Year 6 Science: Blood vessels
Part of the Year 6 Science the circulatory system and transport chapter. Chapter overview · whole chapter on one page
Blood vessels
Blood flows through three kinds of blood vessel:
- Arteries carry blood away from the heart. They have thick, elastic, muscular walls, because the blood is pushed out at high pressure.
- Veins carry blood back to the heart. They have thinner walls, and valves that stop the blood flowing backwards.
- Capillaries are very tiny vessels with walls only one cell thick. Substances pass between the blood and the body cells here.
The table compares the three vessels.
| Vessel | Walls | Direction of blood flow | Oxygen in the blood |
|---|---|---|---|
| Artery | thick, elastic, muscular walls | away from the heart | usually oxygen-rich |
| Vein | thinner walls, with valves inside | back to the heart | usually oxygen-poor |
| Capillary | walls only one cell thick | to and from body cells, where substances are exchanged | both |
Key ideas
- Arteries carry blood away from the heart, and have thick, elastic walls.
- Veins carry blood back to the heart, and have valves.
- Capillaries have walls only one cell thick, where substances are exchanged with body cells.
- The pulse is felt in an artery, because the heart pushes blood along it.
Method. Read the direction column.
- Find the row. The row that says back to the heart is the vein.back to the heart
- Write the name. So the vessel is a vein.Vein
- Write the answer. Vein
Check. Veins have valves to keep the blood moving forward. ✓
Method. Find the vessel with very thin walls.
- Read the walls column. The capillaries have walls only one cell thick.one cell thick
- Write the name. So the vessels are capillaries.Capillaries
- Write the answer. Capillaries
Check. Substances pass through the thin walls of capillaries. ✓
Method. Think about the route of the blood.
- Start at the heart. Blood leaves the heart in an artery.artery
- Name the next vessel. Then it flows into capillaries, which are next.artery, capillary
- Write the answer. artery, capillary
Check. Then the blood flows back to the heart in a vein. ✓
Watch out
Watch out: arteries are not always oxygen-poor. Most arteries carry oxygen-rich blood, but veins usually carry oxygen-poor blood back to the heart.
Exam tip
Exam tip. When you name a vessel, give a reason from the direction of the blood flow or the walls.
Try it (with your teacher, or a grown-up at home). Find your pulse in your wrist with a grown-up. Count it for 15 seconds, and then count it again after you have walked on the spot for one minute. Which vessel are you feeling? Explain why your pulse changes.
Exercise 3B Blood vessels
Method. Read the table in section 3.2.
- Read the direction. Arteries carry blood away from the heart.away
- Write the name. So the vessel is an artery.artery
- Write the answer. artery
Check. The pulse is felt in an artery. ✓
Method. Read the table in section 3.2.
- Read the direction. Veins carry blood back to the heart.back
- Write the name. So the vessel is a vein.vein
- Write the answer. vein
Check. Veins have valves. ✓
Method. Read the walls column.
- Read the walls. The capillaries have walls only one cell thick.one cell thick
- Write the name. So the vessels are capillaries.capillaries
- Write the answer. capillaries
Check. The walls are thin so that substances can pass through. ✓
Method. Read the walls column.
- Read the walls. The vein has thinner walls, with valves inside.valves
- Write the name. So the vessel is a vein.vein
- Write the answer. vein
Check. The valves stop the blood flowing backwards. ✓
Method. Read the walls column.
- Read the walls. The artery has thick, elastic, muscular walls.thick
- Write the name. So the vessel is an artery.artery
- Write the answer. artery
Check. Arteries must stand the high pressure of the blood. ✓
Method. Think about the size of the vessels.
- Think about size. Capillaries are the tiny vessels that connect arteries and veins.tiny
- Write the name. So the smallest vessels are capillaries.capillaries
- Write the answer. capillaries
Check. Capillaries are very tiny. ✓
Method. Read the last column.
- Read the column. The vein is usually oxygen-poor.oxygen-poor
- Write the name. So the vessel is a vein.vein
- Write the answer. vein
Check. Veins carry blood back to the heart. ✓
Method. Think about where the pulse comes from.
- Think about the pulse. A pulse is caused by the heart pushing blood through an artery.pushed
- Write the name. So Ali is feeling an artery.artery
- Write the answer. artery
Check. A vein does not have a pulse you can feel in the same way. ✓
Method. Think about where exchange happens.
- Think about the walls. The walls are one cell thick, so substances can pass through.pass through
- Write the name. So the vessels are capillaries.capillaries
- Write the answer. capillaries
Check. Oxygen, nutrients and waste pass through capillary walls. ✓
Method. Check the direction.
- Read the table. Veins carry blood back to the heart.back to the heart
- Decide. So Ruby is not right.no
- Write the answer. no
Check. Arteries carry blood away from the heart. ✓
Method. Check the oxygen in arteries.
- Read the table. Most arteries carry oxygen-rich blood.oxygen-rich
- Decide. So Mo is not right.no
- Write the answer. no
Check. Veins usually carry oxygen-poor blood. ✓
Method. Think about the blood flow in a vein.
- Think about the blood. Blood in a vein is moving back to the heart, at low pressure.low pressure
- Think about the valves. Valves stop the blood flowing backwards.backwards
- Write the answer. Accept any sentence that says valves stop blood flowing backwards, so the blood keeps moving towards the heart.
Check. Valves are flaps inside the vein. ✓
Method. Think about the job of the capillary.
- Think about the job. Capillaries exchange substances with the body cells.exchange
- Think about the walls. Thin walls let substances pass through easily.pass through
- Write the answer. Accept any sentence that says thin walls let substances pass easily between the blood and the body cells.
Check. Thin walls make the exchange quick. ✓
Method. Follow the route of the blood.
- Leave the heart. Blood leaves the heart in an artery.artery
- Reach the cells, then return. It passes through capillaries, then returns to the heart in a vein.capillary, vein
- Write the answer. artery, capillary, vein
Check. The route is artery, then capillary, then vein. ✓