Transcript Heart and Blood Vessels

Heart and Blood Vessels
By the end of this class you should
understand:
• The path of blood through the body
• The basic functions of the blood vessels of the
body
• The purposes of the four chambers of the
heart
• The cardiac cycle and how it can be measured
through EKG and pressure
Transportation of Blood
• In humans, blood is always
contained within blood vessels
– If a blood vessel leaks blood
into the tissues the result is a
bruise
– Some types of animals, such as
arthropods (insects and spiders)
simply bathe their cells in fluid
called hemolymph
• These blood vessels plus the
heart make up the circulatory
system
Circulation
• All blood is constantly moving
along the circulatory system
• The most vital nutrient which is
used most quickly is oxygen, so
blood is usually divided into
oxygenated and deoxygenated
blood in graphs
– Realistically even “deoxygenated”
blood usually still has about 2550% oxygen load
Road Analogy
• If cells are houses and must receive
service via streets, the largest blood
vessels are freeways
• Note that like a freeway, major
blood vessels such as arteries and
veins do NOT deliver oxygen or
nutrients but rather move blood
quickly to different parts of the
body
• Almost all nutrient and waste
exchange happens in small, leaky
blood vessels called capillaries
Arteries and Veins
• Arteries move blood away from
the heart
• Veins move blood towards the
heart
• Arteries in the body have high
pressure and are bright red from
the oxygen content
• Veins have low pressure and the
blood is dark
– Deoxygenated blood is NOT blue
– It is dark, and vein coverings make
it appear blue
Capillaries
• All tissues (except cartilage,
epidermis and the lens of the
eye) have capillaries that blood
flows into from the arteries
• These capillaries then recollect
the blood into veins
• Veins are under low pressure
so there are valves that keep
the blood from flowing
backwards
– Blood is circulated through
veins partially by muscle
movement, which is why
stretching feels good
Anatomy of Blood Vessels
• Major blood vessels (arteries and
veins) have smooth muscle and
coverings
– Smooth muscle helps squeeze
blood through and constricts
when the blood vessel is damaged
• All blood vessels have a smooth
inner lining which reduces
friction/turbulence
• In capillaries these vessels are
leaky and so allow nutrients in
and out
Variable Flow
• Much like actual freeways,
where lanes can be opened or
closed for more traffic, blood
vessels can constrict or dilate
to bring more or less blood to
parts of the body
– Blood flow to skin = “flush” to
help cooling
– Blood flow to muscles =
adrenaline rush
– Blood flow to digestive system =
food coma
Circulation of Blood
• The blood is pumped by the
heart through two separate
pathways
• The left side of the heart is
larger than the right
because it pumps blood to
the entire body
– This is why your heart is
supposedly on the left side of
your chest
• The right side pumps blood
to the lungs
Blood Pathway
Heart Chambers
• The heart is divided into four
chambers, two on the left
and two on the right
– Entry chamber: atrium (like
the entry room to a building)
– Main force propeller: ventricle
– Division between right and left
heart: septum
• The heart is two pumps in
one, but both contract at the
same time
“Lub Dub” Sound
• The two sounds of the heart beat
are valves closing in the heart to
prevent backflow
– Heart murmurs are caused by
leaky valves
• The atria (plural of atrium)
contract first to fill the ventricles
• The ventricles then start
contracting (“lub”) and squeeze
blood to the lungs and body,
then stop so the atria can refill
(“dub”)
Blood Circuits
• Blood from the right
ventricle goes into the
lungs and back to the
heart (pulmonary circuit)
• Blood from the left
ventricle goes to the
entire body and back to
the heart (systemic
circuit)
– Systemic circuit is under
much higher pressure
Lung Function
• The lungs are basically
organs full of tiny gas bags
wrapped in capillaries
• Carbon dioxide is released
and oxygen is absorbed by
the blood in these
capillaries
• The blood then goes to the
left atrium and ventricle
for pumping to the body
Systemic Circuit
• Blood leaves the left ventricle
through a massive artery called the
aorta, which then splits into all the
major arteries of the body
– Carotid, brachial, renal, iliac,
femoral, etc
• The arteries then feed into
capillaries, which recollect to veins
which recover blood to the heart
• Largest veins reach the right atrium
to begin the pulmonary circuit
again
Heart Blood Supply
• The heart receives its own
blood supply through the
coronary arteries
– Corona = crown
• Arteries can be blocked by
excessive body cholesterol
• Coronary artery blockage
can cut off blood to the
heart, causing a heart
attack
Cardiac Cycle
• The heart goes through a cycle
to contract and pump blood
through the body efficiently
• The cycle is deemed to start
when the sinoatrial node (SA
node) initiates an action
potential
• The SA node is the pacemaker
of the heart and is influenced
by the sympathetic and
parasympathetic nervous
systems
SA node to AV node
• The SA node stimulates the
atria to contract, filling the
ventricles
• The SA node also stimulates
the AV node which then
stimulates the ventricles
– This delay allows the ventricles
to fully fill up before initiating
ventricular contraction (systole)
• If the SA node fails the AV
node can take over but the
ventricles don’t fill all the way
Ventricular Pressure
• When the ventricles
contract, they squeeze
blood at a high pressure
into the major arteries
• The pressure in the major
arteries is approximately
equivalent to the pressure
in the heart
– 120/80 means peak pressure
of 120 when the left ventricle
squeezes, 80 when it relaxes
– These are also called systole
and diastole
Systole and Diastole
• Systole is the peak blood pressure
caused by the left ventricle
squeezing
• When the ventricles are refilling it
is known as diastole
• 120/80 is average healthy blood
pressure, higher may indicate
unhealthy blood pressure
– High blood pressure is known as
hypertension and can be caused by
diet, lack of exercise, etc
Measuring Blood Pressure
• The theory behind measuring blood pressure works on
two principles:
1. The pressure in the major arteries is approximately
equivalent to the left ventricle
2. When the external squeezing pressure on an artery is
greater than its blood pressure, the blood flow stops
•
•
When the arm cuff cuts off blood pressure entirely,
this is systolic pressure
When the arm cuff allows all blood to flow again, this
is diastolic pressure
–
In between these two points, blood only squirts through
at diastole but not systole which makes a distinctive
sound
Measuring Blood Pressure
Systemic Blood Pressure
Electrocardiogram
• The electrocardiogram (ECG/EKG) is the famous
“beep beep” in the hospital
• Measures the electrical activity of the heart
– Small wave corresponds to SA node depolarizing
– Large wave corresponds to AV node and ventricles
depolarizing
• If the SA node fails, only one wave is visible as the
AV node takes over and depolarizes the entire
heart
– Time for an artificial pacemaker!
EKG Readings
Enjoy your weekend!
• Next week: Immunology and the Endocrine
system!