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THE HUMAN CIRCULATORY
SYSTEM
Rosalie Crawford - Veronica Revel
Fondazione Liceo Linguistico Courmayeur
WHY???
• Why are we told not to go swimming for an hour
after eating?
• Why is it important to warm up before doing any
sport?
• Why do we turn red when we’re embarassed?
• Why do we go pale when frightened?
BECAUSE…
• the blood flow through our bodies is under
micromanagement, adapting and moving
according to internal and external events.
Circulation
The human circulatory or
cardiovascular system is
composed of :
THE HEART, situated on the left
side of the thorax and
A NETWORK OF BLOOD
VESSELS, of varying dimension
(arteries, veins and capillaries),
through which blood flows.
The heart pumps blood so that it
flows into increasingly smaller
blood vessels as far as single
cells.
http://www.innerbody.com/anat
omy/cardiovascular/upper-torso
Composition of our blood
Blood is composed of……
 Plasma (55%), which is chiefly water where nutrients,
waste products, ions, antibodies, hormones, enzymes,
plasma proteins and other substances are dissolved or
suspended.
 Red blood cells or erythrocytes (45%) which transport
oxygen to all the tissues of the body. There are about 25
trillion (25 x 10¹²) red blood cells in the adult human body.
Because red blood cells, lacking a nucleaus, cannot repair
themselves, their life span is short, about 120-130 days. At
this moment in our bodies, about 2 million red blood cells
are dying per second!
Blood is composed of……
• White blood cells or leukocytes and platelets (<1%)
which defend the body against invaders such as viruses
and bacteria. They are colourless, contain no hemoglobin,
have a nucleus and are often destroyed in the course of
fighting infection. New white blood cells are formed
constantly in the spleen, in bone marrow and in certain
other tissues.
• Platelets play an essential role in initiating the clotting of
blood and in plugging breaks in the blood vessels.
The function of blood
Transports Regulates
-nourishment
-pH levels
from digestion and
hormones from
glands.
-oxygen from the
lungs to body
tissue
-carbon dioxide
from body tissue
to the lungs
-disease fighting
substances to the
tissue and waste
to the kidneys
Protects
-the immune
system
-blood and pulse
--emostasi
pressure (heart
rate)
-body
temperature
- water and
saline levels
The structure of blood vessels
Types of blood vessels
http://www.bbc.co.uk/schools/gcsebitesize/pe/appliedanatomy/0_anatomy_circ
ulatorysys_rev1.shtml
Arteries
Carry oxygenated blood away from the heart (except for the pulmonary
artery which goes to the lungs)
Have thick muscular walls
Have small passageways for blood (internal lumen)
Contain blood under high pressure
Arterioles
Smaller arteries, have thinner walls and a reduced layer of muscle
Veins
Carry de-oxygenated blood to the heart (except for the pulmonary vein
which goes from the lungs to the heart)
Have thin walls
Have larger internal lumen
Contain blood under low pressure
Have valves to prevent blood flowing backwards
Types of blood vessels
Capillaries
Found in the muscles and lungs
Microscopic – one cell thick
Very low blood pressure
Where gas exchange takes place. Oxygen passes through the capillary wall and
into the tissues, carbon dioxide passes from the tissues into the blood
DID YOU KNOW THAT…?
» The total length of capillaries in a
human adult is more than 80,000
kilometres.
» No cell in the human body is farther
than 130 micrometres – a distance
short enough for rapid diffusion –
from a capillary.
» Even the cells in the walls of the large
veins and arteries depend on
capillaries for their blood supply, as
do the cells of the heart itself.
Anatomy of the human heart and systematic circulation
Blood returning from the
systematic
circulation
through the superior and
inferior venae cavae enters
the right atrium and passes to
the right ventricle, which
propels it through the
pulmonary arteries to the
lungs, where it is oxygenated.
Blood from the lungs enters
the left atrium through the
pulmonary veins, passes to
the left ventricle and then is
pumped through the aorta to
the body tissues.
http://www.bbc.co.uk/schools/gcsebitesize/pe/a
ppliedanatomy/0_anatomy_circulatorysys_rev2.sh
tml
Regulation of heartbeat
• The contraction of cardiac muscle is initiated by a special
area, the sinoatrial node, located in the right atrium.
Acting as a pacemaker, this region of tissue can
spontaneously initiate its own electrical impulse.
• Intercalated disks conduct electrical impulses across the
heart to the right atrium (the atrioventricular node).
From here, impulses are carried by special muscle fibres
(bundle of His) to the walls of the right and left ventricles,
which then contract almost simultaneously.
• As a consequence, there is a delay between the atrial and
ventricular contractions, ensuring that the atrial beat is
completed before the beat of the ventricles begins.
Regulation of heartbeat
• When impulses travel across the heart, electric current
generated on the heart’s surface is transmitted to body
fluids and thus to the body surface. Electrodes placed on
the skin and connected to a recording instrument can
measure the heart’s ability to initiate and transmit
impulses.The output is an electrocardiogram.
• Parasympathetic stimulation has a slowing effect on the
pacemaker and therefore decreases the rate of heartbeat.
• Sympathetic nerves stimulate the pacemaker, increasing
the rate of heartbeat.
• Adrenaline affects the heart in the same way as stimulation
by the sympathetic nerves.
Blood flow
• As blood flows through the circulatory system, its pressure
gradually drops as a consequence of the resistance of
arterioles and capillaries. Thus, blood pressure is not the
same throughout the body. It is highest in the aorta and
other large systematic arteries, much lower in the veins
and lowest in the right atrium.
• Veins, with their relatively thin walls and large diameters,
offer little resistance to flow and allow blood to return to
the heart despite its low pressure.
• Valves in the veins prevent backflow.
• The return of blood to the heart is enhanced by the
contractions of skeletal muscles
How is blood pressure measured?
Your blood pressure is measured with a
device that uses the pressure in the
artery to push up a coloumn of mercury
and registers two numbers.
The first number, which is higher, is
taken when the heart beats during the
systole phase. The second number is
taken when the heart relaxes during the
diastole phase. A column of mercury
rises and falls with the beat of the heart.
The height of the column is measured in
millimeters. Normal blood pressure in a
young adult is about 120 mm of mercury
when the ventricles are contracting
(systolic pressure) and 80 mm when the
ventricles relax (diastolic pressure).
The greater the blood pressure, the
greater the rate of flow. Similarly, the
larger the diameter of the vessel, the
larger the volume of blood that can flow
through it.
Diseases of the heart and blood vessels
Cardiovascular diseases cause 18.65%
of all deaths in Italy.
A heart attack is the result of an
insufficient supply of blood (ischemia)
to an area of heart muscle. A heart
attack can be caused by a blood clot – a
thrombus – that forms in the
coronary arteries, the blood vessels
that supply the heart itself. Or it can be
caused by a wandering clot – an
embolus – that forms elsewhere in the
body and travels to the heart and
lodges in a coronary artery. Thirdly, by
a blockage of a coronary artery due to
artherosclerosis
Look at these statistics from the
World Health Organization
http://www.nationmaster.com/graph/
hea_hea_dis_dea-health-heartdisease-death
•
Diseases of the heart and blood
vessels
• Angina pectoris is a similar
condition whose symptoms, like
those of a heart attack, are pain
in the centre of the chest,
between the shoulder blades of
the back and often in the left
arm and shoulder.
• A stroke is caused by
interference with the blood
supply to the brain which may
be caused by a thrombus, an
embolus or the bursting of a
blood vessel in the brain.
• Atherosclerosis contributes to
both heart attacks and strokes.
This disease occurs when the
linings of the arteries thicken
due to the accumulation of
abnormal smooth muscle cells,
and their inner surfaces become
roughened by deposits of
cholesterol, fibrin and cellular
debris.
• Hypertension- chronically
increased arterial blood
pressure-affects 15 million
people in Italy. It places
additional strain on the arterial
walls and increases the chances
of emboli.
Regulation of blood cholesterol
How does cholesterol cause heart
attacks?
The key organ in cholesterol regulation
is the liver which not only
synthesizes needed cholesterol
from fatty acids but also degrades
excess cholesterol circulating in the
blood as a result of a diet rich in
meat, cheese and egg yolks. Like
other lipids, it is insoluble in
plasma. Low density lipoproteins
(LDLs) function as the delivery
trucks, transporting cholesterol to
various destinations in the body,
including the liver and hormone
synthesizing organs.
Regulation of blood cholesterol
• Normally the system is in
balance. However, a
number of factiors can
throw it out of balance.
• If the dietary intake of
cholestreol is high, the
liver becomes flooded and
cannot degrade all of the
excess. If the quantities of
LDLs taken up by the cells
are high – a sign that blood
cholesterol levels are high
– the cells stop
synthesizing cholesterol.
• When the quantities of
circulating LDLs are
greater than can be
absorbed by the liver and
hormone-synthesizing
organs, they are taken up
by cells lining the arteries
supplying the heart. This
can lead eventually to a
total blockage of an artery
and thus to a heart attack.