AQA GCSE Biology Unit B3 Chapter 2.1/2.2 (Circulation)

Circulation of the blood is called a "double circulation", this is because blood is pumped from the heart to the rest of the body and back then to the lungs and back.

Bit of a simplified diagram but it's fine.

Arteries carry blood away from the heart.

• The blood flows in high pressure waves
• They have thick walls to withstand the high pressure and also because...
• They have a thick layer of muscle and elastic fibres
• Lumen are narrow (comparatively)

Veins carry blood to the heart

• The blood flows slowly and under low pressure
• The walls are slightly elastic - no recoil though
• They have relatively thin walls
• They often have valves
• They have wide lumen (comparatively)

Nice picture, yeah?

Capillaries connect the arteries to the veins

• They are tiny vessels with narrow lumen
• Their walls are a single cell layer thick
• No elasticity at all
• Very narrow lumen (red blood cells pass in single file)
• Blood flows very slowly; glucose and oxygen are delivered to cells (by diffusion)

RIGHT SIDE:

• Deoxygenated blood enters the right atrium via the vena cava
• The right atrium contracts and blood passes through the atrioventricular valve into the right ventricle
• The right ventricle contracts and blood passes out into the pulmonary artery.
• Blood flows to lungs to get oxygen

LEFT SIDE:

• Oxygenated blood enters the left atrium through the pulmonary vein
• Left atrium contracts and the blood passes through the atrioventricular valve into the left ventricle
• The left ventricle contracts and the blood passes out to the body through the aorta, becoming deoxygenated.

Key points

• Your blood is the main transport medium of your body
• Your blood plasma transports dissolved food molecules, carbon dioxide and uea
• Your red blood cells are biconcave discs which have no nucleus and are pack with the red pigment haemoglobin
• Red blood cells are adapted to transport oxygen from your lungs to the organs of your body
• Oxygen is carried by haemoglobin which becomes oxyhaemoglobin in a reversible reaction