Science 8th grade
UNIT 3: The circulatory system 3.4 Blood vessels
Science 8th grade
UNIT 3: The circulatory system 3.4 Blood vessels
The tubes through which blood flows are called blood vessels. We have three main kinds of blood vessels in the body.
• Arteries carry blood away from the heart.
• Veins carry blood back to the heart.
• Capillaries connect the arteries to the veins. They carry blood close to every tissue in the body.
Questions
$A+I$: 1) Kareena says, Arteries carry oxygenated blood, and veins carry deoxygenated blood.' Explain why sheis wrong. (Page 32 will help you.)
$A+I$: 2) Suggest why you can feel your pulse in an artery, but not in a vein.
Arteries
Arteries have very thick, strong, elastic walls. They need to be strong because they have to withstand the strong forces as the heart pumps blood through them. Their clastic walls are able to expand and spring back as the blood surges through. You can feel this happening when you feel your pulse.
The structure of an artery.
Capillaries
Capillaries are very tiny. The smallest ones can only be seen with a microscope. They are just big enough to allow red blood cells to get through them.
Capillaries have thin walls, made up of only one layer of cells. This means that substances in the blood - such as oxygen and sugar-can easily get out. The function of capillaries is to supply cells with things that they need, and take away their waste products.
The structure of a capillary.
Veins
Veins are a similar size to arteries. However, their walls are much thinner, and the space inside them is larger. Veins do not need thick walls, because by the time blood flows into the veins it has lost most of the force that the heart gave it. They do not need very clastic walls cither, because the blood is flowing smoothly rather than in surges.
Veins contain valves, which only let the blood flow one way - towards the heart.
Question
3) Construct a table to summarise the structures and functions of arteries, capillaries and veins.
Activity 3.4 (Circulatory system poster)
Design and make a poster to show information about the human circulatory system.
Begin by deciding what you will try to show. Include no more than one or two of the following:
• a plan of the circulatory system
• the heart and how it works
• blood - what it contains and what it does
• the different kinds of blood vessels.
You may be able to use books and the internet to find out extra information about the topics that you choose. For example:
• What makes blood flow upwards in the veins from your feet to your heart?
• How is the heart muscle supplied with oxygen and sugar?