Biology GCSE

• Artificial pacemakers are used to treat heart failure and irregular heartbeats
• A natural pacemaker is a group of specialised cells that generate electrical impulses that control the heartbeat and make the heart contact
• The systemic circuit is the pathway that carries blood to the rest of the body on the left side of the heart
• Arteries carry blood under high pressure and have thick, muscular, elastic walls
• Veins carry deoxygenated blood under low pressure and have thin walls with a wide lumen
• Capillaries have one cell thick walls allowing the diffusion of molecules between blood and tissue fluid and cells
• Capillaries connect the branches of arteries with branches of veins
• Red blood cells have no nucleus and no mitochondria. They have a large surface area to carry oxygen