The heart:Structure and Cardiac cycle

The double circulatory system

• The circulation of mammals is referred to as a double circulation.

• This means that for each round trip of the body the blood passes through the heart twice - the circuit of blood can be thought of as heart - lungs - heart - body – (and back to the heart)

• So after the blood pumped through a capillary bed (which reduces it's pressure) it receives another pump before it enters another capillary bed.

The Pulmonary Circulation• This is the circulation of blood from the

heart to the lungs and back to the heart again.

The Systemic Circulation• This is the circulation of blood to all

parts of the body (except lungs) and back again to the heart.

The two circulations which make up the double circulatory system are:

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The features you have to learn:

• The chambers• The blood vessels connected to the

heart• The 2 types of valve present• The tendons attached to the valves

So you have to be able to Name 1 - 10

You should find this an easy question

Don’t forget about those tendons

The cardiac cycle

… is is a cycle - there isn’t really a start or end –it goes round & round… When we talk about it we usually start from the point just after blood has been ejected from the heart.

The cardiac cycle

Key point: The contraction of the heart in the cardiac cycle is top down, bottom up - the atria act as pump primers (they ensure that the ventricles are stretched before they contract.)

The cardiac cycle

The following slides detail – the main bits to learn

the movement of bloodthe pressure in the chambersthe valve positions the state of the heart muscle

The cardiac cycle

Main stages:1.Isometric relaxation2.Rapid Filling3.Atrial Systole4.Ventricular Systole

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3.4.

The cardiac cycle

The cardiac cycle1. isometric relaxation. All valves closed - atria and ventricles relaxed (in diastole).

Blood is flowing into the atria from the main veins. As this blood fills the atria the pressure in the atria begins to rise

1.

The cardiac cycle2. This causes the AV valves to open (atrial pressure > ventricular) blood flows through atria to ventricles. This is the rapid filling phase. Atria & ventricles relaxed (diastole) SL valves closed. Blood flow into the heart slows then ceases as pressure in the heart equals pressure in the veins.

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The cardiac cycle3. Atrial systole. Atria contract (systole) blood forced into ventricles,

As soon as Atria relax (diastole) the pressure in the atria drops below the ventricles so AV valves snap shut

4. Ventricular systole. Ventricles start to contract (systole) there’s a short period of isometric contraction the ventricles contract causing pressure in the ventricles to increase but no blood moves (SL valves still closed). Quickly the pressure in the ventricles exceeds that in the arteries this opens the SL valves and ejection occurs.

The cardiac cycle

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4.5 Just after Ventricular systole! As soon as the ventricles start to relax the pressure in the ventricles drops…

The cardiac cycle

The SL valves snap shut…and we go - back to the start again

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The cardiac cycle

http://207.207.4.198/pub/flash/31/cardiacmenu.swf

http://medlib.med.utah.edu/kw/pharm/hyper_heart1.html

Cardiac cycle animations

The cardiac cycle – Pressure, volume, valves, systole and diastole… All in one key diagram

Which examiners love

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This is why that graph needs learning

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why that graph needs learning

Control of the cardiac cycle

Bundle of His

Purkyne tissue

The conduction system of the heart

A wave of impulses are emitted from the SAN & spread through the walls of the atria causing them to contract.

This impulse reaches the atrio ventricular node (AVN).

At the AVN there is a slight time delay.

Control of the cardiac cycle

Bundle of His

Purkyne tissue

The conduction system of the heart

Control of the cardiac cycle

The impulse is then emitted from the AVN and passes through the Purkjne tissue to the apex of the heart.

The impulse now travels from the base of the ventricles upwards, causing the ventricle to contract.

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