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YPHY0001: Your lifestyle and your health
A Healthy Heart
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The heart lies at the centre of the cardiovascular system
The heart is a muscular pump
When heart muscle contracts, it squeezes blood out of the ventricle & into the artery
The heart has 4 chambers: 2 atria and 2 ventricles
The ventricles are the pumping chambers of the heart
The ventricles of the heart eject blood at high pressure & high velocity
After it has been ejected from the heart at high pressure, blood flows through blood vessels
from high to low pressure, until it returns to the low-pressure chambers of the heart (the
atria).
blood = continuously circulated around the vascular system
the heart gives the blood enough ENERGY to keep it flowing through the blood vessels
Structures in the Heart
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1. Ventricles
Ventricles are the muscular pumping chambers of the heart
They convert chemical energy (ATP) to mechanical energy (muscle contraction)
They transfer this energy to the blood by ejecting it out at high pressure & high velocity
The structural properties of the ventricles are ideally suited to the pumping function: thick
muscular walls allow a forceful contraction, which ejects the blood at high pressure
Energy (pressure) required by the blood depends on the distance that the blood will travel
The heart contains 2 pumps:
The right ventricle pumps blood to the pulmonary circulation (lungs) for gas exchange
• This distance is relatively short
• The right ventricular muscle is thinner
• It reaches a pressure of about 25 mmHg during contraction
The left ventricle pumps blood to the systemic circulation (all the rest of the body)
• This distance is longer
• The left ventricular muscle is thicker
• It reaches a pressure of about 120 mmHg during contraction
2. Valves
Entrances to, & exits from, ventricles have valves
Function = to prevent backflow of blood
AV valves are flaps of connective tissue (valve leaflets) anchored to the ventricular muscle
by tough “strings” of connective tissue (chordae tendinae)
Semilunar valves are “pockets” of connective tissue in the walls of the arteries, just where
they exit from the ventricles
When ventricles contract:
• Ventricular pressure = much higher than atrial pressure
• Pressure pushes upwards on AV valve leaflets, which makes them move up to cover
the hole
• Atrio-ventricular (AV) valves close to stop blood flowing backwards from the
ventricles to the atria
• Chordae tendinae are attached to contracting ventricular muscle, which pulls down on
the AV valve leaflets and stops them from being pushed right up into the atrium
YPHY0001: Your lifestyle and your health
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Outflow of blood from the ventricle flattens the semilunar valve pockets against the
artery wall, so blood can flow out unimpeded
When the ventricles relax after their contraction:
• Ventricular pressure drops to zero
• Arterial pressure is higher than ventricular, & blood starts to flow backwards towards
the ventricle
• The backflow fills the “pockets” of the semilunar valves,which occludes the artery
and stops any further backflow
• Semilunar valves close: blood from the arterty is prevented from entering the
ventricle
• Atrial pressure is higher than ventricular, so AV valves open
• Blood flows from the atria into the ventricles
• Blood flow pushes the valve leaflets flat against the ventricular walls so they do not
impede the flow
• Ventricles fill with blood (ready for the next contraction)
3. Atria
Atria = thin-walled: ⇒ contraction is weak (~10mmHg)
Mainly, they act as a passive conducting chamber:
• Venous return of blood back to the heart is continuous
• While the ventricles are contracting, AV valves are closed
• Blood cannot enter the ventricles so it accumulates in the atria, which stretches them,
& gradually raises atrial pressure
When the ventricular contraction stops & the AV valves open, blood rushes from the atria
into the ventricles
Blood continues to flow back from the veins, through the atria, & into the ventricles (passive
flow, pressure gradient)
Just before the ventricular contraction, the atria contract, & squeeze the last ~20% of blood
into the ventricles
The Circulatory (Vascular) System
AORTA
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LARGE ARTERIES
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SMALLER ARTERIES
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ARTERIOLES
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CAPILLARIES
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VENULES
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SMALL VEINS
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LARGE VEINS
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VENA CAVAE
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2 circulatory systems: systemic & pulmonary
• pulmonary - deoxygenated blood through
lungs
• eliminate carbon dioxide
• pick up more oxygen
• systemic - oxygenated blood & nutrients to
body
• oxygen & nutrients diffuse into active
cells
• waste products diffuse from cells to
blood
YPHY0001: Your lifestyle and your health
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Aorta & large arteries
Highly elastic
Large diameter / low resistance
Distribute blood to organs without using up much of its energy (pressure)
Convert pulsatile cardiac output to continuous arterial flow
Function = pressure storage / flow buffering
Small arteries / arterioles
Muscular & thick walled
Spiral orientation of smooth muscle ⇒ contraction reduces diameter
Function = resistance vessels (pre-capillary resistance)
• maintain blood pressure
• control distribution of blood among the various organs & tissues
Control of blood flow rate: flow through a blood vessel depends on:
• The “driving force” along the vessel, which is the pressure gradient
• “How difficult” it is for blood to flow through the particular blood vessel, which is the
resistance
Capillaries
Very thin wall
Minimal barrier to diffusion
Allows materials to exchange easily between the blood and tissues
Veins & venules
Thin wall, mainly smooth muscle
Main function = volume storage
Pressure acts:
• in longitudinal direction to produce flow
• outwards to stretch vessel
Veins have thin walls: ⇒ they stretch easily
Small pressure increase → large volume increase
Veins are usually in a stretched state, which allows them to accommodate 75% of the total
blood volume
If the blood pressure drops, muscular walls of veins contract, which reduces the volume of
the veins
This returns extra blood to the heart, which increases cardiac output and blood pressure
cardiac outpu
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peripheral resistance
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less flow from artery to capillary
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increased volume in artery
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increased stretch of arterial wall
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more potential energy transferred to wall
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higher pressure
Both the heart and the blood vessels contribute equally to the determination of the blood
pressure
YPHY0001: Your lifestyle and your health
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Unusual properties of heart muscle
Heart continues to beat at 75 bts/min (or more) throughout your entire life (= at least once
every 0.8 seconds!)
Cardiac output supplies blood flow to the entire body: ⇒ supplies oxygen & removes waste
products from all cells of the body (including itself!)
If the heart fails, the whole body dies
Strongly dependent on the oxygen supply
• Heart muscle cannot undergo anaerobic metabolism
• At resting heart rates, most oxygen is extracted from the blood
• Little “oxygen reserve” available
Any increase in cardiac work requires an increase in coronary blood flow to supply additional
oxygen for metabolism
If the heart is weak or damaged, it creates a vicious cycle:
Weak or damaged heart
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Weak contraction, smaller cardiac output
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Less blood supply to cardiac muscle
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Insufficient oxygen supply to cardiac muscle
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Further weakening & damage to heart muscle
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Ischaemic heart disease
One of the most common diseases of the heart
Coronary arteries become narrowed
In milder cases, the blood supply to the heart is sufficient at rest, but can not increase when
the heart needs to work harder (e.g. exercise)
In severe cases, the heart can not even get enough blood supply at rest
In the worst cases, a heart attack (myocardial infarction) occurs, and a piece of the heart dies!
Narrowing of coronary arteries can occur in several ways:
• Deposition of fatty material on the arterial wall (atherosclerosis)
• Partial blockage by a blood clot
• Spasm of the muscles in the arterial wall
Consequences of cardiac ischaemia
If the blood supply to the heart muscle is insufficient for its needs
It does not have enough oxygen to create the energy stores (ATP) → feeling of fatigue
It does not have a high enough flow rate to wash out the waste products → pain
The accumulation of waste products further reduces the ability of heart muscle to contract →
cardiac output drops → blood & oxygen supply to other regions is impaired (→
breathlessness)
Mild disease may only be noticeable as poor exercise tolerance (feeling of fatigue &
breathlessness)
As the disease becomes worse, there is chest pain during exercise (exertional angina)
Further progression → fatigue & breathlessness at rest, and chest pain with any mild exertion
Heart attack is an acute event - a sudden decrease in blood supply e.g. blockage by a clot
YPHY0001: Your lifestyle and your health
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Lifestyle factors & heart disease
Many people develop atherosclerosis
In some cases, this is for genetic reasons
In other cases, it occurs due to poor lifestyle choices!
Diet
• Atherosclerosis is more likely to develop if the diet is:
• High in fat
• High in cholesterol
• Low in antioxidants (fresh fruit & vegetables)
• Different people have different tolerances to fat/cholesterol in the diet
• Key factor is the serum level of lipid & cholesterol
Lack of exercise
• Exercise stimulates the growth of new blood vessels in the heart
• During exercise, chemicals (growth factors) are released from the cells lining the
blood vessels
• Therefore, exercise improves the blood supply to the heart muscle
• Exercise also lowers the blood pressure (reduces the hypertension risk factor)
Cigarette smoking
• Chemicals from the cigarette smoke enter the blood through the lungs
• They damage the lining of the blood vessels
• This increases the probability of atherosclerosis forming at the site of damage
• Risk of coronary artery disease is in direct proportion to the number of cigarettes
smoked
• In a smoker, it takes 10 years of zero smoking for the risk to return to normal
High blood pressure (poor compliance with medication)
Diabetes mellitus (uncontrolled blood glucose)
• Either high blood pressure or high blood glucose can damage the blood vessel lining
• This increases the risk of atherosclerosis
• Therefore it increases the risk of coronary artery disease
• Persons with either of these diseases must always comply very carefully with medical
regimes, or they may develop the additional problem of heart disease