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The Cardiac Cycle

describe the cardiac cycle, with reference

to the action of the valves in the heart;

explain how heart action is coordinated

with reference to the sinoatrial node

(SAN), the atrioventricular node (AVN) and

the Purkyne tissue;

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Exam tip

When referring to the bicuspid (on the left)

and tricuspid (on the right) valves, use the

word atrioventricular valves- that way, you

dont have to remember which is which!

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Sequence of Contraction

The sequence of events involved in one

heartbeat is called the cardiac cycle

It is important that the chambers of the

heart contract in a co-ordinated fashion, if

not, this leads to inefficient pumping

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Task

Using this diagram,

outline the main

stages of diastole,

atrial systole andventricular systole

during the cardiac

cycle

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Phase 1: Diastole

Both the atria and ventricles

are relaxing

the internal volume

increases and blood flows

into the heart from the major

veins

The blood flows first into the

atria, then through the

atrioventricular valves into the

ventricles

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Phase 2: Atrial Systole

The atria contract- right and

left together

The small increase in

pressure pushes blood into

the ventricles

This stretches the walls of

the ventricles and ensures

they are full of blood

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Phase 3: Ventricular Systole

Once the ventricles are full they begin tocontract

Blood fills the atrioventricular valve flaps

causing them to snap shut preventing

blood returning to the atria

There is now a short period where all 4valves are closed

The walls of the ventricles continue to

contract raising the pressure

The contraction starts at the base of the

ventricles pushing blood upwards towards

the arteries

The semi-lunar valves open and blood is

pushed out of the heart

The ventricles walls then relax and the

cycle begins again

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Valves

The valves ensure blood flows in the

correct direction

They are opened and closed by changes

in the blood pressure in the various

changes in the heart

Task: You will be given a series of statements about the blood pressure and

valves, arrange them in a sequence and stick them in your book

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Atrioventricular Valves When the ventricular walls relax and recoil after contracting, the

pressure in the ventricles drops below the pressure of the atria- this

causes the atrioventricular valves to open

Blood entering the heart flows straight through the atria and into theventricles

The pressure in the atria and the ventricles slowly rises as they fillwith blood

The valves remain open while the atria contract

As the ventricles begin to contract, the pressure of the blood in the

ventricles rises. When the pressure rises above that in the atria, theblood starts to move upward.

This movement fills the valve pockets and keeps them closed

This prevents blood flowing back into the atria

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Control of Heart Beat

1. What is the patch of muscle called that

controls the heart beat? (2)

2. Name the 2 nerves that carry impulses

from the brain to the heart (2)

3. How do acetylcholine and noradrenaline

affect the heart? (5)

4. What does digoxin do to the heart? (3)

5. What does propanolol do to the heart? (3)

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Control of Heart Beat1. What is the patch of muscle called that controls the heart beat? (2)

pacemaker (1) or sino-atrial node (1)

2. Name the 2 nerves that carry impulses from the brain to the heart

(2) vagus nerve (1) sympathetic nerve (1)

3. How do acetylcholine and noradrenaline affect the heart? (5)

acetylcholine released from the vagus nerve (1) slots into

receptors on the plasma membrane of the heart cells (1) this

makes the heart beat more slowly (1) noradrenaline released from

the sympathetic nerve (1) makes the heart cells beat more rapidly

(1)

4. What does digoxin do to the heart? (3) inhibits and slows the Na-K

pump in the plasma membrane (1) sodium ions accumulate in the

cells (1) this increases calcium ions which increases the force of

muscle contraction (1)

5. What does propanolol do to the heart? (3) a beta blocker (1) which

decreases the effect of noradrenaline on the SAN (1) reducing

heart rate (1)

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Pressure Practice Questions

Try to answer SAQ Q5 on p67

Leave any you cannot do blank

Remember to answer in full sentences tohelp with revision

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