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)
In one heart beat...
- 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
- 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.
Transport in the blood
- 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