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Summary Intro to the cardiovascular system year 1
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Intro to cardiovascular system year 1
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Introduction to the cardiovascularsystem
Systemic circulation: left heart contracts the left ventricle blood into the Aorta
- The blood pressure in the systemic circulation has to be kept high so efficient
distribution to blood to different organs of the body can occur.
- More resistance which increases pressure!
Pulmonary circulation: right heart contracts the right ventricles which pump blood
into the pulmonary arteries.
- No need for high pressure as no distribution of blood to DIFFERENT organs occurs
only the lungs
- Pulmonary vascular resistance is much lower than the systemic vascular resistance
The pulmonary arterial pressures are lower because the total vascular resistance in the
pulmonary vascular bed is much lower than that in the systemic circulation
SYSTEMIC ARTERIES: moderate in size, thick muscular walls
PULMONARY ARTERIES: Large diameter, thin ELASTIC walls
120 – systole
80 - diastole
STERLINGS LAW OF THE HEART:
Ventricular contractile force increases with increased end diastolic volume.
- When the heart works normally, it will pump blood out the ventricles whatever
the volume of blood is delivered by the atria.
More blood delivered = ventricles expand at a greater diameter and makes
contractions more strongly CARDIAC OUTPUT IS CONTROLLED BY PRELOAD
PRELOAD:
Preload is the stretching that the ventricle experiences during diastole.
PRELOAD IS PROPORTIONAL TO END DIASTOLIC VOLUME
An increased preload therefore results in an increased stroke volume – and an
increased cardiac output
During exercise there is an increased preload so a greater cardiac output.
, In heart failure, the ventricles expand beyond a certain volume where they get
overstretched and weakened.
- An increased preload simply enlarges the heart and weakens it further
STARLING’s OF THE HEART:
An increase in preload increases end diastolic volume and end-diastolic myocardial muscle
fibre length.
- This stretching increases the force of contraction of muscle fibres
- Heart therefore contracts MORE strongly expels extra volume of blood.
Over-stretched causing the it
to become WEAKER
- Here starlings law fails
and causes heart
failure
A Plateau formed as a result.
MECHANISM FOR STARLING’S LAW:
Cardiac muscle is striated like skeletal muscle
- The contractile mechanism is the ACTIN AND
MYOSIN filaments
One theory is that these filaments have excess overlap at
rest:
- Stretching increases the amount of overlap of
actin and myosin filaments and therefore
INCREASES THE FORCE OF CONTRACTION!
IMPORTANT:
- The two ventricles eject the same volume of blood which balances the output
of both sides of the heart prevents blood accumulating in the pulmonary or
systemic circulations.
WHY IS AN ENLARGED HEART ON AN X-RAY A BAD SIGN?
- A heart with enlarged ventricles will contract weakly than a smaller heart.
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