Transcript The Circulatory System

The Circulatory System
Unit III
The Circulatory System
• Circulation, or transportation of blood is a
vital function; life can’t go on without it
• The Circulatory System is made up of:
– The heart
– The blood vessels
– The blood
Blood
• Physical Characteristics: red, sticky, distinctive
taste/smell, dries quickly
• Sometimes called ‘life stream’ – it flows through
our bodies carrying necessities of life (oxygen,
nutrients, chemical messengers) to the cells, as
well as transporting away the wastes produced
by the cells (carbon dioxide, heat, extra water)
• It only takes your blood 30 seconds to circulate
through your entire body
• The average human body contains about
5 litres of blood:
– 55% is made up of plasma (straw coloured
fluid which is 90% water and carries many
dissolved substances)
– 45% is solids (red and white blood cells, and
platelets)
Red Blood Cells
• Called erythrocytes
• Produced in bone marrow
• Round with a hollow depression in each
side
• It’s shape gives it a large surface area,
while remaining small, allowing it to pass
through very tiny blood vessels
• No nucleus
– An unusual characteristic for cells; they
start off having one, but as the cells mature
their nucleus shrinks and disintegrates
• Oxygen carriers of the body
• Contain haemoglobin which is a
compound containing iron
• The haemoglobin molecule can combine
with four oxygen molecules creating the
bright red compound called
oxyhaemoglobin
– It releases oxygen when your body needs it
• Red blood cells are responsible for a lot of
work, so they wear out quickly – they only
last 3-4 months
• Old red blood cells are broken down in the
liver and spleen and the iron in them is
returned to the bone marrow for new cells
to use
– The replacement rate is 1-2 million cells per
second
White Blood Cells
• Called leukocytes
• Contain a nucleus
• Colorless, and although are usually
spherical they can change shape
• Larger than red blood cells, but are far
less numerous
• There is 1 white blood cell for every 600
red blood cells
• Most are produced in bone marrow, but
some are also produced in lymph tissue at
several sites in the body
• Several types of white blood cells
• Function – to protect the body from
infection and disease-causing organisms
(pathogens)
• All white blood cells possess the following
characteristics which help them perform
their function:
– Amoeboid Action: can move independently;
can change shape and squeeze through
tiny pores to move into and out of body
tissue
– Phagocytes – can surround bacteria and
digest their toxic proteins; can join together in
order to surround large products which must
be removed from the body
– Chemical Properties – react to charged
particles, proteins and other chemicals which
may be present in areas of injury and
inflammation; some cells produce chemicals
called antibodies (proteins) to neutralize the
effects of certain foreign chemicals
Platelets
• Much smaller than red blood cells – about
250 000 to 300 000 for each mm3
• Responsible for the initial stages of blood
clotting, the process which prevents loss
of blood from a wound. If blood doesn’t
clot, you would loose too much blood and
die.
• No nucleus; not actual cells, but are tiny
fragments of cells that contain a special
enzyme that initiates clotting
Blood Types
• Determined by the presence or absence of
certain antigens on the red blood cells
• Two types of antigens: A and B
• If A is present, type A blood; if B is present,
type B blood; if both present, type AB; if
neither are present, type O blood
• The antibodies found in blood are always
the opposite of their antigen (blood type)
• For example, type A blood contains the A
antigen, but the B antibody (needed to
fight off foreign antigens . . . things other
than A
Type of Blood
A
Antigens
Present on Red
Blood Cells
A
Antibodies
Present in
Blood Plasma
B
B
B
A
AB
A and B
Neither A or B
O
Neither A or B
A and B
Rh factor
• This is an antigen (chemical) found on the
red blood cells of most people
• If your blood has the chemical your blood
is said to be Rh positive (Rh +)
• If your blood does not have it, your are Rh
negative (Rh -)
• Connected to your blood type
– Ex) your blood may be AB+
• It is particularly important for expectant
mothers to know their blood’s Rh factor – if
it is the opposite to the baby’s this could
be a big problem and the baby’s life could
be in danger since the mother’s blood may
attack the baby’s
Moving Blood throughout the Body
• Blood flows through your body through a
closed system of tubes called blood
vessels
• Your body has three main types of blood
vessels:
– Arteries
– Veins
– Capillaries
• Arteries
– Carry blood away from the heart
– Blood is rich in oxygen and nutrients
– Cary the materials needed by the cells
– Arterioles = small arteries
• Veins
– Carry blood from the body back to the heart
– Blood in the veins carries dissolved waste
material
– Venules = smaller veins
• Capillaries
– Tiny and thin tubes that connect arterioles and
venules
– Most of the blood vessels in your body are
capillaries
The Heart
• Blood is pumped throughout your body by
the heart
• The heart is located in the thoratic cavity,
well-protected by the rib cage
• The heart is nestled between the lungs,
with its lower end slightly toward the left
side
• An adult heart is about the size of a large
fist (300 g)
• It is not rigidly attached to any of the
surrounding tissues, but is suspended by
the large blood vessels attached to it
– This allows it to move loosely in place as it
contracts
Parts of the Heart
• The heart muscle has two separate pumps
• Right side: responsible for collecting blood
from the body and pumping it to the lungs
• Blood flows back from the head and arms
to this side of the heart through a large
vein called the superior vena cava, which
leads into the upper right-hand chamber
called the right atrium
• Blood from the trunk and legs enters the
same chamber via the inferior vena cava
• Both the right and left atria are thin-walled
chambers which lie above the ventricles –
their function is to collect blood and to
pass it to the ventricles (contracting
vessels)
• Right ventricle – connected to the right
atrium via the tricuspid valve, which
prevents blood from flowing back into the
atrium when the ventricle contracts
• When the right ventricle contracts, it
pushes blood into the pulmonary artery,
which carries blood into the lungs where
its load of CO2 wastes are released and a
fresh load of oxygen is absorbed
• The newly oxygenated blood flows into the
left atrium through the four pulmonary
veins – this portion of the circulatory
system (the heart to lungs and back) is
called pulmonary circulation
• Contractions of the left atrium push the
blood through the bicuspid valve into the
left ventricle (largest and most heavily
muscled chamber of the heart), which
forces blood to every part of the body as it
contracts
• The blood is pushed out from the left
ventricle to the largest blood vessel in the
body, the aorta – this portion of the
circulatory system is called the systemic
system since it supplies blood to the
remaining body systems
Blood Pressure
• If the blood is to reach the hands and feet,
the brain, and every part of the body, it
must be pumped out of the heart under
very considerable pressure
• Highest pressure occurs in the aorta
• As blood passes into smaller vessels and
the distance from the heart becomes
greater, the pressure decreases
• The pressure in any vessel varies as a
result of 5 major factors:
1. The amount of blood – if there is loss of
blood, the pressure in the system drops
because of the decrease in volume
2. The heart rate – the faster the heart
pumps blood, the greater the pressure
which is built up (there is more blood);
pressure falls as the heart rate
decreases, especially during sleep/rest
3. The size of the arteries – when arteries
dilate (larger in diameter), the volume of
the vessels increases and the pressure
falls (more room to flow). If the arteries
constrict pressure is built up because of
the extra resistance to blood flow
4. Elasticity – the walls of arteries must be
flexible and elastic in order to expand as
blood is forced out of the heart, and then
relax after the blood has flowed through.
If they can’t stretch properly they are
‘hardened.’ This is common in older
people and results in high blood pressure
5. The viscosity of blood – viscosity =
thickness of blood; thick, sticky fluids
flow less readily than thin, watery fluids
Measuring Blood Pressure
• Normal blood pressure is less than or
equal to 120/80 mm Hg
• Systolic Pressure: numerator; the highest
pressure generated when the ventricles
contract
• Diastolic Pressure: denominator; when the
ventricles relax and the elastic walls of the
arteries offer the least resistance