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KS4 Biology

The Heart and Circulatory System

Heartbeat animation

Stages of a heartbeat

Stage 1: A heartbeat begins with the heart muscle relaxed and valves closed.

Blood flows into the two atria and both sides fill up with blood.

This blood has to be pushed through the valves to get into the ventricles. How does this happen?

Stages of a heartbeat

Stage 2: The atria contract and the blood is squeezed which causes the valves leading to the ventricles to open.

Blood then flows from the atria into the ventricles.

What happens to the open valves when the atria are empty?

Stages of a heartbeat

Stage 2 (continued): The valves between the atria and the ventricles close.

This prevents any backflow.

What happens next to the blood in the ventricles?

Stages of a heartbeat

Stage 3: Almost immediately, the ventricles contract and the blood is squeezed again.

The pressure of the blood forces open the valves leading out of the heart.Blood is pumped outof the heart.

What happens to the open valves when the ventricles are empty?

Stages of a heartbeat

Stage 3 (continued): When the ventricles are empty, the valves leading out of the heart close and the heart muscle relaxes.

This completes the sequence of contraction and relaxation in one heartbeat.

What will happen next?

Stages of a heartbeat

Stage 1 (again): The atria fill up with blood as the heartbeat sequence begins again.

Why are the walls of the atria thinner than the walls of the ventricles?

Why is the wall of the left ventricle thicker than the right ventricle?

---Blood vessels on the outside of the heart- coronary arteries

---Muscles of the heart are thick-so nutrients and oxygen in the blood

inside is not able to diffuse to all the muscle quickly

----so heart muscle needs constant supply of nutrients and oxygen –

to keep on working- coronary arteries does it

--- If a coronary artery gets blocked the cardiac muscle run short of

oxygen

--- can not respire, so it does not have the energy to contract-heart stops

beating

--- HEART ATTACK or CARDIAC ARREST

Pacemaker

--The rate at which the heart beats is controlled by a patch of muscle in the

right atrium called PACEMAKER

-- It sends electrical signals through the walls of the heart at regular intervals,

according to the need of the body

-- If it stops working-an artificial pacemaker is placed to do the job

SystoleCardiac muscle contracts-heart becomes smaller-squeezing blood out

DiastoleCardiac muscle relaxes –heart becomes larger-allowing the blood to flow into atria and ventricles

Blood flow through valves --there is a valve each between left and right atrium and ventricle-atrioventricular valves

-- valve on the left side of the heart –made up of 2 parts-bicuspid /mitral valve

-- valve on the right side of the heart –made up of 3 parts-tricuspid valve

Function

-- to stop blood flowing back from ventricles to atria. It is important as when

ventricles contract, the blood is pushed up into the arteries, not back into atria

--tendons attached to the valves stop them from going to far

Questions:

1. What kind of muscle is found in the heart?

2. Which part of the heart receive blood from the a) the lungs b) the body?

3. Which part of the heart pump blood into a) pulmonary artery b) aorta

4. Why do ventricles have thicker walls than atria?

5. Why does the left ventricle have a thicker wall than the right ventricle?

6. What is the function of the coronary arteries?

7. What is a) systole b) diastole

8. Where are the atrioventricular valves? What is their function?

9. Why are these valves supported by tendons?

10. What is pacemaker?

What does a doctor hear when they listen to a patients’ heart?

Listening to a beating heart: lub-dub

The “lub” is caused bythe closing of the valves leading to the ventricles.

The “dub” is caused by the closing of the valvesleading out of the heart.

lub-dub,

The sound of a heartbeat is the sound of the heart valves.

lub-dub, lub-dub, lub-dub, lub-dub, lub-dub…