves can be
taken from other humans or animals such as cows or pigs.
Defective heart valves can be
replaced by m an-made artificial mechanical valves that work in the same
mechanical way as a real heart and the
surgery is much simpler and less risky, but still risks of blood clot
problems.
Replacing a valve is a less
complicated surgery, so less drastic, and therefore less risky,
than doing a full heart transplant operation.
Advantages of artificial
valves:
No rejection
Disadvantages of artificial
valves:
They can damage red blood
cells. Patients need anti-clotting agents because of blood clot
risk.
Advantages of biological
valves:
Red blood cells not damaged.
Disadvantages of biological
valves:
Biological valves can harden
and need replacing.
Artificial pacemakers
For some patients the problem is
an inability of their body to control the heart rate.
The steady beat of the
contraction and relaxation of the heart muscles is obviously
important.
Artificial pacemakers can be
fitted under the skin and a wire connects it to a vein to the right
atrium.
The pacemaker sends electrical
impulses to stimulate and control the heartbeat.
Advantage of artificial
pacemakers:
No major surgery is required.
Disadvantage of artificial
pacemakers:
Our immune system may
reject the pacemaker ('foreign' materials) and may need
replacing.
Use of artificial blood
Blood loss from a serious
accident can lead to death indirectly - loss of available blood means less
oxygen and nutrients are getting the cells of all the tissues and organs -
not good!
If you can keep the volume of
blood 'topped up' life can be preserved for sometime.
Therefore, artificial
blood can be used temporarily as a blood substitute when a patient has lost
a lot of blood, but, as long as the heart can still pump the diluted fluid
(diluted plasma) containing the remaining red blood cells around the
circulatory system.
The simplest artificial blood
(blood substitute) is a saline solution - an aqueous
sodium chloride salt solution NaCl(aq).
Its safe to use, but must NOT
contain air bubbles, and it can keep people alive even if they
have lost 2/3 rds of their red blood cells!
This can now give enough time
e.g. to get the patient to hospital and prepared for surgery if
necessary and also time for the body to produce more red blood
cells.
This can be followed up by a
blood transfusion if the patient cannot make enough red blood cells in time!
Research is being done to
develop artificial blood containing molecules that can carry oxygen just
like haemoglobin in red blood cells, but limited progress so far.
This is an ideal solution, to
produce a product that can temporarily act like the haemoglobin
molecules to transport oxygen to the bodies cells - a sort of
haemoglobin replacement.
This would avoid the need for
a blood transfusion, and presumably the body would gradually
produce enough red blood cells to allow the circulatory systems
to work normally.
TOP OF PAGE
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Possible practical work help develop your skills and understanding
the human circulatory system:
dissection
of the heart
use software simulations of the work of the heart and blood
vessels
observation of arteries and veins from slides
observation of
blood smears
observation of valves in veins preventing backflow of blood
using the ‘athletic’ arm / prominent vein
using sensors to measure blood
pressure before, during and after exercise
Typical learning objectives for
blood and blood system
-
Know and understand that arteries have
thick walls containing muscle and elastic fibres.
-
The arteries carry blood under high
pressure, so their walls need to be thick and strong with muscle
tissue-fibre but these blood vessels must be elastic too,
-
Know that veins have thinner walls
(operating at lower pressure) and periodically have valves to prevent
back-flow of blood.
-
Know and understand that if arteries begin to narrow and restrict blood flow
stents are used to keep them open.
-
You should understand the importance of stents,
particularly with reference to the coronary arteries.
-
Stents are narrow tubes capable
of supplying a blood flow equivalent to an artery.
-
Fatty deposits building up on
the inner surface of the arteries that supply blood to the heart muscles can
cause coronary heart disease.
-
These fatty deposits restrict
the blood flow increasing blood pressure and causing heart attacks.
-
To combat this potential fatal
condition you can insert stents into the arteries to increase blood flow to
the heart muscles.
-
However, there are some
drawbacks eg the stents can irritate the artery lining and cause the growth
of scar tissue and drugs must be taken to avoid blood clots forming in the
stent itself.
-
Know that in the organs, blood flows through very narrow,
thin-walled blood vessels called capillaries which branch out from the arteries.
-
Know that substances
needed by the cells in body tissues pass out of the
blood, and substances produced by the cells pass
into the blood, through the walls of the capillaries.
-
The capillaries are the smallest
blood vessels, and these fine blood tubes carrying blood are dispersed in
all the tissues of every organ.
-
Capillaries are the main interface for
material exchange eg of sugars, amino acids and other nutrients, oxygen and
waste carbon dioxide.
-
Some capillaries are so fine
that blood cells cannot pass through them.
-
The walls of capillaries are
thin with permeable walls only one cell thick, allowing rapid diffusion of
substances into the cells (sugars, minerals, amino acids, oxygen) or out of
surrounding cells (carbon dioxide, urea and other waste products).
-
Capillaries eventually join up
to form wider blood vessels called veins. The blood flows at a lower
pressure in the veins compared to the blood pressure in the arteries and
contain valves to ensure the blood flows in the right direction.
-
Know and understand that blood is a tissue and
consists of a fluid called plasma in which red blood cells, white blood
cells, and platelets are suspended.
-
Blood is considered an irregular
tissue because it doesn't physically support or connect things but it does
involve groups of cells performing particular functions.
-
Plasma is pale straw-coloured
liquid which transports everything around the body
-
What is the function of blood
plasma? .... What does it do? ...
-
Know and understand
that blood plasma
transports:
-
carbon dioxide from the organs to the lungs,
-
soluble products
of digestion from the small intestine to other organs eg glucose, amino
acids, mineral salt ions etc.
-
urea from the liver
to the kidney prior to excretion in urine,
-
hormones which control the
function of various organs and their associated chemical processes in the
body,
-
and obviously, as already
mentioned, red blood cells, white blood cells and platelets are constantly
being carried around the body as well associated oxygen as oxyhaemoglobin
and antibodies and antitoxins produced by the white blood cells.
-
Know and understand that red blood cells transport
oxygen from the lungs to the organs.
-
What do red blood cells do? What
is their function? Know that red blood cells have no nucleus but a large
surface area to chemically absorb oxygen.
-
Know that red blood cells are packed with a red pigment called haemoglobin
which readily combines with oxygen
-
Know that in the lungs haemoglobin
combines with oxygen to form oxyhaemoglobin.
-
Know that in other organs and
all body tissue oxyhaemoglobin splits up into
haemoglobin and oxygen for cell respiration.
-
Know that white blood cells have a nucleus.
What do white blood cells do? What is their function?
-
Know that white blood cells form part of
the body’s defence system against microorganisms eg harmful bacteria.
-
White blood cells can attack and
destroy harmful 'foreign' microorganisms.
-
White blood cells can produce
antibodies to fight microorganisms.
-
White blood cells produce
antitoxins to combat the effect of waste toxins produced by microorganisms.
-
Know that platelets are small fragments of cells.
-
Know that platelets have no
nucleus.
-
Know and understand that platelets help blood to clot at the site of
a wound and a lack of platelets is potentially dangerous from excessive bleeding
and bruising.
-
The clotting action of platelets
allows a skin to form over a wound which hardens into a scab and this
prevents infection of the wound by harmful bacteria or any other
microorganism.
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