The Human Circulatory System

Name: Unit: Staying alive

The Human Circulatory System The Heart and the Circulatory System: The cells in our body need a good supply of oxygen and nutrients. They also need to get rid of waste substances. Our blood carries out both of these functions. The circulatory system consists of blood vessels such as arteries, veins and capillaries and a pump called the heart.

Right ventricle Left ventricle Pulmonary artery Pulmonary vein Aorta Left Atrium Right Atrium Valves Blood circulation around the body: In this section you’ll learn about the flow of blood around the body. This will include how many times blood passes through the heart as it is transported around the body.

A double circulation:  Blood passes through the heart twice on every full circuit of the body. o This is called a double circulatory system.  A double circulatory system separates the blood with oxygen from the blood without oxygen.  Blood with oxygen is called oxygenated blood.  Blood without oxygen is called deoxygenated blood.  The pulmonary circuit pumps blood to the lungs.  The systemic circuit pumps blood to the body systems (i.e. the head, limbs, and trunk).

Each organ has its own blood supply:

 Each organ of the body is supplied with blood from its own artery. This blood is oxygenated.  Deoxygenated blood is taken away from organs by veins. Blood vessels:

In this section you’ll learn about the different blood vessels that carry blood around the body.

Where does the blood flow? When blood has been pumped out the left ventricle of the heart, it begins to make its journey around the body in an artery called the aorta. The blood is rich in oxygen. Oxygen is carried by red blood cells. The oxygen leaves the red blood cells as they pass through the capillaries. Capillaries are the network of blood vessels which pass in between the cells in the body. As blood leaves the capillaries it enters veins. Veins return blood to the heart.

Arteries: When blood flows out the heart, it enters the arteries. The blood is at very high pressure, because it has been forced out of the heart because the ventricles have contracted (squeezed). Arteries have very strong walls to be able to cope with the high pressure of the blood flowing through them. The blood moves through the arteries in pulses, with every heartbeat. The thick muscular walls stretch and then flex back into place because of the elastic fibres in the walls of arteries.

Capillaries Arteries divide into smaller and smaller blood vessels. The smallest blood vessels are called capillaries. The capillaries are very small and penetrate every part of the body. A body cell is never very far away from a capillary. The function of a capillary is to take nutrients and oxygen to cells and take waste products away. The structure of a capillary helps them do this. Capillaries have very thin walls, this means that the substances can get in and out very quickly.

Veins Capillaries eventually join up again and form veins. By the time the blood gets to the veins, it is at a much lower pressure than it was in the arteries. We can see this in the structure of veins. Veins do not have thick, strong, elastic walls. Veins have valves to stop the blood from flowing backwards. Arteries do not have valves because the force of the heart beat keeps the blood moving.

Task: Using the information in the last three paragraphs, complete this summary table What is their What is the How does their structure help job? structure of the them do their job? wall

Arteries

Capillaries Veins

Questions: Why do arteries have elastic walls? ______

What is the function of capillaries? ______

How is blood kept moving in the large veins of the legs? ______

Why do arteries have strong walls? ______

The heart has its own blood supply. Just like the other organs in body, the heart also has its own blood supply. This may seem odd, especially when the heart has so much blood passing through it. The reasons that the heart has its own supply is because it needs a lot of oxygen and nutrients to keep it working at its best and also because the walls of the heart are so thick that oxygen and nutrients cannot easily pass into where it is needed. The artery that supplies the heart with blood is called the coronary artery. If the coronary artery gets blocked, then the cells in the heart may run short of oxygen. If this happens then they will not be able to contract (squeeze). This is called a cardiac arrest or heart attack.

Questions: What is the coronary artery?

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Why does the heart need its own blood supply? ______

Extended answer question: Describe the movement of blood around the body stating at the right atrium. ______

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