The Heart and Circulatory System

DK & PK

Declarative Knowledge

Procedural Knowledge

Name the organs of the circulatory system and describe how they function

Label parts of the human heart and describe the flow of blood through the body

The next organ system we will be considering can be known by two names…..

How are substances transported around the body?

Blood system Circulatory system

The circulatory system is made of three parts:

1. The heart2. The blood vessels3. Blood

One of the substances that the circulatory system transports are respiratory gases.

For example, the Oxygen that the body needs, must be taken to the cells and the Carbon Dioxide waste gas must be taken away from the cells.

As these gases are carried by the blood, it means that in terms of the presence of gas, we have two types of blood.

Blood high in oxygen Blood low in oxygen

DeoxygenatedOxygenated

This section of the system including the rightright side of the heart, deals

with the deoxygenateddeoxygenated

blood.

This section of the system including

the leftleft side of the heart, deals with the oxygenatedoxygenated

blood.

Lungs

Body cells

At all times these two types of blood cannot mix. Why do you think this is? Because of this our circulatory system is in two parts. It is in fact called a double circulatory system.

The Human Circulatory System

The Heart

AortaPulmonary Artery

Left Atrium

Pulmonary Veins

Atrioventricular valve

Semilunar valve

Left ventricle

Right ventricle

Posterior Vena Cava

Atrioventricular valve

Right Atrium

Pulmonary veins

Semilunar valves

Pulmonary Artery

Anterior Vena Cava

Oxygenated Blood

Deoxygenated Blood

Besides the chambers there is also another very important part of the heart – the valves. These valves are found between the top and bottom chambers on both sides of the heart.

blood

valve

These valves are rather like doors that only open in one direction.

As the atrium fills with blood, the

valves are closed.

When the atrium contracts and

squeeze the blood, the valves are pushed open

These valves are connected to the side wall of the heart by tough tendons. These tendons allow the valves to close but not invert.

The blood will naturally

push against the valve.

However, the valves remain

firmly shut.

In this way, the blood can be moved from chamber to chamber quite efficiently. The valves prevent the blood from moving in the wrong direction.

Now that we can name all of the parts of the heart it is time to see how they work to push blood around the body.

The heart pumps blood when its muscle contracts. As the muscle contracts the chamber gets smaller and squeeze the blood out.

The two sides of the heart work together. The atria contract and relax at the same time, as do the ventricles.

The next two slides describe what occurs inside the heart during one heart cycle.

Blood from the body

Blood from the lungs

1. The heart beat begins when the heart muscles relax and blood flows into the atria.

2. The atria then contract and the valves open to allow blood into the ventricles.

The staged cycle then repeats itself.

3. The Ventricles contract forcing the blood to leave the heart. At the same time, the atria are relaxing and once again filling with blood.

Just before we finish our study, let’s take a last look at the heart…..

Do you notice anything different about the two sides of the heart?

Well, the left ventricle wall is clearly thicker than the right ventricle wall.

Why is this?

To answer this question, think about where the blood is going when it leaves the right and left ventricles.

This journey is enormous. The left ventricle has to pump blood all over the body!

This journey is far less demanding. The right ventricle only has to pump blood from the heart to the adjacent lungs.

Therefore, the left ventricle needs a thicker wall to generate a stronger ‘squeeze’ on the blood.

Body cells

Lungs

Lungs

Now, let’s consider the blood vessels...

We can get an idea of what they could look like from considering the job they have to do.

Let us look at a small section of the circulatory system. There seems to be 33 types of blood vessel present

OneOne takes blood away

from the heart

OneOne takes blood to the

heart

OneOne joins the other two together

So we have 3 types of blood vessels doing 3 different jobs.

1.1. Blood vessels that take blood away from the heart are known as

ARTERIESARTERIES.

2.2. Blood vessels that take blood back to

the heart are known as VEINSVEINS.

Remember, aarteries (aaway)

Remember, veinins (ininto the heart)

3.3. Finally, if arteriesarteries take blood away from the heart and veinsveins take blood back to the heart, when does an artery turn into a vein?

Well, our third type of blood vessel links the two. In other words, we find it present where an artery finishes and a vein is about to begin.

This third type of blood vessel is known as a

CAPILLARY.CAPILLARY.

Let us consider each vessel in turn to see how its shape is related to the job it has to do.

ARTERY

In each case we will look at a cross-section of the vessel

small lumen

thick muscle and elastic

fibres

The blood flowing through an artery will be under high pressure and moving extremely fast.

There is no chance that the blood will turn around and start travelling in the opposite direction. Therefore there are no valvesno valves present in arteries.

VEINS

large lumenthin muscle and elastic fibres

The veins are carrying blood back towards the heart. Materials have been exchanged and now it is running out of energy. It needs to return to the heart to receive another pump.

Unfortunately, this could lead to a real Problem..Problem..

human leg

What happens if blood loses so much energy that it stops and turns around?

vein

This situation could arise where blood is flowing against gravity. However, there is a solution to this problem. It comes in two parts.

1.1. Firstly, veins have valves which act to stop the blood from going in the wrong direction.

(These valves are similar to those found in the heart)

valves open

blood

valves close

CAPILLARIES

These vessels link arteries with veins.

They are found all over the body and are essential for the exchange of materials between the blood and other body cells.

artery vein

capillaries

very narrow lumen

The wall of a capillary is only one cell thick!

Capillaries are so small that they can only be seen using a microscope.

A collection of capillaries is known as a capillary bedcapillary bed.

Substances can diffuse across the lining of the capillary. This allows useful substances which are dissolved within the blood to move into surrounding cells whilst cellular waste moves in the opposite direction.

11 2233

The exchange of materials between the blood and the body can only occur through capillaries.

One such exchange that occurs in the capillaries is that of oxygen and carbon dioxide.

Summary

• The respiratory system is responsible for providing the body with oxygen and removing carbon dioxide.

• The circulatory system is responsible for transporting oxygen, carbon dioxide and other substances around the body.

• These two systems work hand-in-hand and are crucial for life.