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B5b circulatory systems and the cardiac cycle

+B5b circulatory systems and the cardiac cycle

Objectives

Describe and explain double and single circulations, structure of the heart and circulatory systems, the cardiac cycle.

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HTTP://WWW.BBC.CO.UK/LEARNINGZONE/CLIPS/INSIDE-THE-HUMAN-BODY-RESPIRATION/12224.HTML

+How is the circulation different?

+The vital pump Circulatory Systems

None – e.g. amoeba

Open – e.g. insects

Closed – single e.g. fish , 2 chambered heart

Double e.g. mammals, 4 chambered heart

Historical contributions about circulatory system:

Galen – 200AD – believed blood flowed between heart & liver

Harvey – 1628 – discovered blood vessels, valves & high pressure blood flows away from heart in arteries

+5b The vital pump Cardiac Cycle – controlled by SAN & AVN

ECG

Effect of adrenaline?

Exercise?

+The Cardiac Cycle – Pay attention!

HTTP://HIGHERED.MCGRAW-HILL.COM/SITES/0072495855/STUDENT_VIEW0/CHAPTER22/ANIMATION__THE_CARDIAC_CYCLE__QUIZ_1_.HTML

+The cardiac cycle

Diastole- the heart relaxes and the atria fill with blood.

Atrial systole- the atria contract and force blood into the ventricles

Ventricular systole- ventricles contract and force blood into the arteries

+Pacemakers control the heart cardiac cycle

Sinoatrial node (SAN) is a patch of specialised tissue that produces electrical impulses, which spreads across the walls of the atria causing them to contract (atrial systole).

This contraction causes increased pressure inside the atria forces blood through opened atrioventricular valves into the ventricles.

+(cont)

When the electrical impulses have spread across the atria, a patch of muscle fibres called the atrioventricular node (AVN), conducts these impulses along Purkyne fibres to the tip of the ventricles, causing them to contract (ventricular systole).

This contraction increases pressure inside the ventricles, which forces the atrioventricular valves shut (this stops back flow of blood into the atria).

Blood forces open semi-lunar valves in the arteries.

The heart relaxes (diastole) and the atria fills with blood, and the cardiac cycle starts again.

Each cycle is one heart beat

+How heart rate is changed?

Exercise – skeletal muscles need more

glucose and oxygen for respiration, and they produce more carbon dioxide. The brain detects the extra carbon dioxide and send impulses to the SAN to speed up heart rate

+(cont)

When you exercise, are frightened, or excited, more adrenaline is produced.

This travels in the blood to the heart and causes heart rate to speed up.

+Monitoring the heart

The electrical activity of the heart can be measure and an electrocardiogram (ECG) produced (see diagram to the left).

+Normal and abnormal ECG

Normal Abnormal

+Artificial pacemakers

People with irregular, too fast, or too slow heart rate may need an artificial pacemaker fitted.

+Echocardiogram

Echocardiogram uses ultrasound (like they use to check unborn babies), to show any heart defects.

+Questions

What is the role of AV valves and semi-lunar valves in the heart?

How does the heart cause blood to move?

Explain why your heart rate increases when you exercise

If a person exercises and has a pulse rate of 120 beats per minute, how long does each cardiac cycle last?

Why do some people need artificial pacemakers?