In I/GCSE Biology, do you remember about circulatory system of human body?

• At the centre of your blood system is your heart and the rest is made up of tubes called blood vessels.
• 3 types of blood vessels: arteries, veins and capillaries.
• ARTERIES carry blood away from the heart
• VEINS carry blood back to the heart
• When they get to an organ, arteries branch many times -> capillaries
• Capillaries join up to form veins.
• Oxygen, food and carbon dioxide pass in and out of the blood in the capillaries.
• Veins have valves to keep the blood flowing in the right direction.

In I/GCSE Biology, please remember the features of each blood vessel!

Arteries:

• When the heart contracts, blood is forced into your arteries
• Each beat of the heart pumps the blood along under high pressure.
• Elastic-like walls -> stretch to take the blood
• When the walls contract and bounce back they force the blood along -> felt as a pulse.
• Thick, muscly walls

Veins:

• Wider than arteries
• Thinner walls
• Lower pressure -> blood flows slower
• Blood controlled by valves to prevent blood flowing backwards.

• Very narrow.
• Blood flows through them slowly to give time for gas exchange to occur.
• Only one cell thick.
• CO₂ passes into capillaries.

In I/GCSE Biology, it's also important to understand what double circulation is.

RIGHT side of the heart

• Pumps blood and then back to the heart again.
• In the lungs, the blood picks up oxygen.
• Carries oxygenated blood.
• CO₂ passes into the blood from body cells

LEFT side of the heart

• Pumps blood , then back to the heart.
• The blood gives up its oxygen to its body cells
• Carries deoxygenated blood
• CO₂ passes into the blood from body cell

William Harvey made discoveries about the circulatory system.

Look at the diagram showing the double circulation below!

References:

1.  "Capillaries Illustrations & Vectors", https://thumbs.dreamstime.com/b/blood-vessels-human-body-capillaries-156698780.jpg
2. "Blood vessels – Grade 9 Understanding for IGCSE Biology 2.68", https://pmgbiology.files.wordpress.com/2015/02/3289630_orig.jpg
3. "What is the Function of Veins in the Circulatory System?", https://www.firstaidforfree.com/wp-content/uploads/2020/05/Pulmonary-Vein-Diagram.jpg

4. "Biology 3 - Blood and Circulation", https://getrevising.co.uk/resources/biology_3_blood_and_circulation

And we're done with this topic! Well Done!

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Drafted by Alyssa (Biology)